Three lanthanide complexes derived from itaconic acid and 2,2'-bipyridine.

The structures of three new polymeric lanthanide complexes, poly[[bis(2,2'-bipyridine)-mu(4)-itaconato-di-mu(3)-itaconato-digadolinium(III)] tetrahydrate], {[Gd(2)(C(5)H(4)O(4))(3)(C(10)H(8)N(2))(2)].4H(2)O}(n), (I), poly[diaqua(2,2'-bipyridine)di-mu(3)-itaconato-mu(2)-itaconato-digadolinium(III)], Gd(2)(C(5)H(4)O(4))(3)(C(10)H(8)N(2))(H(2)O)(2), (II), and poly[[bis(2,2'-bipyridine)-mu(4)-itaconato-di-mu(3)-itaconato-diholmium(III)] dihydrate], {[Ho(2)(C(5)H(4)O(4))(3)(C(10)H(8)N(2))(2)].2H(2)O}(n), (III), have been solved from twinned specimens. Compound (I) presents a two-dimensional polymeric structure parallel to (011) built up around two independent nine-coordinated Gd centres displaying similar GdO(7)N(2) environments, with both N-donor atoms in each provided by a chelating 2,2'-bipyridine (bpy) unit. The coordinating O atoms are from three different itaconate (ita) anions (itaconic acid is 2-methylidenebutanedioic acid). Compound (II) also presents two independent Gd centres (one ten- and the other eight-coordinated), but the overall formula and individual coordinations are different from those of (I). The chemical unit is in this case completed by one bpy ligand, three ita anions (one of them displaying a new, hitherto unreported, mu(3)-O,O':O',O'':O''' binding mode) and two aqua ligands. The whole structure is built up around a twofold rotation axis passing through both cations, as well as through the centre of the bpy ligand and one of the ita anions, thus making only half of the chemical unit independent. Finally, compound (III) presents a single independent Ho centre, a bpy unit and one and a half ita anions (one of them bisected by a twofold rotation axis) in the asymmetric unit, plus two (disordered) nonbonded solvent water molecules. In compounds (II) and (III), those ita anions bisected by a symmetry element incompatible with the internal symmetry of the ligand exhibit disorder in the C=CH(2) group.