Comment

As part of ongoing research into the crystallization preferences of crystalline complexes, the growth of a previously reported three-component crystalline complex (Pedireddi et al., 1996) was attempted. The solvent dimethyl sulfoxide (DMSO) was used to aid dissolution of the components. In several instances, the crystallization unexpectedly resulted in single crystals of the title adduct, (I). The asymmetric unit consists of one molecule each of 3,5-dinitrobenzoic acid (3,5-DNBA) and DMSO (Fig. 1).

Previously reported crystallizations of 3,5-DNBA indicate a dimorphic nature for this substance. Two monoclinic polymorphs have been reported (Prince et al., 1991) and both exhibit the common carboxylic acid dimer hydrogen-bond motif. The interaction between 3,5-DNBA and DMSO described here involves a hydrogen bond between the carboxyl moiety of the acid and the sulfoxide group of the solvent (Fig. 2). It is interesting, therefore, that the title complex represents the disruption of the carboxylic acid dimer by the introduction of the sulfoxide moiety upon complexation.

A search of the Cambridge Structural Database (CSD, Version 5.25, Update 3; Allen, 2002) reveals precedence for this acid-DMSO interaction. Searching for structures which contain both a carboxyl moiety and a DMSO molecule among all organic structures for which three-dimensional coordinates have been determined resulted in 37 hits. Of those, 29 complexes exhibit an O-HO=S hydrogen bond which is shorter than the sum of the van der Waals radii of the two O atoms. The apparent substantial likelihood of the formation of this motif indicates a potential utility for crystal engineering experimental design.

Crystal packing results in what may be perceived as alternating sheets of 3,5-DNBA and DMSO stacking along [001] (Figs. 3 and 4).

Figure 1 The asymmetric unit of (I), showing displacement ellipsoids at the 50% probability level (XP; Sheldrick, 1993).

Figure 2 Crystal packing diagram, showing the intermolecular hydrogen-bonding interactions as dashed lines.

Figure 3 Crystal packing diagram, showing sheets stacking along [001], as viewed along [010]. Dashed lines indicate hydrogen bonds.

Figure 4 Crystal packing diagram showing sheets stacking along [001], as viewed along [100].

Experimental

All starting components were obtained from Sigma Aldrich Ltd. 3,5-Dinitrobenzoic acid (357 mg) and 0.5 equivalents of anthracene (150 mg) were heated to reflux in benzene (ca 50 ml). To dissolve the solids fully, a small quantity of DMSO (ca 2 ml) was added to the slurry. The resulting solution was allowed to cool and evaporate slowly over a period of 24 h. Crystals were observed before all the solvent had evaporated; a single crystal was harvested from this saturated solution for X-ray diffraction analysis.