Searching for LiCrIIPO4

The two new phosphates LiCr4II(PO4)(3) and (Li5Cr2CrIII)-Cr-II(PO4)(4) are discovered as equilibrium phases (v=800 degrees C) in the quartemary system Li/Cr/P/O. Their crystal structures have been determined from single-crystal X-ray diffraction data {LiCr4II(PO4)(3)}: violet-blue, Pnma (no. 62), Z=4, a=6.175(1) angstrom, b=14.316(3) angstrom, c=10.277(2) angstrom, 100 parameters, R-1 =0.028, wR(2)= 0.08, 2060 unique reflections with F-o > 4 sigma(F-o); (Li5CrCrIII)-Cr-II(PO4)(4): greyish-green, P (1) over bar (no. 2), Z=1, a=4.9379(7) angstrom, 6=7.917(2) angstrom, c=8.426(2) angstrom, alpha=109.98(2), beta=90.71(1)degrees, gamma=104.91(1)degrees, 131 parameters, R-1=0.022, wR(2)=0.067, 1594 unique reflections with F-o>4 sigma(F-o)}center dot(Li5Cr2CrIII)-Cr-II(PO4)(4) adopts an hitherto unknown structure type. The crystal structure of LiCrII(PO4)(3) is isotypic to that of NaCd4II(PO4)(3) and related to that of the mineral silicocarnotite Ca-5(PO4)(2)(SiO4). Significant disorder between Li+ and Cr2+ is observed for both crystal structures. The oxidation states assigned to chromium in these two phosphates are in agreement with UV/vis/NIR absorption spectra and magnetic susceptibility data recorded for both compounds. Instead of (LiCr4PO4)-P-II mixtures of LiCr4II(PO4)(3), (Li5Cr2CrIII)-Cr-II(PO4)(4), Cr2O3, and CrP are observed at equilibrium. Instead of (Li2CrP2O7)-P-II four-phase mixtures consisting of Li9Cr3III(P2O7)(3)(PO4)(2), Li3Cr2III(PO4)(3), LiCrP2O7, and CrP were obtained. (C) 2014 Elsevier Inc. All rights reserved.