Coordination asymmetry of a dinuclear copper(II) complex: Synthesis, structure, and magnetism

A dicopper(II) complex with a novel unsymmetric dinucleating ligand, H(2)L-1, which can provide donor atom, coordination number, and geometric asymmetries at metal centers, [Cu-2(L-1)(CH3COO)]ClO4 . H2O . 0.5NaClO(4) (1), was synthesized, where H(2)L-1 is a racemic 1-bis(2-pyridylmethyl)amino-3-salicylideneaminopropan-2-ol. The ligand is a hybrid one of 1,3-bis[bis(2-pyridylmethyl)amino]propan-2-ol (Htpdp) and 1,3-bis(salicylideneamino)propan-2-ol (H(3)L-2). Crystal structure of 1 was determined by X-ray crystallography. Complex 1 crystallizes in monoclinic space group C 2/c with a = 42.704(8), b = 12.689(6), c = 29.008(9) Angstrom, beta = 128.28(1)degrees, and Z = 16. The crystal structure showed that two stereoisomers (la and Ib) are present in solid state. This is attributable to the presence of an enantiomeric pair of L-l. Dinuclear cations consist of one square-planar site with a NO3 donor set and one five-coordinate site with a N3O2 donor set, which are linked by an endogenous alkoxide bridge of L-l and an exogenous acetate bridge. A powdered sample of 1 shows weak antiferromagnetic interaction (2.60 B.M./Cu-2 at 300 and 1.81 B.M./Cu-2 at 5 K). Cryomagnetic data is analyzed using two exchange coupling constants, J(1) = -0.18 cm(-1) and J(2) = -9.05 cm(-1). EHMO calculations revealed that the observed weak antiferromagnetic interaction(s) compared with that found for [Cu-2(L-2)(CH3COO)] (3) (J = -85 cm(-1)) is reasonably interpreted in terms of the energy gap and the nature of HOMO and LUMO. Some other physicochemical properties of the complex are discussed in comparison with those of the parent complexes, [Cu-2(tpdp)(CH3COO)](2+) (2)and [Cu-2(L-2)(CH3COO)] (3).