Synthesis and Study by Moessbauer Spectroscopy of Lipscombite (Fe3+2Fe2+(PO4)2(OH)2) Partially Substituted by Manganese, Cobalt, and Chromium Cations

Abstract

Recent investigations claimed the use of lipscombite, Fe3+2Fe2+(P04)2(0H)2, as a catalyst for the oxidative dehydrogenation of isobutyric acid. In the present study, the synthesis and characterization by Mossbauer spectroscopy of Mn-, Co-, and Cr-substituted lipscombites are described. It is found that lipscombite substituted by lo%, 20%, and 30% of cobalt and manganese could be prepared while the substitution by chromium did not exced 20%. Mossbauer spectroscopy along with other physicochemical characterization techniques showed that [Fe3+2-,M2+,]Fe2+(P04)2-,(HP04),(OH)2 (M = Mn or Co) type solid solutions were obtained instead of Fe3+2[Fe2+~-,M2+,](PO4)2(OH)2 solid solutions which exist for natural compounds. Chromium-substituted compounds belonged to a [Fe3+2-xCr3+,]Fe2+(P04)2(OH)2 limited solid solution ( x 0.3). Mn2+, Co2+, and Cr3+ were found to preferentially occupy in the lipscombite structure two ferric cations sites Fe(3)b and Fe(3)a, which differ by their cationic surrounding.

Synthesis, Crystal Structure, and Electrochemical and Magnetic Study of New Iron (III) Hydroxyl-Phosphates, Isostructural with Lipscombite

“…Gheith applied the name of lipscombite to a series of compounds of general formula Fe 2 - y (PO 4 )(OH) with tetragonal symmetry. Only the tetragonal compounds with y < 2 / 3 have been studied; − for example, the structure of Fe 1.475 (PO 4 )(OH) ( y = 0.525) has P 4 3 2 1 2 symmetry with a = 7.310 Å and c = 13.212 Å . Schmid-Beurmann , showed the existence of a restricted tetragonal solid solution of general formula Fe III 4/3 - z /3 Fe II z (PO 4 )(OH) 1 - z O z (0.18 < z < 0.60).…”