Hydrothermal Synthesis and Comparative Coordination Chemistry of New Rare-Earth V4+ Compounds

Several new hydrated rare earth vanadates and rare earth oxy-vanadates have been synthesized using hydrothermal techniques and characterized using single crystal and powder X-ray diffraction and infrared and UV–vis absorption spectroscopies. The hydrated rare earth vanadates adopt the space group P21/m with general formula A3VO5(OH)3 (A = Y (1), Dy (2), or La (3)) and contain anionic distorted square pyramidal [VO5]−6 units and AO7 and AO8 polyhedra. The oxy-vanadates with the general formula A2O­(VO4) (A = Y (4), Dy (5; 6), or Yb (7)) form two polymorphs in either P21/c or C2/c space groups and contain anionic tetrahedral [VO4]−4 units and nonvanadium bonded O2– anions in distorted [OA4] tetrahedra. In all cases, the vanadium ion is in the tetravalent oxidation state, and its original source was the trace V4+ impurities in YVO4. The observed vanadyl and equatorial vanadium–oxygen bond lengths about the square pyramid in compounds 1–3 and the tetrahedral vanadium coordination found in compounds 4–7 are unusual for V4+. The electronic and vibrational spectra are also reported and correlated with the appropriate coordination environment.