Zn2(Zn1-xFex)FeIII(PO4)3 · 2 H2O: Darstellung, Kristallstruktur und Mößbauer-Untersuchung / Zn2(Zn1-xFex)FeIII(PO4)3 · 2 H2O: Preparation, Crystal Structure and Mössbauer Investigation

Single crystals of the mixed valency phase Zn2(Zn1-xFex)FeIII(PO4)3 · 2 H2O were grown by hydrothermal treatment of phosphophyllite (Zn2Fe(PO4)2 · 4 H2O) at 160 °C in 1 M H3PO4. The crystal structure (tricl., P 1̅; a = 641.5(4) pm, b = 914.4(4) pm, c = 983.4(4) pm, α = 70.79(5)°, β = 78.32(5)°, γ = 73.69(5)°; Ζ = 2) contains PO4 tetrahedra, connected via vertices shared with coordination polyhedra of the metal ions. Cation coordination polyhedra (FeIII(Op)5Ow octahedra, (Zn1-xFex)(Op)5Ow octahedra and Zn(Op)5 trigonal bipyramids) are connected to centrosymmetrical six-membered chains by sharing common Op-edges. These short chains are interconnected by common vertices of Zn(Op)4 tetrahedra to form infinitive ribbons of cation coordination polyhedra. The x-values observed for the substitutional position (Zn1-xFex) varied from x = 0.5 (single crystal determination) to x = 1 (Mössbauer investigation). The Mössbauer parameters are consistent with high-spin iron in a slightly distorted octahedral environment and valence states (II) and (III).