Heterometallic Molecular Architectures Based on Fluorinated β-Diketone Ligands

This review summarizes the data on the synthesis of coordination compounds containing two or more different metal ions based on fluorinated β-diketonates. Heterometallic systems are of high interest in terms of their potential use in catalysis, medicine and diagnostics, as well as in the development of effective sensor devices and functional materials. Having a rich history in coordination chemistry, fluorinated β-diketones are well-known ligands generating a wide variety of heterometallic complexes. In this context, we focused on both the synthetic approaches to β-dicarbonyl ligands with additional coordination centers and their possible transformations in complexation reactions. The review describes bi- and polynuclear structures in which β-diketones are the key building blocks in the formation of a heterometallic framework, including the examples of both homo- and heteroleptic complexes.


Introduction
Combining different metals in coordination structures and inorganic matrices is a concept of high research interest. Its driving force originates not only from the attractive diversity of molecular structures, but mainly from their exceptional physicochemical properties. Organic ligands are crucial for the successful formation of heterometallic coordination complexes with a discrete or polymeric structure [1][2][3][4][5][6][7]. The possible applications of these compounds are widely investigated in catalytic processes [3,5] and in the search for new luminescent and magnetic materials [4,6], sensors [2,3,7], biologically active agents [1,7], etc.
Being able to form complexes with most of the elements of the periodic table, βdiketones occupy an important place among organic ligands [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Moreover, varying substituents at the β-dicarbonyl fragment is an effective tool for the fine-tuning of the physicochemical properties of coordination compounds. In particular, the introduction of one or two fluorinated substituents decreases the intermolecular interactions, thereby reducing the sublimation temperature of the complexes. Along with their thermal stability, these compounds are in high demand in the search for precursors for chemical deposition processes [27]. However, the prevalence of trifluoromethyl β-diketonates compared with non-fluorinated analogues is due to the increased solubility of their complexes and, therefore, the better crystallization [27].

Coordination Modes of Fluorinated β-Diketonates
The variety of coordination structures based on β-diketones arises from their ability to act as bi-and polydentate ligands, depending on the metal ions and coligands used [27]. Moreover, the fluorine atoms of the substituent in the β-dicarbonyl framework can participate in the extra coordination with metal ions. In this case, the interatomic distance M…F is less than the sum of the van der Waals radii of fluorine and metal ions indicating non-covalent interaction between them. The principal coordination modes of fluorinated β-diketonates are shown in Figure 2. The above analysis showed the structures of fluorinated 1,3-diketones used as ligands in the synthesis of organometallic derivatives are limited. In this context, functionalized 1,3-dicarbonyl compounds are the least studied, although they have much potential for the formation of heterometallic complexes.

Coordination Modes of Fluorinated β-Diketonates
The variety of coordination structures based on β-diketones arises from their ability to act as bi-and polydentate ligands, depending on the metal ions and coligands used [27]. Moreover, the fluorine atoms of the substituent in the β-dicarbonyl framework can participate in the extra coordination with metal ions. In this case, the interatomic distance M . . . F is less than the sum of the van der Waals radii of fluorine and metal ions indicating non-covalent interaction between them. The principal coordination modes of fluorinated β-diketonates are shown in Figure 2.

Heterometallic Complexes Containing Bridging β-Diketonate Anions
The co-crystallization of β-diketonates with various metal ions is known as one of the available methods for the synthesis of heterometallic compounds with both discrete and polymer coordination structures. For example, Lindoy et al. described the heterometallic complex [Eu-Co] (11) based on 3d and 4f metal β-diketonates: the stoichiometric structure was formed from two β-diketonates containing europium(III) and cobalt(III) in a CDCl3 solution (Scheme 5) [65]. In this case, oxygen atoms of non-fluorinated β-diketonate acted as bridging atoms between two metal ions ( Figure 3).

Heterometallic Complexes Containing Bridging β-Diketonate Anions
The co-crystallization of β-diketonates with various metal ions is known as one of the available methods for the synthesis of heterometallic compounds with both discrete and polymer coordination structures. For example, Lindoy et al. described the heterometallic complex [Eu-Co] (11) based on 3d and 4f metal β-diketonates: the stoichiometric structure was formed from two β-diketonates containing europium(III) and cobalt(III) in a CDCl 3 solution (Scheme 5) [65]. In this case, oxygen atoms of non-fluorinated β-diketonate acted as bridging atoms between two metal ions ( Figure 3).

