(2-Meth­oxy-3-pyrid­yl)boronic acid

The structure of the title compound, 2-CH₃O-C₅H₃N–3-B(OH)₂ or C₆H₈BNO₃, comprises two crystallographically independent mol­ecules. The molecules are linked to each other by inter­molecular O—H...N and C—H...O bonds to produce an infinite chain, while a two-dimensional structure is formed as a result of π–π inter­actions of planar mol­ecules.

S1. Comment

Recently, pyridineboronic acids have aroused growing interest because of their important applications (Tyrrell & Brookes, 2004). However, their structures are relatively unexplored when compared with those of the benzene analogues [for crystal structures of related pyridylboronic acids, see Parry et al. (2002) and Thompson et al. (2005)]. A pyridine N atom bearing a lone electron pair provides an increased potential for extended supramolecular organization via hydrogen-bonding interactions. This possibility has prompted us to determine the structure of the title compound, (I). It contains two independent molecules A and B. Their geometries differ only marginally (Table 1); the molecular structure of A is shown in Fig. 1. Both molecules are essentially planar, the methoxy groups being only slightly twisted. In both molecules, the boronic acid groups have an exo–endo conformation. The endo-oriented OH groups are engaged in intramolecular O—H···O bonds with methoxy O atoms, thus producing nearly planar six-membered rings. Accordingly, the methoxy group adopts a syn conformation with respect to the C—N bond of the pyridine ring.

Unlike most arylboronic acids, (I) does not form centrosymmetric dimers as a result of hydrogen-bonding interactions of the boronic acid groups (Rettig & Trotter, 1977), which are responsible for extended supramolecular organization in systems based on di- and tetraboronic acids (Fournier et al., 2003; Rodriguez-Cuamatzi et al., 2004); dimeric units also exist in the crystal structures of isomeric 2-methoxypyridine-5-boronic acid (Thompson et al., 2005) and related 2-chloro- and 2-bromopyridine-5-boronic acids (Parry et al., 2002). In the structure of (I), alternate molecules A and B are linked in a unique fashion by means of almost linear O—H···N bridges supported by relatively short C—H···O interactions (Table 2). The boronic acid groups and N1/C5/H5 units of the pyridine rings act simultaneously as H-atom donors and acceptors, forming approximately planar, seven-membered rings. As a result, an infinite zigzag chain is formed (Fig. 2), which can be described as a planar system of fused six- and seven-membered rings. There is only one more example of a simple arylboronic acid, namely 4-formylphenylboronic acid, which does not form centrosymmetric dimers and is assembled primarily in a `head-to-tail' fashion via hydrogen-bonding interactions of boronic acid and formyl groups (Fronczek et al., 2001). A related situation is observed in a few other compounds. In L-p-boronophenylalanine (Shull et al., 2000), interactions between boronic acid groups and zwitterionic amino acid units are preferred, whereas in the monohydrates of 2-acetylphenylboronic (Ganguly et al., 2003) and 5-pyrimidineboronic acids (Saygili et al., 2004), the presence of water must be taken into account in the interpretation of the crystal packing.

The extended supramolecular assembly consists of the aforementioned hydrogen-bonded chains of molecules, aligned along the crystallographic [102] direction, organized perpendicular to this by π–π interactions between alternate molecules; one of the pair of crystallographically independent molecules in the asymmetric unit is involved in such an interaction, the other being involved in a C—H···π interaction with its perpendicular partner (Fig. 3). As a result of the π–π interactions, the pyridine rings are stacked in a face-to-face, center-to-edge fashion (Cozzi et al., 2003). Atom N1A is located approximately over the centre of the pyridine ring of its partner B molecule; the distances to the ring atoms lie in the narrow range 3.571 (N1A···C1B) to 3.622 (2) Å (N1A···C4B), whereas the distance to the ring centre is 3.327 (1) Å. For atom C2B, the distance to the ring centre of the perpendicular partner A is 3.375 (1) Å. C—H···π interactions occur between the methoxy group of molecule B and the pyridine ring of molecule A; the distance of atom H6F from the ring centroid is 2.767 (14) Å.

In conclusion, the one-dimensional supramolecular organization of (I) achieved via to intra- and intermolecular hydrogen-bonding interactions is unique among arylboronic acids. In addition, specific π–π interactions constitute the two-dimensional layer structure.

