pH-dependent assembly of saturated to dilacunary Keggin-based silicotungstate: [Cu(en)₂(H₂O)][H₂en]{γ-SiW₁₀O₃₆[Cu(en)₂(H₂O)]₂}·7.5H₂O

Abstract

By controlling the pH of the reaction system, a dilacunary γ-Keggin silicotungstate [Cu(en)₂(H₂O)][H₂en]{γ-SiW₁₀O₃₆[Cu(en)₂(H₂O)]₂}·7.5H₂O (1) (en = ethylenediamine) has been hydrothermally synthesized by the reaction of CuCl₂ with α-H₄SiW₁₂O₄₀ and characterized by IR spectra, thermogravimetric analysis, and single-crystal X-ray diffraction. The product is prepared in the pH range 7.9–8.2, which reveals that pH plays a key role in the assembly of saturated α-H₄SiW₁₂O₄₀ to dilacunary [γ-SiW₁₀O₃₆]⁸⁻ polyoxometalate. The polyoxoanion {γ-SiW₁₀O₃₆[Cu(en)₂(H₂O)]₂]}⁴⁻ of 1 presents a rare [γ-SiW₁₀O₃₆]⁸⁻-retaining structure, in which two lacunary sites of [γ-SiW₁₀O₃₆]⁸⁻ are unoccupied, meanwhile, two [Cu(en)₂(H₂O)]²⁺ groups are grafted on either side of the [γ-SiW₁₀O₃₆]⁸⁻ unit by Cu–O–W bond.

Keywords:

• pH-Dependent
• Dilacunary
• Hydrothermal synthesis
• Silicotungstate

Acknowledgments

This work was supported by the Natural Science Foundation of China, Special Research Fund for the Doctoral Program of Higher Education, Innovation Scientists and Technicians Troop Construction Projects of Henan Province, the National Science Fund for Young Scholars of China (no. 21101059) and the Open Research Fund of State Key Laboratory of Inorganic Synthesis and Preparative Chemistry (grant no. 2011-26).