2-(Methoxy­carbonyl)phenyl­boronic acid

The structure of the title compound, 2(CH₃OCO)C₆H₄B(OH)₂ or C₈H₉BO₄, involves two crystallographically independent conformers, A and B, in a 1:2 ratio; mol­ecules of conformer A are located on a crystallographic mirror plane. The most striking difference between the two independent mol­ecules is the opposite orientation of the methoxy­carbonyl groups, while the conformations of the boronic acid groups vary more subtly. Mol­ecules of both types are ordered to produce a specific hydrogen-bonding network that can be inter­preted in terms of a layer lying parallel to (100). Within the layer, B mol­ecules are linked with each other by two different O—H...O bonds to form an infinite chain where two centrosymmetric dimeric motifs can be distinguished.

S1. Comment

The use of arylboronic acids in supramolecular assembly is potentially promising (Fournier et al., 2003; Davis et al., 2001) but still relatively unexplored. Arylboronic acids with carbonyl substituents are interesting as they may be able to support supramolecular organization via hydrogen-bonding interactions. For this reason we have determined the structure of the title compound, (I), for crystal structures of related arylboronic acids (see Fronczek et al., 2001; Ganguly et al., 2003; Scouten et al., 1994; Zarychta et al., 2004).

The structure of (I) is unusual in that it displays conformational isomerism, in contrast to the related compounds cited above. It contains two independent molecules (Fig. 1), one of which (A) lies with all non-H atoms except atom O2A in a crystallographic mirror plane, while the other (B) occupies a general position. In molecule A, the methoxycarbonyl group is coplanar by symmetry with the ring. The carbonyl group in molecule A is syn-directed with respect to the boronic acid group, which resembles the situation in 2-acetylphenylboronic acid monohydrate (Ganguly et al., 2003). In contrast, the carbonyl group in molecule B is anti with respect to the boronic acid group. The methoxycarbonyl group in molecule B is not strictly coplanar with the benzene ring; the C4B—C5B—C10B—O11B torsion angle is 165.22 (10)°, which may reflect steric repulsion between functional groups. Some variation of bond lengths and angles is also observed. The C10—O11 bond in molecule B [1.2204 (12) Å] is longer than the corresponding bond in A [1.1951 (17) Å]. Presumably, this effect can be rationalized in terms of hydrogen-bonding interaction between the carbonyl O atom and an OH group from a neighboring molecule B (Fig. 2), which slightly decreases the C10B—O11B bond order. The C4—C5—C10 bond angles are 117.65 (12) and 121.05 (9)°, whereas the C6—C5—C10 bond angles are 120.73 (12) and 117.27 (9)° for molecules A and B, respectively. The situation in molecule A is similar to that observed in 2-acetylphenylboronic acid (Ganguly et al., 2003). It is plausible that a weak boron–oxygen interaction [B1A···O11A = 2.628 (s.u.?) Å], resulting from a partial overlap of an empty 2p orbital of the B atom with the lone pair of the carbonyl O atom, decreases the C4—C5—C10 angle. In molecule B, such an interaction is not possible, and the C4—C5—C10 angle is larger. The conformational isomerism is also reflected in the behaviour of the boronic acid groups. In molecule A, the boronic acid group is rotated more with respect to the ring, as seen from the O2A—B1A—C4A—C5A torsion angle [94.82 (12)°]. In 1B the boronic moiety displays a corresponding O2B—B1B—C4B—C9B torsion angle of −71.88 (13)°. Such flexible behaviour of a boronic acid group was found in other ortho-substituted arylboronic acids (Gainsford et al., 1995; Ganguly et al., 2003) but not for the closely related 2-formylphenylboronic acid (Scouten et al., 1994), where the planar conformation is stabilized by an intramolecular hydrogen bond. Another difference is the conformation within B(OH)₂ groups, reflecting a specific crystal packing imposed by intermolecular hydrogen bonding. In molecule A, both OH bonds are syn directed with respect to the ring, whereas in B they exhibit a syn-anti orientation.