Heterometallic Complexes Containing Bridging β-Diketonate Anions
The co-crystallization of β-diketonates with various metal ions is known as one of the available methods for the synthesis of heterometallic compounds with both discrete and polymer coordination structures. For example, Lindoy et al. described the heterometallic complex [Eu-Co] (11) based on 3d and 4f metal β-diketonates: the stoichiometric structure was formed from two β-diketonates containing europium(III) and cobalt(III) in a CDCl3 solution (Scheme 5) [65]. In this case, oxygen atoms of non-fluorinated β-diketonate acted as bridging atoms between two metal ions ( Figure 3).  The reaction of the iron(II) chloride and the fluorinated lithium β-diketonate led to a tetranuclear heterometallic complex [Li-Fe(II)] (12) (Scheme 6) [66]. The resulting iron(II) bis-β-diketonates were coordinated with two molecules of the initial lithium β-diketonate ( Figure 4). The coordination environment of metal centers [LiO 5 ] and [FeO 6 ] consisted only of the oxygen atoms of β-diketonate anions without involving the fluorine atoms. Hydrogen atoms and some methyl groups have been omitted, C3F7 groups of fod are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1100888.
The reaction of the iron(II) chloride and the fluorinated lithium β-diketonate led to a tetranuclear heterometallic complex [Li-Fe(II)] (12) (Scheme 6) [66]. The resulting iron(II) bis-β-diketonates were coordinated with two molecules of the initial lithium β-diketonate ( Figure 4). The coordination environment of metal centers [LiO5] and [FeO6] consisted only of the oxygen atoms of β-diketonate anions without involving the fluorine atoms.  [66]. Hydrogen atoms have been omitted, CF3 groups of ptac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1518385.
In the synthesis of polynuclear heterometallic complexes 13-17, alkali metal ions act as binders between two fragments of transition metal β-diketonates [67,68]. The initial reagents for these transformations are transition metals(III) β-diketonates based on acac, fluorinecontaining sodium β-diketonates and chlorides of divalent 3d metal ions (Scheme 7, Figures  5-7). The replacement of one CF3 group in the fluorinated ligand with a sterically bulky tbutyl group enables the number of metal atoms to be increased from three to five in the complex (Figures 6 and 7). The assembly of trimetallic complexes 13, 14 was based on the transition metal ions of different oxidation states. In this case, the metal(III) ion was coordinated to non-fluorinated β-diketonate, which was not exchanged for hfac during the reaction.  [66]. Hydrogen atoms have been omitted, CF 3 groups of ptac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1518385.
In the synthesis of polynuclear heterometallic complexes 13-17, alkali metal ions act as binders between two fragments of transition metal β-diketonates [67,68]. The initial reagents for these transformations are transition metals(III) β-diketonates based on acac, fluorine-containing sodium β-diketonates and chlorides of divalent 3d metal ions (Scheme 7, Figures 5-7). The replacement of one CF 3 group in the fluorinated ligand with a sterically bulky t-butyl group enables the number of metal atoms to be increased from three to five in the complex (Figures 6 and 7). The assembly of trimetallic complexes 13, 14 was based on the transition metal ions of different oxidation states. In this case, the metal(III) ion was coordinated to non-fluorinated β-diketonate, which was not exchanged for hfac during the reaction.
containing sodium β-diketonates and chlorides of divalent 3d metal ions (Scheme 7, Figures  5-7). The replacement of one CF3 group in the fluorinated ligand with a sterically bulky tbutyl group enables the number of metal atoms to be increased from three to five in the complex (Figures 6 and 7). The assembly of trimetallic complexes 13, 14 was based on the transition metal ions of different oxidation states. In this case, the metal(III) ion was coordinated to non-fluorinated β-diketonate, which was not exchanged for hfac during the reaction.  [67]. Hydrogen atoms have been omitted, CF3 groups of transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1964370. Figure 6. Molecular structure of 16 [68]. Hydrogen atoms have been omitted, CF3 groups of transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1998878.  [67]. Hydrogen atoms have been omitted, CF3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1964370. Figure 6. Molecular structure of 16 [68]. Hydrogen atoms have been omitted, CF3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1998878. Figure 6. Molecular structure of 16 [68]. Hydrogen atoms have been omitted, CF 3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1998878. Figure 6. Molecular structure of 16 [68]. Hydrogen atoms have been omitted, CF3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1998878. Figure 7. Molecular structure of 17 [68]. Hydrogen atoms have been omitted, CF3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1998879.   [69]. Similarly to heterometallic complexes 13-17, fluorinated β-diketonate was coordinated to a metal ion with the lowest oxidation number. In the structures of 18, 19 the oxygens of non-fluorinated β-diketonate were bridging atoms, which filled the coordination sphere of Mn(II) or Ni(II) ions coordinating the hfac (Figures 8 and 9). Authors have postulated that the transition metal(II) center participating in bridging interactions with oxygen atoms of neighboring unit(s) should be highly Lewis acidic because of the chelation by diketonates with electron-withdrawing groups. In contrast, the transition metal(III) counterpart should have sterically uncongested ligands with electron-donating substituents provoking diketonate oxygen atoms' involvement in bridging interactions with the M(II) center.  [69]. Similarly to heterometallic complexes 13-17, fluorinated β-diketonate was coordinated to a metal ion with the lowest oxidation number. In the structures of 18, 19 the oxygens of non-fluorinated β-diketonate were bridging atoms, which filled the coordination sphere of Mn(II) or Ni(II) ions coordinating the hfac (Figures 8 and 9). Authors have postulated that the transition metal(II) center participating in bridging interactions with oxygen atoms of neighboring unit(s) should be highly Lewis acidic because of the chelation by diketonates with electron-withdrawing groups. In contrast, the transition metal(III) counterpart should have sterically uncongested ligands with electron-donating substituents provoking diketonate oxygen atoms' involvement in bridging interactions with the M(II) center.   [69]. Similarly to heterometallic complexes 13-17, fluorinated β-diketonate was coordinated to a metal ion with the lowest oxidation number. In the structures of 18, 19 the oxygens of non-fluorinated β-diketonate were bridging atoms, which filled the coordination sphere of Mn(II) or Ni(II) ions coordinating the hfac (Figures 8 and 9). Authors have postulated that the transition metal(II) center participating in bridging interactions with oxygen atoms of neighboring unit(s) should be highly Lewis acidic because of the chelation by diketonates with electron-withdrawing groups. In contrast, the transition metal(III) counterpart should have sterically uncongested ligands with electron-donating substituents provoking diketonate oxygen atoms' involvement in bridging interactions with the M(II) center.   [69]. Hydrogen atoms have been omitted, CF3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1040552. Figure 8. Molecular structure of 18 [69]. Hydrogen atoms have been omitted, CF 3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1040552. Molecules 2022, 27, x FOR PEER REVIEW 11 of 51 Figure 9. Molecular structure of 19 [69]. Hydrogen atoms have been omitted, CF3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1040553.
The solid-state reaction of precursors containing metals of different oxidation states led to heteroleptic [Bi(III)-M(II)] (20-22) complexes, where M(II) was a 3d transition metal ion (Scheme 9) [70]. In this case, the bridging oxygen atoms between metal centers were from the hfac ligands of the anionic tris-diketonate fragment ( Figure 10).   [69]. Hydrogen atoms have been omitted, CF 3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1040553.
