The aim of encapsulation of 2,3-dimethylanilinium cation in (H(2)XO(4))(n) polymeric anion chains is to build acentric frameworks that are efficient for non-linear optical (NLO) applications. The synthesis and structures of two new inorganic-organic NLO crystals with general formula (2,3-(CH(3))(2)C(6)H(3)NH(3))H(2)XO(4) (X = P, As) are reported. The magnitude of their second harmonic generations (SHG) responses was found to be between the KDP and urea. They crystallize with monoclinic unit-cells and are isotopic. We have determined the structure of phosphoric salt. The following unit-cell parameters were found: a = 8.866(3) Angstrom, b = 5.909(6) Angstrom, c = 10.644(5) Angstrom, beta = 112.44(1)degrees, V = 515.5(5) Angstrom(3) and D(x) = 1.412 g cm(-3). The space group is P2(1) with Z = 2. The structure was refined with R = 0.041 (R(w) = 0.057) for 1652 reflections with I greater than or equal to 3sigma (I). It exhibits infinite (H(2)PO(4))(n)(n-) chains. The organic groups (2,3-(CH(3))(2)C(6)H(3)NH(3))(+) are anchored between adjacent polyanions through multiple hydrogen bonds. Chemical preparation, crystal structure, calorimetric and spectroscopic investigation are described. (C) 2004 Elsevier Ltd. All rights reserved.