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 {Co(6)Na(8)}, {Co(12)}, {Co(13)Na(6)}, {Co(14)Na(4)} and {Co(15)Na} cages, all of which have been characterized by X-ray crystallography. Using lithium methoxide produces a sixth cage with a {Co(6)Li(9)} 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 chi(m)T with T, but for {Co(13)Na(6)}, {Co(15)Na} 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 {Co(13)Na(6)}, and possibly the {Co(12)} cage, appear to display slow relaxation of magnetisation.