S2. Experimental

Compound (I) was prepared using the published procedure (Thompson et al., 2005). Crystals suitable for single-crystal X-ray diffraction analysis were grown by slow evaporation of a saturated solution in ethyl acetate/acetone (1:1) (m.p. 412–413 K).

S3. Refinement

All H atoms were located in difference syntheses and refined freely [C—H = 0.945 (13)–0.980 (13) Å].

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2005); cell refinement: CrysAlis RED (Oxford Diffraction, 2005); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL97.

Figures

	Fig. 1. The molecular structure of conformer A, showing the atom-labelling scheme. Displacement ellipsoids for all non-H atoms are drawn at the 50% probability level.
	Fig. 2. The hydrogen-bonding pattern for (I). Hydrogen bonds are shown as dashed lines.
	Fig. 3. The crystal packing for (I), with π–π and C—H···π interactions between hydrogen-bonded chains shown as dotted lines. Hydrogen bonds are shown as dashed lines.

(2-Methoxy-3-pyridyl)boronic acid

Crystal data

C6H8BNO3	F(000) = 640
Mr = 152.94	Dx = 1.453 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.6342 (3) Å	Cell parameters from 19088 reflections
b = 25.7404 (10) Å	θ = 2.7–28.9°
c = 7.2444 (3) Å	µ = 0.11 mm^−1
β = 100.857 (3)°	T = 102 K
V = 1398.10 (10) Å^3	Prism, colourless
Z = 8	0.77 × 0.51 × 0.31 mm

