Copper(II) diethylenetriamine perchlorato complexes bridged through varying length dicarboxylato spacers: synthesis, characterization and EPR studies

The synthesis and spectral characterization of dinuclear copper(II) complexes of the composition [(dien)CuLCu(dien)](ClO4)(2), where dien = diethylenetriamine and L2- = oxalato, malonato, succinato, phthalato, isophthalato and terephthalato, are reported. IR spectra reveal that the mode of carboxylato coordination is anti-anti for oxalato complexes while it adopts chelate or polymeric syn-anti coordination for the rest of the complexes. The stereochemistry around copper is distorted square pyramidal. Oxalato forms two types of complexes I and II. EPR for I is characterized by a rhombic g tensor with g(3) < g(1) and g(2) and suggest that the unpaired electron has a predominant d(z)2 character while II and the rest of the dicarboxylato complexes are characterized by an axial g tensor (g(parallel to) > g(perpendicular to)) suggesting the occupancy of unpaired electron in a d(x)2(-y)2 orbital. Frozen solution EPR spectra at 77 K indicate that the solvent molecule coordinates with the metal ion. Magnetic exchange in these complexes is intramolecular and both conjugated and unconjugated spacer dicarboxylato ligands propagate the exchange between the metal ions. (C) 1998 Elsevier Science Ltd. All rights reserved.