Synthesis and characterization of carbonate-encapsulated ytterbium- and yttrium-containing polyoxotungstates.

A sandwiched-type carbonate-encapsulated yttrium-containing arsenotungstate(III) has been synthesized under mild reaction conditions. The polyanion [NaCHCOO{Y(HO)(B-α-AsWO)(WO)(CO)}] (1) was isolated as a solid crystalline material by the reaction of a Y salt with the sodium salt of trilacunary [AsWO] in sodium acetate solution. The sodium salt of the polyanion, i.e. Na[Na(CHCOO){Y(AsWO)(WO)(CO)(HO)}]·22HO (1a), was characterized by various analytical techniques, such as FT-IR, single-crystal X-ray diffraction (SC-XRD), TGA (thermogravimetric analysis), C NMR and ESI-MS (electrospray ionization mass spectrometry). SC-XRD studies revealed that the polyanion crystallizes in the triclinic space group P-1. The structure showed that the polyanion is a carbonate-encapsulated sandwich-type species, consisting of two trilacunary B-α-[AsWO], with a lone-pair-containing As heteroatom, together with two extra tungsten centres and two yttrium cations at the sandwich position, where CHCOO and Na ions act as linkers between the two polyanion units. In addition, we have also synthesized two carbonate-encapsulated germanotungstates(IV), without lone-pair-containing heteroatoms, with the formula [Ln(A-β-GeWO)(CO)(HO)] [Ln = Y (2) and Yb (3)], i.e. YKNa[Y(A-β-GeWO)(CO)(HO)]·19HO (2a) and YbKNa[Yb(A-β-GeWO)(CO)(HO)]·16HO (3a), and characterized them by FT-IR, SC-XRD, TGA and ESI-MS. Here, the lanthanide ions act as linkers, extending the structures into higher dimensions. Sodium and potassium ions also play a key role as linkers, further extending the structure. The packing shows the presence of certain hydrophilic pores within the structure.