Acta Cryst. (2012). C68, o447-o451 [ doi:10.1107/S010827011204067X ]
Abstract: Two concomitant polymorphs of the molecular salt formed by 2,6-dimethoxybenzoic acid, C9H10O4 (Dmb), with benzamidine, C7H8N2 (benzenecarboximidamide, Benzam) from water solution have been identified. Benzamidinidium 2,6-dimethoxybenzoate, C7H9N2+·C9H9O4- (BenzamH+·Dmb-), was obtained through protonation at the imino N atom of Benzam as a result of proton transfer from the acidic hydroxy group of Dmb. In the monoclinic polymorph, (I) (space group P21/n), the asymmetric unit consists of two Dmb- anions and two monoprotonated BenzamH+ cations. In the orthorhombic polymorph, (II) (space group P212121), one Dmb- anion and one BenzamH+ cation constitute the asymmetric unit. In both polymorphic salts, the amidinium fragments and carboxylate groups are completely delocalized. This delocalization favours the aggregation of the molecular components of these acid-base complexes into nonplanar dimers with an R22(8) graph-set motif via N+-HO- charge-assisted hydrogen bonding. Both the monoclinic and orthorhombic forms exhibit one-dimensional isostructurality, as the crystal structures feature identical hydrogen-bonding motifs consisting of dimers and catemers.
Formula: Two polymorphs of C7H9N2+·C9H9O4-
Structure factor file (CIF format) (272.7 kbytes)
Structure factor file (CIF format) (152.7 kbytes)
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