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Open AccessArticle

Halide Ion Embraces in Tris(2,2′-bipyridine)metal Complexes

Department of Chemistry, University of Basel, BPR 1096, Mattenstrasse 24a, CH-4058 Basel, Switzerland
*
Author to whom correspondence should be addressed.
Crystals 2020, 10(8), 671; https://doi.org/10.3390/cryst10080671
Received: 27 July 2020 / Revised: 30 July 2020 / Accepted: 1 August 2020 / Published: 3 August 2020
(This article belongs to the Special Issue Halogen Bonding in Supramolecular Self-Assembly)

Abstract

An analysis of the [M(bpy)3]n+ (bpy = 2,2′-bipyridine) complexes with halide counterions in the Cambridge Structural Database reveals a common structural motif in two thirds of the compounds. This interaction involves the formation of 12 short C–H…X contacts between halide ions lying within sheets of the cations and H-3 and H-3′ of six [M(bpy)3]n+ complex cations. A second motif, also involving 12 short contacts, but with H-6 and H-5, is identified between halide ions lying between sheets of the [M(bpy)3]n+ cations.
Keywords: metal complexes; 2,2′-bipyridine; halide; C–H…X interactions metal complexes; 2,2′-bipyridine; halide; C–H…X interactions

1. Introduction

The established crystallographic databases, including the Inorganic Crystal Structure Database [1], the NIST Inorganic Crystal Structure Database [2], the Protein Data Bank [3,4,5] and the Cambridge Structural Database (CSD) [6,7], have created unprecedented opportunities for data mining and investigating the intramolecular, intermolecular and supramolecular interactions, which are important in determining the spatial arrangement, orientation and packing of molecules and ions in crystal lattices. For the molecular scientist, the visualization program Mercury [8] and the search software Conquest [9], both incorporated within the CSD, are of particular utility. The opportunities presented for the probing and understanding of the intimate details of crystal packing sometimes result in losing the relationship with general chemical properties and reactivity. In many cases, “weak” interactions, such as van der Waals forces, are typically unimportant in solution behaviour. Nevertheless, the field of crystal engineering has emerged predicated upon the importance of weak interactions, including π-π and C–H-π interactions, as well as halide, pnictide and tetrel bonds in the solid state. However, when “moderate” or “strong” interactions are present in the solid-state structure of a compound, it is appropriate to consider their relevance in its more general chemistry.
A few years ago we noticed dramatic variations in the performance of (apparently) chemically similar batches of [Ir(bpy)(ppy)2](PF6) (Hppy = 2-phenylpyridine, bpy = 2,2′-bipyridine) in light-emitting electrochemical cells [10]. This was shown to be due to the carrying through of small amounts of chloride ions from the synthesis and was demonstrated as a significant solution interaction by 1H NMR spectroscopic titrations of solutions of [Ir(bpy)(ppy)2](PF6) with [nBu4N]Cl. A solid state structural determination of the compound [Ir(bpy)(ppy)2]Cl·2CH2Cl2·[H3O]·Cl revealed a chloride ion lying close to H-3 and H-3′ of the bpy ligand (H…Cl, 2.674 and 2.739 Å; C…Cl, 3.627 and 3.794 Å; ∠C–H…Cl, 145.84 and 163.19°; Figure 1a) and we described the interaction as a bifurcated hydrogen bond (Figure 1b). The combination of a crystallographically significant solid-state interaction with related solution behaviour allowed us to interpret the phenomenon in terms of the known acidity of H-3 and H-3′ in the bpy complexes [11,12,13,14,15,16,17,18,19]. Although we are well aware of the dangers of using distance criteria for assessing weak interactions [20,21,22], the H…X distances provide a convenient metric for a first triage of structural data.
In this article, we show that the interaction of the halide or halogen atoms with the H-3 and H-3′ atoms of the oligopyridine ligands in metal complexes is a recurrent phenomenon in [M(bpy)3]n+ complexes and generates a common structural motif.

2. The Choice of Metal Complex Scaffold

2.1. The Oligopyridines

We selected the oligopyridines as the metal-binding domains for this study. There is a large body of crystallographic data for metal complexes of these ligands in the Cambridge Structural Database (using version 5.41) and we have, in general, restricted our coverage to complexes containing the parent compound 2,2′-bipyridine in order to eliminate the influence of other interactions between the halogen and substituents on the ligand. Furthermore, the chemistry of these ligands and their complexes is exceptionally well documented [23,24,25,26,27,28,29,30,31,32,33,34,35,36], facilitating correlations between the solid-state features and chemical behaviour.

