A New Polymorph of VO2Prepared 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 VCl4and NaOH in a molar ratio of 1:4.5 for 96 hours at 200°C. The hydrate crystallizes in the tetragonal space groupI4/mmm, witha=3.7211(6) Å,c=15.421(1) Å,Z=4, andR=0.045 as determined by X-ray single crystal diffraction. The structure consists of layers of VO5square pyramids, each of which shares its four basal edges with four neighboring VO5square pyramids. Water molecules that reside between the layers can be removed reversibly to give the new layered oxide VO2(C).