Synthesis and structural and magnetic characterisation of cobalt(ii)-sodium phosphonate cage compounds

The reaction of cobalt salts with phosphonic acids in the presence of 6-chloro-2-hydroxypyridine as a co-ligand, using sodium methoxide as a base, leads to a series of new polymetallic cobalt cages. Variation of the phosphonate present and the cobalt salt leads to {Co6Na8}, {Co 12}, {Co13Na6}, {Co14Na4} and {Co15Na} cages, all of which have been characterized by X-ray crystallography. Using lithium methoxide produces a sixth cage with a {Co 6Li9} core. The structures are, in general, extremely irregular with no structural motifs common to the six cages. Magnetic studies of these cages show a general decline in the product χmT with T, but for {Co13Na6}, {Co15Na} and {Co 12} there are maxima at low temperature, which suggest non-diamagnetic ground states. Investigation of the dynamic behaviour of the magnetisation of these complexes shows that the {Co13Na6}, and possibly the {Co12} cage, appear to display slow relaxation of magnetisation. © 2009 The Royal Society of Chemistry.