Chlorooxoishwarone and 2,6-dimethoxybenzoic acid

4-Meth-oxy-benzamidinium 2,6-dimeth-oxy-benzoate

The title compound, C₈H₁₁N₂O⁺·C₉H₉O₄⁻, was synthesized by the reaction of 4-meth­oxy­benzamidine (4-amidino­anisole) and 2,6-dimeth­oxy­benzoic acid. The structure consists of non-planar pairs of hydrogen-bonded 4-meth­oxy­benzamidinium cations and 2,6-dimeth­oxy­benzoate anions. In the cation, the amidinium group is tilted by 27.94 (10)° with respect to the benzene ring. In the anion, the sterically bulky ortho-meth­oxy substituents force the carb­oxy­ate group to be twisted away from the plane of the benzene ring by 73.24 (6)°. The ions are further associated in the crystal into chains along the b-axis direction by inter­molecular N—H⋯O hydrogen bonds.

A new polymorph of 2,6-dimeth-oxy-benzoic acid

A new crystalline form of 2,6-dimeth­oxy­benzoic acid, C₉H₁₀O₄, crystallizing in a tetra­gonal unit cell has been identified during screening for co-crystals. The asymmetric unit comprises a non-planar independent mol­ecule with a synplanar conformation of the carb­oxy group. The sterically bulky o-meth­oxy substituents force the carb­oxy group to be twisted away from the plane of the benzene ring by 65.72 (15)°. The carb­oxy group is disordered over two sites about the C—C bond [as indicated by the almost equal C—O distances of 1.254 (3) and 1.250 (3) Å], the occupancies of the disordered carboxym H atoms being 0.53 (5) and 0.47 (5). In the known ortho­rhom­bic form reported by Swaminathan et al. [Acta Cryst. (1976), B32, 1897–1900], due to the anti­planar conformation adopted by the OH group, the mol­ecular components are associated in the crystal in chains stabilized by linear O—H⋯O hydrogen bonds. However, in the new tetra­gonal polymorph, mol­ecules form dimeric units via pairs of O—H⋯O hydrogen bonds between the carb­oxy groups.

Redetermination of 2,6-dimethoxy-benzoic acid

The crystal structure of the title compound, C₉H₁₀O₄, was first reported by Swaminathan, Vimala & Lotter [Acta Cryst. (1976), B32, 1897–1900]. It has been re-examined, improving the precision of the derived geometric parameters. The asymmetric unit comprises a non-planar independent mol­ecule, as the meth­oxy substituents force the carb­oxy group to be twisted away from the plane of the aromatic ring by 56.12 (9)°. Due to the anti­planar conformation adopted by the OH group, the mol­ecular components do not form the conventional dimeric units, but are associated in the crystal in chains stabilized by linear O—H⋯O hydrogen bonds, involving the OH groups and the carbonyl O atoms, which form C(3) motifs.