Data collection

Oxford Diffraction KM-4-CCD diffractometer	3355 independent reflections
Radiation source: fine-focus sealed tube	2873 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.012
Detector resolution: 8.6479 pixels mm^-1	θmax = 28.0°, θmin = 2.7°
ε scans	h = −10→10
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2005)	k = −33→33
Tmin = 0.94, Tmax = 0.97	l = −9→9
25489 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.030	All H-atom parameters refined
wR(F^2) = 0.090	w = 1/[σ^2(Fo^2) + (0.055P)^2 + 0.197P] where P = (Fo^2 + 2Fc^2)/3
S = 1.11	(Δ/σ)max = 0.001
3355 reflections	Δρmax = 0.38 e Å^−3
264 parameters	Δρmin = −0.19 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0061 (12)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1A	0.72237 (9)	0.43329 (3)	1.14395 (9)	0.01646 (16)
O2A	0.54844 (10)	0.42440 (3)	0.77950 (10)	0.01971 (17)
O3A	0.59358 (9)	0.34341 (3)	0.64367 (9)	0.01831 (17)
N1A	0.89858 (10)	0.36830 (3)	1.30134 (10)	0.01354 (17)
C1A	0.79365 (12)	0.38479 (3)	1.14507 (12)	0.01239 (19)
C2A	0.74908 (12)	0.35601 (3)	0.97664 (12)	0.01251 (19)
C3A	0.82341 (12)	0.30675 (4)	0.98138 (13)	0.0146 (2)
C4A	0.93522 (13)	0.28818 (4)	1.14217 (13)	0.0155 (2)
C5A	0.96897 (12)	0.32027 (4)	1.29724 (13)	0.0150 (2)
C6A	0.75668 (14)	0.46262 (4)	1.31640 (13)	0.0174 (2)
B1A	0.62461 (14)	0.37628 (4)	0.79205 (14)	0.0137 (2)
H2OA	0.576 (2)	0.4408 (6)	0.881 (2)	0.046 (4)*
H3OA	0.524 (2)	0.3547 (6)	0.542 (2)	0.048 (4)*
H3A	0.7993 (16)	0.2853 (4)	0.8707 (17)	0.020 (3)*
H4A	0.9879 (16)	0.2539 (5)	1.1498 (16)	0.021 (3)*
H5A	1.0465 (16)	0.3104 (5)	1.4122 (17)	0.022 (3)*
H6A	0.8835 (16)	0.4703 (4)	1.3523 (16)	0.018 (3)*
H6B	0.6911 (16)	0.4950 (5)	1.2852 (17)	0.023 (3)*
H6C	0.7124 (15)	0.4446 (4)	1.4161 (16)	0.016 (3)*
O1B	0.35673 (9)	0.31852 (2)	0.09157 (9)	0.01524 (16)
O2B	0.17608 (10)	0.32792 (3)	−0.26932 (10)	0.01889 (17)
O3B	0.02558 (9)	0.40818 (3)	−0.32972 (10)	0.01861 (17)
N1B	0.36956 (10)	0.38384 (3)	0.31251 (11)	0.01404 (18)
C1B	0.31161 (11)	0.36736 (3)	0.13797 (12)	0.01220 (19)
C2B	0.20520 (11)	0.39654 (3)	−0.00620 (12)	0.01250 (19)
C3B	0.16358 (12)	0.44641 (4)	0.04426 (13)	0.0145 (2)
C4B	0.22221 (12)	0.46509 (4)	0.22576 (13)	0.0159 (2)
