Refinement of the Crystal Structure of Synthetic Chervetite, Pb 2 V 2 O 7

Abstract

The structure of synthetic chervetite has been refined by full matrix least-squares to a ω R = 0.029 using 1105 reflections. Unit cell dimensions are a = 13.3689(7), b = 7.1607(4), c = 7.1027(4) Å, β = 105935(5)°, and the space group is P2 1 /a. The structure, originally solved by Kawahara, is a dichromate-type structure with a V 2 O 7 4− group eclipsed to within 11 ± 5°. The Pb 2+ ions are irregularly coordinated to 8 or 9 oxygens with distances from 2.40 to 3.20 Å. The distortion of the Pb–O distances is considerably greater than the corresponding distortions of the Sr–O distances in the similar β-Sr 2 V 2 O 7 structure and is related to the tendency of Pb 2+ to form directional covalent bonds. The V–O distances range from 1,665 to 1.720 Å for terminal oxygens and are 1.812 and 1.821 Å for the bridging oxygens. The V–O distances are consistent with the strengths of the Pb—O bonds.