3-Aminophenylboronic acid monohydrate

In the title compound, C6H8BNO2·H2O, the almost planar boronic acid molecules (r.m.s. deviation = 0.044 Å) form inversion dimers, linked by pairs of O—H⋯O hydrogen bonds. The water molecules link these dimers into [100] chains by way of O—H⋯O hydrogen bonds, and N—H⋯O links generate (100) sheets.


Comment
Substituted phenylboronic acid derivatives have been prepared mainly for applications in organic synthesis (Miyaura & Suzuki, 1995;Hall, 2005) and for molecular recognition of biochemically active molecules (Shinkai et al., 2001). More recently, such boronic acid derivatives have attracted attention also as building blocks for the self-assembly of macrocyclic and polymeric assemblies. For this purpose, the boronic acid is generally converted to an ester (boronate) via condensation with an aliphatic or aromatic diol, which is then assembled to a macromolecular structure via reaction of the additional functional group attached to the B-phenyl ring (Höpfl, 2002;Fujita et al., 2008;Severin, 2009). In this context, 3-aminophenylboronic acid has been employed for the generation of macrocycles and cages (Dreos et al., 2002;Barba et al., 2004 and2006;Barba & Betanzos, 2007;Christinat et al., 2008).
We report herein on the molecular and crystal structure of 3-aminophenylboronic acid monohydrate (I).
The asymmetric unit of I contains one 3-aminophenylboronic acid and one water molecule (Figure 1). The boronic acid molecules are associated through the well-known -B(OH) 2 ···(HO) 2 B-synthon (motif A) with the graph set R 2 2 (8) (Bernstein et al., 1995), in which each B(OH) 2 group has syn-anti conformation (with respect to the H atoms), thus allowing for the formation of additional hydrogen bonds with the water molecules included in the crystal lattice. These (B)O-H···O w hydrogen bonds give rise to a cyclic water-expanded motif B [graph set R 6 6 (12)] of the boronic acid homodimer, thus generating a 1D chain along axis a (Figure 2). The (OH) 6 ring has chair-conformation and has been observed previously in the crystal structures of 3,5-dibromo-2-formylphenylboronic acid monohydrate (Lulinski et al., 2007), 5-quinolineboronic acid monohydrate (Zhang et al., 2007) and 2,6-dichloro-3-pyridylboronic acid hemihydrate (Smith et al., 2008). The 1D chains are interconnected through O w -H···N, N-H···O w and N-H···O(B) hydrogen bonds to give an overall 3D hydrogen bonded network (Table 1).
Experimental 3-Aminophenylboronic acid monohydrate is a commercially available product that has been crystallized from a solvent mixture of benzene, methanol and water to generate colourless blocks of (I); M.p. 368 K.  Fig. 1. Perspective view of (I) with displacement ellipsoids drawn at the 50% probability level. Fig. 2. In the crystal structure of (I) homodimeric boronic acid motifs A and water-expanded motifs B are linked to 1D hydrogen-bonded chains.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.