Coordination of gadolinium(III) ions with a preformed mu-oxo diiron(III) complex: structural and magnetic data

A hexadentate ligand LH2(LH2= 1,2-bis((3-methoxysalicylidene)amino)ethane) reacts with iron(III) ions to yield a mu-oxo complex (LFe)2O, 1, which may function as a ligand towards gadolinium(III). The resulting product is a tetranuclear complex [LFeGd(NO3)3]2O, 2. Its structure has been determined by single crystal X-ray crystallography: 2, monoclinic P21/n(No. 14), a= 15.346(2), b= 17.372(2), c= 19.625(2), = 100.59(1)°, Z= 4. The thermal dependence of the MT product (M= molar magnetic susceptibility) and the field dependence of the magnetization (M) have been measured and analyzed according to the spin cluster model. In both complexes the Fe-Fe interaction is antiferromagnetic with a magnitude of -115.3 cm-1(1) and -101.4 cm-1(2). In the latter compound an exchange coupling is operative within each (FeIII, GdIII) pair. Modelling of the experimental data (MT and M) leads to the conclusion that this interaction is small and, unexpectedly, antiferromagnetic.