The Solid-State Structures of Cyclic NH Carboximides

The patterns adopted in the solid state structures of over 300 cyclic NH carboximides as determined by X-ray diffraction are reviewed. While the analysis shows that the majority of these fit into just a few common patterns, a significant number exhibit more complex and interesting patterns involving the other functional groups present in addition to the cyclic imide.


Introduction
Cyclic NH carboximides containing the function -C(=O)-NH-C(=O)-are an important class of organic compounds whose physical properties, reactivity and applications have been thoroughly studied [1]. A recent monograph [2] includes detailed coverage of many aspects of their chemistry including synthesis, applications in biotechnology, catalysis, asymmetric synthesis, natural products, and agricultural and medicinal chemistry. Particularly in connection with the last topic, there has been sustained interest in thalidomide and structural analogues for a range of medicinal applications. However, as far as we are aware, there has so far been no systematic survey of the many structures of cyclic carboximides that have been determined by X-ray diffraction. The NH imides are of particular interest in this context since there is the opportunity for the NH and one or both C=O groups to participate in intermolecular hydrogen bonding. In this review we aim to discuss the structures observed for all cyclic NH imides for which details were published as of late 2019. Among the structures found, many belong to just a few common types, whereas others display unique modes of hydrogen bonding. In our survey we have excluded structures involving coordination to metals, coordination to solvents, and extremely complex bonding patterns. The remaining examples, totalling just over 300 structures, are considered in order of increasing ring size with further classification, for the most common five-and six-membered ring systems, according to degree of unsaturation and substitution pattern.

Methodology and Main Hydrogen Bonding Patterns
The Cambridge Structural Database (CSD) was searched using the structural fragment CO-NH-CO in October 2019 and the resulting cyclic compounds were screened to remove entries involving metal complexes and salts, hydrogen-bonding to solvent molecules, and extremely complex hydrogen-bonding patterns. The remaining 311 structures are surveyed according to ring size and substituent pattern and the observed structure types are discussed. The structures are shown with their CSD reference codes and with the atoms involved in hydrogen bonding highlighted in colour, with red for the primary interaction (normally starting from imide NH) and further interactions then coloured blue, green, etc. A total of 16 structures which have been deposited in the Cambridge Database do not have corresponding journal publications and these are referred to as "CSD Communication" with the Reference Code.   A total of eight general patterns of hydrogen bonding were identified and these are illustrated using a generalised succinic anhydride molecule (Figures 1 and 2). Two hydrogen bonding patterns emerge as by far the commonest, together accounting for 193 of the reported structures. These are a simple centrosymmetric dimer (pattern A, 119 examples) and a ribbon with two rows of molecules connected by hydrogen bonding (pattern B, 74 examples). Somewhat less common, but still important, are structures involving an intermolecular hydrogen bonding interaction of the imide NH with a remote hydrogen bond acceptor. Thus we can have dimers formed by interaction of NH with a remote nitrogen atom (

3,4-Disubstituted Maleimides
Of the 27 3,4-disubstituted maleimide structures located, the most commonly observed pattern is the hydrogen-bonded dimer A. The 13 structures noted as exhibiting the dimeric R  Particularly in analysing some of the more complex patterns observed, the "graph set" analysis introduced by Etter and Bernstein [3][4][5], may be useful and the observed pattern is also analysed using that system in many cases. The hydrogen bonding patterns A-H would be described in that system as follows: A = R  (8)]. It is interesting to note that these designations are valid regardless of the ring size of the cyclic imide.

Maleimide and Monosubstituted Maleimides
Two separate structures have been published for the parent maleimide 1 [6,7] (Figure 3), both of which involve hydrogen-bonded dimers A. Among the three monosubstituted maleimide structures located two, compounds 2 [8] and 3 [9] (Figure 3), involve a linear hydrogen-bonded ribbon structure B. The remaining compound 4 [10] involves a more complex pattern in which each imide NH is hydrogen bonded to the acetyl CO forming the link between chains of molecules joined by bonding of one of the imide carbonyls to the acetylamino NH ( Figure 4). In graph set notation C (7) chains of category F combine with C(6) to give R 4 4 (21).

3,4-Disubstituted Maleimides
Of the 27 3,4-disubstituted maleimide structures located, the most commonly observed pattern is the hydrogen-bonded dimer A. The 13 structures noted as exhibiting the dimeric R
Crystals 2020, 10, x FOR PEER REVIEW 4 of 50 compounds 5 [11,12], 6 [12], 7 [12], 8 [13], 9 [14,15], 10 [16] and 11 [17] and unsymmetrical examples 12 [18], 13 [19,20] and 14 [21] ( Figure 5). Eight of the located structures, compounds 15 [22], 16 [22], 17 [23], 18 [18], 19 [24] and 20 [25] (Figure 6), display a linear hydrogen-bonded ribbon pattern B. It would seem that the presence of smaller substituents favours this structure whereas larger substituents more commonly lead to the dimeric pattern A. Three structures, 21, 22 [26] and 23 [27] (Figure 7) show a linear chain where the NH of the imides is hydrogen-bonded to a remote ester or ether oxygen (pattern F or C (8)). In the case of compound 23 there is an additional C (11) interaction between the phenolic OH and a further ether oxygen leading to cross-linking of the chains. Compound 24 [28] forms a linear chain with the imide NH bonded to the remote pyridine nitrogen (pattern E or C (9)) and additionally, an intramolecular (S(6)) hydrogen bond between the 2-NH on the pyridyl ring and the amide oxygen. Three structures, 21, 22 [26] and 23 [27] (Figure 7) show a linear chain where the NH of the imides is hydrogen-bonded to a remote ester or ether oxygen (pattern F or C (8)). In the case of compound 23 there is an additional C(11) interaction between the phenolic OH and a further ether oxygen leading to cross-linking of the chains. Compound 24 [28] forms a linear chain with the imide NH bonded to the remote pyridine nitrogen (pattern E or C(9)) and additionally, an intramolecular (S(6)) hydrogen bond between the 2-NH on the pyridyl ring and the amide oxygen.
Three structures, 21, 22 [26] and 23 [27] (Figure 7) show a linear chain where the NH of the imides is hydrogen-bonded to a remote ester or ether oxygen (pattern F or C (8)). In the case of compound 23 there is an additional C (11) interaction between the phenolic OH and a further ether oxygen leading to cross-linking of the chains. Compound 24 [28] forms a linear chain with the imide NH bonded to the remote pyridine nitrogen (pattern E or C (9)) and additionally, an intramolecular (S(6)) hydrogen bond between the 2-NH on the pyridyl ring and the amide oxygen. The two remaining structures in this category exhibit more complex patterns of hydrogen bonding. In compound 25 [29] (Figure 8) the ribbon structure of pattern B is further reinforced by OH to P=O hydrogen bonding. This basic pattern can be described as C(4) combining with C(7) to give R 3 3 (16). Additional interactions between the P-OH group and the P=O of an adjacent ribbon make for a complex overall structure.
Crystals 2020, 10, x FOR PEER REVIEW 5 of 50 The two remaining structures in this category exhibit more complex patterns of hydrogen bonding. In compound 25 [29] (Figure 8) the ribbon structure of pattern B is further reinforced by OH to P=O hydrogen bonding. This basic pattern can be described as C(4) combining with C(7) to give R 3 3 (16). Additional interactions between the P-OH group and the P=O of an adjacent ribbon make for a complex overall structure. The Hydrogen-bonding pattern of compound 26 [30,31] (Figure 9) involves parallel rows of molecules in which there is a C(8) interaction between imide NH and OMe at the 3-position of the 3,4,5-trimethoxyphenyl substituent. These are then cross-linked by additional C (11) bonding between the OMe at the 4-position and the indole NH giving a 2-dimensional array containing R 4 4 (31) units.   The Hydrogen-bonding pattern of compound 26 [30,31] (Figure 9) involves parallel rows of molecules in which there is a C(8) interaction between imide NH and OMe at the 3-position of the 3,4,5-trimethoxyphenyl substituent. These are then cross-linked by additional C(11) bonding between the OMe at the 4-position and the indole NH giving a 2-dimensional array containing R 4 4 (31) units.
Crystals 2020, 10, x FOR PEER REVIEW 5 of 50 The two remaining structures in this category exhibit more complex patterns of hydrogen bonding. In compound 25 [29] (Figure 8) the ribbon structure of pattern B is further reinforced by OH to P=O hydrogen bonding. This basic pattern can be described as C(4) combining with C(7) to give R 3 3 (16). Additional interactions between the P-OH group and the P=O of an adjacent ribbon make for a complex overall structure. The Hydrogen-bonding pattern of compound 26 [30,31] (Figure 9) involves parallel rows of molecules in which there is a C(8) interaction between imide NH and OMe at the 3-position of the 3,4,5-trimethoxyphenyl substituent. These are then cross-linked by additional C (11) bonding between the OMe at the 4-position and the indole NH giving a 2-dimensional array containing R 4 4 (31) units.

