Coordination Modes in a Tridentate NNS (Thiosemicarbazonato)copper( II ) System Containing Oxygen‐Donor Coligands − Structures of [{Cu(L)(X)}2] (X = Formato, Propionato, Nitrito)

Complexes with the formula [{Cu(L)X}2] [X = HCOO− (1), CH3CH2COO− (2), NO2− (3)], where HL = C7H8N4S (pyridine‐2‐carbaldehyde thiosemicarbazone), have been synthesised and characterised. Single‐crystal X‐ray diffraction studies show that the structures of these compounds consist of centrosymmetric dimers containing distorted square‐pyramidal copper(II) ions. The metal centres are coordinated to the NNS atoms of the tridentate thiosemicarbazonato ligand and one oxygen atom of the X coligand in the basal position. These complexes mainly differ in the atom that occupies the apical position. The structures of compounds 1 and 3 are made up of {Cu2(μ−SL)2} entities in which the sulfur atom of the tridentate ligand acts as a bridge occupying the apical position. Compound 2 contains a {Cu2(μ‐OX)2} species bridged through the oxygen atoms from both propionato ligands. The results demonstrate the influence of the size of the coligand on the structure of these complexes. Structural and spectroscopic results suggest the presence of relevant ligand‐to‐metal charge transfers in these compounds. The EPR spectra exhibit rhombic symmetry. Magnetic measurements show antiferromagnetic couplings. The susceptibility data were fitted using the Bleaney−Bowers equation for copper(II) dimers. The J/k values obtained are −4.0, −4.8 and −4.9 K for compounds 1, 2 and 3, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)