Crystal structure and Hirshfeld surface analysis of 3-cyanophenylboronic acid

In the title boronic acid derivative, the mean plane of the –B(OH)2 group is twisted by 21.28 (6)° relative to the cyanophenyl ring mean plane. In the crystal, molecules are linked by O—H⋯O and O—H⋯N hydrogen bonds, forming chains propagating along [101].

In the title compound, C 7 H 6 BNO 2 , the mean plane of the -B(OH) 2 group is twisted by 21.28 (6) relative to the cyanophenyl ring mean plane. In the crystal, molecules are linked by O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds, forming chains propagating along the [101] direction. Offsetand BÁ Á Á stacking interactions link the chains, forming a three-dimensional network. Hirshfeld surface analysis shows that van der Waals interactions constitute a further major contribution to the intermolecular interactions, with HÁ Á ÁH contacts accounting for 25.8% of the surface.

Chemical context
Boron-containing compounds and particularly arylboronic acid are an important class of compounds in the fields of organic and medicinal chemistry, and have played a role in the development of modern organic synthesis, macromolecular chemistry, crystal engineering and molecular recognition (Fujita et al., 2008;Severin, 2009). As a result of their peculiar dynamic covalent reactivity with alcohols (Jin et al., 2013), arylboronic acids and their dehydrated derivatives enable the self-assembly of a large variety of architectures resulting from boronate esterification (Takahagi et al. 2009) as well as boroxine (Cô té et al., 2005) and spiroborate formation (Du et al., 2016).
Boronic acids form neutral and charge-assisted homo-and heterodimeric hydrogen-bonding patterns resembling characteristics similar to those found for carboxylic acids (see Fig. 1a). However, the -B(OH) 2 moiety contains two O-H  hydrogen-bond donors and can, thus, form two O-HÁ Á ÁX hydrogen bonds and adopt different conformations (see Fig. 1b). This enables the generation of hydrogen-bonding networks with increased dimensionality (one to three dimensions) in the solid state (Fournier et al., 2003;Madura et al., 2015;Georgiou et al., 2017). In recent years, boronic acids have also been explored in the context of forming multicomponent molecular complexes with organic carboxylic acids (-COOH), amides (-CONH 2 ), alcohols (-OH) and pyridines, which are based on molecular recognition processes (Rodríguez-Cuamatzi et al., 2005;Madura et al., 2014;Herná ndez-Paredes et al., 2015;Campos-Gaxiola et al., 2017;Pedireddi & Lekshmi, 2004;Vega et al., 2010;TalwelkarShimpi et al., 2016). As part of our ongoing studies in this area, we report herein on the molecular and crystal structures of 3-cyanophenylboronic acid, I. In addition, a Hirshfeld surface analysis was performed to visualize and quantify the intermolecular interactions in the crystal structure of compound (I).

Structural commentary
The molecular structure of the title compound (I) is illustrated in Fig. 2. It can be seen that the -B(OH) 2 group adopts the most preferred syn-anti conformation (Lekshmi & Pedireddi, 2007). As a result of the HÁ Á ÁH repulsion between the endooriented B-OH hydrogen and the C-H hydrogen in position 2 of the aromatic ring, the -B(OH) 2 mean plane is twisted by 21.28 (6) relative to the cyanophenyl ring mean plane. This torsion disables intramolecular C-HÁ Á ÁO hydrogen bonding between the oxygen atom of the exo-oriented B-OH function and weakens the B-Cbonding interactions (Durka et al., 2012). The B1-O1, B1-O2 and B1-C1 bond lengths are 1.3455 (17), 1.3661 (18) and 1.5747 (18) Å , respectively. For comparison, in coplanar triphenyl boroxine the B-C bond lengths range from 1.544 (4) to 1.549 (4) Å (Brock et al., 1987). The C N bond length of 1.1416 (18) Å is typical for a bond with triple-bond character.

Hirshfeld surface analysis
Hirshfeld surfaces and fingerprint plots were generated for (I) based on the crystallographic information file (CIF) using CrystalExplorer (Hirshfeld, 1977;McKinnon et al., 2004). Hirshfeld surfaces enable the visualization of intermolecular interactions by different colors and color intensity, representing short or long contacts and indicating the relative strength of the interactions. Fig. 4 shows the Hirshfeld surface of the title compound mapped over d norm (À0.60 to 0.90 Å ) and the shape-index (À1.0 to 1.0 Å ). In the d norm map, the vivid red spots in the Hirshfeld surface are due to short normalized OÁ Á ÁH and NÁ Á ÁH distances corresponding to O-HÁ Á ÁO and O-HÁ Á ÁN interactions. The white spots represent the contacts resulting from C-HÁ Á ÁN hydrogen bonding (Fig. 4a). On the shape-index surface for compound (I), convex blue regions represent hydrogen-donor groups and concave red regions represent hydrogen-acceptor groups. The -B(OH) 2 group behaves simultaneously as a donor and an acceptor, meanwhile the -C N group is an acceptor only. The occurrence of offsetinteractions is indicated by adjacent red and blue triangles (Fig. 4b).
The two-dimensional fingerprint plots quantify the contributions of each type of non-covalent interaction to the Hirshfeld surface (McKinnon et al., 2007). The major contribution with 25.8% of the surface is due to HÁ Á ÁH contacts, which represent van der Waals interactions, followed by NÁ Á ÁH and OÁ Á ÁH interactions, which contribute 23.6 and 20.4%, respectively (these contributions are observed as two sharp peaks in the plot of Fig. 5). This behavior is usual for strong hydrogen bonds (Spackman & McKinnon, 2002). Finally, the presence of CÁ Á ÁC (11.4%) and BÁ Á ÁC (2.3%) contacts corresponds to theand BÁ Á Á interactions, respectively, established in the crystal structure analysis section.

Experimental
3-Cyanophenylboronic acid and the solvent used in this work are commercially available and were used without further purification. For single-crystal growth, a solution of 3-cyanophenylboronic acid (0.050 g) in 5 ml of ethanol was heated to reflux for 15 min. The solution was left to evaporate slowly at room temperature, giving after one week colorless crystals suitable for single-crystal X-ray diffraction analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms were positioned geometrically (O-H = 0.82 Å and C-H = 0.93 Å ) and refined using a riding model, with U iso (H) = 1.2U eq (C) and 1.5U eq (O).

Funding information
This work was supported financially by the Consejo Nacional de Ciencia y Tecnología (CONACYT, Project Nos. 177616 and 229929) and Red Temá tica de Química Supramolecular (CONACYT, Project No. 281251