A new polymorph of 2,6-dimeth-oxy-benzoic acid.

A new crystalline form of 2,6-dimeth-oxy-benzoic acid, C(9)H(10)O(4), crystallizing in a tetra-gonal unit cell has been identified during screening for co-crystals. The asymmetric unit comprises a non-planar independent mol-ecule with a synplanar conformation of the carb-oxy group. The sterically bulky o-meth-oxy substituents force the carb-oxy group to be twisted away from the plane of the benzene ring by 65.72 (15)°. The carb-oxy group is disordered over two sites about the C-C bond [as indicated by the almost equal C-O distances of 1.254 (3) and 1.250 (3) Å], the occupancies of the disordered carboxym H atoms being 0.53 (5) and 0.47 (5). In the known ortho-rhom-bic form reported by Swaminathan et al. [Acta Cryst. (1976), B32, 1897-1900], due to the anti-planar conformation adopted by the OH group, the mol-ecular components are associated in the crystal in chains stabilized by linear O-H⋯O hydrogen bonds. However, in the new tetra-gonal polymorph, mol-ecules form dimeric units via pairs of O-H⋯O hydrogen bonds between the carb-oxy groups.

Related literature

For the ortho­rhom­bic polymorph of 2,6-dimeth­oxy­benzoic acid, see: Swaminathan et al. (1976 ▶); Bryan & White (1982 ▶); Portalone (2009 ▶). For mol­ecular packing modes of carb­oxy­lic acids, see: Leiserowitz (1976 ▶); Kanters et al. (1991 ▶); Moorthy et al. (2002 ▶). For analysis of benzene ring deformations induced by substitution, see: Schultz et al. (1993 ▶); Portalone et al. (1998 ▶); For computation of ring patterns formed by hydrogen bonds in crystal structures, see: Etter et al. (1990 ▶); Bernstein et al. (1995 ▶); Motherwell et al. (1999 ▶).

Experimental

Crystal data

C9H10O4

M = 182.17

Tetragonal,

a = 8.1423 (3) Å

c = 27.6814 (18) Å

V = 1835.20 (15) Å3

Z = 8

Mo Kα radiation

μ = 0.11 mm−1

T = 298 K

0.30 × 0.25 × 0.21 mm

Data collection

Oxford Diffraction Xcalibur S CCD diffractometer

Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006 ▶). T min = 0.878, T max = 0.999

11616 measured reflections

1653 independent reflections

1332 reflections with I > 2σ(I)

R int = 0.042

Refinement

R[F 2 > 2σ(F 2)] = 0.062

wR(F 2) = 0.147

S = 1.19

1653 reflections

133 parameters

H atoms treated by a mixture of independent and constrained refinement

Δρmax = 0.18 e Å−3

Δρmin = −0.17 e Å−3

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 ▶); cell refinement: CrysAlis RED (Oxford Diffraction, 2006 ▶); data reduction: CrysAlis RED; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536811049075/xu5390sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811049075/xu5390Isup2.hkl

Supplementary material file. DOI: 10.1107/S1600536811049075/xu5390Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

C9H10O4	Dx = 1.319 Mg m−3
Mr = 182.17	Mo Kα radiation, λ = 0.71069 Å
Tetragonal, P41212	Cell parameters from 4278 reflections
Hall symbol: P 4abw 2nw	θ = 2.9–32.3°
a = 8.1423 (3) Å	µ = 0.11 mm−1
c = 27.6814 (18) Å	T = 298 K
V = 1835.20 (15) Å3	Tablets, colourless
Z = 8	0.30 × 0.25 × 0.21 mm
F(000) = 768

Oxford Diffraction Xcalibur S CCD diffractometer	1653 independent reflections
Radiation source: Enhance (Mo) X-ray source	1332 reflections with I > 2σ(I)
graphite	Rint = 0.042
Detector resolution: 16.0696 pixels mm-1	θmax = 30.0°, θmin = 2.9°
ω and φ scans	h = −11→10
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006).	k = −8→11
Tmin = 0.878, Tmax = 0.999	l = −38→38
11616 measured reflections

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.062	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.147	w = 1/[σ2(Fo2) + (0.0659P)2 + 0.2634P] where P = (Fo2 + 2Fc2)/3
S = 1.19	(Δ/σ)max < 0.001
1653 reflections	Δρmax = 0.18 e Å−3
133 parameters	Δρmin = −0.17 e Å−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.017 (3)