The solid-state reaction of precursors containing metals of different oxidation states led to heteroleptic [Bi(III)-M(II)] (20-22) complexes, where M(II) was a 3d transition metal ion (Scheme 9) [70]. In this case, the bridging oxygen atoms between metal centers were from the hfac ligands of the anionic tris-diketonate fragment ( Figure 10).  [70]. In this case, the bridging oxygen atoms between metal centers were from the hfac ligands of the anionic tris-diketonate fragment ( Figure 10).  [70]. In this case, the bridging oxygen atoms between metal centers were from the hfac ligands of the anionic tris-diketonate fragment ( Figure 10).   [70]. Hydrogen atoms have been omitted, CF 3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1475305. Dikarev et al. described the first example of the heterometallic [Na-Cu] complex (22) resulting from two different fluorinated β-diketonates [64]. The reaction of unsolvated [Cu(L 14 )] and Na(hfac) gave a heterometallic β-diketonate [Na 2 Cu 2 (pfbm) 4 (hfac) 2 ] (22) (Scheme 10). The discrete structure of the solvent-free [Na-Cu] environment consisted of a dimeric [Na 2 (hfac) 2 ] unit surrounded by two Cu(pfbm) 2 fragments ( Figure 11). βdiketonates adopted the chelating-bridging mode between Cu and Na by coordinating through one oxygen atom in the case of F-aryl-containing ligands and two oxygen atoms in the case of hfac anions. The overall distorted square antiprismatic coordination environment for Na was formed by the five primary Na-O interactions (av. 2.41 Å) and three secondary Na-F contacts (av. 2.60 Å).  [70]. Hydrogen atoms have been omitted, CF3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1475305. Dikarev et al. described the first example of the heterometallic [Na-Cu] complex (22) resulting from two different fluorinated β-diketonates [64]. The reaction of unsolvated [Cu(L 14 )] and Na(hfac) gave a heterometallic β-diketonate [Na2Cu2(pfbm)4(hfac)2] (22) (Scheme 10). The discrete structure of the solvent-free [Na-Cu] environment consisted of a dimeric [Na2(hfac)2] unit surrounded by two Cu(pfbm)2 fragments ( Figure 11). β-diketonates adopted the chelating-bridging mode between Cu and Na by coordinating through one oxygen atom in the case of F-aryl-containing ligands and two oxygen atoms in the case of hfac anions. The overall distorted square antiprismatic coordination environment for Na was formed by the five primary Na-O interactions (av. 2.41 Å ) and three secondary Na-F contacts (av. 2.60 Å ).  The methoxy substituent in thd, L 9 , L 10 , participated in the additional coordination with metal ions during the formation of polynuclear structures [71][72][73]. The co-crystallization of two different β-diketonates led to the discrete heterometallic complexes, e.g., [Pb-M] (23-26) ( Figure 12). The thd is the unique structure because it contains a sterically bulky group close to the β-dicarbonyl fragment that is a necessary condition for the synthesis of discrete heterometallic complexes. If this does not happen, then coordination [Pb-Cu] polymers are formed in the absence of methoxy substituents at the β-dicarbonyl fragment [73,74]. In polymeric fluorinated [Pb-Cu] structures 23-26, the square planar chelate   [70]. Hydrogen atoms have been omitted, CF3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1475305. Dikarev et al. described the first example of the heterometallic [Na-Cu] complex (22) resulting from two different fluorinated β-diketonates [64]. The reaction of unsolvated [Cu(L 14 )] and Na(hfac) gave a heterometallic β-diketonate [Na2Cu2(pfbm)4(hfac)2] (22) (Scheme 10). The discrete structure of the solvent-free [Na-Cu] environment consisted of a dimeric [Na2(hfac)2] unit surrounded by two Cu(pfbm)2 fragments ( Figure 11). β-diketonates adopted the chelating-bridging mode between Cu and Na by coordinating through one oxygen atom in the case of F-aryl-containing ligands and two oxygen atoms in the case of hfac anions. The overall distorted square antiprismatic coordination environment for Na was formed by the five primary Na-O interactions (av. 2.41 Å ) and three secondary Na-F contacts (av. 2.60 Å ).  The methoxy substituent in thd, L 9 , L 10 , participated in the additional coordination with metal ions during the formation of polynuclear structures [71][72][73]. The co-crystallization of two different β-diketonates led to the discrete heterometallic complexes, e.g., [Pb-M] (23-26) ( Figure 12). The thd is the unique structure because it contains a sterically bulky group close to the β-dicarbonyl fragment that is a necessary condition for the synthesis of discrete heterometallic complexes. If this does not happen, then coordination [Pb-Cu] polymers are formed in the absence of methoxy substituents at the β-dicarbonyl fragment [73,74]. In polymeric fluorinated [Pb-Cu] structures 23-26, the square planar chelate Figure 11. Molecular structure of 22 [64]. Hydrogen atoms have been omitted, CF 3 groups of hfac are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1850164.
The methoxy substituent in thd, L 9 , L 10 , participated in the additional coordination with metal ions during the formation of polynuclear structures [71][72][73]. The cocrystallization of two different β-diketonates led to the discrete heterometallic complexes, e.g., [Pb-M] (23-26) ( Figure 12). The thd is the unique structure because it contains a sterically bulky group close to the β-dicarbonyl fragment that is a necessary condition for the synthesis of discrete heterometallic complexes. If this does not happen, then coordination [Pb-Cu] polymers are formed in the absence of methoxy substituents at the β-dicarbonyl fragment [73,74]. In polymeric fluorinated [Pb-Cu] structures 23-26, the square planar chelate Cu(dik) 2 built up an octahedral coordination environment due to the bridging oxygen atoms of the ligands from Pb(hfac) 2 moieties. Cu(dik)2 built up an octahedral coordination environment due to the bridging oxygen atoms of the ligands from Pb(hfac)2 moieties.
Molecules 2022, 27, x FOR PEER REVIEW 16 of 51 Figure 14. Structure X-ray structure of one-dimensional chain in 31 [82]. Hydrogen atoms have been omitted, some diketonate ligands and CF3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 922987.
The complexation of ntfa with europium(III) chloride in the presence of sodium alkali in methanol gave the discrete [Eu-Na] tetrakis-β-diketonate (32) containing an acetyl naphthalene (Scheme 12) [83]. The aromatic ketone in the complex 32 indicates a side retro-Claisen reaction involving ntfa. Therefore, coligand contribution led to the change from polymer to discrete tetrakis-β-diketonates ( Figure 15). Heterometallic complex 32 had good luminescent properties, exhibiting a phosphorescence time equal to 0.595 ms with a quantum yield of 47.5%. Photophysical parameters were measured under excitation at a wavelength of 370 nm in CH2Cl2 solution [83]. Figure 14. Structure X-ray structure of one-dimensional chain in 31 [82]. Hydrogen atoms have been omitted, some diketonate ligands and CF 3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 922987.
The complexation of ntfa with europium(III) chloride in the presence of sodium alkali in methanol gave the discrete [Eu-Na] tetrakis-β-diketonate (32) containing an acetyl naphthalene (Scheme 12) [83]. The aromatic ketone in the complex 32 indicates a side retro-Claisen reaction involving ntfa. Therefore, coligand contribution led to the change from polymer to discrete tetrakis-β-diketonates ( Figure 15). Heterometallic complex 32 had good luminescent properties, exhibiting a phosphorescence time equal to 0.595 ms with a quantum yield of 47.5%. Photophysical parameters were measured under excitation at a wavelength of 370 nm in CH 2 Cl 2 solution [83].
Molecules 2022, 27, x FOR PEER REVIEW 16 of 51 Figure 14. Structure X-ray structure of one-dimensional chain in 31 [82]. Hydrogen atoms have been omitted, some diketonate ligands and CF3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 922987.