A crystal packing diagram for (I), showing the effect of mirror symmetry, is depicted in Fig. 2. There are three classical O—H···O hydrogen bonds (Table 2); the strongest hydrogen bonds, O3B—H3B···O11B, are formed between molecules B (motif a in Fig. 2) (Etter, 1990; Bernstein et al., 1995), producing a centrosymmetric dimer [R₂²(14) graph set descriptor]. Furthermore, molecules B are linked with one another by O2B—H2B···O3B hydrogen bonds between B(OH)₂ groups (motif b), to form centrosymmetric dimers [R₂²(8) ring] typical of arylboronic acids (Rettig & Trotter, 1977). Molecules A are linked to boronic acid O atoms of two adjacent molecules B by an O2A—H2A···O2B bridge [motif c, D₂²(7) graph-set descriptor]. The second-level motif N₂(ab) = C₂²(9)[R₄⁴(20)] depicts a characteristic infinite chain of alternating fused rings. Other chains are represented by binary motifs N₂(ac) = C₃³(15) and N₂(bc) = C₃³(10). The hydrogen-bond network produces an infinite two-dimensional structure, where a larger ring depicted by the third-level graph-set descriptor N₃(abc) = C₄⁴(15)[R₈⁸(30)] can be distinguished.

S2. Experimental

Compound (I) was obtained from Aldrich. Crystals of (I) suitable for for single-crystal X-ray diffraction analysis were grown by slow evaporation of a saturated solution in ethyl acetate/toluene (1:1) (m.p. 375–377 K).

S3. Refinement

All H atoms were located in difference syntheses and refined freely [C—H = 0.931 (19)–0.996 (14) 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 structures of conformers A and B, showing the atom-labelling scheme. Displacement ellipsoids for all non-H atoms are drawn at the 50% probability level.
	Fig. 2. The crystal packing and hydrogen-bonding pattern for (I), with the assigned graph-set motifs. Hydorgen bonds are shown as dashed lines.

2-(Methoxycarbonyl)phenylboronic acid

Crystal data

C8H9BO4	Dx = 1.389 Mg m^−3
Mr = 179.96	Melting point = 375–377 K
Monoclinic, P21/m	Mo Kα radiation, λ = 0.71073 Å
a = 8.2764 (2) Å	Cell parameters from 18642 reflections
b = 19.7124 (6) Å	θ = 2.6–29.0°
c = 8.7321 (3) Å	µ = 0.11 mm^−1
β = 115.007 (3)°	T = 100 K
V = 1291.07 (7) Å^3	Prism, colourless
Z = 6	0.46 × 0.32 × 0.21 mm
F(000) = 564

Data collection

Oxford Diffraction KM-4 CCD diffractometer	3268 independent reflections
Radiation source: fine-focus sealed tube	2797 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.012
Detector resolution: 8.6479 pixels mm^-1	θmax = 28.6°, θmin = 2.8°
ω scans	h = −11→11
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2005)	k = −26→26
Tmin = 0.96, Tmax = 0.98	l = −11→11
23407 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.094	All H-atom parameters refined
S = 1.12	w = 1/[σ^2(Fo^2) + (0.0537P)^2 + 0.2342P] where P = (Fo^2 + 2Fc^2)/3
3268 reflections	(Δ/σ)max = 0.001
252 parameters	Δρmax = 0.53 e Å^−3
0 restraints	Δρmin = −0.26 e Å^−3

