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 [NaCH₃COO{Y₂(H₂O)₃(B-α-AsW₉O₃₃)₂(W₂O₅)(CO₃)}]^12- (1) was isolated as a solid crystalline material by the reaction of a Y^III salt with the sodium salt of trilacunary [AsW₉O₃₃]^9- in sodium acetate solution. The sodium salt of the polyanion, i.e. Na₁₂[Na(CH₃COO){Y₂(AsW₉O₃₃)₂(W₂O₅)(CO₃)(H₃O)₃}]·22H₂O (1a), was characterized by various analytical techniques, such as FT-IR, single-crystal X-ray diffraction (SC-XRD), TGA (thermogravimetric analysis), ¹³C 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-[AsW₉O₃₃]^9-, with a lone-pair-containing As^III heteroatom, together with two extra tungsten centres and two yttrium cations at the sandwich position, where CH₃COO^- 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 [Ln₃(A-β-GeW₉O₃₄)₂(CO₃)(H₂O)₃]^13- [Ln = Y^III (2) and Yb^III (3)], i.e. Y₂K₃Na₄[Y₃(A-β-GeW₉O₃₄)₂(CO₃)(H₂O)₃]·19H₂O (2a) and YbK₈Na₂[Yb(A-β-GeW₉O₃₄)₂(CO₃)(H₂O)₃]·16H₂O (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.