C5B	0.32319 (13)	0.43242 (4)	0.35401 (13)	0.0158 (2)
C6B	0.45566 (14)	0.28659 (4)	0.23843 (14)	0.0177 (2)
B1B	0.13326 (14)	0.37601 (4)	−0.21140 (14)	0.0139 (2)
H2OB	0.245 (2)	0.3125 (6)	−0.180 (2)	0.051 (5)*
H3OB	−0.017 (2)	0.3963 (6)	−0.441 (2)	0.048 (4)*
H3B	0.0914 (15)	0.4685 (4)	−0.0473 (16)	0.015 (3)*
H4B	0.1928 (16)	0.4987 (5)	0.2632 (17)	0.022 (3)*
H5B	0.3643 (15)	0.4427 (4)	0.4816 (17)	0.017 (3)*
H6D	0.3883 (16)	0.2823 (4)	0.3400 (17)	0.019 (3)*
H6E	0.4698 (16)	0.2536 (5)	0.1764 (17)	0.023 (3)*
H6F	0.5728 (17)	0.3020 (5)	0.2855 (17)	0.022 (3)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1A	0.0224 (4)	0.0138 (3)	0.0114 (3)	0.0042 (3)	−0.0014 (3)	−0.0026 (2)
O2A	0.0253 (4)	0.0174 (4)	0.0133 (3)	0.0046 (3)	−0.0043 (3)	−0.0023 (3)
O3A	0.0230 (4)	0.0172 (3)	0.0120 (3)	0.0023 (3)	−0.0037 (3)	−0.0018 (3)
N1A	0.0144 (4)	0.0154 (4)	0.0102 (4)	−0.0008 (3)	0.0007 (3)	0.0007 (3)
C1A	0.0127 (4)	0.0126 (4)	0.0117 (4)	−0.0008 (3)	0.0019 (3)	0.0006 (3)
C2A	0.0130 (4)	0.0138 (4)	0.0105 (4)	−0.0019 (3)	0.0018 (3)	−0.0002 (3)
C3A	0.0159 (4)	0.0150 (4)	0.0126 (4)	−0.0020 (3)	0.0023 (3)	−0.0018 (3)
C4A	0.0175 (4)	0.0133 (4)	0.0155 (4)	0.0019 (3)	0.0027 (3)	0.0016 (3)
C5A	0.0154 (4)	0.0160 (4)	0.0128 (4)	0.0004 (3)	0.0009 (3)	0.0026 (3)
C6A	0.0226 (5)	0.0155 (5)	0.0131 (4)	0.0025 (4)	0.0006 (4)	−0.0043 (3)
B1A	0.0137 (5)	0.0157 (5)	0.0111 (5)	−0.0019 (4)	0.0006 (4)	0.0004 (4)
O1B	0.0189 (3)	0.0131 (3)	0.0118 (3)	0.0040 (3)	−0.0021 (2)	−0.0007 (2)
O2B	0.0235 (4)	0.0176 (4)	0.0129 (3)	0.0037 (3)	−0.0033 (3)	−0.0022 (3)
O3B	0.0245 (4)	0.0179 (3)	0.0107 (3)	0.0039 (3)	−0.0037 (3)	−0.0010 (3)
N1B	0.0145 (4)	0.0151 (4)	0.0115 (4)	−0.0002 (3)	0.0000 (3)	−0.0001 (3)
C1B	0.0118 (4)	0.0128 (4)	0.0119 (4)	−0.0010 (3)	0.0021 (3)	0.0000 (3)
C2B	0.0116 (4)	0.0147 (4)	0.0109 (4)	−0.0008 (3)	0.0012 (3)	0.0010 (3)
C3B	0.0145 (4)	0.0154 (4)	0.0130 (4)	0.0006 (3)	0.0007 (3)	0.0019 (3)
C4B	0.0178 (5)	0.0134 (4)	0.0160 (5)	0.0004 (3)	0.0018 (4)	−0.0023 (3)
C5B	0.0168 (4)	0.0173 (5)	0.0123 (4)	−0.0012 (3)	0.0005 (3)	−0.0027 (3)
C6B	0.0221 (5)	0.0144 (4)	0.0144 (4)	0.0044 (4)	−0.0022 (4)	0.0021 (4)
B1B	0.0136 (5)	0.0160 (5)	0.0114 (5)	−0.0009 (4)	0.0009 (4)	0.0006 (4)