The complexation of ntfa with europium(III) chloride in the presence of sodium alkali in methanol gave the discrete [Eu-Na] tetrakis-β-diketonate (32) containing an acetyl naphthalene (Scheme 12) [83]. The aromatic ketone in the complex 32 indicates a side retro-Claisen reaction involving ntfa. Therefore, coligand contribution led to the change from polymer to discrete tetrakis-β-diketonates ( Figure 15). Heterometallic complex 32 had good luminescent properties, exhibiting a phosphorescence time equal to 0.595 ms with a quantum yield of 47.5%. Photophysical parameters were measured under excitation at a wavelength of 370 nm in CH2Cl2 solution [83]. Succinimide can replace one of the water molecules from the coordination environment of alkali metal ions, thereby acting as coligand in heterometallic complex 33 ( Figure  16) [85]. Tetrakis-β-diketonate [Eu-Na] (33) based on tta exhibited the high phosphorescence quantum yield of 71% and the afterglow time of 0.84 ms upon excitation at a wavelength of 365 nm. The functionalized lithium β-diketonate LiL 10 reacted with lanthanide(III) ions to form heterometallic compounds of various structures (Scheme 13) [62,[86][87][88][89]. An extra functional group in the ligand saturated the metal ion coordination sphere with no additional coligands. Such homoleptic [Ln2L6] complexes (34) were obtained in the case of Ln(III) ions with the largest radius. However, the reaction of lithium diketonate LiL 10 with most of the 4f metals led to the discrete β-diketonates 36-38 of three types depending on the solvent used (Scheme 13). The first type included "classical" tetrakis-β-diketonates 35, in which four β-diketonate anions were coordinated to lanthanide(III) ion. The methoxy groups of the ligands participate in the additional coordination with the lithium ion, thereby providing the discrete structure of 35 ( Figure 17). The [Ln-Li] tetrakis-β-diketonates 35 were formed in acetonitrile media and the solvent molecule was also included in The functionalized lithium β-diketonate LiL 10 reacted with lanthanide(III) ions to form heterometallic compounds of various structures (Scheme 13) [62,[86][87][88][89]]. An extra functional group in the ligand saturated the metal ion coordination sphere with no additional coligands. Such homoleptic [Ln 2 L 6 ] complexes (34) were obtained in the case of Ln(III) ions with the largest radius. However, the reaction of lithium diketonate LiL 10 with most of the 4f metals led to the discrete β-diketonates 36-38 of three types depending on the solvent used (Scheme 13). The first type included "classical" tetrakis-β-diketonates 35, in which four β-diketonate anions were coordinated to lanthanide(III) ion. The methoxy groups of the ligands participate in the additional coordination with the lithium ion, thereby providing the discrete structure of 35 ( Figure 17). The [Ln-Li] tetrakis-β-diketonates 35 were formed in acetonitrile media and the solvent molecule was also included in the crystal packing. Heterometallic complexes 35 were the first examples of lanthanide-lithium β-diketonates, which have been obtained and characterized by different spectral and crystallographic methods.  The second and the third types of complexes included the compounds 36, 37, in which the Ln(III) tris-β-diketonate fragment was coordinated to the initial lithium β diketonate LiL 10 (Scheme 13). The solvent choice (methanol or ethanol) influenced the co ligands at the lithium ion in heterometallic complexes 36 (where Ln = Tb, Dy, Eu) ( Figure  18). However, the main distinctive characteristic of these close structures was their differ ent crystal packings. Complexes 36 (where Ln = Tb, Dy, Eu) exhibited mechanolumines  The second and the third types of complexes included the compounds 36, 37, in which the Ln(III) tris-β-diketonate fragment was coordinated to the initial lithium βdiketonate LiL 10 (Scheme 13). The solvent choice (methanol or ethanol) influenced the coligands at the lithium ion in heterometallic complexes 36 (where Ln = Tb, Dy, Eu) ( Figure  18). However, the main distinctive characteristic of these close structures was their different crystal packings. Complexes 36 (where Ln = Tb, Dy, Eu) exhibited mechanoluminescent properties, and one of them, [Dy-Li], was found to be a single-molecule magnet with an energy barrier equal to 53 K. The second and the third types of complexes included the compounds 36, 37, in which the Ln(III) tris-β-diketonate fragment was coordinated to the initial lithium β-diketonate LiL 10 (Scheme 13). The solvent choice (methanol or ethanol) influenced the coligands at the lithium ion in heterometallic complexes 36 (where Ln = Tb, Dy, Eu) ( Figure 18). However, the main distinctive characteristic of these close structures was their different crystal packings. Complexes 36 (where Ln = Tb, Dy, Eu) exhibited mechanoluminescent properties, and one of them, [Dy-Li], was found to be a single-molecule magnet with an energy barrier equal to 53 K. The exception was the trimetallic complex 38 formed by LiL 10 reaction with praseodymium(III) nitrate (Scheme 14) [86]. Its structure contained a ten-coordinated praseodymium(III) ion and two lithium ions in the coordination with four β-diketonate anions ( Figure 19). One of the ligands from the tris-β-diketonate fragment was bound with the lithium atom of the initial molecule LiL 10 . The coordination environment around the praseodymium(III) ion was saturated by nitrate and three β-diketonate anions, one methoxy group and the bridging oxygen atom of the LiL 10 β-dicarbonyl fragment. In addition, an unusual structure of complex 38 included the second lithium ion, which was coordinated to methoxy groups and oxygen atoms from the β-diketonate fragment ( Figure 19).  The exception was the trimetallic complex 38 formed by LiL 10 reaction with praseodymium(III) nitrate (Scheme 14) [86]. Its structure contained a ten-coordinated praseodymium(III) ion and two lithium ions in the coordination with four β-diketonate anions ( Figure 19). One of the ligands from the tris-β-diketonate fragment was bound with the lithium atom of the initial molecule LiL 10 . The coordination environment around the praseodymium(III) ion was saturated by nitrate and three β-diketonate anions, one methoxy group and the bridging oxygen atom of the LiL 10 β-dicarbonyl fragment. In addition, an unusual structure of complex 38 included the second lithium ion, which was coordinated to methoxy groups and oxygen atoms from the β-diketonate fragment ( Figure 19). Increasing the length of the fluoroalkyl substituent from CF3 to C2F5 in acetal-containing β-diketonates LiL 11 did not change the composition and structure of the resulting heterometallic β-diketonate 39 (Scheme 14, Figure 20) [89]. However, the phosphorescence lifetime decreased for the obtained [Tb-Li] diketonate 39 compared with the trifluoromethyl analog.  The exception was the trimetallic complex 38 formed by LiL 10 reaction with praseodymium(III) nitrate (Scheme 14) [86]. Its structure contained a ten-coordinated praseodymium(III) ion and two lithium ions in the coordination with four β-diketonate anions ( Figure 19). One of the ligands from the tris-β-diketonate fragment was bound with the lithium atom of the initial molecule LiL 10 . The coordination environment around the praseodymium(III) ion was saturated by nitrate and three β-diketonate anions, one methoxy group and the bridging oxygen atom of the LiL 10 β-dicarbonyl fragment. In addition, an unusual structure of complex 38 included the second lithium ion, which was coordinated to methoxy groups and oxygen atoms from the β-diketonate fragment ( Figure 19). Figure 19. Molecular structure of 38 [86]. Hydrogen atoms have been omitted, CF3 groups and one ligand molecule are transparent for clarity. The cif has been retrieved from CCDC. CCDC numbers is 2031103. Figure 19. Molecular structure of 38 [86]. Hydrogen atoms have been omitted, CF 3 groups and one ligand molecule are transparent for clarity. The cif has been retrieved from CCDC. CCDC numbers is 2031103.
Increasing the length of the fluoroalkyl substituent from CF 3 to C 2 F 5 in acetal-containing β-diketonates LiL 11 did not change the composition and structure of the resulting heterometallic β-diketonate 39 (Scheme 14, Figure 20) [89]. However, the phosphorescence lifetime decreased for the obtained [Tb-Li] diketonate 39 compared with the trifluoromethyl analog.
Increasing the length of the fluoroalkyl substituent from CF3 to C2F5 in acetal-contain ing β-diketonates LiL 11 did not change the composition and structure of the resulting he erometallic β-diketonate 39 (Scheme 14, Figure 20) [89]. However, the phosphorescenc lifetime decreased for the obtained [Tb-Li] diketonate 39 compared with the trifluorome thyl analog.   Increasing the length of the fluoroalkyl substituent from CF3 to C2F5 in acetal-containing β-diketonates LiL 11 did not change the composition and structure of the resulting heterometallic β-diketonate 39 (Scheme 14, Figure 20) [89]. However, the phosphorescence lifetime decreased for the obtained [Tb-Li] diketonate 39 compared with the trifluoromethyl analog.   [62]. Hydrogen atoms have been omitted, some CF3 groups are transparent for clarity. The cif has been retrieved from CCDC.