Ring-Fused Maleimides
Of the five structures located for ring fused maleimides, two, compounds 27 [32] and 28 [33] (Figure 10), form a linear ribbon of pattern B. The other compounds all form more complex patterns involving groups other than the imide in hydrogen bonding. Compound 29 [34] forms a ribbon structure in which the NH of the imide and the CO away from the NH of the seven-membered ring form a simple R 2 2 (8) dimer. These dimer units are then connected to each other by the supplemental C(8) interaction of the other imide CO with the indole NH of the next unit to give the pattern shown which contains R 4 4 (22) units ( Figure 10). Compound 30 forms C(8) chains by interaction of the imide NH with the remote ester carbonyl oxygen and these are cross-linked by the ring NH to nitro group C(10) interaction resulting in a two-dimensional network containing R  Compound 31 forms dimers of pattern A by imide NH to CO interaction and these are then further linked in a zig-zag arrangement by dimer formation between the other imide CO and the six-membered ring NH ( Figure 12) [36]. This gives an overall designation of C (10)  Compound 30 forms C(8) chains by interaction of the imide NH with the remote ester carbonyl oxygen and these are cross-linked by the ring NH to nitro group C(10) interaction resulting in a two-dimensional network containing R 4 4 (31) units ( Figure 11) [35]. Compound 30 forms C(8) chains by interaction of the imide NH with the remote ester carbonyl oxygen and these are cross-linked by the ring NH to nitro group C(10) interaction resulting in a two-dimensional network containing R  Compound 31 forms dimers of pattern A by imide NH to CO interaction and these are then further linked in a zig-zag arrangement by dimer formation between the other imide CO and the six-membered ring NH ( Figure 12) [36]. This gives an overall designation of C (10) Figure 11. Structure adopted by compound 30.
Compound 31 forms dimers of pattern A by imide NH to CO interaction and these are then further linked in a zig-zag arrangement by dimer formation between the other imide CO and the six-membered ring NH ( Figure 12) [36]. This gives an overall designation of C(10)[ R 2 2 (8), R 2 2 (10)]. Compound 31 forms dimers of pattern A by imide NH to CO interaction and these are then further linked in a zig-zag arrangement by dimer formation between the other imide CO and the six-membered ring NH ( Figure 12) [36]. This gives an overall designation of C(10)[ R

Succinimide
Two separate structures have been published for the parent succinimide 32 [37,38] (Figure 13), both of which involve hydrogen-bonded dimers A.

Succinimide
Two separate structures have been published for the parent succinimide 32 [37,38] (Figure 13), both of which involve hydrogen-bonded dimers A.

Monosubstituted Succinimides
Two of the twelve structures located for monosubstituted succinimides, compounds 33 [39] ( Figure 13) and 34 [40] exist as simple hydrogen-bonded dimers A. A further four compounds: 35 [41], 36 [42], 37 [43] and 38 [44] show linear hydrogen-bonded ribbons of type B. It is interesting to note the variation among these examples in whether it is the carbonyl nearer or more remote from the substituent that is involved in bonding. In compounds 39 [45] and 40 [46] ( Figure 14) the NH of the imide is linearly bonded to a remote heterocyclic nitrogen in the next molecule (pattern E, C(10) and C(7), respectively). One reported structure, the compound 41 [47], forms linear C(7) chains with the NH of the imide interacting with a remote ketone oxygen on the next molecule (pattern F). The three remaining structures all exhibit distinct and more complex patterns of hydrogen bonding. In compound 42 [48] (Figure 15) the imide NH bonds to the oxygen atom of the acyclic secondary alcohol group of another molecule (C(6)), with the hydrogen atom of that alcohol further bonding (C(8)) to the ring secondary alcohol in a third molecule. Since each molecule has two donor sites and two acceptor sites, the end result is a complex three-dimensional network.

Monosubstituted Succinimides
Two of the twelve structures located for monosubstituted succinimides, compounds 33 [39] ( Figure 13) and 34 [40] exist as simple hydrogen-bonded dimers A. A further four compounds: 35 [41], 36 [42], 37 [43] and 38 [44] show linear hydrogen-bonded ribbons of type B. It is interesting to note the variation among these examples in whether it is the carbonyl nearer or more remote from the substituent that is involved in bonding.
In compounds 39 [45] and 40 [46] ( Figure 14) the NH of the imide is linearly bonded to a remote heterocyclic nitrogen in the next molecule (pattern E, C(10) and C(7), respectively). One reported structure, the compound 41 [47], forms linear C(7) chains with the NH of the imide interacting with a remote ketone oxygen on the next molecule (pattern F).
The three remaining structures all exhibit distinct and more complex patterns of hydrogen bonding. In compound 42 [48] (Figure 15) the imide NH bonds to the oxygen atom of the acyclic secondary alcohol group of another molecule (C(6)), with the hydrogen atom of that alcohol further bonding (C(8)) to the ring secondary alcohol in a third molecule. Since each molecule has two donor sites and two acceptor sites, the end result is a complex three-dimensional network.
In compound 43 [49] (Figure 16) two parallel chains of molecules are hydrogen bonded to each other in a C(4) fashion or pattern B. Additionally, the other imide CO of the molecule links with the OH on the pyrrole ring of the next molecule in a C(8) chain, leading to formation of R 3 3 (17) units. In compounds 39 [45] and 40 [46] ( Figure 14) the NH of the imide is linearly bonded to a remote heterocyclic nitrogen in the next molecule (pattern E, C(10) and C(7), respectively). One reported structure, the compound 41 [47], forms linear C(7) chains with the NH of the imide interacting with a remote ketone oxygen on the next molecule (pattern F). The three remaining structures all exhibit distinct and more complex patterns of hydrogen bonding. In compound 42 [48] (Figure 15) the imide NH bonds to the oxygen atom of the acyclic secondary alcohol group of another molecule (C(6)), with the hydrogen atom of that alcohol further bonding (C(8)) to the ring secondary alcohol in a third molecule. Since each molecule has two donor sites and two acceptor sites, the end result is a complex three-dimensional network.  In compound 43 [49] ( Figure 16) two parallel chains of molecules are hydrogen bonded to each other in a C(4) fashion or pattern B. Additionally, the other imide CO of the molecule links with the OH on the pyrrole ring of the next molecule in a C (8) chain, leading to formation of R  Compound 44 [50] (Figure 17) has a complex hydrogen-bonding system with no fewer than four separate interactions which leads to a two-dimensional network. The molecules are arranged in C(13) chains linked both by bonding between the imide NH and the 3-N of adenine and between the CO of the same imide and one NH of the adenine 4-amino substituent forming R 2 2 (8) units. Cross-linking between the chains is also observed with C(6) interactions between the other NH of the 4-amino substituent and 1-N of adenine and C(4) between an amide carbonyl of one chain and the amide NH of the next.   Compound 44 [50] (Figure 17) has a complex hydrogen-bonding system with no fewer than four separate interactions which leads to a two-dimensional network. The molecules are arranged in C(13) chains linked both by bonding between the imide NH and the 3-N of adenine and between the CO of the same imide and one NH of the adenine 4-amino substituent forming R 2 2 (8) units. Cross-linking between the chains is also observed with C (6) interactions between the other NH of the 4-amino substituent and 1-N of adenine and C(4) between an amide carbonyl of one chain and the amide NH of the next. Compound 44 [50] ( Figure 17) has a complex hydrogen-bonding system with no fewer than four separate interactions which leads to a two-dimensional network. The molecules are arranged in C(13) chains linked both by bonding between the imide NH and the 3-N of adenine and between the CO of the same imide and one NH of the adenine 4-amino substituent forming R 2 2 (8) units. Cross-linking between the chains is also observed with C(6) interactions between the other NH of the 4-amino substituent and 1-N of adenine and C(4) between an amide carbonyl of one chain and the amide NH of the next.