2.2. Supramolecular Interactions in Oligopyridine Complexes

Oligopyridine metal-binding domains played a key role in the development of supramolecular and metallosupramolecular [37,38,39,40] chemistry. The oligopyridines provide an ideal scaffold to investigate supramolecular interactions as they interact with most of the elements in the periodic table. Dance has identified a variety of types of supramolecular embraces between the cations in “simple” oligopyridine complexes as well as a number of cation–anion interactions in these species [41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58]. In many cases, these interactions, described as “embraces” by Dance, are responsible for the assembly of the cationic lattice, which acts as the host for the anionic guests that are the focus of this article.

2.3. Outer-Sphere Complexes and Ion-Pairing

Interactions at the periphery of metal complexes have been known to be of importance for many years, although they have not always been associated with the term “supramolecular”. The structural studies of Nassimbeni have been particularly important in identifying the commonest types of interactions and provide a solid body of evidence for the hydrogen-bonding interactions with Werner-type coordination compounds [59,60,61,62,63,64,65]. Studies such as these relate directly to the “outer-sphere” complexes implicated in studies of substitution mechanisms, in which the incoming ligands are non-covalently associated with the starting complexes (A-type mechanisms) or intermediates (D-type mechanisms) [66,67]. Of particular importance are kinetic and thermodynamic studies, establishing both the nature and strength of the outer-sphere interactions between the oligopyridine complexes and halides and their relevance to the reaction chemistry of these species [68,69,70,71,72,73,74,75,76,77,78].

2.4. Methodology

Conquest (version 2020.1) [9] was used for the primary triage of structures in the database. For the complexes with simple halide anions, the halogen atom was constrained to have the number of bonded atoms = 0 and one of the two nitrogens of a 2,2′-bipyridine was bonded with the bond-type “Any” to any metal (atom type 4M). Hydrogen atoms were added explicitly to the 3 and 3′-positions of the 2,2′-bipyridine ligands. This allowed the identification of complexes containing coordinated oligopyridines (but not 1,10-phenanthrolines) and at least one “free” halide ion in the lattice, and the results for the four halide ions are summarized in Table 1. In all searches, normalized C–H distances of 1.089 Å were specified. A preliminary analysis of these data indicated that the presence of multiple ligand types in heteroleptic complexes made the interpretation and identification of the structural paradigms very difficult and we made the decision to consider only complexes containing at least one 2,2′-bipyridine ligand and subsequently restricted the searches to homoleptic 2,2′-bipyridine complexes for the in-depth analysis.
For the subsequent analysis of all data, normalized hydrogen positions were used for the C–H bonds (C–H = 1.089 Å). All graphical representations were generated using Mercury 2020.1 [8] and saved as POV-Ray files and subsequently rendered using POV-Ray v. 3.7.0.8 unofficial [79]. All hydrogen atoms, other than those involved in the interactions with halide or halogen, are generally omitted from the representations whilst the halogen atoms involved in the H…X interactions are represented in a space-filling mode.

3. Ubiquitous Interactions in [M(bpy)3]n+ Complexes

Typically, the cations in [M(bpy)3]n+ complexes form layer structures with extensive supramolecular interactions between the aromatic ligands [41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58]. Anions can be located between the layers of the cations or within them. These two arrangements give rise to different structural archetypes in the complexes with halide anions.
Of the 64 hits for [M(bpy)3]n+ complexes in the CSD (Table 1), only 55 have had their 3D coordinates deposited. Accordingly, the compounds Λ-[Ru(bpy)3]2(C4H4O6)Cl2·12H2O (Refcode BUDLAN) [80], Λ-[Fe(bpy)3]2(C4H4O6)Br2·11H2O (Refcode BUDLER) [80], Λ-[Co(bpy)3]2(C4H4O6)Cl2·nH2O (Refcode BUDLOB) [80], Na{Δ-[Fe(bpy)3]}2(C4H4O6)2Cl·14H2O (Refcode BUDLUH) [80], Na{Δ-[Ru(bpy)3]}2(C4H4O6)2Cl (Refcode BUDMAO) [80], Na{Δ-[Ni(bpy)3]}2(C4H4O6)2Cl·14H2O (Refcode BUDMES) [80], [Ru(bpy)3]2[Cr(CN)6]Br·8H2O (Refcode HIRDUH) [81], [Ru(bpy)3]2[Cr(CN)6]Cl·8H2O (Refcode HIRFAP) [81] and [Ru(bpy)3](N3)Cl·2H2O (Refcode WOYBER) [82] were omitted from the subsequent analysis. A further seven compounds were also omitted as the halide ions were encapsulated within a polyoxometallate anion, [Ni(bpy)3]3[[email protected]15O36]·3H2O (Refcode ADOCOM [83], [Cu(bpy)3]3[[email protected]15O38]·3H2O (Refcode CEJWEU) [84], [Cu(bpy)3]3[[email protected]4V16O38]·3H2O (Refcode CEJWIY) [84], [Cd(bpy)3]3[Cd(bpy)2(OH2)][[email protected]16O38[Cd(bpy)2(OH2)]]·1.5H2O (Refcode JETQUV) [85], [Fe(bpy)3]2[[email protected]16O38]·4.67H2O (Refcode VUFDAC [86], [Zn(bpy)3]3[[email protected]15O36]·3H2O (Refcode WUPWOT) [87] and [Co(bpy)3]3[[email protected]15O36]·3H2O (Refcode WUPWUZ) [87], leaving a total of 48 entries for detailed analysis.