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
B1A	0.7560 (2)	0.2500	0.10927 (19)	0.0147 (3)
O2A	0.84020 (9)	0.19131 (4)	0.10383 (10)	0.01859 (17)
C4A	0.58490 (18)	0.2500	0.14853 (18)	0.0135 (3)
C5A	0.40914 (18)	0.2500	0.02271 (17)	0.0135 (3)
C6A	0.26290 (19)	0.2500	0.06308 (18)	0.0155 (3)
C7A	0.28900 (19)	0.2500	0.23082 (18)	0.0164 (3)
C8A	0.46185 (19)	0.2500	0.35780 (18)	0.0154 (3)
C9A	0.60694 (19)	0.2500	0.31652 (18)	0.0153 (3)
C10A	0.38300 (18)	0.2500	−0.15829 (18)	0.0151 (3)
O11A	0.50296 (14)	0.2500	−0.20031 (13)	0.0217 (2)
O12A	0.21027 (13)	0.2500	−0.26413 (13)	0.0189 (2)
C13A	0.1733 (2)	0.2500	−0.44150 (18)	0.0205 (3)
H2A	0.778 (2)	0.1552 (9)	0.106 (2)	0.040 (4)*
H6A	0.146 (2)	0.2500	−0.024 (2)	0.018 (4)*
H7A	0.186 (3)	0.2500	0.257 (2)	0.020 (4)*
H8A	0.485 (2)	0.2500	0.472 (2)	0.017 (4)*
H9A	0.727 (3)	0.2500	0.410 (2)	0.019 (4)*
H13B	0.2218 (17)	0.2909 (7)	−0.4699 (16)	0.022 (3)*
H13A	0.043 (3)	0.2500	−0.502 (2)	0.022 (5)*
B1B	0.64335 (15)	0.03990 (6)	0.23390 (14)	0.0160 (2)
O2B	0.63920 (11)	0.07786 (4)	0.10208 (10)	0.02110 (18)
O3B	0.59072 (10)	−0.02644 (4)	0.20533 (9)	0.01729 (17)
C4B	0.72656 (13)	0.07235 (5)	0.41676 (12)	0.0148 (2)
C5B	0.62241 (13)	0.09238 (5)	0.50140 (12)	0.0144 (2)
C6B	0.69903 (14)	0.12175 (5)	0.66217 (13)	0.0168 (2)
C7B	0.88173 (14)	0.13109 (5)	0.74235 (13)	0.0195 (2)
C8B	0.98774 (14)	0.11072 (6)	0.66255 (14)	0.0205 (2)
C9B	0.91089 (14)	0.08231 (5)	0.50166 (14)	0.0183 (2)
C10B	0.42559 (13)	0.08558 (5)	0.42013 (13)	0.0151 (2)
O11B	0.32945 (10)	0.08921 (4)	0.49407 (9)	0.01926 (17)
O12B	0.36270 (9)	0.07474 (4)	0.25489 (9)	0.01917 (17)
C13B	0.17208 (15)	0.06358 (7)	0.16598 (15)	0.0253 (2)
H2B	0.574 (2)	0.0605 (9)	0.002 (2)	0.045 (5)*
H3B	0.609 (2)	−0.0490 (10)	0.295 (2)	0.051 (5)*
H6B	0.6238 (16)	0.1378 (6)	0.7136 (16)	0.017 (3)*
H7B	0.9340 (18)	0.1523 (7)	0.8526 (18)	0.025 (3)*
H8B	1.1197 (19)	0.1161 (7)	0.7198 (18)	0.028 (4)*
H9B	0.9892 (19)	0.0696 (7)	0.4494 (18)	0.027 (3)*
H13D	0.152 (2)	0.0539 (8)	0.050 (2)	0.032 (4)*
H13E	0.1379 (19)	0.0251 (8)	0.2171 (18)	0.029 (4)*
H13F	0.1087 (19)	0.1045 (8)	0.1705 (19)	0.030 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
B1A	0.0128 (7)	0.0176 (7)	0.0133 (7)	0.000	0.0053 (6)	0.000
O2A	0.0168 (4)	0.0159 (4)	0.0263 (4)	0.0009 (3)	0.0123 (3)	0.0005 (3)
C4A	0.0141 (6)	0.0107 (6)	0.0167 (6)	0.000	0.0076 (5)	0.000
C5A	0.0147 (6)	0.0115 (6)	0.0152 (7)	0.000	0.0073 (5)	0.000
C6A	0.0129 (6)	0.0171 (7)	0.0160 (7)	0.000	0.0056 (5)	0.000
C7A	0.0155 (7)	0.0171 (7)	0.0193 (7)	0.000	0.0100 (6)	0.000
C8A	0.0190 (7)	0.0151 (6)	0.0135 (6)	0.000	0.0081 (5)	0.000
C9A	0.0144 (6)	0.0155 (7)	0.0152 (6)	0.000	0.0056 (5)	0.000
C10A	0.0113 (6)	0.0100 (6)	0.0211 (7)	0.000	0.0041 (5)	0.000
O11A	0.0197 (5)	0.0297 (6)	0.0180 (5)	0.000	0.0103 (4)	0.000
O12A	0.0152 (5)	0.0292 (6)	0.0125 (5)	0.000	0.0059 (4)	0.000
C13A	0.0192 (7)	0.0301 (8)	0.0125 (7)	0.000	0.0071 (6)	0.000
B1B	0.0158 (5)	0.0175 (6)	0.0161 (5)	−0.0005 (4)	0.0081 (4)	−0.0016 (4)
O2B	0.0294 (4)	0.0190 (4)	0.0156 (4)	−0.0077 (3)	0.0102 (3)	−0.0021 (3)
O3B	0.0227 (4)	0.0154 (4)	0.0142 (3)	−0.0021 (3)	0.0082 (3)	−0.0007 (3)
C4B	0.0173 (5)	0.0121 (4)	0.0152 (4)	−0.0007 (3)	0.0071 (4)	0.0004 (3)
C5B	0.0155 (5)	0.0124 (4)	0.0146 (5)	0.0003 (3)	0.0057 (4)	0.0017 (3)
C6B	0.0209 (5)	0.0149 (5)	0.0151 (5)	0.0012 (4)	0.0080 (4)	0.0001 (4)
C7B	0.0219 (5)	0.0179 (5)	0.0149 (5)	−0.0019 (4)	0.0041 (4)	−0.0019 (4)
C8B	0.0158 (5)	0.0197 (5)	0.0224 (5)	−0.0027 (4)	0.0045 (4)	−0.0011 (4)
C9B	0.0178 (5)	0.0175 (5)	0.0215 (5)	−0.0005 (4)	0.0100 (4)	−0.0011 (4)
C10B	0.0180 (5)	0.0115 (4)	0.0151 (5)	0.0015 (4)	0.0065 (4)	0.0015 (3)
O11B	0.0182 (4)	0.0214 (4)	0.0198 (4)	0.0018 (3)	0.0097 (3)	0.0031 (3)
O12B	0.0149 (4)	0.0253 (4)	0.0145 (3)	0.0011 (3)	0.0035 (3)	−0.0017 (3)
C13B	0.0160 (5)	0.0303 (6)	0.0217 (6)	0.0000 (4)	0.0003 (4)	−0.0020 (5)