Heteronuclear Complexes with Isolated Metal Centers
This part describes complexes in which metal centers are not connected by bridging oxygen atoms of both β-diketonates and other coligands.
The co-crystallization of equimolar amounts of Dy(III) and Cu(II) β-diketonates afforded the heterometallic complex 43 in a good yield (Scheme 16) [90]. Coligands' exchange around metal ions did not occur in this case ( Figure 22 [62]. Hydrogen atoms have been omitted, some CF 3 groups are transparent for clarity. The cif has been retrieved from CCDC.

Heteronuclear Complexes with Isolated Metal Centers
This part describes complexes in which metal centers are not connected by bridging oxygen atoms of both β-diketonates and other coligands.
The co-crystallization of equimolar amounts of Dy(III) and Cu(II) β-diketonates afforded the heterometallic complex 43 in a good yield (Scheme 16) [90]. Coligands' exchange around metal ions did not occur in this case ( Figure 22). The Cu . . . Dy had the smallest distance between metal centers in the crystal lattice equal to 5.874 Å. Unlike the original [Dy(hfac) 3 [62]. Hydrogen atoms have been omitted, some CF3 groups are transparent for clarity. The cif has been retrieved from CCDC.

Heteronuclear Complexes with Isolated Metal Centers
This part describes complexes in which metal centers are not connected by bridging oxygen atoms of both β-diketonates and other coligands.
The co-crystallization of equimolar amounts of Dy(III) and Cu(II) β-diketonates afforded the heterometallic complex 43 in a good yield (Scheme 16) [90]. Coligands' exchange around metal ions did not occur in this case ( Figure 22) Figure 22. A crystal packing fragment of 43 [90]. Hydrogen atoms have been omitted, some ligand groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1938913.
The solid-state redox reaction between tin(II) and 3d metal β-diketonates proceeded with the ligand exchange around the metal centers to give the heterometallic compounds 44-46 (Scheme 17) [91]. The obtained bimetallic complexes consisted of two homoleptic tris-β-diketonate fragments forming an ion pair ( Figure 23).  The solid-state redox reaction between tin(II) and 3d metal β-diketonates proceeded with the ligand exchange around the metal centers to give the heterometallic compounds 44-46 (Scheme 17) [91]. The obtained bimetallic complexes consisted of two homoleptic tris-β-diketonate fragments forming an ion pair ( Figure 23). The solid-state redox reaction between tin(II) and 3d metal β-diketonates proceeded with the ligand exchange around the metal centers to give the heterometallic compounds 44-46 (Scheme 17) [91]. The obtained bimetallic complexes consisted of two homoleptic tris-β-diketonate fragments forming an ion pair ( Figure 23).    [91]. Hydrogen atoms have been omitted, CF3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC numbers is 1811494.
Copper(II) β-diketonate reacted with tin(II) alkoxide to give the six-nuclear [Sn-Cu] complex (47) (Scheme 18) [92]. Similarly to bimetallic [Sn-M] complexes 44-46, an ion pair was formed as a result of the redox reaction. Copper(II) tris-β-diketonate represented the anionic part, while the oxygen atoms of tin(II) alkoxides were coordinated to copper(I) ions in the cationic part ( Figure 24).   [92]. Hydrogen atoms have been omitted, some ligand groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC numbers is 1056284.

Binuclear Complexes Based on β-Diketones with an Additional Chelating Cavity
The fluorinated β-diketonates with 2,2′-bipyridinyl or phenanthrolinyl substituents (HL 2 , HL 3 [91]. Hydrogen atoms have been omitted, CF3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC numbers is 1811494. Copper(II) β-diketonate reacted with tin(II) alkoxide to give the six-nuclear [Sn-Cu] complex (47) (Scheme 18) [92]. Similarly to bimetallic [Sn-M] complexes 44-46, an ion pair was formed as a result of the redox reaction. Copper(II) tris-β-diketonate represented the anionic part, while the oxygen atoms of tin(II) alkoxides were coordinated to copper(I) ions in the cationic part ( Figure 24).   [92]. Hydrogen atoms have been omitted, some ligand groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC numbers is 1056284.

