Cu(2-methylpyrazine-5-carboxylate)2 hydrate: a metal-containing-ligand for the construction of organic–inorganic framework materials. Four new one-, two- and three-dimensional mixed-valent CuI–CuII coordination polymers

The copper containing building block, Cu(C6H5N2O2)2·H2O (1) was used in the synthesis of four new mixed-valent organic–inorganic coordination polymers, each of which adopted a different structural motif. Synthesis, X-ray structure determinations, thermogravimetric analyses and magnetic properties are presented. The reaction between 1 and CdCl2 afforded a one-dimensional chain structure, [Cu(C6H5N2O2)2(H2O)2Cu2Cl2(H2O)2]n (2). When CdCl2 was replaced by CuCl, the reaction yielded a polymer, [Cu(C6H5N2O2)2(H2O)2Cu2Cl2(H2O)2]n having the same empirical formula, but a completely different two-dimensional framework (3). The reaction of CdBr2 and 1 resulted in the formation of two different coordination polymers: [Cu(C6H5N2O2)2(H2O)2Cu(C6H5N2O2)2Cu2Br2·3(H2O)]n (4) as a minor phase and [Cu(C6H5N2O2)2Cu2Br2·]n (5) as the major phase. Compound 4 adopts a two-dimensional structure, while 5 is three-dimensional. The structural classification of these Cu(I) containing coordination polymers is discussed. These new coordination polymers feature mixed-valent Cu(I)–Cu(II) frameworks and exhibit impressive thermal stability (the frameworks collapse between 236 and 246 °C). The magnetic susceptibilities for 2, 3 and 5 followed the Curie law, indicating simple paramagnetic behavior.