Autori: M. Viciano-Chumillas, S. Tanase, G. Aromí, J. M. M. Smits, R. de Gelder , X. Solans, E. Bouwman, J. Reedijk

Editorial: Eur. J. Inorg. Chem., 18, p.2635-2640, 2007.

Rezumat:

New complexes with 5(3)-(2-hydroxyphenyl)-3(5)-methylpyrazole (H2phpz), [Co2(H2phpz)(Hphpz)2(phpz)2]·3CH3CN (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 CoIII 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 [Co2(N-N)2O] core with a Co···Co distance of 3.154 Å. Additionally, the H2phpz ligand shows four different coordination modes with the metal ions, demonstrating its versatility. The dinuclear unit of 1 is stabilized by strong intramolecular N-H···O hydrogen-bonding interactions involving the phenol oxygen atom of the H2phpz 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 = NiII (2), CuII (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 H2phpz ligand as acceptor. Spectroscopic studies, ESI-MS and cyclic voltammetry were performed, supporting the crystallographic analysis.

Cuvinte cheie: Cobalt, Nickel, Copper, Pyrazoles, Phenols, Crystal structures