Synthesis and magnetism of the first tetranuclear copper(II)-iron(III) complexes of macrocyclic oxamides

Four novel tetranuclear macrocyclic complexes of the formula [(CuL')(3)Fe]( ClO4)(3). 3H(2)O (i = 1-4, L' are the dianions of the [14]N-4 and [15]N-4 m acrocyclic oxamides, namely 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarb onyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene, 2,3-dioxo-5,6:13, 14-dibe nzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11- diene and 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tet raazacyclotetradeca-7,12-diene] have been prepared and characterized. These complexes are the first examples of oxamido-bridged Cu(II)-Fe(III) heterom etallic species. Cryomagnetic studies on [(CuL1)(3)Fe](ClO4)(3). 3H(2)O (1) and [(CuL3)(3)Fe](ClO4)(3). 3H(2)O (3) (77-300 K) revealed that the Cu(II) and Fe(III) ions interact antiferromagnetically through the oxamido bridge , with the exchange integral J=-30.8 cm(-1) for 1 and J=-28.7 cm(-1) for 3 based on (H) over cap = -2J Sigma (S) over cap(i)(S) over cap(j). The inter action parameters have been compared with that of the related [Cu3Mn] compo und. (C) 1999 Elsevier Science Ltd. All rights reserved.