Modulating the structures of copper(I) cyanide coordination polymers by rigid bis(imidazole) ligands and solvents: An experimental and theoretical study

Four novel copper(I) cyanide coordination polymers, namely, Cu2(CN)2(L1) (1), Cu2(CN)2(L2) (2), Cu2(CN)2(L3) (3) and Cu2(CN)2(L3) (4), have been prepared via the reaction of Cu2+, [Fe(CN)6]4− and three structurally related rigid bis(imidazole) ligands 1,4-bis(1-imidazolyl)benzene (L1), 4,4′-bis(1-imidazolyl)biphenyl (L2) and 5-methyl-1,3-bis(1-imidazolyl)benzene(L3) under solvothermal conditions. Although all complexes contain 1D copper(I) cyanide chains, they have completely different structures of 21 helical chain, zigzag chain, and meso-helical chain for complexes 1, 2, and 3, respectively. Complex 1 presents a distorted 2D (6, 3) layer, and further forms a 3D supramolecular structure by π⋯π interactions. Complex 2 shows a 3D network with (10, 3)-b topology and exhibits an interesting 3-fold interpenetration structures attributed Class Ia type. Most interestingly, complexes 3 and 4 are a pair of polymorphs, which are yielded simply depending upon the reaction solvent, and also generate a 3D network with (10, 3)-b topology, which display an interesting 4-fold interpenetration, and belong to unusual Class IIIa type. Meanwhile, the nature of metal–ligand bonds in all complexes was further confirmed by density functional theoretical calculations. It was found that the metal–ligand bonds are basically intermediate and covalent dominant interactions in all complexes. An extended analysis of the experimental and theoretical results indicates that the organic ligands play a crucial role in the self-assembly of the final product structures. Moreover, the thermal properties of complexes 1–3 have also been investigated.