Initial use of di-2-pyridyl ketone oxime in chromium carboxylate chemistry: Triangular {Cr-3(III)(mu(3)-O)}(7+) compounds and unexpected formation of a carboxylate-free dichromium(II,II) complex

摘要

A systematic investigation of the [Cr3O(O2CCMe3)(6)(H2O)(3)](O2CCMe3)/(py)(2)CNOH [(py)(2)CNOH = di-2-pyridyl ketone oxime] reaction system is described, involving the determination of the influence of the Cr-III:(py)(2)CNOH ratio, the temperature and the presence of counterions on the identity of the reaction products. As a consequence, complexes [Cr-2{(py)(2)CNO}(4)].2H(2)O (1 . 2H(2)O), [Cr3OCl(O2CCMe3)(4){(py)(2)CNO}(2)] . 2Me(2)CO (2 . 2Me(2)CO) and [Cr3O(O2CCMe3)(4){(py)(2)CNO}(2)(H2O)](NO3) . H2O . 0.5Me(2)CO (3 . H2O . 0.5Me(2)CO). have been isolated and structurally characterized by single-crystal X-ray studies. (py)(2)CNO- behaves as a N,N'-bidentate chelating and/or N,N',O-tridentate bridging ligand binding through one 2-pyridyl and the oximate nitrogen atoms, and/or the oximate oxygen atom. I is a relatively stable air-stable dinuclear Cr(II) complex with no metal-metal bonding arising, from the ligand-assisted reduction of the 'basic carboxylate' Cr(III) triangle. The structures of 2 and 3 consist of similar neutral and cationic triangles of Cr-III ions, respectively, centered by a triply bridging oxo ligand and with two edge-bridging oximate groups from the two 2.1110 (py)(2)CNO- ligands, Variable-temperature magnetic susceptibility studies and EPR data for 2 reveal an antiferromagnetically-coupled system with an S-T = 3/2 ground state. Solid-state IR and ligand field spectra of 2 are briefly discussed in terms of its structure. (c) 2006 Elsevier B.V. All rights reserved.