Synthesis of a serious of copper(II)-pyrazolyl complexes in different solvents and anions

After obtaining a mononuclear complex [Cu(Hpz)4SO4](H2O) (1) (Hpz=pyrazole) through the reaction of CuSO4 · 5H2O and pyrazole in water solution, we repeated the synthesis process in methanol solution and got an unexpected 1D complex [Cu(Hpz)4SO4]n(CH3OH)n (2), which has the same [Cu(Hpz)4SO4] unit but different coordination motif with 1. While we used Cu(ClO4)2 · 6H2O in the synthesis system of 2, a rarely cyclic tri-nuclear copper(II) complex [Cu3(μ3-O)(pz)3(Hpz)3(μ1,μ2-ClO4)](CH3OH) (3) was obtained. The Cu3(μ3-O)(pz)3 unit in 3 consists of an almost flat Cu3N6 ring and a pyramidal Cu3O group with the average Cu–O distances of 1.998 Å and the average Cu–O–Cu angle of 108°. Complexes 1–3 were characterized by X-ray structural analysis and ESR spectra.