3,3-Disubstituted Succinimides
Eleven structures were located for 3,3-disubstituted succinimides. Two of these structures, compounds 45 [51] and 46 [52] (Figure 18) show simple dimer hydrogen-bonding of pattern A. Five reported structures of three compounds: racemic 47 [53], (S)-48 [53] and (R)-49 [53] exhibit linear ribbon type hydrogen-bonding (pattern B). It is again interesting to note that the carbonyl nearer the substituent is involved in the former cases whereas in the latter, it is the one away from the substituents. Three reported structures of compounds 50 [54], 51 [54] and 52 [55] (Figure 19) show linearly hydrogen-bonded C(8) chains with the NH of the succinimimide bonded to the more remote of the two six-membered ring imide CO in pattern F. The remaining structure, compound 53 [56] involves a linear C(6) chain of type E with the NH of the imide bonded to the remote pyrrolidine nitrogen of the next molecule with an additional intramolecular S(6) interaction of the imide CO and the pyrrolidine NH as shown.

3,3-Disubstituted Succinimides
Eleven structures were located for 3,3-disubstituted succinimides. Two of these structures, compounds 45 [51] and 46 [52] (Figure 18) show simple dimer hydrogen-bonding of pattern A. Five reported structures of three compounds: racemic 47 [53], (S)-48 [53] and (R)-49 [53] exhibit linear ribbon type hydrogen-bonding (pattern B). It is again interesting to note that the carbonyl nearer the substituent is involved in the former cases whereas in the latter, it is the one away from the substituents.

3,3-Disubstituted Succinimides
Eleven structures were located for 3,3-disubstituted succinimides. Two of these structures, compounds 45 [51] and 46 [52] (Figure 18) show simple dimer hydrogen-bonding of pattern A. Five reported structures of three compounds: racemic 47 [53], (S)-48 [53] and (R)-49 [53] exhibit linear ribbon type hydrogen-bonding (pattern B). It is again interesting to note that the carbonyl nearer the substituent is involved in the former cases whereas in the latter, it is the one away from the substituents. Three reported structures of compounds 50 [54], 51 [54] and 52 [55] (Figure 19) show linearly hydrogen-bonded C(8) chains with the NH of the succinimimide bonded to the more remote of the two six-membered ring imide CO in pattern F. The remaining structure, compound 53 [56] involves a linear C(6) chain of type E with the NH of the imide bonded to the remote pyrrolidine nitrogen of the next molecule with an additional intramolecular S(6) interaction of the imide CO and the pyrrolidine NH as shown.  Three reported structures of compounds 50 [54], 51 [54] and 52 [55] (Figure 19) show linearly hydrogen-bonded C(8) chains with the NH of the succinimimide bonded to the more remote of the two six-membered ring imide CO in pattern F. The remaining structure, compound 53 [56] involves a linear C(6) chain of type E with the NH of the imide bonded to the remote pyrrolidine nitrogen of the next molecule with an additional intramolecular S(6) interaction of the imide CO and the pyrrolidine NH as shown.

3,3-Disubstituted Succinimides
Eleven structures were located for 3,3-disubstituted succinimides. Two of these structures, compounds 45 [51] and 46 [52] (Figure 18) show simple dimer hydrogen-bonding of pattern A. Five reported structures of three compounds: racemic 47 [53], (S)-48 [53] and (R)-49 [53] exhibit linear ribbon type hydrogen-bonding (pattern B). It is again interesting to note that the carbonyl nearer the substituent is involved in the former cases whereas in the latter, it is the one away from the substituents. Three reported structures of compounds 50 [54], 51 [54] and 52 [55] (Figure 19) show linearly hydrogen-bonded C(8) chains with the NH of the succinimimide bonded to the more remote of the two six-membered ring imide CO in pattern F. The remaining structure, compound 53 [56] involves a linear C(6) chain of type E with the NH of the imide bonded to the remote pyrrolidine nitrogen of the next molecule with an additional intramolecular S(6) interaction of the imide CO and the pyrrolidine NH as shown.

Tri-and Tetra-Substituted Succinimides
Five structures have been located for tri-and tetra-substituted succinimides. Three of these structures, compounds 62 [64], 63 [65] and 64 [66] (Figure 22) exist as simple hydrogen-bonded dimers, pattern A. Compound 65 [67] forms a ribbon structure of type B. Compound 60 [62] (Figure 21) exhibits type F hydrogen bonding with the imide NH-bonded to the remote ester CO in a single linear C(15) chain. The remaining compound 61 [63] exhibits a rare double-hydrogen-bonded ribbon pattern with two parallel rows and each imide NH bonded equally to the CO of two different molecules to give a C 2 1 (4)[R 2 2 (8)] pattern. It is notable that within this racemic compound the molecules are arranged in complementary rows consisting each of a single enantiomer.
The remaining compound 66 [19,20] (Figure 23) has a more complex linkage. Two molecules dimerise, with imide NH and CO (methylthio side) interacting. The dimers are further linked to each other by the other imide CO bonding to the OH of another dimer. As for compound 31 this has designation C(10)[ R 2 2 (8), R 2 2 (10)]. The compound is racemic and the enantiomers alternate within the structure as shown. The remaining compound 66 [19,20] (Figure 23) has a more complex linkage. Two molecules dimerise, with imide NH and CO (methylthio side) interacting. The dimers are further linked to each other by the other imide CO bonding to the OH of another dimer. As for compound 31 this has designation C(10)[ R

Succinimides Fused to Three-Membered Rings
Among the three reported structures for succinimides fused with three-membered rings, compound 67 [68] (Figure 24) shows no hydrogen bonding probably due to the high degree of steric hindrance. Compound 68 [69] exists in a ribbon, pattern B. The remaining compound 69 [70] exhibits C(6) chains with the imide NH linked to the remote nitrogen of the CN substituent in the form of pattern E.

Succinimides Fused to Four-Membered Rings
Of the seven reported structures for succinimides fused to four-membered rings, compound 70 [71] (Figure 25) exists as a linear hydrogen-bonded ribbon of type B. Compound 71 [72] exists as a square of four molecules in the rather uncommon pattern G (R 4 4 (16)). The compound 72 [73] exhibits a linear C(8) chain pattern F where the imide NH is bonded to the remote CO of the cyclohexenone ring. Two structures, compounds 73 [73] and 74 [74] exist as dimers of category D (R  The remaining compound 66 [19,20] ( Figure 23) has a more complex linkage. Two molecules dimerise, with imide NH and CO (methylthio side) interacting. The dimers are further linked to each other by the other imide CO bonding to the OH of another dimer. As for compound 31 this has designation C(10)[ R

Succinimides Fused to Three-Membered Rings
Among the three reported structures for succinimides fused with three-membered rings, compound 67 [68] (Figure 24) shows no hydrogen bonding probably due to the high degree of steric hindrance. Compound 68 [69] exists in a ribbon, pattern B. The remaining compound 69 [70] exhibits C(6) chains with the imide NH linked to the remote nitrogen of the CN substituent in the form of pattern E.

Succinimides Fused to Four-Membered Rings
Of the seven reported structures for succinimides fused to four-membered rings, compound 70 [71] (Figure 25) exists as a linear hydrogen-bonded ribbon of type B. Compound 71 [72] exists as a square of four molecules in the rather uncommon pattern G (R 4 4 (16)). The compound 72 [73] exhibits a linear C(8) chain pattern F where the imide NH is bonded to the remote CO of the cyclohexenone ring. Two structures, compounds 73 [73] and 74 [74] exist as dimers of category D (R

Succinimides Fused to Three-Membered Rings
Among the three reported structures for succinimides fused with three-membered rings, compound 67 [68] (Figure 24) shows no hydrogen bonding probably due to the high degree of steric hindrance. Compound 68 [69] exists in a ribbon, pattern B. The remaining compound 69 [70] exhibits C(6) chains with the imide NH linked to the remote nitrogen of the CN substituent in the form of pattern E. The remaining compound 66 [19,20] (Figure 23) has a more complex linkage. Two molecules dimerise, with imide NH and CO (methylthio side) interacting. The dimers are further linked to each other by the other imide CO bonding to the OH of another dimer. As for compound 31 this has designation C(10)[ R

Succinimides Fused to Three-Membered Rings
Among the three reported structures for succinimides fused with three-membered rings, compound 67 [68] (Figure 24) shows no hydrogen bonding probably due to the high degree of steric hindrance. Compound 68 [69] exists in a ribbon, pattern B. The remaining compound 69 [70] exhibits C(6) chains with the imide NH linked to the remote nitrogen of the CN substituent in the form of pattern E.

