Effect of pyrazole-substitution on the structure and nuclearity of Cu(II)-pyrazolato complexes

Trinuclear Cu(II)-pyrazolates of the general formula (Bu4N)2[Cu3(μ3-Cl)2(μ-4-R-pz)3Cl3] (pz=pyrazolato anion, R=Cl, Br, I, Me), 1–4, have been prepared and characterized by X-ray diffraction and/or 1H NMR, IR, UV–Vis spectroscopy and elemental analysis. Their structure and spectroscopic properties match the ones of the parent unsubstituted complex (Bu4N)2[Cu3(μ3-Cl)2(μ-pz)3Cl3], indicating that 4-substitution of the pyrazole ligands with halogen or methyl groups does not induce structural variation. In contrast, dinuclear complexes (Bu4N)4[Cu2(μ-3-Me-pz)2Cl4]Cl2 · 4H2O, Cu2(μ-Cl)(μ-3,5-Me2-pz)(3,5-Me2-pzH)4Cl2, Cu2(μ-Cl)(μ-OH)(3-Me-5-Ph-pzH)4Cl2 · 3-Me-5-Ph-pzH and Cu2(μ-Cl)2(3,5-Ph2-pzH)4Cl2, 5–8, have been prepared with 3- and 3,5-substituted pyrazoles by the same or similar synthetic protocols.