Synthesis, crystal structure and intercalation behaviour of hafnium phosphate dihydrogenphosphate dihydrate

A highly crystalline compound Hf(PO4)(H2PO4)·2H2O (γ-HfP) has been prepared via the partially substituted γ-HfP sodium phase, by the reflux method. Its crystalline structure was solved by X-ray powder diffractometry: monoclinic, space group P21, a = 5.3499(3), b = 6.5949(4), c = 12.3939(8) A, β = 98.594(5)° and Z = 2. The final agreement factors are: Rwp = 0.054, Rexp = 0.031 and RF = 0.033. The compound is isostructural with γ-ZrP and has a layered structure built from PO4 tetrahedra and HfO6 octahedra stacked along the [001] direction. Its intercalation behaviour with n-alkylamines (n = 1–6) and cyclic amines (aniline, benzylamine, cyclohexylamine, piperidine and pyridine) was studied. The intercalation solids obtained present expanded interlayer distances and a general composition Hf(PO4)(H2PO4)·xamine·H2O where x varies from 0.8 to 2.