Synthesis of Cyclic Phosphates in Hot,Concentrated Phosphoric Acid

The synthesis of transition metal phosphates in hot, concentrated phosphoric acid medium leads to highly crystalline materials and to increased condensation of the phosphate at higher temperatures. Aluminum extraction from the porcelain crucible is also observed in some circumstances. Two new compounds were produced: (Al_3.28Cr_0.72)(P₄O₁₂)₃ a = 13.512(8) Å, cubic, I-43d, V = 2470(3) ų, Z = 6, density = 2.887 mg/m³, R = 0.055, GOF = 1.29 for 254 data points, was prepared at 748 K whereas (Al_1.97Cr_1.03)P₉O₂₇ a = b = 11.170(6), c = 9.412(9) Å, trigonal P – 3c1, V = 1017(1) ų, Z = 2, density = 2.669 mg/m³, R = 0.0581, GOF = 0.87 for 676 data points, was produced at 798 K from the heating of Cr₂O₃ in H₃PO₄ in a porcelain crucible. Crystal structures of both materials show mixed metal sites containing Al and Cr.