Reaction of cobalt salts with phosphonic acids in the presence of 6-chloro-2-hydroxypyridine as a co-ligand, normally in its deprotonated form, leads to a series of new polymetallic cobalt cages. The most common structural type is a {CO14} cage which resembles a fragment of cobalt hydroxide. Variation of the phosphonate present and the cobalt salt leads to {CO6}, {CO8}, {CO10}, {CO11}, {CO12}, {CO13}, and {CO20} cages, all of which have been characterized by X-ray crystallography. Magnetic studies of these cages show a general decline in the product chi(m) T with T, but for {CO6}, {CO8}, and {CO12} there are maxima at low temperature, which suggests nondiamagnetic ground states. Investigation of the dynamic behavior of the magnetization of these complexes shows that the octanuclear cage displays slow relaxation of magnetization.