Synthesis and crystal structures of (pyH)2[Mo2O4F6] and (pipH2)[Mo2O4F6]; vibrational band assignment for [Mo2O4F6]2− anion

The two closely related compounds (pyH)2[Mo2O4F6] and (pipH2)[Mo2O4F6], (Py = pyridine, pip = piperazine), were synthesized by the reaction of MoBr3Py3 and [Mo(CO)5]2pip with anhydrous HF in a FEP (fluorinated ethylene propylene) reaction vessel. The presence of traces of water resulted in the formation of oxyfluorides. (pyH)2[Mo2O4F6] and (pipH2)[Mo2O4F6] were characterized by X-ray diffraction and Raman spectroscopy. Geometry of the anion [Mo2O4F6]2− was optimized using DFT/B3LYP with cc-PVDZ basis set and the interpretation of the measured Raman spectra was offered based on normal modes of calculated spectrum.