EXCHANGE INTERACTIONS THROUGH HYDROGEN-BOND BRIDGES - CRYSTAL-STRUCTURE, SPECTROSCOPIC CHARACTERIZATION AND MAGNETIC-PROPERTIES OF THE COMPLEX ARBOXYMETHYL)-6,9-DIOXA-3,12-DIAZATETRADECANEDIOIC ACID)

The structure and spectroscopic and magnetic properties of [{Cu(en)}(2 )(mu-egta)]. 4H(2)O (H(4)egta = 3,12-bis(carboxymethyl)-6,9-dioxa-3,12 -diazatetradetanedioic acid) are described. The compound is built of centrosymmetric neutral dimeric [{Cu(en)}(2)(gamma-egta)] entities lin ked through hydrogen bonds involving water molecules, -NH2 groups and -CO2- groups, affording a three-dimensional framework. The egta anion displays an opened-up structure acting as a bridging ligand between tw o copper atoms. The coordination geometry about the metal atoms tan be viewed as 4 + 1 + 1 (CuN3OO'O '' chromophores). The EPR spectra are i ndicative of an essentially d(x2-y2) ground state for the copper(II) i ons. Magnetic susceptibility measurements in the range 1.8-200 K show weak antiferromagnetic exchange interactions (2J= - 1.51(1) cm(-1)). T he observed behaviour is discussed based on the crystal structure and compared with that observed in the related compound [{Cu(H2O)}(2)(mu-e gta)]. 2H(2)O. From this study, the triatomic N-H...O bridges between the dimeric [{Cu(en)}(2)(mu-egta)] units are thought to be the suitabl e pathway for the exchange interaction. (C) 1998 Elsevier Science S.A. All rights reserved.