Synthesis, molecular structure and magnetic properties of tetranuclear copper(II) complexes with pendant-arm macrocyclic ligands

The condensation of sodium 2,6-diformyl-4-X-phenolate (X=Cl, CH3) with the reduced 1:1 Schiff base of 2,2',2 " -tris(aminoethyl) amine (tren) and 2-formylfuran (or benzaldehyde) followed by in situ transmetallation with copper(II) perchlorate results in the production of four novel tetranuclear copper(II) complexes of 2 : 2 macrocyclic Schiff bases with functional pendant-arms (H2L1-4), which have been spectroscopically characterized. A typical complex [(Cu4LCl2)-Cl-1-(OH)(2)](ClO4)(2) (1) has been structurally studied by X-ray diffraction. In the cation of complex 1, [(Cu4LCl2)-Cl-1(OH)(2)](2+), a chair-shaped Cu4O4 core with two mu (3)-hydroxide groups inside is composed of two kinds of crystallographically independent Cu(II) atoms, each of which possesses a distorted square pyramidal configuration. The four metal atoms are in an approximate parallelogram. Two pendant-arms, bonding in a monodentate fashion to their adjacent metal atoms, lie in the 'trans' position to the macrocycle. The variable temperature magnetic susceptibility of 1 has been measured over the temperature range 4-300 K. The best fitting with a quasi-butterfly magnetostructural model shows antiferromagnetic exchanges within this compound, with J(bb) = -270.8 cm(-1), J(wb1) = -40.3 cm(-1) and J(wb2) = -37.5 cm(-1).