Space-group revision for 4-formylphenylboronic acid

The space group of the title compound, C₇H₇BO₃, previously reported to be P, is properly Cc. There is no disorder of the formyl group or in the H atoms of the B(OH)₂ group. Molecules lie on approximate twofold axes and are related by approximate centers, which relate all but the formyl O atom and boronic acid H atoms. The B-O distances are 1.363 (2) and 1.370 (2) Å.

S1. Comment

During the course of studying the structure and the mechanism of formation of colored products in resorcinarene solutions (Davis et al., 1999; Lewis et al., 2000), the model compound, (I), was investigated. Thermolysis of (I) led to the formation of the title compound, (II), and its structure was determined to ascertain its identity. \sch

The published crystal structure of (II) (Feulner et al., 1990) is in space group P1 with Z' = 1 at 293 K, and has some unsettling features. In their model, the CHO group has a twofold disorder which superimposes its C—H and C═O bonds. The boronic acid H-atom positions are not sensible for the expected hydrogen bonding, and form impossibly short intermolecular H···H contacts. Their model fits the data poorly (R = 0.097 and wR = 0.181), despite the fact that this compound forms high quality crystals. Furthermore, the triclinic cell can be transformed (011,011,100) to a C-centered cell with a monoclinic metric. Feulner et al. recognized this transformation, and attempted a structure solution in C2/c with Z' = 1/2. Their reported C-centered cell has dimensions a = 11.177 (5), b = 9.891 (4) and c = 7.339 (4) Å, and β = 118.37 (3)° (Note: transformation of their triclinic cell yields β = 119.11°, which more closely matches our value). Their model, deposited as the `monoclinic form' (refcode VEXFUZ01) in the Cambridge Structural Database (Allen & Kennard, 1993) has the molecule on a twofold axis, which requires a similar disorder in the formyl group. This model produced worse R values (R = 0.145 and wR = 0.151). Despite intensity statistics suggesting a centrosymmetric structure, Feulner et al. also attempted structure solution in space group Cc, but were unsuccessful for reasons which are unclear.

Our structure of (II), with Z' = 1 in space group Cc (Fig. 1), exhibits none of these troubling features. The formyl group is ordered, and the H atoms of the B(OH)₂ group are ordered and in sensible positions for intermolecular hydrogen bonds (Table 2). The packing (Fig. 2) exhibits a pseudocenter near (1/2,1/2,1/2) and a pseudo-twofold axis near (1/2,y,3/4), running along the long axis of the molecule. The two molecules near the center of the cell are related by the c glide, and are approximately related by the pseudocenter. Treating the center as exact rather than the glide leads to the P1 model, while treating both the center and the glide as exact leads to the C2/c model. The cause of the disordered formyl group and boronic acid H atoms in the P1 model can be seen in Fig. 2 by examination of the relative orientations of the two glide-related molecules about (1/2,1/2,1/2). The formyl O and boronic acid H atoms do not conform to the inversion, while the remainder of the molecule nearly does. The pseudosymmetry does not lead to exceptionally high correlations, with the largest being 0.63, between displacement parameters of atoms related by the approximate twofold axis.

We have ruled out the possibility that a phase change on cooling causes the difference between the Cc structure which we observe at 120 K and that reported by Feulner et al. at room temperature. Using the same crystal, we collected intensity data at 296 K and obtained the same Cc structure, with cell dimensions a = 11.1932 (4), b = 9.8820 (5) and c = 7.3373 (3) Å, β = 119.336 (3)° and R = 0.043. Using this data set, we were also able to reproduce the results of Feulner et al., refining their P1 model to R = 0.099.

The structure of the molecule itself is unremarkable. The formyl group is essentially coplanar with the phenyl ring, while the B(OH)₂ group is rotated by 20.6 (3)° out of the phenyl plane. One hydroxyl H atom is syn to the phenyl group, while the other is anti, as is typical for phenylboronic acids (Bradley et al., 1996; Gainsford et al., 1995; Pilkington et al., 1995; Shull et al., 2000; Soundararajan et al., 1993), including unsubstituted phenylboronic acid (Rettig & Trotter, 1977) and the ortho isomer of the title compound (Scouten et al., 1994).

Baur & Kassner (1992) and Marsh (1997) have warned of the perils of space group Cc. In the present structure, more perilous is the imposition of centrosymmetry on the basis of centric intensity statistics. From our data, a chemically correct structure, albeit unnecessarily low symmetry, may be easily obtained in space group P1 Not P1?. However, no chemically correct model can be obtained in any centrosymmetric space group.

