A new polymorph of VO2 prepared by soft chemical methods

A novel polymorph of VO2, designated VO2(C), has been prepared by dehydration of the new layered vanadium oxide hydrate, VO2 . 1/2 H2O. The hydrate is prepared in high yield as a single phase from the hydrothermal reaction of the hydrolyzate of VCl4 and NaOH in a molar ratio of 1:4.5 for 96 hours at 200 degrees C. The hydrate crystallizes in the tetragonal space group I4/mmm, with a = 3.7211(6) Angstrom, 15.421(1) Angstrom, Z = 4, and R = 0.045 as determined by X-ray single crystal diffraction. The structure consists of layers of VO5 square pyramids, each of which shares its four basal edges,vith four neighboring VO5 square pyramids. Water molecules that reside between the layers can be removed reversibly to give the new layered oxide VO2(C). (C) 1998 Academic Press.