Département de chimie moléculaire

A linear trinuclear Cu(II) complex contg. phenoxido- and alkoxido-bridges between the metal centers, [Cu3(py2O)2(MeOH)2](BF4)2·0.75MeOH (py2O = 6-(bis(2-pyridylmethyl)aminomethyl)-4-methylbenzene-1,2-diol), was isolated and structurally characterized. The complex cation consists of a linear array of three Cu ions, assembled by two doubly deprotonated ligands. The octahedral coordination sphere of the two peripheral Cu(II) ions is completed by weakly bound MeOH mols., and the square-planar central metal ion is located on an exact, crystallog. inversion center. Temp.-dependent magnetic susceptibility studies reveal antiferromagnetic exchange coupling between the Cu(II) ions in the trinuclear unit along with small intermol. antiferromagnetic interactions in the low temp. range. The results were fitted in two different ways, (i) taking into account solely the exchange interaction between the adjacent metal centers or, (ii) regarding exchange interactions between both adjacent and nonadjacent Cu(II) ions. Solid-state temp.-dependent X-band EPR studies in the range 4.2-250 K indicate a doublet ground spin state 11/2, 1. In soln., the ground spin state of the complex is a quartet (S = 3/2), suggesting a modification of the exchange coupling interactions between the Cu(II) ions. The simulation of the 4.2 K soln. spectrum gives rise to the best parameters D {\textgreater} 0.8 cm-1, g⊥ = 2.04 and g‖ = 2.21. [on SciFinder(R)]