Discrete and 1D polymeric copper(II) complexes of tetranuclear cubane-like units : structural and magnetic characterization

Two novel copper(II) complexes, [Cu4(L)2(LH)2(H2O)2]2(NO3)2. (pydc).9H2O (1) and {[Cu4(L)2(LH)2(H2O)2(ppda)].5H2O}n (2) [H2L=2-[(2-hydroxy-ethylimino)-methyl]-6-methoxy-phenol, pydc=pyridine-3,5-dicarboxylate, ppda=phenylene-1,4-diacrylate]have been synthesized and characterised by X-ray single crystal diffraction analysis and low temperature magnetic study. The structural determination reveals for complex 1 a tetranuclear species exhibiting a double-open cubane like core framework, whereas use of ppda anions results 1D coordination polymer where tetranuclear double-open cubane cores are connected by bridging ppda ligands. In both the complexes, hydrogen bonding interactions lead to 3D supramolecular structures. Low temperature magnetic study indicates antiferromagnetic coupling in both the complexes. A model based on an effective square tetramer of Heisenberg spins was used to determine exchange strengths of 174(2) K for 1 and 107.4(4) K for 2