Synthesis, Crystal Structures, and Thermal and Thermodynamic Properties of Dimorphic Copper(l) Coordination Polymers

A second modification of the literature-known copper(l) coordination polymer CuCI(pyridazine)was prepared by the reaction of CuCI with pyridazine in acetonitrile. The crystal structure of catena[CuCI(2-pyridazine-N,N] is built up of CuCI chains of which each two are connected by the pyridazine ligands to form double chains that are directed parallel to the crystallographic a-axis. In the literature known form LI (CuCI)2 dimers occur that are connected to chains by the pyridazine ligand. On heating, compound I and LI lose half of the pyridazine ligands and transform to the new 2:1 coordination polymer poly[(CuCI)2(pyridazine-/V,N)] (II), which transforms at higher temperatures to CuCI. The crystal structure of II is composed of discrete CuCI tetra-chains that are linked by the pyridazine ligands to sheets parallel to (010). The same thermal reactivity is found for the literature-known compound CuBr(pyridazine) (Lll), which is isotypic to LI. On heating Lll a transformation into the new 2:1 compound poly[(CuBr)2(pyridazineN,N)] (III) is observed, which is isotypic to II. The thermal reactivity of all compounds and the transformation behavior as well as the range of thermodynamic stability of the dimorphic modifications were studied using DTATG-MS and DSC measurements, temperature dependent X-ray powder investigations, and crystallization experiments.