Succinimides Fused to Four-Membered Rings
Of the seven reported structures for succinimides fused to four-membered rings, compound 70 [71] (Figure 25) exists as a linear hydrogen-bonded ribbon of type B. Compound 71 [72] exists as a square of four molecules in the rather uncommon pattern G (R 4 4 (16)). The compound 72 [73] exhibits a linear C(8) chain pattern F where the imide NH is bonded to the remote CO of the cyclohexenone ring. Two structures, compounds 73 [73] and 74 [74] exist as dimers of category D (R

Succinimides Fused to Four-Membered Rings
Of the seven reported structures for succinimides fused to four-membered rings, compound 70 [71] (Figure 25) exists as a linear hydrogen-bonded ribbon of type B. Compound 71 [72] exists as a square of four molecules in the rather uncommon pattern G (R 4 4 (16)). The compound 72 [73] exhibits a linear C(8) chain pattern F where the imide NH is bonded to the remote CO of the cyclohexenone ring. Two structures, compounds 73 [73] and 74 [74] exist as dimers of category D (R 2 2 (16) and R 2 2 (12), respectively) where the NH of the imide is bonded to the remote O of the other molecule. The two remaining structures exhibit more complex patterns of hydrogen bonding. Compound 75 [75] (Figure 26) forms a ribbon structure of pattern B, with the imide NH and the CO (away from the isopropyloxy substituent) interacting. Additionally, the NH and CO of the six-membered rings link to the corresponding groups on adjacent ribbons creating a two-dimensional network with the combination of the two C(4) interactions forming R 4 4 (23) units. The two remaining structures exhibit more complex patterns of hydrogen bonding. Compound 75 [75] (Figure 26) forms a ribbon structure of pattern B, with the imide NH and the CO (away from the isopropyloxy substituent) interacting. Additionally, the NH and CO of the six-membered rings link to the corresponding groups on adjacent ribbons creating a two-dimensional network with the combination of the two C(4) interactions forming R  Compound 76 [73] (Figure 27) shows two linear antiparallel chains where each imide NH is bonded to the CO both of the pyranone ring of the next molecule in the same chain and to the one opposite in the other chain. Likewise, each pyranone CO is bonded to two imine NH groups, one in the same chain and one opposite to give a series of four-membered ring interactions holding the chains together. This pattern can be designated as C(8)R 2 2 (6) giving rise also to R 2 2 (16).There are no hydrogen-bonding interactions with the imide carbonyl groups.   Compound 76 [73] ( Figure 27) shows two linear antiparallel chains where each imide NH is bonded to the CO both of the pyranone ring of the next molecule in the same chain and to the one opposite in the other chain. Likewise, each pyranone CO is bonded to two imine NH groups, one in the same chain and one opposite to give a series of four-membered ring interactions holding the chains together. This pattern can be designated as C(8)R 2 2 (6) giving rise also to R 2 2 (16).There are no hydrogen-bonding interactions with the imide carbonyl groups. The two remaining structures exhibit more complex patterns of hydrogen bonding. Compound 75 [75] (Figure 26) forms a ribbon structure of pattern B, with the imide NH and the CO (away from the isopropyloxy substituent) interacting. Additionally, the NH and CO of the six-membered rings link to the corresponding groups on adjacent ribbons creating a two-dimensional network with the combination of the two C(4) interactions forming R  Compound 76 [73] (Figure 27) shows two linear antiparallel chains where each imide NH is bonded to the CO both of the pyranone ring of the next molecule in the same chain and to the one opposite in the other chain. Likewise, each pyranone CO is bonded to two imine NH groups, one in the same chain and one opposite to give a series of four-membered ring interactions holding the chains together. This pattern can be designated as C(8)R 2 2 (6) giving rise also to R 2 2 (16).There are no hydrogen-bonding interactions with the imide carbonyl groups.

Succinimides Fused to Five-Membered Rings
Fifteen structures have been reported for succinimides fused to five-membered rings. Two of these, compounds 77 [76] and 78 [77] (Figure 28) exist as simple dimers of type A. Four compounds, 79 [78], 80 [79], 81 [80] and 82 [45] exhibit linear ribbon type hydrogen bonding of category B. Two structures, compounds 83 [76] which is a stereoisomer of 77, and 84 [81] (Figure 29), exist in type E linear chains (C(11) and C (6), respectively) where the imide NH is linked to a remote nitrogen of the next molecule. Compound 85 [81] shows a linear C(10) chain of molecules in pattern F where the imide NH is interacting with the remote CO of the methyl ester group in the next molecule.  Two structures, compounds 83 [76] which is a stereoisomer of 77, and 84 [81] (Figure 29), exist in type E linear chains (C(11) and C(6), respectively) where the imide NH is linked to a remote nitrogen of the next molecule. Compound 85 [81] shows a linear C(10) chain of molecules in pattern F where the imide NH is interacting with the remote CO of the methyl ester group in the next molecule.

Succinimides Fused to Five-Membered Rings
Fifteen structures have been reported for succinimides fused to five-membered rings. Two of these, compounds 77 [76] and 78 [77] (Figure 28) exist as simple dimers of type A. Four compounds, 79 [78], 80 [79], 81 [80] and 82 [45] exhibit linear ribbon type hydrogen bonding of category B. Two structures, compounds 83 [76] which is a stereoisomer of 77, and 84 [81] (Figure 29), exist in type E linear chains (C(11) and C (6), respectively) where the imide NH is linked to a remote nitrogen of the next molecule. Compound 85 [81] shows a linear C(10) chain of molecules in pattern F where the imide NH is interacting with the remote CO of the methyl ester group in the next molecule.  (14)) where the imide NH is bonded to a remote CO of another molecule and vice versa. Compound 86 [82] (Figure 30) is one example of a category H pattern where there is a bis imide linkage. It forms dimers by bonding between the pyrrolidine-fused succinimide's NH and CO and these are then further linked into a chain by bonding between the CO and NH of the spirocyclically linked succinimides, giving an overall C (14) (14)) where the imide NH is bonded to a remote CO of another molecule and vice versa.

Succinimides Fused to Five-Membered Rings
Fifteen structures have been reported for succinimides fused to five-membered rings. Two of these, compounds 77 [76] and 78 [77] (Figure 28) exist as simple dimers of type A. Four compounds, 79 [78], 80 [79], 81 [80] and 82 [45] exhibit linear ribbon type hydrogen bonding of category B. Two structures, compounds 83 [76] which is a stereoisomer of 77, and 84 [81] (Figure 29), exist in type E linear chains (C(11) and C (6), respectively) where the imide NH is linked to a remote nitrogen of the next molecule. Compound 85 [81] shows a linear C(10) chain of molecules in pattern F where the imide NH is interacting with the remote CO of the methyl ester group in the next molecule.  (14)) where the imide NH is bonded to a remote CO of another molecule and vice versa. The three remaining structures display more complex patterns. In compound 89 [85] (Figure 31) imide NH to CO dimers are linked in a row held together by OH to benzoyl CO hydrogen bonding. The combination of C(8) and R 2 2 (8) creates R 4 4 (32) rings. The three remaining structures display more complex patterns. In compound 89 [85] (Figure 31) imide NH to CO dimers are linked in a row held together by OH to benzoyl CO hydrogen bonding.
The combination of C(8) and R   In the final compound 91 [87] (Figure 33) there is C(5) hydrogen bonding between the imide NH of one molecule and the oxazoline nitrogen of the next molecule. This compound thus exists as a helix with a five molecule repeat unit. The three remaining structures display more complex patterns. In compound 89 [85] (Figure 31) imide NH to CO dimers are linked in a row held together by OH to benzoyl CO hydrogen bonding.
The combination of C(8) and R   In the final compound 91 [87] (Figure 33) there is C(5) hydrogen bonding between the imide NH of one molecule and the oxazoline nitrogen of the next molecule. This compound thus exists as a helix with a five molecule repeat unit. In the final compound 91 [87] (Figure 33) there is C(5) hydrogen bonding between the imide NH of one molecule and the oxazoline nitrogen of the next molecule. This compound thus exists as a helix with a five molecule repeat unit. The three remaining structures display more complex patterns. In compound 89 [85] (Figure 31) imide NH to CO dimers are linked in a row held together by OH to benzoyl CO hydrogen bonding.
The combination of C(8) and R   In the final compound 91 [87] (Figure 33) there is C(5) hydrogen bonding between the imide NH of one molecule and the oxazoline nitrogen of the next molecule. This compound thus exists as a helix with a five molecule repeat unit.

