Studies of lanthanide (III) dipicolinate complexes in aqueous solution. Part 2. Hydration

Abstract

A method for obtaining the hydration numbers of some lanthanide(III) complexes has been developed. Proton relaxation rates of the hydrogen atoms which are a constituent part of the ligands, A_n, bound to Ln^III ions in the complex [MA_n(OH₂)_xn] are compared with those of bound water, which is in fast exchange with bulk water (A = dipicolinate). The mehtod is applied to the lanthanide (III) mono- and bis-dipicolinate complexes and shows that they are bound to six and three water molecules respectively, resulting in nine-co-ordinate complexes. The tris complexes have no inner-sphere water.