Single‐Atom O‐Bridged Urea in a Dinickel(II) Complex together with NiII4, CuII2 and CuII4 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 NiII2 (1), NiII4 (2), CuII2 (3) and CuII4 (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 NiII 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. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)