Syntheses and crystal structures of two compounds based on saturated keggin-type polyoxotungstates and mixed ligands

Abstract

Two new polyoxotungstates with dafo and 4,4′-bipy ligands, [Ag(dafo)₂]₂{[Ag(4,4′-bipy)]₂SiW₁₂O₄₀} (1) and [Cd₂(dafo)₄(4, 4′-bipy)(H₂O)₂](dafo) SiW₁₂O₄₀ (2) (dafo = 4, 5-diazafluoren-9-one, 4,4′-bipy = 4,4′-bipyridine), have been hydrothermally synthesized and characterized by elemental analyses, IR, TG and single crystal X-ray diffraction. Compound 1 consists of a one-dimensional (1D) chain constructed from [Ag(4,4′-bipy)]⁺ cations. With the connection of [Ag(4,4′-bipy)]⁺ cations and α-[SiW₁₂O₄₀]⁴⁻ anions, two-dimensional (2D) structure was built. Because of the π–π stacking interactions between pyridyl rings of 4,4′-bipy from adjacent chains, three-dimensional (3D) structure was generated. Furthermore, the C–H ··· O weak interaction between and polytungstate made the structure more stable. Like 1, compound 2 is a three-dimensional (3D) supramolecular compound constructed from a transition-metal complex fragment [Cd₂(dafo)₄(4,4′-bipy)(H₂O)₂]⁴⁺, and free dafo through C–H ··· O weak interactions. To our best knowledge, it is the first time that saturated Keggin-type polyoxotungstates interact with dafo and 4,4′-bipy at the same time.

Keywords:

• Polyoxotungstates
• Keggin
• Weak interaction
• Dafo
• 4,4′-bipy

Acknowledgements

The authors thank National Science Foundation of China (No. 20371011), Science and Technology Development Project Foundation of Jilin Province (No. 20060420), Analysis and testing foundation of Northeast Normal University (No. 201586000/201372000), Ph.D station Foundation of Ministry of Education (No. 20060200002) for financial support.