Crystal structure,thermal behavior and IR investigation of 1,6‐diammonium hexan dihydrogenodiphosphate dihydrate

Physicochemical properties of (C₆H₁₈N₂)H₂P₂O₇·2H₂O denoted DHDP are discussed on the basis of X‐ray crystal structure investigation. The compound crystallises in the triclinic system with P space group. Its unit cell dimensions are a = 13.719(1) Å, b = 14.188(3) Å, c = 9.177(1) Å, α = 108.50(1)°, β = 91.11(1)°, γ = 115.47(1)°, V = 1503.8(4) ų and Z = 4. The structure has been solved using direct methods and refined to a reliability R factor 0.0401 for 4778 reflections. The main feature of the atomic arrangement of DHDP is the existence of infinite rows, parallel to the c direction of the unit cell, composed of H₂P₂O₇ groups. These phosphoric rows are organised to create, with the help of the organic cation, large rectangular channels in which the unstable water molecule are located since they have high thermal parameters. Phosphoric anions and organic cations have no internal symmetry. DSC and TG‐DTA show that dehydration occurs in one step. Such dehydration process may be related to the similar environments on the water molecules residing in the channel. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)