Synthesis, Structure and Magnetic Properties of a μ‐Carboxylato‐Bridged Ferromagnetic Trinuclear Copper( II ) Complex with Lariat Tetraazacrown Ether as Ligand

Four o ‐toluic acid pendant groups have been attached to a tetraaza crown ether to prepare the novel tetraazamacrocyclic ligand H 4 L, 4,7,13,16‐tetrakis(2‐carboxybenzyl)‐1,10‐dioxa‐4,7,13,16‐tetraazacyclooctadecane. The trinuclear copper( II ) complex of the ligand, [Cu 3 L·2H 2 O] 2+ ·2NO 3 − ·2H 2 O, has been newly synthesized, and its subsequent structural characterization has revealed that it consists of three Cu II cores with a isosceles triangular array and that there is a twofold rotation axis that passes through the Cu2 center. The complex contains two symmetry‐related CuN 2 O 3 cores in a distorted square‐pyramidal geometry and one CuO 4 core in a distorted square‐plane geometry. The two μ‐bidentate syn ‐ anti carboxylate groups bridge Cu1 with Cu2, and Cu1A with Cu2. The trinuclear copper( II ) complex units are connected in a one‐dimensional zigzag chain via μ‐H 2 O−NO 3 − ‐bridged hydrogen bonds. Variable‐temperature susceptibility measurements (2−300 K) reveal a ferromagnetic coupling, J a = 8.08 cm −1 , between the μ‐carboxylato‐bridged Cu1 and Cu2, or Cu1A and Cu2, and a weak antiferromagnetic interaction, J b = −0.40 cm −1 , between Cu1 and Cu1A. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)