Geometric parameters (Å, º)

O1A—C1A	1.3612 (11)	O1B—C1B	1.3622 (11)
O1A—C6A	1.4408 (11)	O1B—C6B	1.4404 (11)
O2A—B1A	1.3641 (12)	O2B—B1B	1.3663 (12)
O2A—H2OA	0.840 (16)	O2B—H2OB	0.850 (17)
O3A—B1A	1.3533 (12)	O3B—B1B	1.3531 (12)
O3A—H3OA	0.871 (17)	O3B—H3OB	0.866 (17)
N1A—C1A	1.3273 (12)	N1B—C1B	1.3281 (12)
N1A—C5A	1.3506 (12)	N1B—C5B	1.3489 (12)
C1A—C2A	1.4133 (12)	C1B—C2B	1.4125 (12)
C2A—C3A	1.3868 (13)	C2B—C3B	1.3880 (13)
C2A—B1A	1.5763 (13)	C2B—B1B	1.5758 (13)
C3A—C4A	1.3926 (13)	C3B—C4B	1.3924 (13)
C3A—H3A	0.963 (12)	C3B—H3B	0.965 (11)
C4A—C5A	1.3790 (13)	C4B—C5B	1.3766 (13)
C4A—H4A	0.967 (12)	C4B—H4B	0.945 (13)
C5A—H5A	0.961 (12)	C5B—H5B	0.956 (12)
C6A—H6A	0.975 (12)	C6B—H6D	0.980 (12)
C6A—H6B	0.977 (13)	C6B—H6E	0.976 (12)
C6A—H6C	0.971 (12)	C6B—H6F	0.980 (13)
C1A—O1A—C6A	117.91 (7)	C1B—O1B—C6B	117.77 (7)
B1A—O2A—H2OA	111.2 (11)	B1B—O2B—H2OB	109.8 (11)
B1A—O3A—H3OA	116.8 (10)	B1B—O3B—H3OB	116.8 (10)
C1A—N1A—C5A	116.92 (8)	C1B—N1B—C5B	117.00 (8)
N1A—C1A—O1A	118.34 (8)	N1B—C1B—O1B	118.38 (8)
N1A—C1A—C2A	125.25 (8)	N1B—C1B—C2B	125.18 (8)
O1A—C1A—C2A	116.40 (8)	O1B—C1B—C2B	116.44 (8)
C3A—C2A—C1A	115.28 (8)	C3B—C2B—C1B	115.18 (8)
C3A—C2A—B1A	120.13 (8)	C3B—C2B—B1B	120.15 (8)
C1A—C2A—B1A	124.58 (8)	C1B—C2B—B1B	124.68 (8)
C2A—C3A—C4A	121.20 (8)	C2B—C3B—C4B	121.28 (8)
C2A—C3A—H3A	119.4 (7)	C2B—C3B—H3B	119.6 (7)
C4A—C3A—H3A	119.4 (7)	C4B—C3B—H3B	119.1 (7)
C5A—C4A—C3A	117.83 (9)	C5B—C4B—C3B	117.77 (9)
C5A—C4A—H4A	119.2 (7)	C5B—C4B—H4B	119.9 (7)
C3A—C4A—H4A	123.0 (7)	C3B—C4B—H4B	122.4 (7)
N1A—C5A—C4A	123.52 (8)	N1B—C5B—C4B	123.57 (9)
N1A—C5A—H5A	113.9 (7)	N1B—C5B—H5B	114.8 (7)
C4A—C5A—H5A	122.6 (7)	C4B—C5B—H5B	121.6 (7)
O1A—C6A—H6A	110.3 (7)	O1B—C6B—H6D	110.0 (7)
O1A—C6A—H6B	104.2 (7)	O1B—C6B—H6E	104.1 (7)
H6A—C6A—H6B	109.2 (10)	H6D—C6B—H6E	111.5 (10)
O1A—C6A—H6C	111.2 (7)	O1B—C6B—H6F	110.0 (7)
H6A—C6A—H6C	111.4 (10)	H6D—C6B—H6F	111.0 (10)
H6B—C6A—H6C	110.2 (10)	H6E—C6B—H6F	109.9 (10)
O3A—B1A—O2A	120.40 (8)	O3B—B1B—O2B	120.79 (9)
O3A—B1A—C2A	117.02 (8)	O3B—B1B—C2B	117.04 (8)
O2A—B1A—C2A	122.57 (8)	O2B—B1B—C2B	122.17 (8)
C5A—N1A—C1A—O1A	−179.21 (8)	C5B—N1B—C1B—O1B	179.79 (8)
C5A—N1A—C1A—C2A	0.57 (14)	C5B—N1B—C1B—C2B	−0.31 (14)
C6A—O1A—C1A—N1A	−3.65 (12)	C6B—O1B—C1B—N1B	3.73 (12)
C6A—O1A—C1A—C2A	176.54 (8)	C6B—O1B—C1B—C2B	−176.17 (8)
N1A—C1A—C2A—C3A	0.18 (14)	N1B—C1B—C2B—C3B	1.04 (14)
O1A—C1A—C2A—C3A	179.97 (8)	O1B—C1B—C2B—C3B	−179.05 (7)
N1A—C1A—C2A—B1A	−179.81 (8)	N1B—C1B—C2B—B1B	−178.38 (8)
O1A—C1A—C2A—B1A	−0.02 (13)	O1B—C1B—C2B—B1B	1.52 (13)
C1A—C2A—C3A—C4A	−0.65 (13)	C1B—C2B—C3B—C4B	−0.86 (13)
B1A—C2A—C3A—C4A	179.34 (9)	B1B—C2B—C3B—C4B	178.59 (9)
C2A—C3A—C4A—C5A	0.36 (14)	C2B—C3B—C4B—C5B	0.03 (14)
C1A—N1A—C5A—C4A	−0.91 (13)	C1B—N1B—C5B—C4B	−0.65 (14)
C3A—C4A—C5A—N1A	0.46 (14)	C3B—C4B—C5B—N1B	0.79 (15)
C3A—C2A—B1A—O3A	0.87 (13)	C3B—C2B—B1B—O3B	−2.58 (13)
C1A—C2A—B1A—O3A	−179.14 (8)	C1B—C2B—B1B—O3B	176.82 (8)
C3A—C2A—B1A—O2A	−179.83 (9)	C3B—C2B—B1B—O2B	177.58 (9)
C1A—C2A—B1A—O2A	0.16 (15)	C1B—C2B—B1B—O2B	−3.02 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3B—H3OB···N1A^i	0.866 (17)	1.992 (17)	2.8567 (10)	176.6 (15)
O2B—H2OB···O1B	0.850 (17)	1.999 (17)	2.7272 (9)	143.1 (15)
O3A—H3OA···N1B	0.871 (17)	1.996 (17)	2.8666 (10)	177.3 (15)
O2A—H2OA···O1A	0.840 (16)	2.026 (16)	2.7323 (10)	141.3 (14)
C5A—H5A···O2B^ii	0.961 (12)	2.376 (12)	3.245 (1)	150.2 (10)
C5B—H5B···O2A	0.965 (12)	2.390 (12)	3.241 (1)	148.1 (10)

Symmetry codes: (i) x−1, y, z−2; (ii) x+1, y, z+2.