Homodinuclear lanthanide complexes:: Ln2L3 (H2L equals tetradentate Schiff bases).: Magnetic properties (solid state) and spectroscopic studies (solution)

The Ln(2)L(3) complexes have been known for a long time but no structural characterization is yet available. A first hypothetical structure supposed that the two lanthanide centres were isolated while a second structure, based on spectroscopic arguments, indicated that the two lanthanide centres are held together by one of the three L2- deprotonated Schiff bases acting as a bridging ligand via its two phenoxo oxygen atoms. It is the reason why we studied the magnetic properties of Gd2L3 complexes. Indeed, the temperature dependence of the magnetic susceptibility of Gd2L3 complexes suggest the presence of an antiferromagnetic interaction in both complexes. The parameters resulting from the fitting process give J values varying from -0.140(3) to -0.100(2) cm(-1). The Gd-2(thd)(6) complex which has been structurally characterized elsewhere and which comprises gadolinium ions doubly bridged by oxygen atoms gives a J value of -0.082(1) cm(-1). Such results confirm the presence of oxygen bridges between the two gadolinium centres in the Gd2L3 complexes. Solution studies show that both Ln(2)L(3) complexes are dissociated into [LnL(2)](-) and [LnL](+) C species. These mononuclear species have been isolated and characterized. (C) 1998 Elsevier Science S.A.