Chemical preparation, crystal structure, calorimetric and spectroscopic investigations (IR and RMN) are given for a new non-centrosymmetric organic-cation dihydrogen phosphate-arsenate [H-2(C4H10N2)][H-2(As, P)O-4](2). This compound is triclinic P1 with the following unit-cell parameters: a = 7.082(2) angstrom, b = 7.796(1) angstrom, c = 12.05(3) angstrom, alpha = 95.37(2)degrees, beta = 98.38(3)degrees, gamma = 62.98(1)degrees, Z = 2, V = 586.2(1)angstrom(3) and D-x = 1.836 g cm(-3). The crystal structure has been solved and refined to R = 0.03 using 2328 independent reflections. The structure can be described as infinite (H2XO)(n) chains spreading parallel to the b direction. These chains are themselves interconnected by a set of N-(HO)-O-... hydrogen bonds generated by the organic entities, alternating with the chains. Solid-state C-13, N-15 and P-31 MAS NMR spectroscopies are in agreement with the X-ray structure. (c) 2005 Elsevier Ltd. All rights reserved.