The monoclinic crystal structure of (C9H15N3OP2)(2)P2O7 center dot H2O denoted DLTHDP [a = 14.626(1), b = 6.1990(2), c = 14.562(1)A, beta = 97.289(3)degrees, Z = 2, monoclinic P2(1), D-cal = 1.508, D-mes = 1.49 g cm(-3)] has been solved using direct methods and refined to a reliability factor R = 4.37% for 2079 independent reflections. The DLTHDP structure can be described by infinite polyanions [P2O7 center dot H2O](n)(4n)- organized in chains parallel to the b-direction and located at z = 1/2, alternating with organic cations associated in ribbons spreading along the a-direction. Multiple hydrogen bonds originating from amine, hydroxyl groups and water molecules donors [N-H...O(N) and O(W)-H...O] connect the different components of the lattice. The IR data of DLTHDP is reported and discussed according to the theoretical group analysis and by comparison with IR results of similar compounds. The coupled thermogravimetric analysis (TGA)-differential thermal analysis (DTA) thermal study shows the departure of one water molecule, confirming the hydrated character of this compound. (c) 2006 Elsevier Ltd. All rights reserved.