Syntheses, crystal structures, and electronic structures of new barium fluoromolybdates

Four new barium fluoromolybdates, Ba₂Mo₆O₁₉F₂ (1), BaMoO₃F₂ (2), Ba₂Mo₂O₅F₆ (3), and Ba₃Mo₂O₅F₄(H₂O)₂·4IO₃ (4) were synthesized under hydrothermal conditions, and their crystal structures were determined using single-crystal X-ray diffraction (SCXRD). By adjusting the amount of HF during synthesis, four distinct types of MoO_6-xF_x (X = 0 to 3) octahedra were identified: MoO₆, MoO₅F, MoO₄F₂, and MoO₃F₃, all exhibiting pronounced out-of-center distortions. Compound 1 features a three-dimensional (3D) framework composed of MoO₆ and MoO₅F octahedra, while compound 2 adopts a one-dimensional (1D) chain structure built from MoO₅F and MoO₃F₃ octahedra. Compounds 3 and 4 are discrete dimers formed by corner-sharing two MoO₃F₃ octahedra in compound 3 and two MoO₄F₂ octahedra in compound 4. The assignment of Ba, Mo, I, O, and F in these compounds was validated using bond valence sum (BVS) calculations. Additionally, compound 4 was analyzed further using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), infrared (IR) spectroscopy, thermogravimetric analysis (TGA) and ultraviolet–visible–near infrared spectroscopy (UV–Vis–NIR). Band structures and density of states were calculated for all four compounds to provide insight into their electronic structures.