A new crystal of 2-amino-3-methylpyridinium dihydrogenomonoarsenate has been prepared and characterized by X-ray crystallography, thermal analysis and spectroscopic studies. This compound crystallizes in the triclinic space group P (1) over bar with a = 7.2689 (2) angstrom, b = 8.0975 (2) angstrom, c = 8.3969 (4) angstrom, alpha = 77.09 (3)degrees, beta = 79.20 (3)degrees, gamma = 88.16 (2)degrees, V = 473.19 (3) angstrom(3), Z = 2. The crystal structure was solved and refined to R = 0.027 with 3375 independent reflections. The atomic arrangement can be described as (H(2)AsO(4)(-))(n), polymeric chains anchoring the 2-amino-3-methylpyridinium cations through short hydrogen bonds. All the ring atoms of the organic entity are coplanar. The exocyclic N atom is an electron receiving center, which is consistent with features of imino resonance evidenced by bond lengths and angles. Solid-state (13)C and (15)N CP-MAS-NMR spectroscopies are in agreement with the X-ray structure. Ab initio calculations allow the attribution of carbons and nitrogen to the independent crystallographic sites. (C) 2005 Elsevier Ltd. All rights reserved.