Succinimides Fused to Six-Membered Rings
Twenty-seven structures were located for succinimides fused to six-membered rings. Of these six structures, compounds 92 [88], 93 [89], 94 [90], 95 [91], 96 [92] and 97 [93] (Figure 34), exist as simple dimers of type A. Six of the reported structures, compounds 98 [94], 99 [95,96], 100 [97], 101 [89], 102 [98] and 103 [99] (Figure 35) exhibit a linear ribbon structure of pattern B. Six compounds, 104 [85], 105 [100], 106 [101], 107 [102,103], 108 [104] and 109 [105] (Figure 36) are observed in a linear chain with the imide NH bound to a remote oxygen of the next molecule in the type F pattern (respective designations C(10), C(6), C(9), C(8), C (11) and C (7)). As shown there is an additional intramolecular S(6) interaction in 104.             The structure of 114 [109] (Figure 39) shows imide NH to imide CO R 2 2 (8) dimers further bonded to adjacent such dimers by an indole NH to imide CO C(7) interaction giving rise to a complex cross-linked network.  Three more compounds also show more complex patterns of hydrogen bonding. Compound 116 [110] (Figure 41) is a bis imide but one of the imide groups is not involved in the hydrogen bonding. The other imide group forms linear C(4) chains of type B. to adjacent such dimers by an indole NH to imide CO C(7) interaction giving rise to a complex cross-linked network.  Three more compounds also show more complex patterns of hydrogen bonding. Compound 116 [110] (Figure 41) is a bis imide but one of the imide groups is not involved in the hydrogen bonding. The other imide group forms linear C(4) chains of type B.  Three more compounds also show more complex patterns of hydrogen bonding. Compound 116 [110] (Figure 41) is a bis imide but one of the imide groups is not involved in the hydrogen bonding. The other imide group forms linear C(4) chains of type B. Compound 117 [111] (Figure 42) displays linear C(10) chains with imide NH to ester CO links.
These chains are further linked by R  Figure 41. Structure adopted by compound 116. Compound 117 [111] (Figure 42) displays linear C(10) chains with imide NH to ester CO links. These chains are further linked by R 2 2 (18) dimer formation between the imide CO and the alcohol OH on the eight-membered ring. Compound 117 [111] (Figure 42) displays linear C(10) chains with imide NH to ester CO links.
These chains are further linked by R 2 2 (18) dimer formation between the imide CO and the alcohol OH on the eight-membered ring. The final structure, compound 118 [112] ( Figure 43) exists as imide NH to sulfonyl SO R 2 2 (16) dimers that are further cross-linked to each other by an R 2 2 (12) interaction of sulfonamide NH and an imide CO in the same unit, thus setting up also two R 2 2 (8) units.

Monocyclic Unsaturated Glutarimides
Six structures have been reported for monocyclic unsaturated glutarimides. Four of these structures, compounds 166 [143], 167 [144], 168 [145] and 169 [146] (Figure 51) exist as simple R 2 2 (8) dimers of category A, with 166 and 168 displaying an additional intramolecular S(6) interaction. Compound 170 [147] exists as a simple linear C(5) chain with the imide NH bonded to a remote oxygen on the next molecule in a type F pattern.
The remaining structure, compound 171 [148] (Figure 52) exhibits a more complex pattern similar to 31 and 66, with imide NH to imide CO dimers forming R 2 2 (8) units which are linked to each other by R 2 2 (10) interaction of the other imide CO with the OH substituent giving a chain with overall designation C(11)[ R 2 2 (8), R 2 2 (10)].
Six structures have been reported for monocyclic unsaturated glutarimides. Four of these structures, compounds 166 [143], 167 [144], 168 [145] and 169 [146] (Figure 51) exist as simple R 2 2 (8) dimers of category A, with 166 and 168 displaying an additional intramolecular S(6) interaction. Compound 170 [147] exists as a simple linear C(5) chain with the imide NH bonded to a remote oxygen on the next molecule in a type F pattern.

Ring-Fused Unsaturated Glutarimides
Nine structures were located for ring-fused glutarimides of which six compounds 172 [149], 173 [150], 174 [151], 175 [152], 176 [153] and 177 [154] (Figure 53), exist as simple imide NH-CO R  The three remaining structures have complex hydrogen-bonding networks. Compound 178 [155] (Figure 54) forms C(6) chains linked both by interactions of imide NH to aldehyde CO and imide CO to pyrazole NH, forming R 2 2 (10) units. A series of antiparallel chains are then cross-linked by C(8) amino to imide CO bonding, forming a two-dimensional network incorporating R 4 4 (21) units. Compound 179 [155] (Figure 55) exists as one of the most complex structures observed in this area. In each molecule, one imide CO is intramolecularly S(6) hydrogen bonded to the enol OH. The structure then consists of an alternating chain of two different types of R 2 2 (8) dimer, one formed by imide NH to intramolecularly hydrogen-bonded imide CO interaction, and the other by imide NH to non-intramolecularly hydrogen-bonded CO interaction. These are then linked in a single C(22) chain by bonding of the free imide CO of the former type to the pyrazolyl amino group of the latter.
The three remaining structures have complex hydrogen-bonding networks. Compound 178 [155] (Figure 54) forms C(6) chains linked both by interactions of imide NH to aldehyde CO and imide CO to pyrazole NH, forming R 2 2 (10) units. A series of antiparallel chains are then cross-linked by C(8) amino to imide CO bonding, forming a two-dimensional network incorporating R  Compound 179 [155] (Figure 55) exists as one of the most complex structures observed in this area. In each molecule, one imide CO is intramolecularly S(6) hydrogen bonded to the enol OH. The structure then consists of an alternating chain of two different types of R 2 2 (8) dimer, one formed by imide NH to intramolecularly hydrogen-bonded imide CO interaction, and the other by imide NH to non-intramolecularly hydrogen-bonded CO interaction. These are then linked in a single C (22) chain by bonding of the free imide CO of the former type to the pyrazolyl amino group of the latter.

Glutarimide
One structure has been published for parent glutarimide 181 [157] (Figure 57) which exhibits a ribbon structure of type B with C(4) imide NH-imide CO bonding between two rows of molecules. Compound 180 [156] (Figure 56) exists as imide NH to imide CO R 2 2 (8) dimers further linked in a chain by pyrrole NH to ester CO R 2 2 (10) interactions.

Glutarimide
One structure has been published for parent glutarimide 181 [157] (Figure 57) which exhibits a ribbon structure of type B with C(4) imide NH-imide CO bonding between two rows of molecules.

Glutarimide
One structure has been published for parent glutarimide 181 [157] (Figure 57) which exhibits a ribbon structure of type B with C(4) imide NH-imide CO bonding between two rows of molecules. The remaining three structures exist with more complex forms of hydrogen bonding. Compound 195 [171] (Figure 58) is a second form of 191 whose structure is quite different. The primary interaction is between the imide NH and the lactam carbonyl, leading to a C(7) ribbon structure as shown. However, this is then linked to further such chains both behind and in front of the plane by both imide carbonyls being bonded to amino NH and each amino group bonding to the imide CO of two separate molecules, forming a complex three-dimensional network. Compound 196 [163] (Figure 59), forms imide NH to imide CO R
The remaining three structures exist with more complex forms of hydrogen bonding. Compound 195 [171] (Figure 58) is a second form of 191 whose structure is quite different. The primary interaction is between the imide NH and the lactam carbonyl, leading to a C(7) ribbon structure as shown. However, this is then linked to further such chains both behind and in front of the plane by both imide carbonyls being bonded to amino NH and each amino group bonding to the imide CO of two separate molecules, forming a complex three-dimensional network. The remaining three structures exist with more complex forms of hydrogen bonding. Compound 195 [171] (Figure 58) is a second form of 191 whose structure is quite different. The primary interaction is between the imide NH and the lactam carbonyl, leading to a C(7) ribbon structure as shown. However, this is then linked to further such chains both behind and in front of the plane by both imide carbonyls being bonded to amino NH and each amino group bonding to the imide CO of two separate molecules, forming a complex three-dimensional network. Compound 196 [163] (Figure 59), forms imide NH to imide CO R  Compound 196 [163] (Figure 59), forms imide NH to imide CO R 2 2 (8) dimers. These dimer units are further linked in C(8) chains by the head-to-tail interaction of the phenylamino NH and one phthalimide CO between adjacent dimers, leading to formation of R 4 4 (38) units.

