1D polyoxometalate-based composite compounds derived from the wells-dawson subunit:: Synthesis and crystal structure of [{Ce(DMF)4(H2O)3}{Ce(DMF)4(H2O)4}(P2W18O62)]•H2O and [{La(DMF)6(H2O)}{La(DMF)4.5(H2O)2.5}(P2W18O62)]

Two composite compounds, [{Ce(DMF)(4)(H2O)(3)}{Ce(DMF)(4)(H2O)(4)}(P2W18O62)](H2O)-H-. (1) (DMF = N,N-dimethylformamide) and [{La(DMF)(6)(H2O)}{La(DMF)(4.5)(H2O)(2.5)}(.)(P2W18O62)] (2), have been constructed at room temperature and characterized by single crystal X-ray structural analyses, ESR spectroscopy, and thermogravimetric (TG) and differential thermal analysis (DTA) measurements. Single crystal X-ray structural analyses reveal that the adjacent polyanions are polymerized to form a ID infinitely linear chain by the bridging RE coordination cations and exhibit an -ACACAC- type of structure, and that two types of terminal oxygen atoms of the Wells-Dawson polyanion located in the "cap" and "belt" sites are involved in coordination with the RE3+ ions, respectively. ESR spectra indicate that after irradiation with sunlight, compound 2 forms a mixed-valence heteropoly compound with unshared electrons. From TG-DTA analyses, we surmise that the frameworks of polyanions of this kind of compound decompose at ca. 620 degreesC.