3.1. The Structural Motifs

Of the 48 compounds investigated, 20 (41.7%) exhibit an interaction between the halide ion and 12 hydrogen atoms of six 2,2′-bipyridine ligands from six different [M(bpy)3]n+ cations within a sheet, as presented in Figure 2a–c and listed in Table 2. We denote this as Structure Type 1. Apparently, [Ru(bpy)3]Cl2·6H2O (Refcode HAXHIZ) [88] adopts Structure Type 1, but unfortunately the disordered water and chloride were removed from the data deposited and no metrical analysis can be made. The halogen and metal centres in the sheet can be co-planar (Figure 3a) or may be ruffled about a mean plane (Figure 3b). An extreme case of ruffling occurs in Δ-[Co(bpy)3]Cl2·2H2O·EtOH (Refcode CAMHED) in which the six Co atoms deviate by 0.81 to 3.52 Å from the mean plane through them. The metal–metal distances within the six-sided polygon are remarkably similar in the entries listed in Table 2, with a mean value of 7.70(20) Å. One special case deserves mention at this point: in [Ni(bpy)3]2(Hbpy)[Ag3I5]I (Refcode DUYBIK) [89], the host motif of six [M(bpy)3]n+ cations is maintained, but the iodide is too large to fit in the cavity as a guest and lies above and below the centre. As a result, there are six “normal” H-3 and six longer H-3 interactions with the halide, as well as six additional H-4 interactions (Figure 4a).
The Structure Type 1 arrangement can be disrupted by the presence of other anions, solvent molecules or additional species capable of hydrogen bonding. However, even in such cases, there is a tendency to retain a significant part of the Structure Type 1 motif and the four entries exhibiting this phenomenon are listed in Table 3. The commonest motif is shown in Figure 4b,c and retains three adjacent [M(bpy)3]n+ cations, interacting through atoms H-3 and H-3′ of a bpy from each cation.
In total, 24 of the 48 (50%) entries for the [M(bpy)3]n+ complexes with halide anions exhibit short interactions between the halogen and H-3 and H-3′ of the bpy ligands. Furthermore, seven of the nine compounds excluded on the basis that the CSD contains no coordinates (Refcodes BUDLAN, BUDLER, BUDLOB, BUDLUH, BUDMAO, BUDMES and HIRDUH) were all reported as being isostructural with established Structural Type 1 compounds, bringing the total to 31 examples (64.6%).
Another common motif has been identified in nine entries (18.8%) that involve halide ions that are located between sheets containing [M(bpy)3]n+ cations. In this case, the interactions are with only two cations and with three bpy ligands from each cation. However, in contrast to Structure Type 1, the interactions are not with H-3 and H-3′ but rather with an H-5 and H-6 from each ligand (Figure 5a). The distances are typically longer than those observed in Structure Type 1. Nevertheless, the result is once again 12 C–H…halogen interactions but involving only two cations (Figure 5b). Typically, the halide ion also exhibits stronger hydrogen-bonding interactions with water molecules lying in the sheet between the cations. This motif will now be described as Structure Type 2 (Table 4). The interactions with H-6 are typically shorter than those with H-5, but the distances and C–H…X angles all indicate that these interactions only represent the weakest of hydrogen bonds and are better described as between a halide guest in a C–H bond-lined host cavity.

