Crystal Structures and Polymorphism of Nickel and Copper Coordination Polymers with Pyridine Ligands

The crystal structures of a series of pyridine coordination polymers [(MCl2)-Cl-II(C5H5N)(x)](n) (M = Ni, Cu), prepared via thermal decomposition are reported. [NiCl2(C5H5N)(4)] (1) decomposes stepwise via [NiCl2(C5H5N)(2)](n) (2), [NiCl2(C5H5N)](n) (3), and [NiCl2(C5H5N)(2/3)](n) (4), to NiCl2 with increasing temperature. The thermal decomposition of [CuCl2(C5H5N)(2)] n (5), progresses via two polymorphs of [CuCl2(C5H5N)](n) (6a and 6b), and [CuCl2(C5H5N)(2/3)](n) (7), to CuCl2. The compounds 3, 4, and 7 were prepared as pure phases. All crystal structures were determined by X-ray powder diffraction. Notably, the crystal structures of the polymorphs 6a and 6b were determined from powder diffraction data of a mixture of both phases. Crystal structures of [(MCl2)-Cl-II(C5H5N)(x)](n) with the same x, but different metal atoms (Ni, Cu) are homeotypic, compounds 4 and 7 are isotypic. Compounds with x = 1 (3, 6a, 6b) are composed of polymeric octahedra double chains (1)(infinity)[MCl3/3Cl2/2(C5H5N)] and in case of x = 2/3 (4, 7) of triple chains. The Jahn-Teller distortion in the copper compounds was observable with the pair distribution function (PDF) analysis.