Anilinium-3-carboxylate 3-carboxyanilinium nitrate

The title compound, C7H8NO2 +·NO3 −·C7H7NO2, exists in the form of a protonated dimer of two anilinium-3-carboxylate molecules related by an inversion center, and a nitrate anion located on a twofold rotation axis. The bridging H atom occupies, with equal probability, the two sites associated with the carboxyl atoms. In addition to the strong O—H⋯O hydrogen bond, in the crystal, the various units are linked via N—H⋯O and C—H⋯O hydrogen bonds forming a three-dimensional structure.

anticancer agents (Congiu et al., 2005). Benzoic acid, its derivatives and their complexes are also used as food preservatives and as antiseptic agents applied in various industrial branches: pharmaceutics, textile and cosmetics (Swislocka et al., 2005). In view of this interest, the crystal structures of various amino derivatives of benzoic acid (Hansen et al., 2007;Lai et al., 1967;Lu et al., 2001;Smith et al., 1995), and their ammonium salts (Arora et al., 1973;Bahadur et al., 2007;Zaidi et al., 2008), have been reported in the literature. The crystal structures of these compounds are characterized by strong hydrogen bonding.
The ammonium salts of 2-aminobenzoic acid are monomers (Bahadur et al., 2007;Zaidi et al., 2008), whereas the chloride salt of the anilinium-3-carboxylate ion (Arora et al., 1973) exists in the form of hydrogen-bonded dimers formed through the carboxylic acid groups of inversion related molecules. In the present study, we attempted to prepare a cerium(III) complex of 3-aminobenzoic acid but the resulting product was a simple nitrate salt of the acid. Herein, we present the crystal structure of this salt.
In the title compound two anilinium-3-carboxylate molecules related by an inversion center are bound to a proton to form a protonated dimer through strong O-H···O hydrogen bonds ( Fig. 1 and Table 1). A nitrate anion located on a 2fold rotation axis is present as counter ion. The bridging H atom (H1O) occupies, with equal probability, the two sites associated with the carboxyl atoms, O1 and O1a [symmetry code: (a) = -x, -y + 2, -z]. The ammonium groups are involved in strong hydrogen bonds to the carbonyl as well as to the nitrate O atoms (Table 1).
In the crystal, ( Fig. 2

Experimental
The title compound was prepared by adding one equivalent of 3-aminobenzoic acid (0.07 g) in 15 ml methanol to a solution of cerium nitrate (0.22 g, 0.5 mmol) in 15 ml me thanol. The brown solution was stirred for one hour, after which it was filtered and the filtrate was kept for crystallization at room temperature. The solution was covered with aluminium foil. After 3 days large orange-brown crystals were obtained (M.p. = 492 (1) K). A plate-shaped fragment cut from a large crystal was used for data collection.

Refinement
The OH H atom was located in a difference Fourier map and refined freely with a fixed occupancy of 0.5. The NH 3 atoms were located from a difference Fourier map and refined freely. The C-H atoms were placed in calculated positions and treated as riding atoms: C-H = 0.93 Å with U iso (H) = 1.2U eq (C).