Related literature

For related literature, see: Allen & Kennard (1993); Baur & Kassner (1992); Bradley et al. (1996); Davis et al. (1999); Feulner et al. (1990); Gainsford et al. (1995); Lewis et al. (2000); Marsh (1997); Pilkington et al. (1995); Rettig & Trotter (1977); Scouten et al. (1994); Shull et al. (2000); Soundararajan et al. (1993).

S2. Experimental

The preparation of the title compound has been previously described by Feulner, et al. (1990). In our preparation, compound (I) (300 mg, 0.448 mmol), 27 ml of dimethylsulfoxide (DMSO), and 3 ml of water were mixed and heated for 5 days at 493 K in a sealed tube. The reaction mixture was cooled, filtered, and DMSO/H₂O was removed in vacuo. The yellowish substance is washed with ethyl acetate (EtOAc) and upon drying afforded colorless crystals of the title compound (.210 g) in 72% yield. Diffraction-quality crystals of (II) were grown by evaporation of an EtOAc solution.

S3. Refinement

Systematic absences indicate space groups Cc or C2/c. Although intensity statistics suggest C2/c (|E²-1| = 0.992), the noncentrosymmetric Cc proved correct. The absolute structure could not be determined. The coordinates of hydroxyl H atoms were refined. Other H atoms were treated as riding in idealized positions, with C—H distances of 0.95 Å. Displacement parameters for H were assigned as U_iso = 1.2U_eq of the attached atom (1.5 for OH).

Computing details

Data collection: COLLECT (Nonius, 2000); cell refinement: DENZO and SCALEPAK; data reduction: DENZO and SCALEPAK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular view of (II) with the atom-numbering scheme and displacement ellipsoids at the 50% probability level. H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A stereoview of the unit cell of (II), illustrating the hydrogen bonding and pseudosymmetry. The a axis is horizontal and b is vertical.

4-formylphenylboronic acid

Crystal data

C7H7BO3	F(000) = 312
Mr = 149.94	Dx = 1.441 Mg m^−3
Monoclinic, Cc	Mo Kα radiation, λ = 0.71073 Å
a = 11.1238 (3) Å	Cell parameters from 1107 reflections
b = 9.8718 (3) Å	θ = 2.5–32.0°
c = 7.1988 (2) Å	µ = 0.11 mm^−1
β = 119.071 (2)°	T = 120 K
V = 690.92 (3) Å^3	Lath fragment, colorless
Z = 4	0.37 × 0.25 × 0.22 mm

Data collection

Nonius KappaCCD (with Oxford Cryostream) diffractometer	1110 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.021
Graphite monochromator	θmax = 32.0°, θmin = 2.5°
ω scans with κ offsets	h = −15→16
4518 measured reflections	k = −14→14
1192 independent reflections	l = −10→10