3.2. A Closer Look at Structure Type 1

In this section, we look briefly at complexes exhibiting Structure Type 1 and in particular their metrical properties. The detailed analyses were made for the complexes with coordinates in the CSD. In some cases, missing hydrogen atoms were added in normalized positions. All analyses used normalized hydrogen positions. In Figure 2, the archetypical motifs looking down onto the chloride, bromide and iodide ions hosted in the cation sheets were presented, and Figure 6a,b show how the motifs attenuate within the sheet.
Following the approach of Steiner [114], we present data characterizing the interactions of the halide ions with the cations, hosting them in Table 2 and Table 3. The mean H…Cl and C…Cl distances are 2.80 Å and 3.87 Å, respectively, and the mean C–H…Cl is 168.7°; these are slightly longer than the mean distances reported by Steiner for (NN)C(sp2)–H…Cl (2.54, 3.57 Å) and (NC)C(sp2)–H…Cl (2.64, 3.66 Å) [114], although if the increase in mean distance were constant, the expectation values for (CC)C(sp2)–H…Cl would be 2.74 and 3.75 Å. The mean H…Br and C…Br distances are 2.87 Å and 3.95 Å and the mean C–H…Br is 171.9°; Steiner reports 2.73 and 2.74 Å for H…Br and 3.72 and 3.74 Å for C…Br distances in (NN)C(sp2)–H…Br and (NC)C(sp2)–H…Br, respectively. In this case, the expectation values for (CC)C(sp2)–H…Br of H…Br 2.75 Å and C…Br 3.78 Å correspond reasonably well to our values. The mean H…I and C…I distances are 3.10 Å and 4.16 Å and the mean C–H…I 167.7°; Steiner reports 2.90 and 2.99 Å for H…I and 3.85 and 4.00 Å for C…I distances in (NN)C(sp2)–H…I and (NC)C(sp2)–H…I, respectively. In this case, the expectation values for (CC)C(sp2)–H…I of H…I 3.08 Å and C…I 4.15 Å correspond well. The interactions are close to linear and it is reasonable to interpret them in terms of weak hydrogen bonds.
We note that closely related motifs containing functionalized [M(bpy)3]n+ scaffolds are observed in a variety of metallosupramolecular structures [115,116,117,118].

3.3. An Aside on Chirality

Tris-chelate complexes such as [M(bpy)3]n+ cations are chiral with the metal acting as a stereogenic centre. The absolute configurations of the two enantiomeric forms are denoted as Δ and Λ (Figure 7). Eleven of the entries for Structure Type 1 are enantiopure tartrate compounds: (Λ−[Ni(bpy)3]2(C4H4O6)Cl2·12H2O (Refcode BPNTAR) [95], Λ-[Ru(bpy)3]2(C4H4O6)Cl2·12H2O (Refcode BUDLAN) [80], Λ-[Fe(bpy)3]2(C4H4O6)Br2·11H2O (Refcode BUDLER) [80], Λ-[Co(bpy)3]2(C4H4O6)Cl2·nH2O (Refcode BUDLOB) [80], Na{Δ-[Fe(bpy)3]}2(C4H4O6)2Cl·14H2O (Refcode BUDLUH) [80], Na{Δ-[Ru(bpy)3]}2(C4H4O6)2Cl (Refcode BUDMAO) [80], Na{Δ-[Ni(bpy)3]}2(C4H4O6)2Cl·14H2O (Refcode BUDMES) [80], Δ-[Ru(bpy)3]3[Sb2(C4H2O6)2]2I2·19.5H2O (Refcode BUCNUK) [103], Δ-[Ni(bpy)3]4[Ge2(C4H4O6)2(H2O)2]Cl2·1.5H2O (Refcode EFOWAA), Λ-[Fe(bpy)3]2(C4H4O6)Cl2·11H2O (Refcode BUDKUG) [80,94] and Na[Co(bpy)3]2(C4H4O6)2Cl·6.5H2O (Refcode BUDLIV [80,94]. These compounds, therefore, contain only cations with the Δ or Λ absolute configurations around the halide.
Of the remaining Structure Type 1 compounds, four are found in the Sohncke Space Groups [119] with [Ni(bpy)3]2(Hbpy)[Ag3I5]I (Space group C2, Refcode DUYBIK) [89], [Ni(bpy)3]2[Ag3Mo3S12]Cl·2DMF·2H2O (Space group P2221 Refcode TIMSOY) [93] and [Co(bpy)3]Cl2·2H2O·EtOH (Space group P6522, Refcode CAMHED) [96] all being homochiral. In all of the compounds in non-Sohncke space groups, the cations form homochiral sheets with alternating Δ and Λ chirality (Figure 8). As a result, every halide ion in the Structure Type 1 motif is surrounded by six homochiral [M(bpy)3]n+ cations.

