(2,4-Dipropoxyphenyl)boronic acid

In the crystal, the title compound, C12H19BO4, exists as a centrosymmetric O—H⋯O hydrogen-bonded dimer. Dimers are linked via C—H⋯O hydrogen bonds, generating an infinite zigzag chain oriented parallel to [11]. The chains are assembled, giving sheets aligned parallel to (21) and interconnected by weak C—H⋯π interactions, producing a three-dimensional network.

In the crystal, the title compound, C 12 H 19 BO 4 , exists as a centrosymmetric O-HÁ Á ÁO hydrogen-bonded dimer. Dimers are linked via C-HÁ Á ÁO hydrogen bonds, generating an infinite zigzag chain oriented parallel to [111]. The chains are assembled, giving sheets aligned parallel to (211) and interconnected by weak C-HÁ Á Á interactions, producing a threedimensional network.
Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXS97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2005); software used to prepare material for publication: PLATON (Spek, 2009). 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 Aldrich Chemical Co. through donation of chemicals and equipment, and by Warsaw University of Technology.

Comment
The ability of arylboronic acids to form supramolecular assemblies due to intermolecular hydrogen bonding is well known.
Our interest has focused on ortho-alkoxy derivatives and the influence of various factors (including the number and length of the alkoxy group) on their structural behaviour.
The molecular structure of (I) shows the boronic groups possesses an exo-endo conformation. The entire molecule including both propoxy groups remains essentially planar. The endo-oriented OH group is engaged in an intramolecular O-H···O hydrogen bond (Table 1) with the 2-propoxy O atom, resulting in the formation of a six-membered ring. This motif is generally typical for structures of all ortho-alkoxyarylboronic acids (Yang et al., 2005;Dąbrowski et al., 2008;Luliński, 2008).
Centrosymmetric O-H···O hydrogen-bonded dimers of (I) are linked by weaker C-H···O hydrogen bonds connecting the H5 atom attached to aromatic ring with the O atom of the 4-propoxy group in the adjacent molecule. Thus, another centrosymmetric dimeric motif can be distinguished. These two alternating dimeric motifs generate a zig-zag chain which runs along the [111] direction. Adjacent chains are ordered due to van der Waals interactions of propoxy groups which leads to the formation of a 2D layer aligned parallel to the (211) plane. The supramolecular architecture extends further due to weak C-H···O contacts between α-methylene units of 4-propoxy groups and one of O atoms of the boronic group. Finally, C-H···π interactions occur between the β-methylene units of the 2-propoxy group and the aromatic ring of a molecule in the adjacent layer. As a result, a three-dimensional network is formed.

Experimental
The title compound was received from Aldrich. Crystals suitable for single-crystal X-ray diffraction analysis were grown by slow evaporation of a solution of the acid (0.2 g) in acetone/water (10 ml, 1:1).

Refinement
All hydrogen atoms were placed in calculated positions with C-H distance of 0.95Å (phenyl), 0.98Å (methyl), 0.99Å (methylene) and O-H distance of 0.84 Å.They were visible in difference maps and they were included in the refinement Fig. 1. The molecular structure of the title compound (I) with the atom numbering scheme. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level. Fig. 2. Formation of two-dimensional layer constructed from one-dimensional chains, which are generated through O-H···O and C-H···O interactions (red and blue colours, respectively). Fig. 3. The three-dimensional supramolecular structure of (I). Intermolecular C-H···O and C-H···π interactions formed between two-dimensional layers are depicted as blue and green lines, respectively.