A Quasi-Tetrahedral Cu4 Cluster and a Helical-Chain Copper(II) Complex with Single Syn-Anti Carboxylate Bridges: Crystal Structure and Magnetic Properties

A tridentate Schiff base carboxylate ligand, derived from the condensation of pyridine 2-carboxaldehyde with anthranilic acid, reacts with copper trifluoroacetate salt to give rise to the helical chain complex [Cu(C13H9N2O2)(F3CCO2)]n (1) and with copper nitrate to give rise to the tetranuclear complex [{Cu4(C13H9N2O2)4(H2O)4}·3.5NO3·0.5N3] (2) with the addition of azide salt. The structures of these complexes have been solved by X-ray crystallography. The Cu(II) ions are in a distorted square-pyramidal environment in complex 1. They are sequentially bridged by carboxylate groups in the syn-anti conformation, resulting in the formation of an infinite helix like chain along the crystallographic c-axis. The crystal structure of complex 2 consists of tetranuclear [Cu4(L)4(H2O)4]4+ (L = C13H9N2O2-) cations and isolated NO3- and N3- anions in the ratio 1:3.5:0.5, respectively, involving bridging carboxylate groups in the syn-anti conformation. For 1 the carboxylato-Cu(II) coordination is apical-basal, while for 2 it is basal-basal. From the magnetic susceptibility measurements the complex 1 is found to exhibit very weak antiferromagnetic interaction whereas a weak ferromagnetic coupling has been established for complex 2. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.