Crystallization of ultraphosphates via the gas phase. The crystal structures of FeP4O11, ZnP4O11 and CdP4O11

The new ultraphosphates FeP₄O₁₁, ZnP₄O₁₁ and CdP₄O₁₁ of the CuP₄O₁₁ structure type were synthesized from the corresponding meta- or polyphosphates and P₄O₁₁. Crystallization via the gas phase has been achieved at elevated temperatures using a mixture of P (3 mg) and I₂ (50 mg) as mineralizer. The crystal structure consists of a two-dimensional phosphate network, built from four crystallographically independent 10-membered polyphosphate rings. Each ring contains four secondary and six tertiary PO₄-groups. Two crystallographically independent metal sites showing sixfold coordination by terminal oxygen atoms are located inbetween the phosphate layers. FeO₆-octahedra (2.028(3) Å < d̄ FeO₆ < 2.268(3) Å) and ZnO₆ octahedra (2.002(2) Å < d̄ ZnO₆ < 2.256(2) Å) exhibit slightly larger radial distortion than the CdO₆-octahedra (2.215(7) Å < d̄ CdO₆ < 2.383(3) Å).