4-Monosubstituted Glutarimides
Five structures have been published for 4-monosubstituted glutarimides. Compound 198 [172] and 199 [173] (Figure 61) exist as simple R 2 2 (8) dimers of type A with additional intramolecular S(6) interactions as shown. The compounds 200 [174] and 201 [175] exhibit the linear C(4) ribbon pattern B and again 200 has the intramolecular S(6) interaction shown.  The remaining structure involves more complex bonding. Compound 202 [176] (Figure 62) displays primarily an imide NH to CO C(4) ribbon pattern of type B which is supplemented by an interaction of the same imide CO to an alcohol OH in a separate ribbon above or below the plane.

3,3-Disubstituted Glutarimides
Of the twelve reported structures for 3,3-disubstituted glutarimides, four compounds 203 [177], 204 [178], 205 [177] and 206 [179] (Figure 63) exist as simple R 2 2 (8) dimers of pattern A. It should be noted, however, that while 203 and 204 bond using the imide 6-CO away from the substituents, compound 205 uses the more hindered 2-CO, and for compound 206 one carbonyl of each type is involved, giving an unsymmetrical dimer. Five structures, viz. compounds 207 [160], 208 [160], 209 [180], 210 [180] and 211 [181] display simple linear ribbon type hydrogen bonding of category B. In the case of 207 and 208 either the CO nearer the substituents of the CO further away can be involved, giving two different structures. The remaining structure involves more complex bonding. Compound 202 [176] (Figure 62) displays primarily an imide NH to CO C(4) ribbon pattern of type B which is supplemented by an interaction of the same imide CO to an alcohol OH in a separate ribbon above or below the plane.  The remaining structure involves more complex bonding. Compound 202 [176] (Figure 62) displays primarily an imide NH to CO C(4) ribbon pattern of type B which is supplemented by an interaction of the same imide CO to an alcohol OH in a separate ribbon above or below the plane.

3,3-Disubstituted Glutarimides
Of the twelve reported structures for 3,3-disubstituted glutarimides, four compounds 203 [177], 204 [178], 205 [177] and 206 [179] (Figure 63) exist as simple R 2 2 (8) dimers of pattern A. It should be noted, however, that while 203 and 204 bond using the imide 6-CO away from the substituents, compound 205 uses the more hindered 2-CO, and for compound 206 one carbonyl of each type is involved, giving an unsymmetrical dimer. Five structures, viz. compounds 207 [160], 208 [160], 209 [180], 210 [180] and 211 [181] display simple linear ribbon type hydrogen bonding of category B. In the case of 207 and 208 either the CO nearer the substituents of the CO further away can be involved, giving two different structures. Compound 212 [182] ( Figure 64) exhibits a linear C(8) chain of molecules where the imide NH is bonded to the remote nitrogen of the pyridine ring in pattern E. The racemic compound 213 [160] exists as a cyclic R 2 2 (14) dimer of category D where the imide NH is linked to the phthalimide CO. Compound 214 [182] exhibits a more complex pattern. The imide NH is again connected to the remote nitrogen of the pyridine ring in a C(8) chain of pattern E but instead of a linear chain it forms a helix with a four-molecule repeat unit.

3,5-Disubstituted Glutarimides
Two structures have been reported for 3,5-disubstituted glutarimides of which compound 217 [184] (Figure 65) exhibits a linear ribbon pattern B. Compound 218 [185] (Figure 66) exhibits a more complex pattern with imide NH to imide CO R Compound 212 [182] (Figure 64) exhibits a linear C(8) chain of molecules where the imide NH is bonded to the remote nitrogen of the pyridine ring in pattern E. The racemic compound 213 [160] exists as a cyclic R 2 2 (14) dimer of category D where the imide NH is linked to the phthalimide CO. Compound 212 [182] ( Figure 64) exhibits a linear C(8) chain of molecules where the imide NH is bonded to the remote nitrogen of the pyridine ring in pattern E. The racemic compound 213 [160] exists as a cyclic R 2 2 (14) dimer of category D where the imide NH is linked to the phthalimide CO. Compound 214 [182] exhibits a more complex pattern. The imide NH is again connected to the remote nitrogen of the pyridine ring in a C(8) chain of pattern E but instead of a linear chain it forms a helix with a four-molecule repeat unit.

3,5-Disubstituted Glutarimides
Two structures have been reported for 3,5-disubstituted glutarimides of which compound 217 [184] (Figure 65) exhibits a linear ribbon pattern B. Compound 218 [185] (Figure 66) exhibits a more complex pattern with imide NH to imide CO R  Compound 214 [182] exhibits a more complex pattern. The imide NH is again connected to the remote nitrogen of the pyridine ring in a C(8) chain of pattern E but instead of a linear chain it forms a helix with a four-molecule repeat unit.

3,4-Disubstituted Glutarimides
Two structures were located for 3,4-disubstituted glutarimides of which one, compound 215 [183] ( Figure 65) exists as a simple R 2 2 (8) dimer of category A. The second compound, 216 [183] exhibits a linear C(4) ribbon pattern B. Compound 212 [182] ( Figure 64) exhibits a linear C(8) chain of molecules where the imide NH is bonded to the remote nitrogen of the pyridine ring in pattern E. The racemic compound 213 [160] exists as a cyclic R 2 2 (14) dimer of category D where the imide NH is linked to the phthalimide CO. Compound 214 [182] exhibits a more complex pattern. The imide NH is again connected to the remote nitrogen of the pyridine ring in a C(8) chain of pattern E but instead of a linear chain it forms a helix with a four-molecule repeat unit.

3,5-Disubstituted Glutarimides
Two structures have been reported for 3,5-disubstituted glutarimides of which compound 217 [184] ( Figure 65) exhibits a linear ribbon pattern B. Compound 218 [185] (Figure 66) exhibits a more complex pattern with imide NH to imide CO R 2 2 (8) dimer units linked to each other by further head-to-tail C(8) interactions of a phthalimide CO and the OH substituent on the glutarimide ring, forming a ribbon incorporating R 4 4 (24) units.

4,4-Disubstituted Glutarimides
Four structures have been reported for 4,4-disubstituted glutarimides. Two structures, compounds 219 [186] and 220 [187] (Figure 67) exist as simple R 2 2 (8) dimers of Type A. Compound 221 [188] exists as a linear ribbon of pattern B. The remaining compound 222 [189] exists as an imide NH to remote oxygen R 2 2 (16) dimer of type D with the imide NH hydrogen bonding to one of the ester CO groups.

Trisubstituted Glutarimides
Three structures have been published for trisubstituted glutarimides. Two of these structures: compounds 223 [190] and 224 [191,192] (Figure 67) exist as simple imide NH to imide CO R 2 2 (8) dimers of category A. Compound 225 [193] (Figure 68) exhibits a more complex pattern with imide NH to imide CO R

4,4-Disubstituted Glutarimides
Four structures have been reported for 4,4-disubstituted glutarimides. Two structures, compounds 219 [186] and 220 [187] (Figure 67) exist as simple R 2 2 (8) dimers of Type A. Compound 221 [188] exists as a linear ribbon of pattern B. The remaining compound 222 [189] exists as an imide NH to remote oxygen R 2 2 (16) dimer of type D with the imide NH hydrogen bonding to one of the ester CO groups.

4,4-Disubstituted Glutarimides
Four structures have been reported for 4,4-disubstituted glutarimides. Two structures, compounds 219 [186] and 220 [187] (Figure 67) exist as simple R 2 2 (8) dimers of Type A. Compound 221 [188] exists as a linear ribbon of pattern B. The remaining compound 222 [189] exists as an imide NH to remote oxygen R 2 2 (16) dimer of type D with the imide NH hydrogen bonding to one of the ester CO groups.

Trisubstituted Glutarimides
Three structures have been published for trisubstituted glutarimides. Two of these structures: compounds 223 [190] and 224 [191,192] (Figure 67) exist as simple imide NH to imide CO R 2 2 (8) dimers of category A. Compound 225 [193] (Figure 68) exhibits a more complex pattern with imide NH to imide CO R

Trisubstituted Glutarimides
Three structures have been published for trisubstituted glutarimides. Two of these structures: compounds 223 [190] and 224 [191,192] (Figure 67) exist as simple imide NH to imide CO R 2 2 (8) dimers of category A. Compound 225 [193] (Figure 68) exhibits a more complex pattern with imide NH to imide CO R 2 2 (8) dimer units further linked to each other by a head-to tail R 2 2 (16) interaction of phenol OH and ester CO forming a C(16) ribbon.

