Chemical preparation, crystal structure and NMR spectroscopy of a new organic cation 5-chloro(2,4-dimethoxy)anilinium monophosphate H2PO4 are given. This new compound crystallizes in the monoclinic system, with the space group P2(1)/c and the following parameters: a=5.524(2)angstrom, b=9.303(2)angstrom, c=23.388(2)angstrom, beta=90.66(4), V=1201.8(2)angstrom(3), Z=4 and D-x = 1.573 g cm(-3). Crystal structure has been determined and refined to R = 0.031 and R-w = 0.080 using 1702 independent reflections. Structure can be described as an infinite (H2PO4)(n)(n-) corrugated chains in the a-direction. The organic groups (5-Cl-2,4-(OCH3)(2)C6H2NH3)(+) are anchored between adjacent polyanions through multiple hydrogen bonds. This compound is also investigated by IR, thermal, and solid-state, C-13, P-31 MAS NMR spectroscopies. (C) 2006 Elsevier Ltd. All rights reserved.