2,4-Dibutoxyphenylboronic acid

In the crystal of the title compound, C14H23BO4, centrosymmetric dimers linked by pairs of O—H⋯O hydrogen bonds occur. The dimers are linked via C—H⋯O contacts, generating a two-dimensional array parallel to (12). These are interconnected by weak O—H⋯O hydrogen bonds, as well as C—H⋯π interactions.

In the crystal of the title compound, C 14 H 23 BO 4 , centrosymmetric dimers linked by pairs of O-HÁ Á ÁO hydrogen bonds occur. The dimers are linked via C-HÁ Á ÁO contacts, generating a two-dimensional array parallel to (121). These are interconnected by weak O-HÁ Á ÁO hydrogen bonds, as well as C-HÁ Á Á interactions.
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 Warsaw University of Technology and by the Aldrich Chemical Co through donation of chemicals and equipment..

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 and is slightly twisted with respect to the benzene ring, Fig. 1. However, the entire molecule including both butoxy groups remains essentially planar. The endo-oriented OH group is engaged in an intramolecular O-H···O hydrogen bond with the 2-butoxy-O atom, resulting in the formation of a six-membered ring, Table 1. This motif is generally typical of ortho-alkoxyarylboronic acids structures (Yang et al., 2005;Dąbrowski et al., 2006Dąbrowski et al., , 2008Luliński, 2008). The supramolecular assembly of (I) is similar to that observed previously for 2,4-dimethoxyphenylboronic acid (Yang et al., 2005). Centrosymmetric hydrogen-bonded dimers of (I) are linked by weaker C-H···O contacts, of which there are two types ( Table 1). The first one connects the terminal methyl of the 2-butoxy group with the O atom of the adjacent molecule whereas the second one is formed between the γ-methylene unit of the 4-butoxy group and the O atom of the exo-OH group.
As a result a 2-D array is formed, aligned parallel to the (121)  1 + z], respectively. As a result, a 3-D network is formed. In conclusion, the hydrogen-bonded dimeric structure of (I) is typical of boronic acids whereas the unique secondary supramolecular assembly is achieved due to weaker hydrogen bonds and C-H-π interactions.

Experimental
Crystals were grown by slow evaporation of a hexane/acetone (10 ml, 1:1) solution of (I) (Aldrich, 0.3 g).  Fig. 1. The molecular structure of (I) showing the atom-labelling scheme. The intramolecular hydrogen bond is shown as a dashed line. Displacement ellipsoids for all non-H atoms are drawn at the 50% probability level.