Vanadium I 5000 Hydrothermal Synthesis and Crystal Structure of a Three-Dimensional Polyoxovanadate. -Yellow crystals of HV 3 O 8 ·H 2 O are hydrothermally synthesized by reaction of NH4VO3, CuCl2, La(NO3)3, and isonicotinic acid in H2O (pH 8.3 adjusted with NaOH, 160°C, autoclave, 7 d, 63% yield). The compound crystallizes in the monoclinic space group P21/m with Z = 2 (single crystal XRD) and exhibits a three-dimensional framework structure containing VO5 trigonal bipyramids and VO6 octahedra. -(MA*, H.; WANG, X.; DONG, B.; LI, C.; WU, L.; Cryst.