COORDINATIVE VERSATILITY OF THE DMCPZ LIGAND (HDMCPZ = 3,5-DIMETHOXYCARBONYLPYRAZOLE) IN COPPER-COMPOUNDS - SYNTHESIS, CHARACTERIZATION AND CRYSTAL-STRUCTURES OF [CU(DMCPZ)2(PY)2] AND [CU3(DMCPZ)6] (PY = PYRIDINE)

The oxidation of [{Cu(dmcpz)}n] (Hdmcpz = 3,5-dimethoxycarbonylpyrazole) with dioxygen in pyridine (py) leads to the formation of the violet complex [Cu(dmcpz)2(py)2] 1. Crystals of 1 are monoclinic, space group P2(1)/n (no. 14), a = 11.441(2), b = 9.339(3), c = 12.493(3) angstrom, beta = 99.95(1)-degrees, Z = 2; R = 0.033 for 2308 reflections having I > 3sigma(I). Pyridine abstraction from 1 via azeotropic distillation with benzene allows the isolation of the blue trinuclear linear complex, [Cu3(dmcpz)6] 2. Crystals of 2 are monoclinic, space group P2(1)/c (no. 14), a = 17.286(3), b = 20.649(4), c = 16.498(2) angstrom, beta = 114.51 (1)-degrees, Z = 4; R = 0.034 for 4710 reflections having I > 3sigma(I). Rapid equilibria between 1, 2 and a still uncharacterized species 3 have been verified to occur in solution. A CH2Cl2 solution of 1 is violet below -10-degrees-C, deep blue at around 15-degrees-C and green at temperatures higher than 35-degrees-C; it has been confirmed that these colours are associated with the presence of the distinct species 1, 2 and 3. The chemical, spectroscopic and structural properties of 1 and 2 are discussed.