Binuclear Complexes Based on β-Diketones with an Additional Chelating Cavity
The fluorinated β-diketonates with 2,2′-bipyridinyl or phenanthrolinyl substituents (HL 2 , HL 3 ) were used in the two-step synthesis of bimetallic [Ir-Eu] complexes 48, 49 Figure 24. Molecular structure of 47 [92]. Hydrogen atoms have been omitted, some ligand groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC numbers is 1056284.
Ln(III)-Ir(III) (Ln = Eu, Nd, Yb, Er, Gd) complexes [52,53,93,94]. As a result, heterometallic [Ir-Eu] compounds 50, 51 with bpy fragments demonstrated the higher values of phosphorescence lifetimes (up to 440 μs) compared with phen analogs. Replacing the CF3 group with C2F5 substituent slightly shifted the triplet state in [Ir-Eu] complexes towards the higher side [52]. Therefore, the C2F5-diketonate modified by bpy moiety represents an example of the efficient europium(III) sensitization through the excitation transferring from the Ir(III) to Eu(III) center [52].  Figure 25. Molecular structure of 50 [52]. Hydrogen atoms have been omitted, some ligand groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 730200.

Metallocene-Containing Heterometallic β-Diketonates
Metallocene derivatives are convenient molecules for the synthesis of heterometallic compounds with predictable composition and structure. One of the approaches is based on the co-crystallization of the modified ferrocene with transition metal β-diketonates.   [52]. Hydrogen atoms have been omitted, some ligand groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 730200.

Metallocene-Containing Heterometallic β-Diketonates
Metallocene derivatives are convenient molecules for the synthesis of heterometallic compounds with predictable composition and structure. One of the approaches is based on the co-crystallization of the modified ferrocene with transition metal β-diketonates. For example, 1,2-di(4-pyridylthio)ferrocene in reaction with Cu(hfac) 2 gave 1D coordination polymer [Cu-Fe] (51) (Figure 26) [95].  The β-diketones HL 15 reacted with Ln(III) chloride in the presence of triethylamine in methanol at room temperature to yield the clusters 54 containing four 4f metal ions decorated with ferrocene rings (Scheme 21) [97]. The organic base promoted the deprotonation of methanol and water molecules followed by the formation of a tetranuclear lanthanide(III) framework due to methanolate and hydroxide anions, which act as O-bridging ligands ( Figure 28).  [96]. Hydrogen atoms have been omitted, some ligands groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1811780.
The β-diketones HL 15 reacted with Ln(III) chloride in the presence of triethylamine in methanol at room temperature to yield the clusters 54 containing four 4f metal ions decorated with ferrocene rings (Scheme 21) [97]. The organic base promoted the deprotonation of methanol and water molecules followed by the formation of a tetranuclear lanthanide(III) framework due to methanolate and hydroxide anions, which act as O-bridging ligands ( Figure 28).  [96]. Hydrogen atoms have been omitted, some ligands groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1811780.
The β-diketones HL 15 reacted with Ln(III) chloride in the presence of triethylamine in methanol at room temperature to yield the clusters 54 containing four 4f metal ions decorated with ferrocene rings (Scheme 21) [97]. The organic base promoted the deprotonation of methanol and water molecules followed by the formation of a tetranuclear lanthanide(III) framework due to methanolate and hydroxide anions, which act as O-bridging ligands ( Figure 28).

Scheme 21.
Reaction of β-diketones HL 15 with Ln(III) chloride [98]. The reaction of diketone HL 16 with aluminum(III) sulfate in methanol in the presence of aqueous ammonia resulted in the aluminum tris-β-diketonate 55 in 32% yield (Scheme 22) (Figure 29) [98]. The cytotoxicity of complex 55 against the human HeLa neoplastic cells was investigated: it was about 5 times less cytotoxic than the neutral diketone and approximately 50 times less toxic compared with a reference drug cisplatin.  [97]. Hydrogen atoms have been omitted, C 2 F 5 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 984498.
The reaction of diketone HL 16 with aluminum(III) sulfate in methanol in the presence of aqueous ammonia resulted in the aluminum tris-β-diketonate 55 in 32% yield (Scheme 22) (Figure 29) [99]. The cytotoxicity of complex 55 against the human HeLa neoplastic cells was investigated: it was about 5 times less cytotoxic than the neutral diketone and approximately 50 times less toxic compared with a reference drug cisplatin. Figure 28. Molecular structure of 54 [97]. Hydrogen atoms have been omitted, C2F5 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 984498.
The reaction of diketone HL 16 with aluminum(III) sulfate in methanol in the presence of aqueous ammonia resulted in the aluminum tris-β-diketonate 55 in 32% yield (Scheme 22) (Figure 29) [98]. The cytotoxicity of complex 55 against the human HeLa neoplastic cells was investigated: it was about 5 times less cytotoxic than the neutral diketone and approximately 50 times less toxic compared with a reference drug cisplatin.  The oxidative addition of methyl iodide to the [Rh-Fe] compound 59 proceeded un der mild conditions to afford the Rh(III) complex 60 in 90% yield (Scheme 25, Figure 30 [101]. Based on spectral data, the authors postulate that methyl-containing complex 6 and its acyl derivative exist in equilibrium with each other. However, since the 19 F NMR spectra have not been registered, the transformations of the β-dicarbonyl framework ac companied by the isomers' formation can proceed as well.  The oxidative addition of methyl iodide to the [Rh-Fe] compound 59 proceeded under mild conditions to afford the Rh(III) complex 60 in 90% yield (Scheme 25, Figure 30) [101]. Based on spectral data, the authors postulate that methyl-containing complex 60 and its acyl derivative exist in equilibrium with each other. However, since the 19 F NMR spectra have not been registered, the transformations of the β-dicarbonyl framework accompanied by the isomers' formation can proceed as well. The oxidative addition of methyl iodide to the [Rh-Fe] compound 59 proceeded un der mild conditions to afford the Rh(III) complex 60 in 90% yield (Scheme 25, Figure 30 [101]. Based on spectral data, the authors postulate that methyl-containing complex 60 and its acyl derivative exist in equilibrium with each other. However, since the 19 F NMR spectra have not been registered, the transformations of the β-dicarbonyl framework ac companied by the isomers' formation can proceed as well.  The oxidative addition of methyl iodide to the [Rh-Fe] compound 59 proceeded under mild conditions to afford the Rh(III) complex 60 in 90% yield (Scheme 25, Figure 30) [101]. Based on spectral data, the authors postulate that methyl-containing complex 60 and its acyl derivative exist in equilibrium with each other. However, since the 19 F NMR spectra have not been registered, the transformations of the β-dicarbonyl framework accompanied by the isomers' formation can proceed as well.   [101]. Hydrogen atoms have been omitted, CF3 group is transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 646438.   [102]. Hydrogen atoms have been omitted for clarity. The cif has been retrieved from CCDC. CCDC number is 1996249.