Geometric parameters (Å, º)

B1A—O2A^i	1.3616 (11)	B1B—O3B	1.3677 (14)
B1A—O2A	1.3616 (11)	B1B—C4B	1.5823 (15)
B1A—C4A	1.592 (2)	O2B—H2B	0.880 (19)
O2A—H2A	0.883 (17)	O3B—H3B	0.858 (19)
C4A—C9A	1.3997 (19)	C4B—C9B	1.3998 (14)
C4A—C5A	1.4042 (19)	C4B—C5B	1.4083 (14)
C5A—C6A	1.3963 (19)	C5B—C6B	1.3984 (14)
C5A—C10A	1.502 (2)	C5B—C10B	1.4825 (14)
C6A—C7A	1.387 (2)	C6B—C7B	1.3840 (15)
C6A—H6A	0.945 (18)	C6B—H6B	0.962 (12)
C7A—C8A	1.392 (2)	C7B—C8B	1.3906 (16)
C7A—H7A	0.973 (19)	C7B—H7B	0.968 (14)
C8A—C9A	1.392 (2)	C8B—C9B	1.3915 (15)
C8A—H8A	0.931 (19)	C8B—H8B	0.996 (14)
C9A—H9A	0.983 (19)	C9B—H9B	0.970 (14)
C10A—O11A	1.1951 (17)	C10B—O11B	1.2204 (12)
C10A—O12A	1.3344 (17)	C10B—O12B	1.3280 (12)
O12A—C13A	1.4462 (17)	O12B—C13B	1.4507 (13)
C13A—H13B	0.978 (13)	C13B—H13D	0.969 (15)
C13A—H13A	0.976 (19)	C13B—H13E	0.981 (15)
B1B—O2B	1.3610 (13)	C13B—H13F	0.972 (16)
O2A^i—B1A—O2A	116.34 (12)	O3B—B1B—C4B	122.67 (9)
O2A^i—B1A—C4A	121.50 (6)	B1B—O2B—H2B	114.3 (11)
O2A—B1A—C4A	121.50 (6)	B1B—O3B—H3B	114.1 (13)
B1A—O2A—H2A	112.0 (10)	C9B—C4B—C5B	117.04 (9)
C9A—C4A—C5A	116.93 (12)	C9B—C4B—B1B	120.21 (9)
C9A—C4A—B1A	119.48 (12)	C5B—C4B—B1B	122.76 (9)
C5A—C4A—B1A	123.59 (12)	C6B—C5B—C4B	121.63 (9)
C6A—C5A—C4A	121.62 (13)	C6B—C5B—C10B	117.27 (9)
C6A—C5A—C10A	120.73 (12)	C4B—C5B—C10B	121.05 (9)
C4A—C5A—C10A	117.65 (12)	C7B—C6B—C5B	119.85 (10)
C7A—C6A—C5A	120.12 (13)	C7B—C6B—H6B	120.3 (7)
C7A—C6A—H6A	119.8 (11)	C5B—C6B—H6B	119.8 (7)
C5A—C6A—H6A	120.1 (11)	C6B—C7B—C8B	119.60 (10)
C6A—C7A—C8A	119.36 (13)	C6B—C7B—H7B	119.6 (8)
C6A—C7A—H7A	119.0 (11)	C8B—C7B—H7B	120.8 (8)
C8A—C7A—H7A	121.6 (11)	C7B—C8B—C9B	120.41 (10)
C7A—C8A—C9A	120.18 (13)	C7B—C8B—H8B	120.5 (8)
C7A—C8A—H8A	121.9 (11)	C9B—C8B—H8B	119.1 (8)
C9A—C8A—H8A	118.0 (11)	C8B—C9B—C4B	121.46 (10)
C8A—C9A—C4A	121.80 (13)	C8B—C9B—H9B	117.9 (9)
C8A—C9A—H9A	117.5 (11)	C4B—C9B—H9B	120.6 (9)
