3-Carboxy-2-methoxyphenylboronic acid

The molecular structure of the title compound, 3-COOH-2-CH3O—C6H3B(OH)2 or C8H9BO5, is stabilized in part due to the presence of an intramolecular O—H⋯O hydrogen bond. In the crystal structure, molecules are linked by intermolecular O—H⋯O hydrogen bonds, generating a two-dimensional sheet structure aligned parallel to the (11) plane.

The molecular structure of the title compound, 3-COOH-2-CH 3 O-C 6 H 3 B(OH) 2 or C 8 H 9 BO 5 , is stabilized in part due to the presence of an intramolecular O-HÁ Á ÁO hydrogen bond. In the crystal structure, molecules are linked by intermolecular O-HÁ Á ÁO hydrogen bonds, generating a twodimensional sheet structure aligned parallel to the (112) plane.
The X-ray measurements were undertaken in the Crystallographic Unit of the Physical Chemistry Laboratory at the Chemistry Department of the University of Warsaw. This work was supported by the Warsaw University of Technology and by the Polish Ministry of Science and Higher Education (grant No. N N205 055633). The molecular structure of (I) shows the boronic groups possesses an exo-endo conformation and is slightly twisted with respect to the benzene ring (Table 1). The methoxy group is twisted almost perpendicularly with respect to the aromatic ring. The endo-oriented OH group is engaged in an intramolecular O-H···O hydrogen bonds with the methoxy O atom, resulting in the formation of a six-membered ring. This motif is generally typical of structures of ortho-alkoxyarylboronic acids (Yang et al., 2005;Dąbrowski et al., 2006). The carboxyl group is almost coplanar with respect to the benzene ring.

Structure Reports Online
The molecules are linked via almost linear O-H···O bridges in a "head-to-head, tail-to-tail" fashion, i.e., equivalent groups interact with each other forming two alternate centrosymmetric dimeric motifs, Table 2. As a result, an infinite, zigzag chain is formed (Fig. 2). The chain structure resembles the situation found for the related 2-methoxy-1,3-phenylenediboronic acid The 1D supramolecular architecture extends through cross-linking weak O-H···O bonds between twisted boronic groups. As a result a 2D array is formed, aligned parallel to the (11-2) plane. In conclusion, the intermolecular hydrogenbonding interactions of boronic and carboxyl groups result in the formation of the infinite chain structure. Chains are interconnected by means of weaker hydrogen-bonds, thus forming the layer structure.

Experimental
The compund was prepared according to the published procedure (Kurach et al., 2008). Crystals suitable for single-crystal X-ray diffraction analysis were grown by slow evaporation of a solution of the acid (0.15 g) in ethyl acetate/acetone (10 ml, 1:1).

Refinement
All hydrogen atoms were located in difference syntheses and refined freely so that O-H = 0.802 (19) -1.03 (2) Å and C-H = 0.942 (17) -1.029 (17) Å. Fig. 1. The molecular structure of (I) showing the atom-labelling scheme. The intramolecular hydrogen bond is shown as a dashed lines. Displacement ellipsoids for all non-H atoms are drawn at the 50% probability level.