Ring-Fused Glutarimides
Four structures were reported for ring-fused glutarimides. Of these, compound 233 [197] ( Figure 70) consists of equal quantities of two distinct molecules, one forming simple dimers of category A and the other linear ribbons of pattern B with these structural elements intermixed in the unit cell. Compound 234 [198] forms an imide NH to imide CO linear ribbon of pattern B. Compound 235 [199] forms simple linear C(8) chains of type F where the imide NH is H-bonded to the remote CO of the indolinone ring.

Ring-Fused Glutarimides
Four structures were reported for ring-fused glutarimides. Of these, compound 233 [197] ( Figure 70) consists of equal quantities of two distinct molecules, one forming simple dimers of category A and the other linear ribbons of pattern B with these structural elements intermixed in the unit cell. Compound 234 [198] forms an imide NH to imide CO linear ribbon of pattern B. Compound 235 [199] forms simple linear C(8) chains of type F where the imide NH is H-bonded to the remote CO of the indolinone ring.

Ring-Fused Glutarimides
Four structures were reported for ring-fused glutarimides. Of these, compound 233 [197] (Figure 70) consists of equal quantities of two distinct molecules, one forming simple dimers of category A and the other linear ribbons of pattern B with these structural elements intermixed in the unit cell. Compound 234 [198] forms an imide NH to imide CO linear ribbon of pattern B. Compound 235 [199] forms simple linear C(8) chains of type F where the imide NH is H-bonded to the remote CO of the indolinone ring.

Ring-Fused Glutarimides
Four structures were reported for ring-fused glutarimides. Of these, compound 233 [197] ( Figure 70) consists of equal quantities of two distinct molecules, one forming simple dimers of category A and the other linear ribbons of pattern B with these structural elements intermixed in the unit cell. Compound 234 [198] forms an imide NH to imide CO linear ribbon of pattern B. Compound 235 [199] forms simple linear C(8) chains of type F where the imide NH is H-bonded to the remote CO of the indolinone ring. The remaining structure, compound 236 [200] (Figure 71) exhibits a more complex pattern of bonding. Linear antiparallel chains facing each other are linked together by C(8) imide NH to remote bridging oxygen interaction and this is supplemented by an imide CO to alcohol OH interaction, forming R 2 2 (8) units.

Six-Membered Ring Imides with More than One Heteroatom
Fourteen structures have been reported for six-membered ring imides with more than one heteroatom in the ring. Three structures 264 [221], 265 [222] and 266 [223] (Figure 75) exist as simple Crystals 2020, 10, x FOR PEER REVIEW 32 of 50 [216] and 257 [216] display pattern C bonding with imide NH forming dimers with a remote nitrogen and designations R 2 2 (22) and R 2 2 (26), respectively. In the latter case, there is an additional amino to imide CO interaction. The compounds 258 [217] and 259 [217] are bis imides that exhibit imide NH to imide CO doubly linked bonding pattern H or C 2 2 (6)[R 2 2 (8)]. Two more extended bis imides 260 [218] and 261 [201] also exhibit pattern H bonding with respective designations   Compound 263 [220] (Figure 74) also exhibits an unusual bonding pattern. The imide NH of one molecule interacts with the imide CO of the other molecule but the reciprocal interaction is not observed. As shown, it is the more hindered imide CO that is involved in the D type bonding while the less hindered one is not.

Six-Membered Ring Imides with More than One Heteroatom
Fourteen structures have been reported for six-membered ring imides with more than one heteroatom in the ring. Three structures 264 [221], 265 [222] and 266 [223] (Figure 75) exist as simple Compound 263 [220] (Figure 74) also exhibits an unusual bonding pattern. The imide NH of one molecule interacts with the imide CO of the other molecule but the reciprocal interaction is not observed. As shown, it is the more hindered imide CO that is involved in the D type bonding while the less hindered one is not.

Six-Membered Ring Imides with More than One Heteroatom
Fourteen structures have been reported for six-membered ring imides with more than one heteroatom in the ring. Three structures 264 [221], 265 [222] and 266 [223] (Figure 75) exist as simple imide NH to imide CO R 2 2 (8) dimers of pattern A. In compound 265 [222], the imide NH of one molecule is hydrogen bonded to the imide CO of another molecule, but the reciprocal interaction does not occur, resulting in a D type interaction. Compounds 267 [224] and 268 [225] exist as simple hydrogen-bonded ribbons of pattern B. Compound 269 [226] shows two crystal forms both as C (7) chains with the imide NH bonded to the remote CO of the pyrrolidinone ring in pattern F.  [222], the imide NH of one molecule is hydrogen bonded to the imide CO of another molecule, but the reciprocal interaction does not occur, resulting in a D type interaction. Compounds 267 [224] and 268 [225] exist as simple hydrogen-bonded ribbons of pattern B. Compound 269 [226] shows two crystal forms both as C (7) chains with the imide NH bonded to the remote CO of the pyrrolidinone ring in pattern F. Five structures, compounds 270 [227], 271 [228], 272 [229], 273 [229] and 274 [230] (Figure 76  Five structures, compounds 270 [227], 271 [228], 272 [229], 273 [229] and 274 [230] (Figure 76) [222], the imide NH of one molecule is hydrogen bonded to the imide CO of another molecule, but the reciprocal interaction does not occur, resulting in a D type interaction. Compounds 267 [224] and 268 [225] exist as simple hydrogen-bonded ribbons of pattern B. Compound 269 [226] shows two crystal forms both as C (7) chains with the imide NH bonded to the remote CO of the pyrrolidinone ring in pattern F. Five structures, compounds 270 [227], 271 [228], 272 [229], 273 [229] and 274 [230] (Figure 76) are bis imides that hydrogen bond to give a doubly linked chain of pattern H with respective  Compound 276 [231,232] (Figure 78) exists in a complex pattern of hydrogen bonding. It involves formation of a two-dimensional network in which alternate molecules are arranged perpendicularly to each other and each imide NH is bonded equally between two imide CO groups.
There are both R  Compound 277 [233] (Figure 79) has two linear parallel chains of molecules linked to each other by interactions of one imide CO of each molecule to both the imide NH of one molecule in the opposite chain and an alcohol OH of an adjacent molecule also in the opposite chain. In this way each molecule has two donor and two acceptor interactions and is involved in two R    Compound 276 [231,232] (Figure 78) exists in a complex pattern of hydrogen bonding. It involves formation of a two-dimensional network in which alternate molecules are arranged perpendicularly to each other and each imide NH is bonded equally between two imide CO groups. There are both R 2 1 (5) and R 4 4 (16) units present. Compound 276 [231,232] (Figure 78) exists in a complex pattern of hydrogen bonding. It involves formation of a two-dimensional network in which alternate molecules are arranged perpendicularly to each other and each imide NH is bonded equally between two imide CO groups.

Eight-and Nine-Membered Cyclic Carboximides
There are both R  Compound 277 [233] (Figure 79) has two linear parallel chains of molecules linked to each other by interactions of one imide CO of each molecule to both the imide NH of one molecule in the opposite chain and an alcohol OH of an adjacent molecule also in the opposite chain. In this way each molecule has two donor and two acceptor interactions and is involved in two R    Compound 277 [233] (Figure 79) has two linear parallel chains of molecules linked to each other by interactions of one imide CO of each molecule to both the imide NH of one molecule in the opposite chain and an alcohol OH of an adjacent molecule also in the opposite chain. In this way each molecule has two donor and two acceptor interactions and is involved in two R 2 2 (9) units, one as the four atom component and one as the five atom component and the two enantiomeric chains are strongly bound into a ribbon structure. Compound 276 [231,232] (Figure 78) exists in a complex pattern of hydrogen bonding. It involves formation of a two-dimensional network in which alternate molecules are arranged perpendicularly to each other and each imide NH is bonded equally between two imide CO groups.

Eight-and Nine-Membered Cyclic Carboximides
There are both R  Compound 277 [233] (Figure 79) has two linear parallel chains of molecules linked to each other by interactions of one imide CO of each molecule to both the imide NH of one molecule in the opposite chain and an alcohol OH of an adjacent molecule also in the opposite chain. In this way each molecule has two donor and two acceptor interactions and is involved in two R

Eight-and Nine-Membered Cyclic Carboximides
Four structures have been reported for eight-and nine-membered cyclic NH carboximides all of which, viz. 278 [234], 279 [235], 280 [235] and 281 [236] (Figure 80) exist as simple NH to CO hydrogen-bonded R 2 2 (8) dimers of pattern A. It is notable that between the closely similar compounds 279 and 280 the opposite imide CO is involved. Four structures have been reported for eight-and nine-membered cyclic NH carboximides all of which, viz. 278 [234], 279 [235], 280 [235] and 281 [236] (Figure 80) exist as simple NH to CO hydrogen-bonded R 2 2 (8) dimers of pattern A. It is notable that between the closely similar compounds 279 and 280 the opposite imide CO is involved. Figure 80. Eight-and nine-membered ring imides and spiro imides of patterns A and F.

