Theoretical Analysis of CuII···Cl Semicoordination Bond in Supramolecular Heterometallic {CuII}{SnIV} Cocrystals

Detailed theoretical analysis of the CuII···Cl interaction nature in a series of three-component supramolecular heterometallic {CuII}{SnIV} cocrystals with the general formula of (H2ED)2+·2[CuL]·[SnXnCl6–n]2– [H2L = N,N′-ethylenebis(3-OR-salicylaldimine), R = Me (H2L1) or Et (H2L2); ED = 1,2-ethylenediamine; X = Me, Et, Bun, or Ph; n = 2 or 0] was performed. The neutral metal complex [CuL] and the [SnXnCl6–n]2– anion in their crystal structures (1–8) interact via a CuII···Cl interaction, along with H-bonds. Structural comparison reveals that the CuII···Cl interaction (2.886–3.247 Å) in (H2ED)2+·2[CuL]·[SnX2Cl4]2– cocrystals (1–6, type A, X = Me, Et, Bun, or Ph) is shorter than that (3.407–3.454 Å) in the inorganic tin(IV) containing versions (H2ED)2+·2[CuL]·[SnCl6]2– (7 and 8, type B), despite both types (A and B) having similar molecular or supramolecular arrangements. Interaction energies among the components (cation, neutral, and anion) present a triangular energy framework. An attempt has been made to find a correlation between the interaction energies and the concerned noncovalent interactions. Further, the nature of CuII···Cl interaction in 1 and 7 (as representatives of types A and B, respectively) was understood as being a semicoordination bond by DFT calculations with application of the QTAIM, ELF, IGM, EDD, and CDF analyses and IBSI calculation. The ranges of the CuII···Cl interactions in these cocrystals and in other related systems are also discussed. Preliminary catalytic studies on Strecker type cyanation revealed that the catalytic ability of the chloro-tin(IV) precursor, i.e., [Sn(Me)2Cl2] or [SnCl4]·5H2O, was greatly reduced upon conversion into the corresponding dianion, i.e., [Sn(Me)2Cl4]2– or [SnCl6]2– in 1 or 7, respectively.