The Monophosphate Pb2V2VO(PO4)4: A Tunnel Structure with the Mixed Valence V(III)-V(IV)

✍ Scribed by A. Leclaire; J. Chardon; A. Grandin; M.M. Borel; B. Raveau

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 420 KB
• Volume: 108
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1994.1045

✦ Synopsis

A new vanadium monophosphate, (\mathrm{Pb}{2} \mathrm{~V}{2} \mathrm{VO}\left(\mathrm{PO}{4}\right){4}), characterized by the mixed valence V(III)-V(IV), has been synthesized. It crystallizes in the space group (C 2 / c) with (a=17.747(2) \AA, b=) 18.051(2) (\AA, c=9.344(1) \AA), and (\beta=117.03(1)^{\circ}). This structure can be described from the (\left[{ }{2} \mathrm{P}{4} \mathrm{O}{16}\right]{\infty}) framework built up from corner-sharing (\mathrm{PO}{4}) tetrahedra and (\mathrm{VO}{6}) octahedra. This host lattice consists of cross-linked (\left[\mathrm{VPO}{8}\right]{\infty}) chains forming (\left[\mathrm{VP}{2} \mathrm{O}{10}\right]{\infty}) layers parallel to (001); the whole (\left[\mathrm{V}{2} \mathrm{P}{4} \mathrm{O}{16}\right]{\infty}) framework results from the stacking along [104] of identical (\left[\mathrm{VP}{2} \mathrm{O}{10}\right]{\infty}) layers. This threedimensional framework delimits tunnels running along the [001] and ([102]) where (\mathrm{Pb}^{2+}) ions are located; it forms also large tunnels running along [110] and [110] which are obstructed by vanadyl ions. The latter form (\mathrm{VO}{5}) pyramids with the surrounding oxygens; each (\mathrm{VO}{5}) pyramid shares one edge with one (\mathrm{PO}{4}) tetrahedron, forming (\mathrm{VPO}{7}) units. Bond valence calculations show that V(IV) and V(III) species are distributed in an ordered way, in (\mathrm{VO}{5}) pyramids and (\mathrm{VO}{6}) octahedra, respectively, whereas lead is in the divalent state. (\mathrm{The} \mathrm{Pb}(\mathrm{II})) cations, which exhibit two kinds of coordination, 7 and 8, show a stereoactivity of their (6 s^{2}) lone pair. O 1994 Acadernic Press, Inc.