Controlled assembly of polyoxometalate-based composite materials containing zero- and one-dimensional structures

Abstract

Three polyoxometalate-based composite compounds containing zero-dimensional cross-like and one-dimensional chain-like structures, [Gd(DMF)₆(H₂O)₂]₂·[P₂W₁₈O₆₂]·4DMF·2H₂O (1), [Ce(NMP)₃(H₂O)₅][Ce(NMP)₃(H₂O)₄][(P₂W₁₈O₆₂)]·4H₂O (2) and [{Gd(DMF)₆}{Gd(DMF)₇}(P₂W₁₈O₆₂)]·0.5DMF (3), were constructed from octadecatungstodiphosphorate clusters interacting with [RE(donor)]³⁺ [RE = Gd(III), Ce(III); donor = DMF (N,N-dimethylformamide), NMP (N-methyl-2-pyrrolidone)] groups. Single crystal X-ray structural analyses reveal that, for compound 1, the interactions between the polyanions and the charge compensating cations are mainly hydrogen bonds, van der Waals forces and electrostatic forces; for compound 2, two terminal oxygen (O_t) atoms located in “belt” sites of the polyanion are coordinated by RE cations, which generates an unprecedented zero-dimensional isolated structure; for compound 3, the adjacent polyanions are polymerized to form a one-dimensional infinite linear chain by the bridging RE coordination cations and exhibit the type –ACACAC–. The apparent difference in the ESR spectra of the two compounds containing Gd(III) ions seems to be related to different coordination environments of the Gd(III) ions. Thermal analyses show that the frameworks of the polyanions decompose at 611, 615 and 602 °C in compounds 1–3, respectively, and the stability of polyanions in compounds 1–3 is much stronger than that in the parent acid.