The preparation, crystal structure, TG-DTA analysis and spectroscopy investigation are reported for the 2,5-dimethoxy phenyl ammonium cyclotetraphosphate dihydrate [2,5-(CH3O)(2)C6H3NH3](4)P(4)O(12)center dot 2H(2)O. This new compound is triclinic P (1) over bar with unit cell dimensions: a = 7.438(5) angstrom, b = 11.841(7) angstrom, c = 12.354(4) angstrom, alpha = 96.61(4)degrees, beta = 98.35(4)degrees, gamma = 102.60(6)degrees, Z = 1 and V = 1038.0(1) angstrom(3). Its crystal structure has been determined and refined to R = 0.049, with 5128 independant reflections. The structure can be described by rows of P4O12 ring anions along the a axis; between these rows are located the organic groups, connected to them by hydrogen bonds. (C) 2005 Elsevier Ltd. All rights reserved.