The Crystal Structure of Synthetic Fe₄²⁺Fe₃³⁺(PO₃OH)(PO₄)₅

Fe6.67(PO4)5.35(HPO4)0.65and Fe6.23(PO4)4.45(HPO4)1.55: two new mixed-valence iron phosphates

“…Both structures were refined in the space group P1 (No. 2) and are similar to those of corresponding iron phosphates and iron hydrogen phosphates reported in the literature (Redhammer et al, 2004;Vencato et al, 1994). The structures are characterized by isolated PO 4 tetrahedra and four different types of Fe polyhedra.…”

“…Consequently, the general chemical formula of these phosphates can be expressed as Fe II 1+2x Fe III 4 (PO 4 ) 4x+2 (HPO 4 ) 4À4x , in which x = 0.84 (sample H.339) or 0.61 (sample H.347). The substitution mechanism observed in the title compounds is completely different from that described by Lightfoot & Cheetham (1986) and Vencato et al (1994), which corresponds to Fe III + PO 4 3À = Fe II + HPO 4…”

“…Redhammer et al (2004) refined the structure of a similar compound containing a very small amount of sodium, Na 0.1 Fe 7 (PO 4 ) 3 , and demonstrated that this phosphate was isotypic with the vanadate howerdevansite, NaCu II Fe III 2 (VO 4 ) 6 (Hughes et al, 1988). Lightfoot & Cheetham (1986) and Vencato et al (1994) have shown that the reduction of Fe III in Fe II 3 Fe III 4 (PO 4 ) 6 can induce the formation of isostructural hydrogen phosphates, with compositions Fe II 7Àx Fe III x (PO 4 ) 2+x (PO 3 OH) 4Àx (0 < x < 4).…”

Mixed-valence phosphato–hydrogenphosphato–iron network compounds1∞{[C4N2H11.6]1.5[FeIIFeIII(PO4)(H0.8PO4)2]·H2O} and3∞[FeII5FeIII2(PO4)2(H0.5PO4)4]: structure elucidation with the help of Mössbauer spectroscopy and a caveat on X-ray diffraction

“…Therefore, we suggest that compound 2 and 2Ј is the same material and that the hydrogen occupancy has not been correctly assigned in compound 2Ј. Furthermore, compound 2 is similar in formula to two reported iron phosphate compounds, namely Fe 7 (PO 4 ) 5 (HPO 4 ) 54 and Fe 7 (PO 4 ) 6 . 55 The simulated X-ray powder diffractograms for the latter two compounds (not shown here), however, exhibit different patterns than for compound 2.…”