Solid state coordination chemistry of copper(II)/α-hydroxycarboxylato/2,2′-bipyridine systems

Four new two-ligand complexes of copper(II) with 2,2'-bipyridine and one of three different alpha-hydroxycarboxylic acids (lactic, H(2)LACO; 2-methyllactic, H(2)MLACO; and mandelic, H(2)MANO) were prepared. Complexes 1-3 of general formula [Cu(HL)(2)(bipy)].nH(2)O (HL=monodeprotonated acid), were characterized by elemental analysis, IR, electronic and EPR spectroscopy, magnetic measurements and thermogravimetric analysis. Complexes 1 (HL = HLACO, n = 2), 2 (HL = HMLACO, n = 1) and 3a the result of attempted recrystallization of 3, of formula [Cu(HMANO)(bipy)(2)](HMANO).H(2)MANO.CH3CN were studied by X-ray diffractometry. The copper atom is in an elongated, tetragonally distorted octahedral environment in 1 and 2 and in 3a has a coordination polyhedron intermediate between a square pyramid and a trigonal bipyramid, as evaluated in terms of the parameter tau. In 1 and 2 the alpha-hydroxycarboxylato ligand is bidentate and monoanionic but in 3a there are three forms:. a monodentate monoanion, a monoanionic counterion, and a neutral molecule. (C) 2002 Elsevier Science Ltd. All rights reserved.