Single-atom O-bridged urea in a dinickel(II) complex together with Ni4IICu2II and Cu4II complexes of a pentadentate phenol-containing Schiff base with (O,N,O,N,O)-donor atoms

A pentadentate phenol-containing ligand (H3L) with N2O3 donor atoms yields Ni-2(II) (1), Ni-4(II) (2), Cu-2(II) (3) and Cu-4(II) (4) complexes, which have been structurally characterized by X-ray diffraction. Complex 1 contains a single-atom O-bridged urea. The compounds were characterized by IR, UV/Vis, mass spectrometry, electrochemistry and variable-temperature (2-295 K) magnetic susceptibility measurements. Analysis of the susceptibility data shows antiferromagnetic interactions between the metal centers indicating a diamagnetic ground state for complexes 1, 3 and 4, whereas complex 2, a tetranuclear Ni-II cubane, has a complicated low-lying magnetic structure with a non-diamagnetic ground state. A plot of J vs. Ni-O-Ni angles for all structurally characterized Ni4O4 cubane cores, including 2, irrespective of their symmetry exhibits a large variation of J values within a small range of Ni-O-Ni angles. The electrochemistry of all complexes was investigated in detail and the ligand-centered oxidation to a radical-ligand is inferred from the occurrence of oxidation processes at potentials which are similar. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).