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).