3.4. From 2,2′-bipyridine to 1,10-phenanthroline

The chemistry of bpy complexes usually very closely resembles that of the analogous compounds with phen ligands. We wondered whether the packing motifs would be repeated in [M(phen)3]n+ complexes and therefore made a scouting survey of the [M(phen)3]n+ compounds in the CSD. The typical layer structures of the cations were observed in the majority of cases. However, in no case did we find structures analogous to the Type 1 with [M(bpy)3]n+, involving the phen H-5 and H-6 protons. Rather, the halide ions are located between the sheets, with typically Type 2 interactions involving phen H-2(9) and H-3(8). This observation also confirms our belief that Structure Type 1 involves direct C–H…X interactions rather than a simple host–guest binding in a cavity.

4. Conclusions

We have carried out a detailed analysis of the interactions between homoleptic 2,2′-bipyridine metal complexes [M(bpy)3]n+ and halide ions in the solid state. Two recurring packing motifs are found among the 48 compounds investigated. Structure Type I comprises an interaction between a halide ion and 12 hydrogen atoms of six 2,2′-bipyridine ligands from six different [M(bpy)3]n+ cations within a sheet. This motif involves the H-3 and H-3′ of each bpy ligand. The Structure Type 1 motif may persist with fewer than six bpy ligands if other anions, solvent molecules or hydrogen-bond donors are present. Structure Type 2 involves halide ions located between sheets of the [M(bpy)3]n+ cations; in this motif, three bpy ligands of each of the two [M(bpy)3]n+ cations interact with the halide ions positioned between the sheets of cations, resulting in a set of six H-6 and six H-5 interactions.

Author Contributions

Conceptualization, E.C.C. and C.E.H.; methodology, E.C.C.; formal analysis, E.C.C.; writing—original draft preparation, E.C.C.; writing—review and editing, E.C.C. and C.E.H. Both authors have read and agreed to the published version of the manuscript.

Funding

This research was partially funded by the Swiss National Science Foundation (grant number 200020_182559).

