Crystals of 2-amino-6-methylpyridinium dihydrogenmonophosphate (denoted as 2A6MPas) and 2-amino-6-methylpyridinium dihydrogenmonoarsenate (denoted as 2A6MPAs), have been prepared and grown at room temperature. They crystallize with triclinic unit cells and are isotopic. The following unit cell parameters were found, (2-NH2-6-CH3C5H4N)H2PO4: a = 7.5165(6), b = 8.2640(5), c = 8.5674(7) angstrom = 64.845(5), beta = 80.156(3), gamma = 85.783(5), Z = 2, V = 474.61(6) angstrom(3); (2-NH2-6CH(3)C(5)H(4)N)H2AsO4: a = 7.6011(4), b = 8.4261(6), c = 8.7074(6) angstrom, alpha = 64.228(3), beta = 81.047(4), gamma = 85.972(4), Z = 2, V = 496.09(6) angstrom(3). The common space group is P (1) over bar. We have determined the structure of the phosphate. It exhibits infinite (H2PO4)(n)(-n) chains. The organic groups (2-NH2-6-CH3C5H4N)(+) are anchored between adjacent polyanions through multiple hydrogen bonds. The thermal property of the compound was investigated as well as was the IR property supported by group theoretical analyses. (c) 2005 Elsevier Ltd. All rights reserved.