Supramolecular association in proton‐transfer adducts containing benzamidinium cations. II. Concomitant polymorphs of the molecular salt of 2,6‐dimethoxybenzoic acid with benzamidine

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+—H⋯O− 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.