Crystal structure of (V0.94Co0.46)[PO4(OH)(0.74)(OH2)(0.26)]: a mixed-valence phosphate related to the mineral caminite and the synthetic lipscombite

The new compound Vsimilar to 0.94Cosimilar to 0.46[PO4(OH)(similar to 0.74) (H2O)(similar to 0.26)] has been isolated from soft hydrothermal treatment. X-ray single crystal diffraction data gave a tetragonal cell (space group I41/amd, Z = 4) with a = 5.2130(5) and c = 12.959(1). It is isostructural w ith the caminite Mg-1.33[SO4(OH)(0.66)(H2O)(0.33)] and is closely related t o the mixed-valence iron phosphate Lipscombite Fe(2-3x)2+Fe2x3+ [PO4OH] wit h x varying in the range 0 less than or equal to x less than or equal to 2/ 3, Vsimilar to 0.94Cosimilar to 0.46[PO4(OH)(similar to 0.74)(H2O)(similar to 0.26)] orders antiferromagnetically below 7 K (theta = -18.7 K) as sugge sted by the broad maximum observed from susceptibility measurements. The ma gnetic data are discussed together with the susceptibility data of the tetr agonal and monoclinic forms of the trivalent vanadium orthophosphate VPO4(H 2O). (C) 2000 Editions scientifiques et medicales Elsevier SAS, All rights reserved.