Synthesis and Structural Characterization of Inorganic-Organic-Inorganic Hybrids of Dipalladium-Substituted γ‑Keggin Silicodecatungstates

Three inorganic-organic-inorganic hybrids of dipalladium-substituted
γ-Keggin silicodecatungstates with organic linkers of different
lengths, TBA8[{(γ-H2SiW10O36Pd2)­(O2C­(CH2)nCO2)}2] (n = 1 (II), 3 (III), and 5 (IV), TBA = [(n-C4H9)4N]+), were synthesized by exchange of the acetate ligands
in TBA4[γ-H2SiW10O36Pd2(OAc)2] (ITBA) with malonic, glutaric, and pimelic acids, respectively.
The X-ray crystallographic analysis of II, IIIA (IIIA: III with DCE, DCE = 1,2-dichloroethane), and IVA (IVA: IV with 10DCE) revealed that the anion parts of II, IIIA, and IVA were inorganic-organic-inorganic hybrids
composed of two dipalladium-substituted γ-Keggin silicodecatungstates
connected by two dicarboxylate ligands. In the crystal structure of IVA, 10 DCE molecules per polyanion
were present in the vicinity of polyanions. Compound IVB (IVB: IV with 0.2DCE) was obtained by the evacuation of IVA. The DCE sorption–desorption
isotherms of IVB showed that
the amount of DCE sorbed was saturated at 10.5 mol mol–1, of which the amount was close to that (10 mol mol–1) of crystallographically assigned DCE molecules. In the DCE sorption–desorption
isotherms, a low-pressure hysteresis was observed probably because
of hydrogen-bonding interaction between DCE molecules and polyanions.
The powder X-ray diffraction (XRD) pattern of IVA changed with decrease in the relative DCE vapor
pressure to form IVC (IVC: IV with 0.7DCE) at P/P0 = 0.0. The in situ powder
XRD study showed reversible structure transformation between IVA and IVC driven by the sorption–desorption of DCE.