Crystal structure of diethylammonium aniline-4-sulfonate anilinium-4-sulfonate

The title compound consists of an diethylammonium–anilinesulfonate ion pair and a zwitterionic aniliniumsulfonate molecule.

The title compound, C 4 H 12 N + ÁC 6 H 6 NO 3 S À ÁC 6 H 7 NO 3 S, consists of an ion pair and a zwitterionic neutral molecule. The cation adopts an extended conformation [C-C-N-C torsion angles = 177.1 (3) and À178.4 (3) ]. In the crystal, the components are linked by N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds, generating a three-dimensional network, which is consolidated by weak C-HÁ Á ÁO interactions.

Chemical context
Acids such as sulfuric, nitric, oxalic, phosphoric, substituted sulfonic, etc. when mixed in water with amines give acidic or neutral salts that may be soluble in organic solvents: this solubility allows for the study of their interactions with metal halides, acetates, nitrates, perchlorates, etc, which yield new adducts and complexes in which the conjugate anion of the acid behaves as a ligand, usually coordinating the metal ion (Najafi et al., 2011a,b;Ittyachan et al., 2016;Majeed & Wendt, 2016).

Figure 2
Packing diagram, viewed along the b axis. Hydrogen bonds are represented by light-blue dashed lines.
hydrogen bonds establishing the three-dimensional array are the contacts to sulfonate oxygen atoms and the N2Á Á ÁN3 aniline interactions. All amine hydrogen atoms form good hydrogen-bond contacts to neighboring hydrogen-bond acceptor atoms.

Database survey
A search of the Cambridge Structural Database (Version 5.37 + one update; Groom et al., 2016) shows 46 hits concerning the anilinesulfonate anion, three containing aniliniumsulfonate and one hit with both (Fun et al., 2008), while 303 hits concern the diethylammonium ion.

Synthesis and crystallization
Dimethyl amine was mixed in water with aniline sulfonic acid in a 1:1 ratio. Colorless block-like crystals were obtained on allowing the water to evaporate at 333 K.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms bonded to carbon were included in geometrically calculated positions and allowed to ride on the parent atom. All amine hydrogen atoms were located in a difference Fourier map and refined freely. As the molecules are achiral, only the correct enantiomorph of the space group was determined: this was determined by comparison of intensities of Friedel pairs of reflections yielding a Flack x parameter of 0.03 (6)    Data collection: APEX3 (Bruker, 2015); cell refinement: SAINT (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: publCIF (Westrip, 2010).

Diethylammonium aniline-4-sulfonate anilinium-4-sulfonate
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.