C4A—C9A—H9A	120.7 (11)	O11B—C10B—O12B	122.72 (9)
O11A—C10A—O12A	124.97 (14)	O11B—C10B—C5B	124.87 (9)
O11A—C10A—C5A	123.66 (13)	O12B—C10B—C5B	112.42 (8)
O12A—C10A—C5A	111.37 (12)	C10B—O12B—C13B	116.35 (8)
C10A—O12A—C13A	114.93 (11)	O12B—C13B—H13D	104.9 (9)
O12A—C13A—H13B	110.3 (8)	O12B—C13B—H13E	109.3 (8)
O12A—C13A—H13A	105.2 (11)	H13D—C13B—H13E	111.4 (13)
H13B—C13A—H13A	109.9 (9)	O12B—C13B—H13F	109.6 (9)
O2B—B1B—O3B	118.63 (9)	H13D—C13B—H13F	110.3 (13)
O2B—B1B—C4B	118.41 (9)	H13E—C13B—H13F	111.1 (12)
O2A^i—B1A—C4A—C9A	−85.18 (12)	O2B—B1B—C4B—C9B	−71.88 (13)
O2A—B1A—C4A—C9A	85.18 (12)	O3B—B1B—C4B—C9B	101.97 (12)
O2A^i—B1A—C4A—C5A	94.82 (12)	O2B—B1B—C4B—C5B	108.12 (11)
O2A—B1A—C4A—C5A	−94.82 (12)	O3B—B1B—C4B—C5B	−78.04 (13)
C9A—C4A—C5A—C6A	0.0	C9B—C4B—C5B—C6B	0.83 (14)
B1A—C4A—C5A—C6A	180.0	B1B—C4B—C5B—C6B	−179.17 (9)
C9A—C4A—C5A—C10A	180.0	C9B—C4B—C5B—C10B	178.36 (9)
B1A—C4A—C5A—C10A	0.0	B1B—C4B—C5B—C10B	−1.63 (15)
C4A—C5A—C6A—C7A	0.0	C4B—C5B—C6B—C7B	−0.63 (15)
C10A—C5A—C6A—C7A	180.0	C10B—C5B—C6B—C7B	−178.26 (9)
C5A—C6A—C7A—C8A	0.0	C5B—C6B—C7B—C8B	−0.43 (16)
C6A—C7A—C8A—C9A	0.0	C6B—C7B—C8B—C9B	1.27 (16)
C7A—C8A—C9A—C4A	0.0	C7B—C8B—C9B—C4B	−1.07 (16)
C5A—C4A—C9A—C8A	0.0	C5B—C4B—C9B—C8B	0.02 (15)
B1A—C4A—C9A—C8A	180.0	B1B—C4B—C9B—C8B	−179.98 (10)
C6A—C5A—C10A—O11A	180.0	C6B—C5B—C10B—O11B	−17.14 (15)
C4A—C5A—C10A—O11A	0.0	C4B—C5B—C10B—O11B	165.22 (10)
C6A—C5A—C10A—O12A	0.0	C6B—C5B—C10B—O12B	163.00 (9)
C4A—C5A—C10A—O12A	180.0	C4B—C5B—C10B—O12B	−14.64 (13)
O11A—C10A—O12A—C13A	0.0	O11B—C10B—O12B—C13B	−3.24 (14)
C5A—C10A—O12A—C13A	180.0	C5B—C10B—O12B—C13B	176.62 (9)

Symmetry code: (i) x, −y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2A—H2A···O2B	0.883 (17)	1.901 (17)	2.7835 (11)	177.8 (16)
O2B—H2B···O3B^ii	0.880 (19)	1.870 (19)	2.7451 (11)	172.8 (16)
O3B—H3B···O11B^iii	0.858 (19)	1.87 (2)	2.7187 (11)	172.6 (18)

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