Synthesis, structure and electrochemical properties of a nickel complex with the hydrotris[thioxotriazolyl-3-(2-pyridyl)]borate podand ligand

The complex [Ni(Tr-Me,Tr-o-PY)(2)] (2) {Tr-Me,Tr-o-Py = hydrotris[1,4-dihydro-4-methyl-3-(2-pyridyl)-5-thioxo-1,2,4-triazolyl]borate} was synthesized and characterized by UV-Vis spectroscopy, ESI-mass spectrometry and X-ray crystallography. Complex 2 crystallizes in the tetragonal I-42d space group. The metal presents a slightly distorted octahedral geometry (N4S2 co-ordination) bound by two ligands that behave in the S,NIN' co-ordination mode: one of the three arms of each tripod is bound to the metal with the thioxo group, the second chelates NIN' with the triazoline and pyridine nitrogen atoms and the third does not participate in the metal coordination. Ni/Tr-Me,Tr-o-Py complexation was studied by collecting visible spectra of 16 batch samples (10 ml) containing a fixed concentration of metal (9.994 x 10(-4) mol dm(-3)) with increasing concentrations of ligand up to Ni/L = 1/3 (L = Tr-Me,Tr-o-Py). For a Ni/L ratio of 1/2, approximate to38% of NiL+ and approximate to56% of NiL2 are present with respect to the total Ni(H) concentration. Conductivity (Lambda(M) range 112-55 ohm(-1) cm(2) mole(-1) in acetonitrile and Lambda(M) range 15-8 ohm(-1) cm(2) mole(-1) in DMF) and ESI-mass spectrometry results are consistent with a partial dissociation of 2 in acetonitrile and DMF solutions according to the equilibrium NiL2 = NiL+ + L- in agreement with the spectrophotometric titration results. Cyclic voltammetry performed on acetonitrile solutions of 2 reveals the electrochemical activity of the Tr-Me,Tr-o-Py ligand, which undergoes irreversible oxidation and reduction processes at potential > +0.7 and similar to0 V, respectively. The occurrence of the Ni(II)/Ni(III) and Ni(II)[Ni(l) electrochemical events could not be determined. (C) 2004 Elsevier Ltd. All rights reserved.