Crystal structure, thermal analysis and IR spectroscopic investigation of (C6H9N2)H2XO4 (X=As, P)

Crystals of 2-amino-4-methylpyridinium dihydrogenmonoarsenate (C{sub 6}H{sub 9}N{sub 2})H{sub 2}AsO{sub 4} and 2-amino-4-methylpyridinium dihydrogenmonophosphate (C{sub 6}H{sub 9}N{sub 2})H{sub 2}PO{sub 4} have been prepared and grown at room temperature. These materials are isotypic with the following unit cell dimensions (C{sub 6}H{sub 9}N{sub 2})H{sub 2}AsO{sub 4}: a=12.4415(5)A, b=6.8224(3)A, c=11.3524(5)A, Z=4, V=963.60(6)A{sup 3}; (C{sub 6}H{sub 9}N{sub 2})H{sub 2}PO{sub 4}: a=12.4410(9)A, b=6.7165(3)A, c=11.3417(5)A, Z=4, V=925.09(10)A{sup 3}. The common space group is Pnma. The structure of these compounds has been determined by X-ray data collection on single crystals of (C{sub 6}H{sub 9}N{sub 2})H{sub 2}AsO{sub 4} and (C{sub 6}H{sub 9}N{sub 2})H{sub 2}PO{sub 4}. Due to the strong hydrogen-bond network connecting the H{sub 2}XO{sub 4} groups, the anionic arrangement must be described as a linear organization. The chains composed by the (H{sub 2}XO{sub 4}){sub n}{sup n-} macroanion spread along the b-direction, approximately centered by x=0 and 1/2. All atoms of the structure, except one oxygen atom, are located in the mirror planes situated at y=1/4 and 3/4, imparting an internal mirror symmetry to the anionic and the cationic entities. The linear macroanions are crossed by organic cations lying in mirrors perpendicular to the b-direction; this atomic arrangement is then described by a three-dimensional network of hydrogen bonds, builtmore » up by two types, O-H...O bonds inside the chains and N-H...O bonds linking adjacent chains. The thermal properties of both compounds are investigated as well as the IR properties supported by group theoretical analyses. yses.« less