Tri- and pentanuclear CuII–CdII complexes of N2O2 donor ligands with the variation of carboxylate coligands: Structural elucidation and theoretical study

Abstract

Three new heterometallic copper(II)-cadmium(II) complexes [(CuL1)2Cd3(C6H5CO2)6] (1), {[(CuL2)2Cd(o-(NO2)C6H4CO2)2]·2NCMe} (2), and [{CuL2(H2O)0.65(NCMe)0.35}2Cd3(m-(NO2)C6H4CO2)6] (3) have been synthesized using [CuL1]/[CuL2] as metalloligand (where H2L1 = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine, H2L2 = N,Ń-bis(methyl2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Single crystal structure analyses reveal that complexes 1 and 3 exist as pentanuclear entities in which the [CuL1]/[CuL2] units are bonded to the terminal CdII centres of the benzoate (for 1)/m-nitro benzoate (for 3) bridged linear [Cd3(C6H5CO2)6] (for 1)/[Cd3(m-(NO2)C6H4CO2)6] (for 3) unit through double phenoxido oxygen atoms. On the other hand, complex 2 contains a linear, trinuclear structure in which the square pyramidal [CuL2] units are connected with the central octahedral CdII ion via double phenoxido bridges and also additionally through a syn-syn bridging o-nitro benzoate group. A theoretical investigation on the geometries and energies of the complexes reveals that in the presence of the naphthalene group in H2L1 the pentanuclear geometry of complex 1 is favored over the trinuclear ones, usually formed with the salen type ligands. In addition, substitution of benzoate ion at meta position by nitro group stabilizes pentanuclear structure more than ortho-substitution, corroborating the formation of pentanuclear complex 3 and trinuclear complex 2.