Chemical preparation, crystal structure and NMR spectroscopy of a new organic cation p-phenylenediammonium monophosphate [p-NH3C6H4NH3][H2PO4](2) are presented. This new compound crystallizes in the orthorhombic system, with the space group Pnma and the following parameters: a = 7.970 (2) angstrom; b = 22.770 (7) angstrom; c = 7.000 (7) angstrom, V = 1270.3 (11) angstrom(3), Z = 4 and D-x = 1.590 g cm(-3). The crystal structure has been determined and refined to R = 0.043 and R-(w) = 0.057 using 2623 independent reflections. The structural arrangement can be described as inorganic layers of (H8P4O16)(4-) units, parallel to (a, c) planes. The organic groups (p-H3NC6H4NH3)(2+) are anchored between the phosphoric layers to form a three-dimensional infinite network. This compound is also investigated by IR and solid-state H-1, C-13 and P-31 MAS NMR spectroscopies. The ab initio method is used in the calculation of chemical shifts. (C) 2006 Elsevier Ltd. All rights reserved.