Spectroscopic and structural characterizations of water-soluble peroxo complexes of niobium(V) with N-containing heterocyclic ligands

New water-soluble heteroleptic peroxo complexes of niobium(V) have been prepared with N-containing heterocyclic ligands. The compounds correspond to the general formula (gu)(x)[Nb(O-2)(3)(L)]center dot nH(2)O (gu = guanidinium). Three different ligands (L) have been used: picolinic acid (Hpic), picolinic acid N-oxide (HpicO) and pyrazine 2,5-dicarboxylic acid (2,5-H(2)pzdc). The Nb-V complexes have been characterized on the basis of elemental and thermal analysis as well as by IR and ESI-rnass spectrometry. The crystal structure of the peroxo complex with the picolinato N-oxide ligand, (gu)(2)[Nb(O-2)(3)(picO)] (II) has been determined, showing an eightfold-coordinated Nb atom surrounded by three peroxide groups and a picO ligand bound in a bidentate mode via the carboxylato and the N-oxide groups. The coordination polyhedron around the metal is a triangular dodecahedron. (c) 2005 Elsevier B.V. All rights reserved.