Two- and three-dimensional hydrated coordination polymers of diaqualanthanum(3+) ions with 2-hydroxypropanedioate, oxalate and acetate anions as bridging ligands.

The title compounds, poly[[tetraaquadi-mu-2-hydroxypropanedioato-mu-oxalato-dilanthanum(III)] tetrahydrate], {[La(2)(C(2)O(4))(C(3)H(2)O(5))(2)(H(2)O)(4)].4H(2)O}(n), (I), and poly[[tetra-mu-acetato-tetraaqua-mu-oxalato-dilanthanum(III)] dihydrate], {[La(2)(C(2)O(4))(C(2)H(3)O(2))(4)(H(2)O)(4)].2H(2)O}(n), (II), represent crystalline hydrates of coordination polymers of diaqualanthanum(3+) ions with different combinations of bridging carboxylate ligands, viz. 2-hydroxypropanedioate and oxalate in a 2:2:1 ratio in (I), and acetate and oxalate in a 2:4:1 ratio in (II). While the acetate component was one of the reactants used, the other ligands were obtained in situ by aerial oxidation of the dihydroxyfumaric acid present in the reactions. The crystal structure of (I) consists of two-dimensional polymeric arrays with water molecules intercalated between and hydrogen bonded to the arrays. The oxalate components are located on inversion centres. The crystal structure of (II) reveals an open three-dimensional polymeric connectivity between the interacting components, with the solvent water molecules incorporated within the intralattice voids and hydrogen bonded to the polymeric framework. The La(III) ion and the noncoordinated water molecules are located on axes of twofold symmetry. The oxalate group is centred at the 222 symmetry site, the intersection of the three rotation axes. The coordination number of the La(III) ion in the two structures is 10. The significance of this study lies mainly in the characterization of two new coordination polymers, as well as in the confirmation that dihydroxyfumaric acid tends to rearrange to form smaller components in standard laboratory procedures, and should be considered a poor reagent for formulating hybrid coordination polymers with metal ions.