Heteroleptic Complexes Involving β-Diketonates and Polytopic Coligands
The trifluoromethyl β-diketone HL 1 with dithienylethene substituent was used as a ligand in the synthesis of heterometallic [Yb-Ru] complex 63 exhibiting the redox/optical control of emission ( Figure 32) [51]. The bimetallic complex 63 was formed due to the coordination of the tris-β-diketonate Yb(L 1 )3 fragment with the functionalized 2,2′-bipyridine containing a ruthenium(III) ion.   [102]. Hydrogen atoms have been omitted for clarity. The cif has been retrieved from CCDC. CCDC number is 1996249.

Heteroleptic Complexes Involving β-Diketonates and Polytopic Coligands
The trifluoromethyl β-diketone HL 1 with dithienylethene substituent was used as a ligand in the synthesis of heterometallic [Yb-Ru] complex 63 exhibiting the redox/optical control of emission ( Figure 32) [51]. The bimetallic complex 63 was formed due to the coordination of the tris-β-diketonate Yb(L 1 )3 fragment with the functionalized 2,2′-bipyridine containing a ruthenium(III) ion.  [102]. Hydrogen atoms have been omitted for clarity. The cif has been retrieved from CCDC. CCDC number is 1996249.
The Schiff base with two different coordination modes formed the heterometallic 3d-4f binuclear complexes 65 (Scheme 27) [103,104]. The lanthanide(III) ions had an [LnO 8 ] environment, whereas 3d metals ions preferably coordinated with the less "hard" nitrogen centers ( Figure 33). The complexes with a combination of anisotropic Co(II) or Ni(II) ions with Tb(III) exhibited slow magnetic relaxation at low temperatures and, therefore, represented promising structures for single-molecular magnets' design [103]. On the other hand, the heterometallic complexes containing Zn(II) and Tb(III) or Eu(III) ions showed luminescent properties [104]. In this case, the replacement of the bridging acetate anion by 1-pyrenbutanoic acid (complex 66, Figure 33) reduced the phosphorescence lifetime. Molecules 2022, 27, x FOR PEER REVIEW 33 of 51 Figure 32. Molecular structure of 63 [51]. Hydrogen atoms have been omitted, some ligand groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1959918.
The Schiff base with two different coordination modes formed the heterometallic 3d-4f binuclear complexes 65 (Scheme 27) [103,104]. The lanthanide(III) ions had an [LnO8] environment, whereas 3d metals ions preferably coordinated with the less "hard" nitrogen centers (Figure 33). The complexes with a combination of anisotropic Co(II) or Ni(II) ions with Tb(III) exhibited slow magnetic relaxation at low temperatures and, therefore, represented promising structures for single-molecular magnets' design [103]. On the other hand, the heterometallic complexes containing Zn(II) and Tb(III) or Eu(III) ions showed luminescent properties [104]. In this case, the replacement of the bridging acetate anion by 1-pyrenbutanoic acid (complex 66, Figure 33) reduced the phosphorescence lifetime.   [103,104]. Hydrogen atoms have been omitted, some ligand groups are transparent for clarity. The cif has been retrieved from CCDC.
Due to deprotonation of the hydroxy group, 8-hydroxyquinoline acted as a bridging ligand in the reaction with transition metal β-diketonates resulting in the homobimetallic complexes (Scheme 28) [106][107][108]. However, in the presence of a chromium(III) ion a trimetallic complex 68 was formed, in which a bridging phenolate anion connected the different metal ions (Figure 35) [108]. Figure 34. Molecular structure of 67 [105]. The cif has been retrieved from CCDC. CCDC number is 1961116.
In most cases, the co-crystallization of 3d and 4f β-diketonates proceeded in the presence of the aza-heteroaryl-substituted nitronyl nitroxyls to provide the additional coordination centers with metal ions (Figure 37) [113][114][115][116][117][118][119]. The Ln(III) center predominantly formed an [LnO 8 ] environment due to both the β-diketonate anions and nitroxyl oxygen atoms. In turn, 3d metal bis-diketonates were coordinated by either two nitrogen atoms of the heterocyclic substituents in a ligand or a nitroxyl oxygen atom and aza-heterocycle.
A strong base used in the formation of a β-diketonate anion caused the destruction or transformation of the initial β-diketone. In work [126], the deprotonation with sodium
A strong base used in the formation of a β-diketonate anion caused the destruction or transformation of the initial β-diketone. In work [126], the deprotonation with sodium hydroxide resulted in two possible routes of the retro-Claisen reaction (Scheme 30). Surprisingly, in the presence of two different carboxylates, a tetranuclear [Eu-Na] complex (84) was formed, including the β-diketonate anions and tris(3,5-dimethyl-1-pyrazolyl)methane (tpm) (Figure 38). The main phosphorescence characteristics were determined for the complex 84: the observed lifetime was 0.68 ms with a quantum yield of 39% and quantum efficiency equal to 58% [126].   [126]. Some ligand groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1008766.
The nitrogen base, as an initial part of the complex, can further participate in the cocrystallization with fluorinated β-diketonate [129]. In particular, the tetranuclear bimetallic complex 91 was obtained by the reaction of Cd(pymt)2(phen)2 (90) with Cu(hfac)2 in acetonitrile (Scheme 32) [129]. The heterometallic structure 91 was formed based on the ttpt derived from hfac. Cadmium(II) both coordinated the diketonate anion and built a heterometallic framework of 91 due to the bridging oxygen atoms of ttpt ( Figure 40). In addition, three hydroxyl oxygen atoms of two tpt and phen molecules formed the [CuO3N2] coordination environment of copper(II) ions. [129]. . Figure 39. Molecular structure of 87 [127]. CF3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1556429.

