Tetrapodal amidoxime ligands I. Coordination isomerism due to self-complementary dimerization of a pyramidal cobalt(iii) coordination module

A bis-μ-amidoximato-bridged cobalt(III) dimer obtained with a new tetrapodal ligand possesses interesting structural parameters as a consequence of intramolecular hydrogen bonding intentionally built into the complex. Its synthesis and properties are described. The new ligand type combines attributes of two previously described ligand classes: It binds a metal ion in a tetrapodal pentadentate fashion and forms a pseudomacrocycle through hydrogen bonds, characteristic of chelating oxime ligands. Coordination isomerism, which is a consequence of dimer formation, has been analyzed by means of X-ray crystallography and carbon-13 nuclear magnetic resonance spectroscopy.