Spiro Imides
Five structures have been reported for Spiro-imides. Compound 282 [237] (Figure 80) exists as a simple hydrogen-bonded dimer of pattern A where the CO away from the spiro ring is involved in interaction. Compound 283 [237] in contrast, exhibits imide NH to remote CO bonding, giving a linear C(8) chain of pattern F.
Compound 284 [237] (Figure 81) involves a more complex form of bonding where dimers are formed by head-to tail R 2 2 (8) linkage of the imide NH from one ring with one imide CO of the other. These are then further linked into a ribbon by imide NH to imide CO R 2 2 (12) bonding using the remaining CO from the imide involved the first interaction and the NH of the other imide.

Spiro Imides
Five structures have been reported for Spiro-imides. Compound 282 [237] (Figure 80) exists as a simple hydrogen-bonded dimer of pattern A where the CO away from the spiro ring is involved in interaction. Compound 283 [237] in contrast, exhibits imide NH to remote CO bonding, giving a linear C(8) chain of pattern F.
Compound 284 [237] (Figure 81) involves a more complex form of bonding where dimers are formed by head-to tail R 2 2 (8) linkage of the imide NH from one ring with one imide CO of the other. These are then further linked into a ribbon by imide NH to imide CO R 2 2 (12) bonding using the remaining CO from the imide involved the first interaction and the NH of the other imide.
In Compound 285 [238] (Figure 82) a complex two-dimensional network pattern is observed made up of imide NH to lactam CO R 2 2 (12) dimers which are arranged in a herring-bone pattern. Each dimer is then linked to four further dimers in the adjacent rows by C(7) lactam NH to CO hydrogen bonding. In this case the imide carbonyls are not involved.
The compound 286 [239] (Figure 83) exists as a complex two-dimensional network in which imide NH to imide CO R 2 2 (8) dimer units are arranged in lines with alternating orientation and each dimer is further linked to two separate dimers in the lines on either side by a C(8) interaction of the remaining CO of the dimer-forming imide function with the NH of the non-dimer-forming imide. In Compound 285 [238] (Figure 82) a complex two-dimensional network pattern is observed made up of imide NH to lactam CO R 2 2 (12) dimers which are arranged in a herring-bone pattern. Each dimer is then linked to four further dimers in the adjacent rows by C(7) lactam NH to CO hydrogen bonding. In this case the imide carbonyls are not involved. In Compound 285 [238] (Figure 82) a complex two-dimensional network pattern is observed made up of imide NH to lactam CO R 2 2 (12) dimers which are arranged in a herring-bone pattern. Each dimer is then linked to four further dimers in the adjacent rows by C(7) lactam NH to CO hydrogen bonding. In this case the imide carbonyls are not involved. The compound 286 [239] (Figure 83) exists as a complex two-dimensional network in which imide NH to imide CO R 2 2 (8) dimer units are arranged in lines with alternating orientation and each dimer is further linked to two separate dimers in the lines on either side by a C(8) interaction of the remaining CO of the dimer-forming imide function with the NH of the non-dimer-forming imide.

Propellanes
Two structures have been reported for imide-containing propellanes. One of these, compound 287 [240] (Figure 84) shows no hydrogen bonding probably due to the high degree of steric hindrance. The other, compound 288 [241], exhibits linear chains with the imide NH hydrogen equally bonded to both bridging oxygens, resulting in designation C

Conclusion
A large number of cyclic NH carboximides have been subject to X-ray structure determination, allowing meaningful conclusions to be drawn from analysis of the patterns observed. It is clear that imide NH to imide CO dimers are the commonest single structure observed followed by linear imide NH to imide CO ribbons, with larger substituents often favouring the dimers whereas smaller substituents are more conducive to ribbon formation. Where additional oxygen or nitrogen atoms are present in the structure, dimers and chains involving imide NH and these remote acceptors are also observed and there are a total of 52 compounds, mainly of this type, in which neither imide CO is involved in hydrogen bonding. In contrast to this situation, the imide NH is involved in hydrogen bonding whenever it occurs, although there are four cases (compounds 67, 161, 162 and 287) where a high degree of steric hindrance prevents any hydrogen bonding at all. The presence of further hydrogen bonding groups of various types may lead to more complex two-and three-dimensional structures and over 40 such diverse patterns are presented. There are relatively few cases where a single compound has been shown to have several different types of structure but compound 191/195/197 provides a good example, and in one case, compound 233, two separate structural types

Propellanes
Two structures have been reported for imide-containing propellanes. One of these, compound 287 [240] (Figure 84) shows no hydrogen bonding probably due to the high degree of steric hindrance. The other, compound 288 [241], exhibits linear chains with the imide NH hydrogen equally bonded to both bridging oxygens, resulting in designation C 2 1 (6)[R 2 1 (6)].
The compound 286 [239] (Figure 83) exists as a complex two-dimensional network in which imide NH to imide CO R 2 2 (8) dimer units are arranged in lines with alternating orientation and each dimer is further linked to two separate dimers in the lines on either side by a C(8) interaction of the remaining CO of the dimer-forming imide function with the NH of the non-dimer-forming imide.

Propellanes
Two structures have been reported for imide-containing propellanes. One of these, compound 287 [240] (Figure 84) shows no hydrogen bonding probably due to the high degree of steric hindrance. The other, compound 288 [241], exhibits linear chains with the imide NH hydrogen equally bonded to both bridging oxygens, resulting in designation C

Conclusion
A large number of cyclic NH carboximides have been subject to X-ray structure determination, allowing meaningful conclusions to be drawn from analysis of the patterns observed. It is clear that imide NH to imide CO dimers are the commonest single structure observed followed by linear imide NH to imide CO ribbons, with larger substituents often favouring the dimers whereas smaller substituents are more conducive to ribbon formation. Where additional oxygen or nitrogen atoms are present in the structure, dimers and chains involving imide NH and these remote acceptors are also observed and there are a total of 52 compounds, mainly of this type, in which neither imide CO is involved in hydrogen bonding. In contrast to this situation, the imide NH is involved in hydrogen bonding whenever it occurs, although there are four cases (compounds 67, 161, 162 and 287) where a high degree of steric hindrance prevents any hydrogen bonding at all. The presence of further hydrogen bonding groups of various types may lead to more complex two-and three-dimensional structures and over 40 such diverse patterns are presented. There are relatively few cases where a single compound has been shown to have several different types of structure but compound 191/195/197 provides a good example, and in one case, compound 233, two separate structural types

Conclusions
A large number of cyclic NH carboximides have been subject to X-ray structure determination, allowing meaningful conclusions to be drawn from analysis of the patterns observed. It is clear that imide NH to imide CO dimers are the commonest single structure observed followed by linear imide NH to imide CO ribbons, with larger substituents often favouring the dimers whereas smaller substituents are more conducive to ribbon formation. Where additional oxygen or nitrogen atoms are present in the structure, dimers and chains involving imide NH and these remote acceptors are also observed and there are a total of 52 compounds, mainly of this type, in which neither imide CO is involved in hydrogen bonding. In contrast to this situation, the imide NH is involved in hydrogen bonding whenever it occurs, although there are four cases (compounds 67, 161, 162 and 287) where a high degree of steric hindrance prevents any hydrogen bonding at all. The presence of further hydrogen bonding groups of various types may lead to more complex two-and three-dimensional structures and over 40 such diverse patterns are presented. There are relatively few cases where a single compound has been shown to have several different types of structure but compound 191/195/197 provides a good example, and in one case, compound 233, two separate structural types (A and B) occur together in a 1:1 ratio in the unit cell. It is also clear that for certain classes of cyclic imides, relatively few structures have so far been determined and there is ample scope for the further exploration of this area.
Author Contributions: D.K.S. located and analysed the structural data and prepared the original draft of the paper; R.A.A. conceived the study, defined the scope, resolved problems in analysis and wrote the final version. All authors have read and agreed to the published version of the manuscript.