Two-Dimensional Bicapped Supramolecular Hybrid Semiconductor Material Constructed from the Insulators α‑Keggin Polyoxomolybdate and 4,4′-Bipyridine

A new organic–inorganic hybrid material [SiMo₁₄O₄₄]­(H4,4′-bpy)₂·xH₂O (4,4′-bpy = 4,4′-bipyridine) was synthesized using a hydrothermal method. The compound was characterized using single crystal X-ray diffraction (XRD), infrared spectroscopy (IR), ultraviolet–visible spectroscopy (UV–vis), and X-ray photoelectron spectroscopy (XPS). XRD studies on selected single crystals suggested that the compound consists of supramolecular 2D layer structures composed of capped α-Keggin polyoxomolybdate anions and 4,4′-bpy organic ligands. Absorption measurements show a band gap of 2.99 eV in the hybrid which suggests a semiconducting nature compared to the insulating free α-Keggin and 4,4′-bpy. The magnetic susceptibility of the hybrid material was investigated in the temperature range 1.8–300 K obeying the Curie–Weiss law above 70 K. Experimentally measured magnetic moment of 2.71 μ_B/formula indicates possible mixed valent molybdenum in the compound. The XPS measurements confirm the presence of both Mo^V and Mo^VI in the ratio 15:85 resulting in the structural formula of the hybrid as [SiMo^V₂Mo^VI₁₂O₄₄]­(H4,4′-bpy)₂·xH₂O.