Scheme 31. Synthesis of heterometallic [Ln-Ni] complexes 85-89
The nitrogen base, as an initial part of the complex, can further participate in the cocrystallization with fluorinated β-diketonate [129]. In particular, the tetranuclear bimetallic complex 91 was obtained by the reaction of Cd(pymt)2(phen)2 (90) with Cu(hfac)2 in acetonitrile (Scheme 32) [129]. The heterometallic structure 91 was formed based on the ttpt derived from hfac. Cadmium(II) both coordinated the diketonate anion and built a heterometallic framework of 91 due to the bridging oxygen atoms of ttpt ( Figure 40). In addition, three hydroxyl oxygen atoms of two tpt and phen molecules formed the [CuO3N2] coordination environment of copper(II) ions.  [127]. CF 3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1556429.
The nitrogen base, as an initial part of the complex, can further participate in the cocrystallization with fluorinated β-diketonate [129]. In particular, the tetranuclear bimetallic complex 91 was obtained by the reaction of Cd(pymt) 2 (phen) 2 (90) with Cu(hfac) 2 in acetonitrile (Scheme 32) [129]. The heterometallic structure 91 was formed based on the ttpt derived from hfac. Cadmium(II) both coordinated the diketonate anion and built a heterometallic framework of 91 due to the bridging oxygen atoms of ttpt ( Figure 40). In addition, three hydroxyl oxygen atoms of two tpt and phen molecules formed the [CuO 3 N 2 ] coordination environment of copper(II) ions. After the decomplexation of heteronuclear [Cu-Cd] complex 91, all hydroxyl groups of tris-CF3-tetrahydropyran-2,4,6-triol were in the cis-configuration based on XRD data [129]. The proposed mechanism of pyran formation involves a retro-Claisen reaction followed by a condensation of trifluoroacetone enol with fluorinated copper diketonate (Scheme 33). Obviously, the triol formation led to the assembly of the tetranuclear [Cu-Cd] core, while the oxygen atoms of the hydroxyl groups in ligand acted as bridging atoms between metal ions. The other bases, including DMF, diethylformamide, formamide and sodium hydroxide, can also be used in the template reaction affording the ttpt.  After the decomplexation of heteronuclear [Cu-Cd] complex 91, all hydroxyl groups of tris-CF3-tetrahydropyran-2,4,6-triol were in the cis-configuration based on XRD data [129]. The proposed mechanism of pyran formation involves a retro-Claisen reaction followed by a condensation of trifluoroacetone enol with fluorinated copper diketonate (Scheme 33). Obviously, the triol formation led to the assembly of the tetranuclear [Cu-Cd] core, while the oxygen atoms of the hydroxyl groups in ligand acted as bridging atoms between metal ions. The other bases, including DMF, diethylformamide, formamide and sodium hydroxide, can also be used in the template reaction affording the ttpt.  [129]. CF 3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 616292.
After the decomplexation of heteronuclear [Cu-Cd] complex 91, all hydroxyl groups of tris-CF 3 -tetrahydropyran-2,4,6-triol were in the cis-configuration based on XRD data [129]. The proposed mechanism of pyran formation involves a retro-Claisen reaction followed by a condensation of trifluoroacetone enol with fluorinated copper diketonate (Scheme 33). Obviously, the triol formation led to the assembly of the tetranuclear [Cu-Cd] core, while the oxygen atoms of the hydroxyl groups in ligand acted as bridging atoms between metal ions. The other bases, including DMF, diethylformamide, formamide and sodium hydroxide, can also be used in the template reaction affording the ttpt.

Conclusions
The described analysis of the literature demonstrates the wide scope of fluorin β-diketones in the synthesis of heterometallic compounds. In most cases, the avai diketones with trifluoromethyl and perfluoropropyl substituents (hfac, fod) form pol clear systems containing up to five different metal ions. Moreover, fluorinate diketones as coligands can be used in the design of the heterometallic architectur combination with other organic polydentate molecules. However, the potential of co nation compounds containing two or more different metal ions has not been fully rea in terms of practice. This is mainly because of the limited number of transition metals Scheme 35. Proposed mechanism for trifluoromethylated dioxane-diol formation. . Figure 41. Crystal structure of [Pr(hfac)2(CF3-diol)Cu(Hbdmap)2(tfa)] (93) [131]. CF3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1232922.

Conclusions
The described analysis of the literature demonstrates the wide scope of fluorinated β-diketones in the synthesis of heterometallic compounds. In most cases, the available diketones with trifluoromethyl and perfluoropropyl substituents (hfac, fod) form polynuclear systems containing up to five different metal ions. Moreover, fluorinated βdiketones as coligands can be used in the design of the heterometallic architectures in combination with other organic polydentate molecules. However, the potential of coordination compounds containing two or more different metal ions has not been fully realized in terms of practice. This is mainly because of the limited number of transition metals used in the synthesis of heterometallic structures. The specific chemical properties of the initial β-diketones should be considered when planning conditions for the synthesis of coordination compounds. In particular, the action of bases causes the β-diketones' destruction  [131]. CF 3 groups are transparent for clarity. The cif has been retrieved from CCDC. CCDC number is 1232922.

Conclusions
The described analysis of the literature demonstrates the wide scope of fluorinated β-diketones in the synthesis of heterometallic compounds. In most cases, the available diketones with trifluoromethyl and perfluoropropyl substituents (hfac, fod) form polynuclear systems containing up to five different metal ions. Moreover, fluorinated β-diketones as coligands can be used in the design of the heterometallic architectures in combination with other organic polydentate molecules. However, the potential of coordination compounds containing two or more different metal ions has not been fully realized in terms of practice. This is mainly because of the limited number of transition metals used in the synthesis of heterometallic structures. The specific chemical properties of the initial β-diketones should be considered when planning conditions for the synthesis of coordination compounds. In particular, the action of bases causes the β-diketones' destruction to form heteroleptic complexes. In this context, the directed synthesis of β-diketones containing additional coordination centers is a more attractive design strategy for the heterometallic complexes [51][52][53]93,94,132]. This area is promising for obtaining not only discrete structures but also 2D/3D organometallic polymers, which are of applied interest in the development of magnetic, fluorescent, catalytic or sensor devices. Therefore, using polydentate fluorinated β-diketonates allows the heterometallic composition of structurally diverse coordination compounds to be varied, which, in turn, may give rise to advanced materials with interesting physicochemical properties.