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)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.104	H atoms treated by a mixture of independent and constrained refinement
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0689P)^2 + 0.1001P] where P = (Fo^2 + 2Fc^2)/3
1192 reflections	(Δ/σ)max < 0.001
106 parameters	Δρmax = 0.44 e Å^−3
2 restraints	Δρmin = −0.22 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
O1	0.40379 (15)	0.06712 (11)	0.7216 (3)	0.0272 (3)
O2	0.37961 (12)	0.79497 (11)	0.6533 (2)	0.0201 (3)
H2O	0.390 (3)	0.882 (3)	0.664 (4)	0.030*
O3	0.61978 (12)	0.80567 (12)	0.8461 (2)	0.0211 (3)
H3O	0.694 (3)	0.765 (3)	0.919 (4)	0.032*
B1	0.5035 (2)	0.72881 (13)	0.7509 (4)	0.0157 (3)
C1	0.5029 (2)	0.56955 (10)	0.7475 (3)	0.0145 (2)
C2	0.61997 (15)	0.49629 (15)	0.7820 (3)	0.0166 (3)
H2	0.7007	0.5436	0.8061	0.020*
C3	0.61955 (16)	0.35504 (14)	0.7813 (3)	0.0170 (3)
H3	0.6993	0.3066	0.8039	0.020*
C4	0.5014 (2)	0.28490 (12)	0.7473 (4)	0.0163 (2)
C5	0.38315 (15)	0.35606 (15)	0.7117 (2)	0.0166 (3)
H5	0.3027	0.3085	0.6882	0.020*
C6	0.38449 (15)	0.49707 (15)	0.7111 (3)	0.0160 (3)
H6	0.3040	0.5453	0.6856	0.019*
C7	0.5022 (2)	0.13559 (13)	0.7469 (4)	0.0205 (3)
H7	0.5831	0.0904	0.7673	0.025*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0225 (6)	0.0138 (5)	0.0429 (7)	−0.0026 (4)	0.0140 (5)	−0.0017 (5)
O2	0.0149 (5)	0.0105 (5)	0.0293 (7)	0.0002 (4)	0.0062 (5)	0.0001 (4)
O3	0.0133 (5)	0.0141 (5)	0.0287 (7)	−0.0010 (4)	0.0044 (5)	0.0002 (4)
B1	0.0148 (5)	0.0125 (6)	0.0178 (5)	−0.0008 (7)	0.0064 (4)	−0.0001 (8)
C1	0.0141 (5)	0.0115 (5)	0.0160 (5)	0.0006 (6)	0.0059 (4)	0.0009 (7)
C2	0.0139 (7)	0.0149 (6)	0.0195 (7)	−0.0016 (5)	0.0071 (6)	−0.0005 (6)
C3	0.0142 (7)	0.0138 (6)	0.0212 (8)	0.0024 (5)	0.0073 (7)	−0.0004 (5)
C4	0.0168 (5)	0.0118 (5)	0.0193 (5)	−0.0004 (6)	0.0079 (4)	−0.0007 (7)
C5	0.0145 (7)	0.0144 (7)	0.0200 (9)	0.0000 (5)	0.0076 (7)	0.0009 (6)
C6	0.0140 (7)	0.0137 (6)	0.0188 (8)	−0.0005 (5)	0.0068 (6)	0.0000 (6)
C7	0.0193 (6)	0.0118 (5)	0.0276 (6)	0.0029 (7)	0.0092 (5)	−0.0007 (8)

Geometric parameters (Å, º)

O1—C7	1.222 (2)	C2—H2	0.9500
O2—B1	1.370 (2)	C3—C4	1.398 (3)
O2—H2O	0.87 (3)	C3—H3	0.9500
O3—B1	1.363 (2)	C4—C5	1.401 (2)
O3—H3O	0.83 (3)	C4—C7	1.4740 (17)
B1—C1	1.5724 (17)	C5—C6	1.392 (2)
C1—C2	1.403 (2)	C5—H5	0.9500
C1—C6	1.407 (2)	C6—H6	0.9500
C2—C3	1.394 (2)	C7—H7	0.9500
B1—O2—H2O	111.8 (17)	C4—C3—H3	120.1
B1—O3—H3O	117.3 (19)	C3—C4—C5	120.21 (11)
O3—B1—O2	117.70 (11)	C3—C4—C7	119.34 (18)
O3—B1—C1	124.09 (16)	C5—C4—C7	120.45 (18)
O2—B1—C1	118.21 (15)	C6—C5—C4	119.43 (15)
C2—C1—C6	118.39 (10)	C6—C5—H5	120.3
C2—C1—B1	121.06 (15)	C4—C5—H5	120.3
C6—C1—B1	120.55 (16)	C5—C6—C1	121.24 (15)
C3—C2—C1	120.91 (14)	C5—C6—H6	119.4
C3—C2—H2	119.5	C1—C6—H6	119.4
C1—C2—H2	119.5	O1—C7—C4	123.21 (19)
C2—C3—C4	119.82 (15)	O1—C7—H7	118.4
C2—C3—H3	120.1	C4—C7—H7	118.4
O3—B1—C1—C2	−20.6 (3)	C2—C3—C4—C7	180.00 (18)
O2—B1—C1—C2	159.8 (2)	C3—C4—C5—C6	−0.2 (4)
O3—B1—C1—C6	159.0 (2)	C7—C4—C5—C6	−179.48 (18)
O2—B1—C1—C6	−20.6 (3)	C4—C5—C6—C1	−0.6 (3)
C6—C1—C2—C3	−0.3 (3)	C2—C1—C6—C5	0.8 (3)
B1—C1—C2—C3	179.28 (17)	B1—C1—C6—C5	−178.76 (16)
C1—C2—C3—C4	−0.4 (3)	C3—C4—C7—O1	178.8 (2)
C2—C3—C4—C5	0.7 (4)	C5—C4—C7—O1	−1.8 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2O···O1^i	0.87 (3)	1.86 (3)	2.7209 (16)	171 (3)
O3—H3O···O2^ii	0.83 (3)	2.02 (3)	2.8321 (13)	165 (3)

Symmetry codes: (i) x, y+1, z; (ii) x+1/2, −y+3/2, z+1/2.