Steric effects on the stereochemistry of copper complexes of 2,6-bis(pyrazol-1-ylmethyl)pyridines

The stereochemical preferences of copper complexes of 2,6-bis-(3,5-dimethylpyrazol-1-ylmethyl)pyridine ((LMe2)-Me-1) and of 2,6-bis(phenylpyrazol-1-ylmethyl)pyridine ((LPh)-Ph-1) have been investigated. The single crystal X-ray structures of [Cu(OH2)((LMe2)-Me-1)]BF4)(2) and [CuCl(HOMe)((LMe2)-Me-1)]BF4 show near-regular tetragonal geometries with one or two axial solvent and/or BF4- ligands. In contrast, [Cu(OH2)(2)((LPh)-Ph-1)](BF4)(2) adopts an irregular geometry in the crystal mid-way between square-pyramidal and trigonal-bipyramidal. The single crystal X-ray structure of [Cu(NCMe)((LMe2)-Me-1)]BF4 exhibits a distorted tetrahedral geometries, while [Cu((LPh)-Ph-1)]BF4 adopts a T-shaped stereochemistry. By a combination of UV-Vis, EPR and conductivity studies, the solution structures Of [CuC(l)2(L)], [CuCl(solv)(L)]BF4 and [Cu(solv)(x)(L)](BF4)(2) (L = (LMe2)-Me-1, (LPh)-Ph-1; solv = H2O, MeCN; x = 1, 2) have, in many cases, been shown to be the same as in the crystalline state. The cyclic voltammograms of [Cu(OH2)((LMe2)-Me-1)](BF4)(2) and [Cu(OH2)(2)((LPh)-Ph-1)](BF4)(2) in MeCN/0.1 M (NBu4BF4)-B-n exhibit chemically reversible Cu(II/I) couples. (C) 2002 Elsevier Science Ltd. All rights reserved.