4-Chloroanilinium 3-carboxyprop-2-enoate

In the title compound, C6H7ClN+·C4H3O4 −, the cations and anions lie on mirror planes and hence only half of the molecules are present in the asymmeric unit. The 4-chloroanilinium cation and hydrogen maleate anion in the asymmetric unit are each planar and are oriented at an angle of 15.6 (1)° to one another and perpendicular to the b axis. A characterestic intramolecular O—H⋯O hydrogen bond, forming an S(7) motif, is observed in the maleate anion. In the crystal, the cations and anions are linked by N—H⋯O hydrogen bonds, forming layers in the ab plane. The aromatic rings of the cations are sandwiched between hydrogen-bonded chains and rings formed through the amine group of the cation and maleate anions, leading to alternate hydrophobic (z = 0 or 1) and hydrophilic layers (z = 1/2) along the c axis.

In the title compound, C 6 H 7 ClN + ÁC 4 H 3 O 4 À , the cations and anions lie on mirror planes and hence only half of the molecules are present in the asymmeric unit. The 4-chloroanilinium cation and hydrogen maleate anion in the asymmetric unit are each planar and are oriented at an angle of 15.6 (1) to one another and perpendicular to the b axis. A characterestic intramolecular O-HÁ Á ÁO hydrogen bond, forming an S(7) motif, is observed in the maleate anion. In the crystal, the cations and anions are linked by N-HÁ Á ÁO hydrogen bonds, forming layers in the ab plane. The aromatic rings of the cations are sandwiched between hydrogen-bonded chains and rings formed through the amine group of the cation and maleate anions, leading to alternate hydrophobic (z = 0 or 1) and hydrophilic layers (z = 1/2) along the c axis.  Smith et al. (2005Smith et al. ( , 2007Smith et al. ( , 2009. For the importance of 4-chloroaniline, see: Ashford (2011);Amoa (2007). For hydrogen-bond motifs, see: Bernstein et al. (1995).  Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x À 1; Ày þ 1 2 ; z; (ii) x À 1; y; z; (iii) x; Ày þ 3 2 ; z.

Experimental
Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL/PC (Sheldrick, 2008); program(s) used to refine structure: SHELXTL/PC; molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXTL/PC. diflubenzuron), azo dyes, pigments, pharmaceutical and cosmetic products. It is a precursor to the widely used antimicrobial and bacteriocide chlorhexidine and is used in the manufacture of pesticides, including pyraclostrobin, anilofos, monolinuron and chlorphthalim (Ashford, 2011). Maleic acid can be converted into maleic anhydride by dehydration, to malic acid by hydration, and to succinic acid by hydrogenation (Amoa, 2007). The maleate ion is the ionized form of maleic acid (a monoanion in the present structure). It is useful in biochemistry as an inhibitor of transminase reactions. The maleate ion is used with pheniramine as an antihistamine drug in day-to-day use to treat allergic conditions such as hay fever or urticaria. Also we continuously seek to identify hydrogen bond enriched assemblies by means of a single efficient organic hydrogen bonding synthon. Substituted anilines are good candidates for this type of supramolecular synthon. In a continuation of our previous report on nitro substituted aniline (Anitha et al., 2011), the title compound is presented here derived from a chloro substituted aniline with maleic acid.
As the molecules lie on adjacent mirror planes, the asymmetric unit of the title compound, (I), contains half of a 4chloroanilinium cation and half of a hydrogen maleate anion (Fig. 1). The bond distances and angles of the cation are comparable with the related 4-chloroanilinium structures (Balamurugan et al., 2010;Ploug-Sørenson & Andersen, 1985;Rahmouni et al., 2010;Smith et al., 2005Smith et al., , 2007Smith et al., , 2009. The planes of the cation and the hydrogen maleate anion are oriented at an angle of 15.6 (1)° to each other. Cations and anions are oriented perpendicular to the b axis (mirror plane) of the unit cell. A characterestic intramolecular O-H···O hydrogen bond, forming an S(7) motif, is observed in the maleate anion (Bernstein et al., 1995).
The crystal packing is stabilized through a two dimensional hydrogen bonding network which connects cations and anions through intermolecular N-H···O hydrogen bonds on the ab-plane. Cations are linked through anions making a chain C 2 2 (9) motif extending parallel to the b axis of the unit cell through an N1-H1N···O2 hydrogen bond. This leads to molecular aggregations of cations and anions perpendicular to the ac-plane of the unit cell. These cationic and anionic molecular aggregations make an angle of 15.7 (1)° to each other. These two-dimensional molecular aggregations are further connected through another two hydrogen bonds, namely N1-H2N···O2 (i) and N1-H2N···O2 (ii) (For symmetry codes: see Table 1), leading to unusal ring R 3 4 (6) motifs which are arranged in tandem along a axis of the unit cell. The aromatic rings of the cations are sandwiched between hydrogen bonded chains and rings formed through the amine group of the cations and maleate anions leading to alternate hydrophobic (z = 0 or 1) and hydrophilic layers (z = 1/2) along c axis of the unit cell (Fig. 2). Notably, the electronegative chlorine atom does not participate as an acceptor in any hydrogen bonding interaction.

Experimental
The title compound was crystallized from an aqueous mixture containing 4-chloroaniline and maleic acid in the stoichiometric ratio of 1:1 at room temperature by the slow evaporation technique.

Refinement
All the H atoms except the atoms involved in hydrogen bonds were positioned geometrically and refined using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2 U eq (parent atom). H atoms bound to N and O were located in a difference Fourier map and refined isotropically.

Figure 1
The structure of the title compound (I) with the numbering scheme for the atoms and 50% probability displacement  Packing diagram of the molecules viewed down the a-axis. H bonds are drawn as dashed lines.