Acknowledgments

We thank the University of Basel and the Swiss National Science Foundation for ongoing support.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) The chloride ion interaction with H-3 and H-3′ of the 2,2′-bipyridine ligand in the complex [Ir(bpy)(ppy)2]Cl·2CH2Cl2·[H3O]·Cl (Hppy = 2-phenylpyridine, bpy = 2,2′-bipyridine) [10]. The chloride ion is shown in a space-filling representation; only the hydrogen atoms involved in the interaction with the chloride ion are shown. The hydrogen atom positions are normalized (C–H = 1.089 Å) and the H…Cl distances are 2.674 and 2.739 Å; (b) the generic representation of the bifurcated hydrogen bond to H-3 and H-3′ of a 2,2′-bipyridine ligand. The atoms in red are those used to define the various metrical parameters.
Figure 1. (a) The chloride ion interaction with H-3 and H-3′ of the 2,2′-bipyridine ligand in the complex [Ir(bpy)(ppy)2]Cl·2CH2Cl2·[H3O]·Cl (Hppy = 2-phenylpyridine, bpy = 2,2′-bipyridine) [10]. The chloride ion is shown in a space-filling representation; only the hydrogen atoms involved in the interaction with the chloride ion are shown. The hydrogen atom positions are normalized (C–H = 1.089 Å) and the H…Cl distances are 2.674 and 2.739 Å; (b) the generic representation of the bifurcated hydrogen bond to H-3 and H-3′ of a 2,2′-bipyridine ligand. The atoms in red are those used to define the various metrical parameters.
Crystals 10 00671 g001
Figure 2. Structure Type 1 with (a) chloride ([Ni(bpy)3]Cl2·5.5H2O, Refcode EGOVEB) [90], (b) bromide ([Fe(bpy)3]Br2·5.5H2O, Refcode IFAFUR) [91] and (c) iodide ([Li(bpy)3]I·bpy, Refcode REXVOF) [92] ions hosted. Halogen is shown in the space-filling mode, metal atoms in the ball and stick representation and orange, and all the other elements CPK colours. Hydrogen atoms, other than those involved in the interactions with the halide, are omitted.
Figure 2. Structure Type 1 with (a) chloride ([Ni(bpy)3]Cl2·5.5H2O, Refcode EGOVEB) [90], (b) bromide ([Fe(bpy)3]Br2·5.5H2O, Refcode IFAFUR) [91] and (c) iodide ([Li(bpy)3]I·bpy, Refcode REXVOF) [92] ions hosted. Halogen is shown in the space-filling mode, metal atoms in the ball and stick representation and orange, and all the other elements CPK colours. Hydrogen atoms, other than those involved in the interactions with the halide, are omitted.
Crystals 10 00671 g002
Figure 3. The Structure Type 1 halide ions are located in a sheet of [M(bpy)3]n+ cations. (a) The halogen and metal centres in the sheet can define a plane ([Ni(bpy)3]Cl2·5.5H2O, Refcode EGOVEB) [90] viewed along a or (b) the sheet may be ruffled ([Ni(bpy)3]2[Ag3Mo3S12]Cl·2DMF·2H2O, Refcode TIMSOY) [93] viewed along b). Structure Type 1 halogen shown in space-filling mode, metal atoms and other anions and solvent molecules between the cation sheets as ball and stick representations, metal atoms in orange and all other elements CPK colours. Hydrogen atoms are only shown for the [M(bpy)3]n+ cations.
Figure 3. The Structure Type 1 halide ions are located in a sheet of [M(bpy)3]n+ cations. (a) The halogen and metal centres in the sheet can define a plane ([Ni(bpy)3]Cl2·5.5H2O, Refcode EGOVEB) [90] viewed along a or (b) the sheet may be ruffled ([Ni(bpy)3]2[Ag3Mo3S12]Cl·2DMF·2H2O, Refcode TIMSOY) [93] viewed along b). Structure Type 1 halogen shown in space-filling mode, metal atoms and other anions and solvent molecules between the cation sheets as ball and stick representations, metal atoms in orange and all other elements CPK colours. Hydrogen atoms are only shown for the [M(bpy)3]n+ cations.
Crystals 10 00671 g003
Figure 4. The Structure Type 1 motif can persist with fewer interactions with the [M(bpy)3]n+ cations if other anions, solvent molecules or hydrogen bonding species are present. Once again, the halide ions are in a sheet of [M(bpy)3]n+ cations. (a) The halide ion does not always lie in the centre of the host constructed from [M(bpy)3]n+ cations. In [Ni(bpy)3]2(Hbpy)[Ag3I5]I (Refcode DUYBIK) [89], the iodide ions lie above and below the host motif of six cations and each iodide ion exhibits six shorter C–H…I H-3 interactions, six longer contacts with H-3 and also a set of six short C–H…I interactions with the H-4 of the ring, with a shorter H-3 interaction; hydrogen atoms, other than those involved in interactions with the halide, are omitted and H-4 is shown in green. (b) Interactions with three cations result in a set of six H-3 and H-3′ interactions in [Rh(bpy)3]Cl3·4H2O (Refcode DIWGIZ) and (c) the sheet structure found with just three cations (Refcode DIWGIZ); hydrogen atoms are only shown for the [M(bpy)3]n+ cations. In each figure, Structure Type 1 halide ions are shown in a space-filling mode, metal atoms and other anions and solvent molecules between the cation sheets as ball and stick representations, metal atoms in orange and all other elements CPK colours.
