Hydrogen bonding in 2-carboxyanilinium dihydrogen phosphite at 100 K

The title compound, C7H8NO2 +·H2PO3 −, is formed from alternating layers of organic cations and inorganic anions stacked along the a-axis direction. They are associated via O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonding, giving rise to two different R 2 2(8) graph-set motifs and generating a three-dimensional network.


Comment
The crystal structures of organic-inorganic hybrid materials have been extensively investigated due to their interest in the field of new materials, and the number of reported structures is rapidly growing owing to their applications in medicine, material science and to their electrical, magnetic and optical properties (Kagan et al., 1999;Mazeaud et al., 2000) and the hydrogen bonding richness of these structures. This kind of hydrogen bonding appears in the active sites of several biological systems and is observed in similar previously studied hybrid compounds .
As well as being a biochemical precursor of the amino acids tryptophan, phenylalanine and tyrosine, anthranilic acid is used as a useful derivating agent for carbohydrate analysis (He et al., 2003). 2-Aminobenzoic acid is present as a part of the core structure of certain alkaloids, synthetic drugs (Per Wiklund et al., 2004), antiinflammatory, anticancer agents (Congiu et al., 2005) and as inhibitor of Hepatitis C NS5B polymerase (Nittoli et al., 2005). The three H atoms of the anilinium group are subsequently involved in extensive N-H···O hydrogen-bonding (Table   1) interactions with O4 being a multiple acceptor of three different phosphite anions, while O3 behaves as double acceptor of hydrogen bonds from one cation, via O1 in the carboxylic group, and one anion, via O5 in the phosphite anion. These interactions give raise to two different R 2 2 (8) graph set motifs (Bernstein et al. 1995), shown in Fig. 2. In addition, there are intramolecular interactions involving the benzene ring and the carboxylic group ensuring cohesion and stability of the crystal structiure.

Experimental
Crystals of anthranilicium phosphite are prepared by slow evaporation at room temperature of an aqueous solution of 2aminobenzoic acid and H 3 PO 3 in a 1:1 stochiometric ratio.

Refinement
The title compound crystallizes in the centrosymmetric space group P-1. A l l non-H atoms were refined with anisotropic atomic displacement parameters. All H-atoms were located in difference Fourier syntheses and refined as riding model with Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1  (17)