Synthesis, crystal structure and magnetic studies of linear and cubane-type tetranuclear Cu(II) complexes obtained by stoichiometric control of the reagents

Abstract Two new tetranuclear Cu(II) complexes, [Cu 4 (L) 2 (μ-OAc) 2 (CH 3 OH) 2 ] ( 1 ) and [Cu 4 (HL) 4 (CH 3 OH) 2 ] ( 2 ), were synthesized from the reaction of copper(II) acetate with a polydentate Schiff base ligand in different molar ratios in methanol solvent (H 3 L = 2-{[(1 E )-(5-bromo-2-hydroxyphenyl)methylene]amino}-2-methylpropane-1,3-diol). These complexes were characterized by elemental analysis, spectroscopic methods and single crystal X-ray analysis. Complex 1 is a linear tetranuclear Cu(II) complex while complex 2 has a cubane-like arrangement. The results show that the reaction of H 3 L with Cu(OAc) 2 ·H 2 O in 1:2 molar ratios afforded complex 1 as sole product. By changing the molar ratios into 2:2 in the same reaction system, cubane-like tetranuclear copper(II) complex (complex 2 ) was isolated. Crystal structures of complexes indicate that part of the acetate anions remain coordinated to the Cu(II) ions when a higher amount of metal salt employees in the reaction. In this condition the ligand uses all of its donor atoms. When the reagents are added in equimolar ratio, all the acetate anions are replaced by ligand and one of the alcoholic donor groups of the ligand do not coordinate to the metal ion. The magnetic behavior of both compounds is closely related to their crystal structures showing antiferromagnetic couplings between nearest neighbors copper ions in 1 and both ferro and antiferromagnetic exchanges in the cubane like 2 .