Figure 4. The Structure Type 1 motif can persist with fewer interactions with the [M(bpy)3]n+ cations if other anions, solvent molecules or hydrogen bonding species are present. Once again, the halide ions are in a sheet of [M(bpy)3]n+ cations. (a) The halide ion does not always lie in the centre of the host constructed from [M(bpy)3]n+ cations. In [Ni(bpy)3]2(Hbpy)[Ag3I5]I (Refcode DUYBIK) [89], the iodide ions lie above and below the host motif of six cations and each iodide ion exhibits six shorter C–H…I H-3 interactions, six longer contacts with H-3 and also a set of six short C–H…I interactions with the H-4 of the ring, with a shorter H-3 interaction; hydrogen atoms, other than those involved in interactions with the halide, are omitted and H-4 is shown in green. (b) Interactions with three cations result in a set of six H-3 and H-3′ interactions in [Rh(bpy)3]Cl3·4H2O (Refcode DIWGIZ) and (c) the sheet structure found with just three cations (Refcode DIWGIZ); hydrogen atoms are only shown for the [M(bpy)3]n+ cations. In each figure, Structure Type 1 halide ions are shown in a space-filling mode, metal atoms and other anions and solvent molecules between the cation sheets as ball and stick representations, metal atoms in orange and all other elements CPK colours.
Crystals 10 00671 g004
Figure 5. (a) The Structure Type 2 has three bpy ligands of each of the two [M(bpy)3]n+ cations interacting with halide ions located between the sheets of cations, resulting in a set of six H-6 and six H-5 interactions as seen in [Os(bpy)3]2[Cr(CN)6]Cl·8H2O (Refcode HIRDOB) [81]. The halide ion is shown in a space-filling mode, and the metal atoms in ball and stick representations. (b) The 12 C–H bonds provide a cavity for the halide guest, as seen in [Ru(bpy)3]2[Cr(CN)6]Br·8H2O (Refcode HIRDUH01) [109]. The Structure Type 2 halide ion and the interacting hydrogens are shown in a space-filling mode, and the metal atoms in ball and stick representations.
Figure 5. (a) The Structure Type 2 has three bpy ligands of each of the two [M(bpy)3]n+ cations interacting with halide ions located between the sheets of cations, resulting in a set of six H-6 and six H-5 interactions as seen in [Os(bpy)3]2[Cr(CN)6]Cl·8H2O (Refcode HIRDOB) [81]. The halide ion is shown in a space-filling mode, and the metal atoms in ball and stick representations. (b) The 12 C–H bonds provide a cavity for the halide guest, as seen in [Ru(bpy)3]2[Cr(CN)6]Br·8H2O (Refcode HIRDUH01) [109]. The Structure Type 2 halide ion and the interacting hydrogens are shown in a space-filling mode, and the metal atoms in ball and stick representations.
Crystals 10 00671 g005
Figure 6. (a) The arrangement of adjacent anions in the typical Structure Type 1 sheet of ([Li(bpy)3]I·bpy (Refcode REXVOF) [92]. (b) In a variant found in [Ni(bpy)3]2(C4H4O6)Cl2·12H2O (Refcode BPNTAR) [95], alternating rows of halides are missing from the sheets. Halide ions are shown in a space-filling representation, metal atoms (orange) in ball and stick representations and all other elements in CPK colours. Hydrogen atoms are omitted for clarity.
Figure 6. (a) The arrangement of adjacent anions in the typical Structure Type 1 sheet of ([Li(bpy)3]I·bpy (Refcode REXVOF) [92]. (b) In a variant found in [Ni(bpy)3]2(C4H4O6)Cl2·12H2O (Refcode BPNTAR) [95], alternating rows of halides are missing from the sheets. Halide ions are shown in a space-filling representation, metal atoms (orange) in ball and stick representations and all other elements in CPK colours. Hydrogen atoms are omitted for clarity.
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Figure 7. IUPAC recommends the notation Δ and Λ for denoting the absolute configuration of octahedral metal complexes. The Δ (pale blue) and Λ (pink) enantiomers of an [M(bpy)3]n+ complex are presented here.
Figure 7. IUPAC recommends the notation Δ and Λ for denoting the absolute configuration of octahedral metal complexes. The Δ (pale blue) and Λ (pink) enantiomers of an [M(bpy)3]n+ complex are presented here.
