Synthesis, crystal structure and thermal properties of poly[di-μ-bromido-(μ-2,5-di­methyl­pyrazine)cadmium(II)]

Abstract

In the title compound, the cadmium cations are octa­hedrally coordinated by four bromide anions and two 2–5-di­methyl­pyrazine ligands and linked into chains via pairs of μ-1,1-bridging Br⁻ anions that are further connected into layers by the bridging 2,5-di­methyl­pyrazine coligands.

The title compound, [CdBr₂(C₆H₈N₂)]_n, was prepared by the reaction of cadmium bromide with 2,5-di­methyl­pyrazine in water. Its asymmetric unit consists of one Cd cation and one 2,5-di­methyl­pyrazine ligand that are located on a crystallographic mirror plane as well as one bromide anion that occupies a general position. The Cd cations are sixfold coordinated by four bromide anions and two 2,5-di­methyl­pyrazine ligands within slightly distorted trans-CdBr₄N₂ octa­hedra. The cations are linked into [100] chains via pairs of bridging bromide anions that are further connected into (001) layers by the bridging 2,5-di­methyl­pyrazine ligands. Powder X-ray diffraction (PXRD) shows that a pure crystalline phase has been obtained. Thermogravimetry coupled to differential thermoanalysis (TG-TDA) reveal that the 2,5-di­methyl­pyrazine ligands are removed in two separate steps leading to the formation of a compound with the composition (CdBr₂)₂(2,5-di­methyl­pyrazine) that decomposes into CdBr₂ upon further heating. PXRD measurements of the residue obtained after the first mass loss show that a new crystalline phase has been formed.