Synthesis, Structures, Thermal and Luminescence Properties of Zn and Cd Halide Coordination Polymers with 2‐Cyanopyrazine

Abstract

Reaction of MX2 (M = Cd, Zn; X = Cl, Br, I) with 2‐cyanopyrazine leads to the formation of compounds with the composition CdX2(2‐cyanopyrazine)2 (X = Cl; CdCl, X = Br; CdBr and X = I; CdI) and ZnX2(2‐cyanopyrazine)2 (X = Cl; ZnCl, X = Br; ZnBr and X = I; ZnI/I). In the crystal structures of the Cd compounds and in ZnCl, the metal cations are octahedrally coordinated and are linked into chains by the halide anions via common edges. In contrast, in the crystal structures of ZnBr and ZnI/I the metal cations are tetrahedrally coordinated into discrete complexes. Further investigations show that a second modification of ZnCl2(2‐cyanopyrazine)2 exists (ZnI/II), which is formed by kinetic control. The thermal properties of the 2‐cyanopyrazine rich compounds were investigated by TG‐DTA and temperature dependent XRPD measurements. Upon heating the Cd compounds, all 2‐cyanopyrazine ligands are removed in a single step with no indication of the formation of a 2‐cyanopyrazine deficient phase. A similar behavior is observed for ZnI, whereas for ZnCl and ZnBr, TG‐DTA measurements suggest the formation of a 2‐cyanopyrazine deficient phase that, in case of ZnBr, cannot be isolated and, for ZnCl, cannot be obtained pure. The emission of these compounds is shifted from the blue to orange depending on the crystal structure and the nature of the halide anion.