Acta Crystallographica Section C

Crystal Structure Communications

Volume 68, Part 11 (November 2012)


organic compounds



uk3051 scheme

Acta Cryst. (2012). C68, o447-o451    [ doi:10.1107/S010827011204067X ]

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

S. Irrera, G. Ortaggi and G. Portalone

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+-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.

Formula: Two polymorphs of C7H9N2+·C9H9O4-


hkldisplay filedownload file

Structure factor file (CIF format) (272.7 kbytes)
[ doi:10.1107/S010827011204067X/uk3051Isup2.hkl ]
Contains datablock I


hkldisplay filedownload file

Structure factor file (CIF format) (152.7 kbytes)
[ doi:10.1107/S010827011204067X/uk3051IIsup3.hkl ]
Contains datablock II


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