Synthesis, Crystal Structure And Characterization Of Novel Tungstogermanates

Polyoxometalates (POMs) have received much attention due to their fascinating variety of structure and chemical composition, and potential applications in catalysis, materials science, environmental protection and medicine. The synthesis of new type compounds with special structures and compositions is the research hotspot and nodus in this field all the time. In this paper, the main work has been focused on the rare reported tungstogermanates, and eight novel polyoxotungstates have been synthesized. Dimeric disubstitutedα-Keggin tungstogermanates:K₁₄[α-GeFe₂W₁₀O₃₈(OH)]₂·34H₂O(1)Na₁₂[Zr₄O₂(OH)₂(CH₃COO)₂(α-GeW₁₀O₃₇)₂]·30H₂O(2) Co-contained sandwich-type Keggin tungstogermanates:Na₁₂[Co₄(H₂O)₂(GeW₉O₃₄)₂]·30H₂O(3)Na₂₀[((CoOH₂)Co₂GeW₉O₃₄)₂(GeW₆O₂₆)]·47H₂O(4) Monsubstituted Keggin tungstogermanate:[H₂N(CH₃)₂]₆[GeW_11.25Ni_0.75O₃₉(HCO₂)]·5H₂O(5) Infinitely one-dimensional chain-like structure:Na₂(C₆H₅NO₂)(H₃O)[Na(C₆H₅NO₂)₃(H₂O)₂GeW₁₂O₄₀]·2H₂O(6) Sandwich-type Keggin polyoxotungstates with transition metal as the central heteroatoms:Na₁₄[Co₂Bi₂(CoW₉O₃₄)₂]·48H₂O(7)Na₁₄[Zn₂Bi₂(ZnW₉O₃₄)₂]·51H₂O(8)All of the above polyoxotungstates were characterized by IR spectroscopy, UV-vis, elemental analysis, and single-crystal X-ray analysis to identify their structural and chemical composition. Otherwise, some of them were characterized by electrochemistry and TG-DSC. The dimeric disubstitutedα-Keggin tungstogermanates 1 and 2 are based on two new kinds of [α-GeW₁₀O₃₇]^10- ions respectively. The tungstogermanate moieties of 1 are divacant lacunary versions of the Keggin [GeW₁₂O₄₀]^4- anion from which two of the tungstens from different adjacent W₃O₁₃ triads were replaced by two iron atoms. And the hypothetical [α-GeZr₂W₁₀O₃₈(OH)(CH₃COO)]^6- unit of 2 contains two Zr atoms in the same W₃O₁₃ triad. One of the Zr atoms is seven-coordinate, and the other is eight-coordinate which is bonded with an acetate group. The dimeric polyoxotungstates 3 consists of two lacunary B-α-[GeW₉O₃₄]^10- Keggin moieties linked via a rhomblike Co₄O₁₆ group leading to a sandwich-type structure. The double-sandwich structure polyoxoanion 4 consists of two [B-α-(CoOH₂)Co₂GeW₉O₃₄]^4- Keggin moieties linked via a unique [B-GeW₆O₂₆]^12- fragment. Compound 4 is the first reported C-type polyoxotungstate with tetravalent atoms as the central heteroatoms. Monosubstitutive Keggin polyoxoanion 5 is formed by a formate coordinated Ni atom replaceing a W atom of the saturated Keggin [α-GeW₁₂O₄₀], and the site occupancy of Ni is 0.75, and that of W is 0.25. The crystal structure of 6 can be described as an infinitely one-dimensional zigzag chain-like tungstogermanate with alternating cations and [GeW₁₂O₄₀]^4- anions through W-O_d-Na-O_d-W links. Polyoxotungstates 7 and 8 are sandwich-type Keggin polyoxotungstates with transition metal as the central heteroatoms, which consist of two unprecedented [B-β-MW₉O₃₄]^12- subunits linked by coplanar two transition metal and two Bi³⁺ ions, and the polyanions are also the first example of dimeric heteropolyanions with Bi^III only as the second (linking) heteroatom and the transition metals (Co^II or Zn^II) as the first and the second heteroatoms as well.The investigation of this paper indicates that the formation and successful isolation of these new type compounds depend on many factors, such as the composition and the ratio of reactants, temperature, solvent, counterion and pH value in which the last two are especially important.