Bis(3-carboxyanilinum) bis(perchlorate) monohydrate

In the structure of the title compound, 2C7H8NO2 +·2ClO4 −·H2O, the ions are connected via N—H⋯O, N—H⋯(O,O), O—H⋯O, O—H⋯(O,O) and C—H⋯O hydrogen bonds into a three-dimensional network.

Technical support (X-ray measurements at SCDRX) from Université Henry Poincaré, Nancy 1, is gratefully acknowledged. Hydrogen bonds play a crucial role in supramolecular organization (Jeffrey, 1997;Nangia & Desiraju, 1998). Knowledge of hydrogen-bond geometries (Taylor & Kennard, 1984;Murray-Rust & Glusker, 1984) and motif formation is vital in the modeling of protein-ligand interactions (Tintelnot & Andrews, 1989;Böhm & Klebe, 1996). The supramolecular networks become especially interesting when the cation and anion can participate in hydrogen-bonding. In this regard previous studies have been concerned with organic salts of carboxylic acids (Bendjeddou et al., 2003), Cherouana et al., 2003). The asymmetric unit of (I) (Fig. 1) contains two carboxyanilinium cations (A and B), two perchlorate anion and one water molecule. A proton transfer from the perchloric acid to atom N1 and N2 of m-carboxyalinine resulted in the formation of salts.

1-Supramolecular organization:
The structure is formed by double anionic and cationic chains that extend along the b axis, giving rise to layers parallel to the plane (b, c). Chains of water molecules are sandwiched between the anionic double chains (Fig2.).

1-1-Overview.
The supramolecular architecture is generated by the nineteen independent interactions of the Table 1. Three types of intermolecular interactions are present in the structure, including O-H···O, N-H···O and C-H···O hydrogen bonds.
The presence of water molecule in the structure results in the presence of additional hydrogen bonds. The construction of graphs-set of the twenty hydrogen bonds in this compound has led to a first-level graph set noted: N1 = R 2 2 (8)R 2 2 (8) (Bernstein et al., 1995) (Table 1.).

1-2-The O-H···O hydrogen-bonded network
The carboxylic acid groups at the opposite end of the carboxyanilinium cations forms a centrosymmetric hydrogenbonded dimers with its counterpart in a cation from an adjacent ribbon and are centered at (0 1/2 0) and (1/2 0 0) respectively for cation A and cation B (Fig. 3). These interactions lead to the graph-set motif R 2 2 (8), which is a characteristic feature found in most salts of 3-and 4-aminobenzoic acid (Cambridge Structural Database; Allen, 2002).
The water molecule, bridges the anionic perchlorate via the O-H···O hydrogen bonds. The centrosymmetric hydrogenbonded rings formed by two water molecules and two Cl(1)O4-anions can be described by the graph-set R 4 4 (12) and R 2 4 (8). The aggregation of this two ring motifs results in an overall one-dimensional hydrogen-bonded chain structure along the [100] direction (Fig. 4).

1-3-The N-H···O hydrogen-bonded network
In the first cationic (A) entity, all ammonium H atoms are involved in hydrogen bonds with the perchlorate (Cl(2) O 4 -) anion and water molecule. Two of these interactions link the anions and cations in an alternating fashion into extended chains along the [100] direction, which can be described by the graph-set C 2 2 (4). The two other interactions are in a sup-2 crosslink from an adjacent chain C 2 2 (4). The combination of these two chain motifs generates noncentrosymmetric fused rings which can be described by the graph-set motif R 3 4 (10). In the second cationic (B) entitie, all ammonium H atoms are involved in hydrogen bonds, with the two different perchlorate ion, so forming an alternating noncentrosymmetric rings a long [100] direction which can be described by the graph-set R 3 4 (10). Only one H atom (H2C) is involved in bifurcated hydrogen bonds with O(3) and O(4) perchlorate atoms, to form a four-membered hydrogen bonded ring R 2 1 (4). The junction betwen this two different cations (A and B) entities are assured by the perchlorate (Cl(2) O 4 -) anion via N1-H1B···O6, N1-H1B···O8, N2-H2A···O6, N2-H2A···O7 hydrogen bonds, so generete R 3 2 (6) rings along [100] direction (Fig. 5) 1-4-The C-H···O hydrogen-bonded network: The junction between the cationic entity is consolidated by five weak independent C-H···O hydrogen bonds via the perchlorate anions, forming an alternating of R 4 6 (22) and R 5 6 (30)centrosymmetric Rings a long b axis (Fig. 6).