Crystals 10 00671 g007
Figure 8. Unless the [M(bpy)3]n+ cations in the Structure Type 1 complexes are homochiral, alternating homochiral sheets have opposite Δ and Λ chiralities, as seen in [Li(bpy)3]I·bpy (Refcode REXVOF) [92] (Li, orange; I violet).
Figure 8. Unless the [M(bpy)3]n+ cations in the Structure Type 1 complexes are homochiral, alternating homochiral sheets have opposite Δ and Λ chiralities, as seen in [Li(bpy)3]I·bpy (Refcode REXVOF) [92] (Li, orange; I violet).
Crystals 10 00671 g008
Table 1. Metal oligopyridine complexes containing halide anions found in the Cambridge Structural Database (version 5.41).
Table 1. Metal oligopyridine complexes containing halide anions found in the Cambridge Structural Database (version 5.41).
HalideNumber of HitsNumber of Hits Containing a 2,2′-bipyridine LigandNumber of Hits for [M(bpy)3]n+ Complexes
F750
Cl64327047
Br126469
I105538
Table 2. Structure Type 1 complexes.
Table 2. Structure Type 1 complexes.
REFCODE
Space Group
X
M
H…X/ÅMean H…X/ÅC…X/ÅMean C…X/Å C–H…X/°Mean C–H…X/°Ref
BUDKUG
No. 5
Cl
Fe
2.746–3.0572.8493.809–4.1453.928165.19–179.21172.32[80,94]
BPNTAR
No. 5
Cl
Ni
2.706–2.97842.8573.7663–4.06683.937164.39–178.41172.8[95]
BUDLIV
No. 5
Cl
Co
2.573–3.2362.9043.596–4.3043.950153.90–172.82162.43[80]
CAMHED
No. 179
Cl
Co
2.525–2.9202.6963.610–3.9893.771164.97–174.56169.45[96]
EFOWAA
No. 5
Cl
Ni
2.666–3.0742.8193.729–4.1573.893159.7–177.2169.85[97]
EGOVEB
No. 15
Cl
Ni
2.777–2.8922.8443.856–3.9773.925170.4–174.6172.0[90]
IPIMAW
No. 5
Cl
Co
2.699–2.8702.8093.767–3.9553.888166.9–176.3172.1[98]
HUKWER
No. 192
Cl
Ni
2.90452.90453.9863.986172.0172.0[99]
TIMSOY
No. 17
Cl
Ni
2.736–3.723.0243.68–4.754.06144.9–178.6162.5[93]
XUJQEA *
No. 2
Cl
Cu
2.742–2.9742.8453.828–4.063.927167.9–177.8173.0[100]
CIBDOH
No. 190
Br
Co
2.8444–2.89352.86893.929–3.9823.955174.2–178.1176.15[101]
IFAFUR
No. 190
Br
Fe
2.8118–3.03012.920953.88–4.124.00168.4–175.8172.1[91]
UBIWEK
No. 54
Br
Fe
2.777–2.91772.84393.854–4.0063.921167.2–177.8170.9[102]
UBIXEL
No. 54
Br
Ni
2.7900–2.93072.85673.866–4.0183.934167.1–176.4170.85[102]
UBIXIP
No. 54
Br
Co
2.7860–2.94922.85623.853–4.0373.932165.3–176.8170.4[102]
UBIXOV
No. 54
Br
Zn
2.8000–2.96032.8823.878–4.0483.959166.7–177.0170.7[102]
BUCNUK
No. 18
I
Ru
2.936–3.2053.0213.99–4.294.09160–178170[103]
DUYBIK
No. 5
I
Ni
2.899–3.219
3.874–4.585
(H-4) 3.176–3.618
3.083
4.247
(H-4) 3.421
3.797–3.972
4.864–5.538
(C-4) 3.909–4.127
3.885
5.227
(C-4) 4.037
125.8–141.8
148.9–155.0
(C-4) 112.8–127.7
133.4
152.2
(C-4) 120.6
[89]
REXVOF
No. 15
I
Li
2.947–3.5043.1793.966–4.5604.235155.9–175.1165.4[92]
* The 12 C–H bonds come from four [Cu(bpy)3]2+ cations and two [Cu[py-3,3-(CO2)2](bpy)2] molecules; The iodide lies above and below the host motif of six cations and exhibits six shorter C–H…I H-3 interactions, six longer with H-3 and also a set of six short C–H…I interactions with the H-4 of the ring with the shorter H-3 interaction.
Table 3. Structure Type 1 sub-motifs with three cations interacting with chloride.
Table 3. Structure Type 1 sub-motifs with three cations interacting with chloride.
REFCODE
Metal
Space Group
H…Cl/ÅMean H…Cl/ÅC…Cl/ÅMean C…Cl/Å C–H…Cl/°Mean C–H…Cl/°Ref
DIWGIZ
Rh
No. 62
2.516–3.1082.7173.54–4.183.753151.2–169.5160.5[104]
CAMHIH
Co
No. 33
2.536–3.1192.7523.605–4.0783.795147.21–178.60164.60[96]
POMHAB
Co
No. 64
2.463–2.97622.6233.478–4.0473.692161.1–178.5169.1[105]
POMHAB01
Co
No. 64
2.4134–2.93912.6013.463–4.0133.672161.4–178.2169.5[106]
Table 4. Structure Type 2 sub-motifs with twelve C–H…X interactions with two cations.
Table 4. Structure Type 2 sub-motifs with twelve C–H…X interactions with two cations.
REFCODE
Space Group
X
M
H-6…X/ÅMean
H–6…X/Å
H–5…X/ÅMean
H–5…X/Å
Ref
HIGZAY
No. 5
Cl
Ru
3.132–3.4973.3203.327–4.2173.669[107]
HIRDOB
No. 5
Cl
Os
3.061–3.5903.3043.353–4.1103.700[81]
HIRDOB01 *,†
No. 15
Cl
Os
3.050–3.7493.4213.484–4.3203.743[108]
HIRFAP01
No. 5
Cl
Ru
3.145–3.5783.3763.312–4.2493.664[109]
INIYIN
No. 15
Cl
Ru
3.140–3.7123.4083.407–4.2163.696[110]
HIRDUH01
No. 5
Br
Ru
3.189–3.5523.4303.323–4.0913.678[109]
ISIMOM
No. 33
I
Ga
3.171–3.4433.3263.796–4.2003.942[111]
TAHNOG
No. 9
I
Ru
3.141–4.1633.6413.383–4.9803.984[112]
TAHNOG01
No. 9
I
Ru
3.108–4.17623.6313.2959–4.9083.923[113]
* Hydrogen atoms added in normalized positions; Redetermination and correction of space group for HIRDOB.
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