Two forms of (naphthalen-1-yl)boronic acid

Two polymorphs of the title compound, C10H9BO2, were prepared by recystallization from different solvents at room temperature. Both forms demonstrate nearly identical molecular structures with all naphthalene group atoms located in one plane and all boronic acid atoms in another. In each extended structure, molecules form dimers, connected via two O—H⋯O hydrogen bonds. The dimers are connected by further O—H⋯O hydrogen bonds, forming layered networks. The resulting layers are practically identical in both forms but are shifted along the [010] axis in the two forms, resulting in a slightly more effective packing for the monoclinic structure compared to the orthorhombic form.

Two polymorphs of the title compound, C 10 H 9 BO 2 , were prepared by recystallization from different solvents at room temperature. Both forms demonstrate nearly identical molecular structures with all naphthalene group atoms located in one plane and all boronic acid atoms in another: the dihedral angles between these planes are 39.88 (5) and 40.15 (5) for the two asymmetric molecules of the orthorhombic form and 40.60 (3) for the single asymmetric molecule in the monoclinic form. In each extended structure, molecules form dimers, connected via two O-HÁ Á ÁO hydrogen bonds. The dimers are connected by further O-HÁ Á ÁO hydrogen bonds, forming layered networks in the (001) plane and the (100) plane in the orthorhombic and monoclinic forms, respectively. The resulting layers are practically identical in both forms. However, these layers are shifted along the [010] axis in the two forms, resulting in a slightly more effective packing for monoclinic structure (packing index = 0.692) compared to the orthorhombic form (0.688).

Chemical context
Naphthalene boronic acids (-and -) were first synthesized by Michaelis (1894) along with other arylboronic acid by reaction of diarylmercury with boron trichloride with subsequent hydrolysis. A more practical procedure (Kö nig & Scharrnbeck, 1930) included the reaction of naphthylmagnesium bromide with tri-(isobutyl)borate. In both cases, the existence of two different forms of title compound was suggested, one forming plate-like crystals and another one forming needles.
These compounds were originally investigated because of their potential in biochemistry (Kö nig & Scharrnbeck, 1930;Gao et al., 2003;Hall, 2011) and later as reactants in the Suzuki reaction (Hall, 2011). 1-Naphthalene boronic acid is now commercially available and was the source for this study.

Synthesis and crystallization
A sample of 1-naphthalene boronic acid was purchased from Aldrich. Its FTIR spectrum coincided with that reported by ISSN 2056-9890 the manufacturer. Under the microscope, a number of relatively large (up to 0.5 mm) crystals were visible, some of them suitable for single crystal X-ray data collection (Fig. 1). Experimental data revealed an orthorhombic structure for the plate-shaped crystals. Recrystallization from hot water yielded very thin plates. This polycrystalline sample showed a powder diffractogram that was slightly different from the raw material and the calculated pattern of the orthorhombic form. Attempts at slow crystallization from ethanol and toluene solution resulted in larger and better shaped crystals, some of which were orthorhombic plates and other were visibly nonorthorhombic needles (Fig. 1). Several such crystals were tested: here we report the best data for both the orthorhombic and monoclinic forms.

Structural commentary
The molecules of naphthalene boronic acid in both crystal structures (Figs. 2 and 3) have the usual bond distances and angles. There is one molecule in the asymmetric unit of the monoclinic structure. In the non-centrosymmetric orthorhombic structure, the two molecules in the asymmetric unit have very similar structures: they almost coincide (after inversion for one of them) with each other as well, as with the unique molecule from the monoclinic structure (Fig. 4).
In the monoclinic structure, the mean plane of the naphthalene fragment is tilted from plane of boron and two oxygen atoms with an angle of 40.60 (3) . The boron atom deviates by 0.0449 (16) Å from the mean plane of the naphthalene ring system.
In the orthorhombic structure, there are two independent molecules. When superimposed, the angle between the mean planes of the naphthalene ring systems is only 0.88 (6) . Two boron atoms and four oxygen atoms are located at another plane together with adjacent hydrogen atoms. These planes are tilted to a similar extent to the monoclinic structure, with dihedral angles to the mean plane of each naphthalene group of 39.88 (5) and 40.15 (5) [mean tilt = 39.83 (5) ]. These numbers differ from those for the monoclinic form by less than 1 .

Figure 2
Numbering scheme of the title compound with 50% probability displacement ellipsoids (orthorhombic polymorph).

Figure 3
Numbering scheme of the title compound with 50% probability displacement ellipsoids (monoclinic polymorph).

Figure 4
Overlay of the two polymorph molecules (red & green -orthorhombic, blue -monoclinic) with appropriate inversion.

Supramolecular features
In both forms, pairs of molecules are connected through a pair of O-HÁ Á ÁO hydrogen bonds (Tables 1 and 2) into dimers. There is also an intramolecular C-HÁ Á ÁO contact. The dimers are further connected via O-HÁ Á ÁO hydrogen bonds, forming a layered network in plane (001) and in plane (100) in the orthorhombic and monoclinic forms, respectively (Figs. 5 and 6). The resulting layers are practically identical in both forms (compare Figs. 7 and 8,Figs. 9 and 10).

Figure 5
Layered network of hydrogen bonds in the orthorhombic form. View is along the [001] axis, only boronic acid groups are shown.

Figure 6
Layered network of hydrogen bonds in the monoclinic form. View is along the [001] axis, only boronic acid groups are shown.

Figure 8
Packing of the monoclinic form. View is along the [010] axis.

Figure 7
Packing of the orthorhombic form. View is along the [010] axis. more effective packing of the monoclinic structure (packing index = 0.692) (Kitaigorodskii, 1961;Spek, 2009) compared to the orthorhombic structure (packing index = 0.688). This layer-shift is the only visible difference between the two forms.

Database survey
There are no naphthalene boronic acid structures deposited in the Cambridge Structural Database (CSD Version 5.37; Groom et al., 2016). The simplest arylboronic acid, phenylboronic acid, crystallizes in a non-centrosymmetric ortho-rhombic space group (refcodes PHBORA and PHBORA01). Instead of a layered network, its molecules form an infinitive chain in the crystal (Cyrá nski et al., 2008;Rettig & Trotter, 1977).
1288 Bemisderfer and Nazarenko Two polymorphs of C 10 H 9 BO 2 Acta Cryst. Packing diagram of the orthorhombic form. View is along the [100] axis. Hirshfeld surface shown for some molecules.

Figure 10
Packing diagram of the monoclinic form. View is along the [001] axis. Hirshfeld surface shown for some molecules.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All hydrogen atoms of hydroxyl groups were refined in an isotropic approximation. Aromatic hydrogen atoms were refined with riding coordinates and U iso (H) = 1.2 U iso (C). Two forms of (naphthalen-1-yl)boronic acid Kayleigh Bemisderfer and Alexander Y. Nazarenko
(1) (Naphthalen-1-yl)boronic acid  (6) 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.