Co-ordinative 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 P21/n(no. 14), a= 11.441(2), b= 9.339(3), c= 12.493(3)Å, β= 99.95(1)°, Z= 2; R= 0.033 for 2308 reflections having I > 3σ(I). Pyridine abstraction from 1via azeotropic distillation with benzene allows the isolation of the blue trinuclear linear complex [Cu3(dmcpz)6]2. Crystals of 2 are monoclinic, space group P21/c(no. 14), a= 17.286(3), b= 20.649(4), c= 16.498(2)Å, β= 114.51(1)°, Z= 4; R= 0.034 for 4710 reflections having I > 3σ(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 °C, deep blue at around 15 °C and green at temperatures higher than 35 °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.