Coordination versatility of 5(3)-(2-hydroxyphenyl)-3(5)-methylpyrazole: Synthesis, crystal structure and properties of Co-III, Ni-II and Cu-II complexes

Abstract

New complexes with 5(3)-(2-hydroxyphenyl)-3(5)-methylpyrazole (H(2)phpz), [Co-2(H(2)phpz)(Hphpz)(2)(phpz)(2)](.)3CH(3)CN (1), [Ni(Hphpz)(2)] (2) and [Cu(HphpZ)(2)] (3), were synthesized and structurally characterized. The ligand coordinates in the form of 3-(2-hydroxyphenyl)-5-methylpyrazole in all cases, except for one ligand in the Co-III complex, where it coordinates in the 5-(2-hydroxyphenyl)-3-methylpyrazole mode. Crystallographic analysis revealed that 1 contains two chemically and crystallographically distinct cobalt(III) ions triply bridged by one phenoxide and two pyrazolate groups, giving rise to a [Co-2(N-N)(2)O] core with a (CoCo)-Co-... distance of 3.154 angstrom. Additionally, the H(2)phpz ligand shows four different coordination modes with the metal ions, demonstrating its versatility. The dinuclear unit of 1 is stabilized by strong intramolecular N-(HO)-O-... hydrogen-bonding interactions involving the phenol oxygen atom of the H(2)phpz ligand and the N-H functionality of the pyrazole ring. The crystal structure of the isomorphous complexes 2 and 3 reveals the presence of centrosymmetric mononuclear units with the MN2O2 [M = Ni-II (2), Cu-II (3)] chromophore displaying a slightly distorted square-planar geometry. The mononuclear structures of 2 and 3 are further stabilized by intramolecular hydrogen bonds established between the acid N-H group as donor and the phenoxide group of the H(2)phpz ligand as acceptor. Spectroscopic studies, ESI-MS and cyclic voltammetry were performed, supporting the crystallographic analysis. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).