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	0.7090 (3)	0.1661 (3)	0.71019 (8)	0.0558 (6)
H1	0.733 (5)	0.209 (5)	0.7340 (15)	0.023 (14)*	0.53 (5)
O2	0.5271 (3)	0.3665 (2)	0.70822 (7)	0.0508 (6)
H2	0.566 (7)	0.393 (7)	0.7333 (17)	0.031 (18)*	0.47 (5)
O3	0.7742 (3)	0.2435 (3)	0.60828 (6)	0.0652 (7)
O4	0.2838 (3)	0.1176 (3)	0.68526 (7)	0.0618 (6)
C1	0.5250 (3)	0.1775 (3)	0.64409 (7)	0.0362 (6)
C2	0.6221 (4)	0.1801 (3)	0.60276 (8)	0.0456 (7)
C3	0.5579 (5)	0.1225 (4)	0.55922 (9)	0.0644 (9)
H3	0.6230	0.1245	0.5299	0.077*
C4	0.3993 (6)	0.0628 (5)	0.55889 (11)	0.0749 (11)
H4	0.3547	0.0220	0.5287	0.090*
C5	0.3025 (5)	0.0583 (4)	0.59895 (12)	0.0653 (9)
H5	0.1917	0.0147	0.5972	0.078*
C6	0.3652 (4)	0.1176 (3)	0.64256 (9)	0.0447 (7)
C7	0.5920 (3)	0.2410 (3)	0.69057 (7)	0.0329 (5)
C8	0.8729 (5)	0.2678 (4)	0.56701 (12)	0.0722 (11)
H8A	0.889 (3)	0.164 (2)	0.5507 (7)	0.108*
H8B	0.978 (3)	0.312 (3)	0.5767 (3)	0.108*
H8C	0.819 (2)	0.344 (3)	0.5453 (7)	0.108*
C9	0.1147 (5)	0.0710 (6)	0.68556 (15)	0.0917 (14)
H9A	0.0518 (15)	0.147 (3)	0.6655 (11)	0.138*
H9B	0.0730 (16)	0.074 (4)	0.7186 (7)	0.138*
H9C	0.1036 (7)	−0.040 (3)	0.6728 (11)	0.138*

	U11	U22	U33	U12	U13	U23
O1	0.0679 (14)	0.0562 (13)	0.0432 (9)	0.0162 (11)	−0.0267 (10)	−0.0181 (9)
O2	0.0616 (13)	0.0497 (12)	0.0412 (9)	0.0118 (10)	−0.0217 (10)	−0.0159 (9)
O3	0.0665 (15)	0.0862 (17)	0.0428 (10)	−0.0139 (13)	0.0104 (10)	−0.0077 (11)
O4	0.0504 (13)	0.0836 (16)	0.0513 (10)	−0.0242 (12)	−0.0085 (10)	0.0041 (11)
C1	0.0506 (15)	0.0330 (12)	0.0251 (9)	−0.0008 (11)	−0.0133 (10)	−0.0031 (9)
C2	0.0618 (18)	0.0448 (15)	0.0302 (10)	0.0038 (14)	−0.0069 (12)	−0.0045 (11)
C3	0.094 (3)	0.069 (2)	0.0306 (12)	0.014 (2)	−0.0103 (15)	−0.0175 (14)
C4	0.095 (3)	0.083 (2)	0.0461 (16)	0.007 (2)	−0.0347 (18)	−0.0298 (17)
C5	0.068 (2)	0.064 (2)	0.0636 (17)	−0.0076 (16)	−0.0356 (17)	−0.0177 (17)
C6	0.0530 (17)	0.0412 (14)	0.0400 (12)	−0.0028 (13)	−0.0173 (12)	−0.0035 (11)
C7	0.0373 (13)	0.0370 (13)	0.0242 (8)	−0.0047 (10)	−0.0050 (9)	−0.0023 (9)
C8	0.095 (3)	0.057 (2)	0.0641 (18)	−0.0006 (19)	0.0319 (19)	−0.0022 (17)
C9	0.063 (3)	0.123 (4)	0.089 (3)	−0.034 (2)	−0.007 (2)	0.003 (3)

O1—C7	1.254 (3)	C3—C4	1.380 (6)
O1—H1	0.77 (4)	C3—H3	0.9700
O2—C7	1.250 (3)	C4—C5	1.361 (5)
O2—H2	0.79 (5)	C4—H4	0.9700
O3—C2	1.350 (4)	C5—C6	1.397 (4)
O3—C8	1.411 (4)	C5—H5	0.9700
O4—C6	1.355 (4)	C8—H8A	0.9684
O4—C9	1.428 (5)	C8—H8B	0.9684
C1—C2	1.391 (4)	C8—H8C	0.9684
C1—C6	1.391 (4)	C9—H9A	0.9766
C1—C7	1.490 (3)	C9—H9B	0.9766
C2—C3	1.395 (4)	C9—H9C	0.9766
C7—O1—H1	110 (3)	O4—C6—C1	115.5 (2)
C7—O2—H2	113 (4)	O4—C6—C5	125.1 (3)
C2—O3—C8	119.0 (2)	C1—C6—C5	119.3 (3)
C6—O4—C9	118.5 (3)	O2—C7—O1	123.3 (2)
C2—C1—C6	120.8 (2)	O2—C7—C1	117.8 (2)
C2—C1—C7	119.8 (2)	O1—C7—C1	118.9 (2)
C6—C1—C7	119.4 (2)	O3—C8—H8A	109.5
O3—C2—C1	115.7 (2)	O3—C8—H8B	109.5
O3—C2—C3	124.8 (3)	H8A—C8—H8B	109.5
C1—C2—C3	119.5 (3)	O3—C8—H8C	109.5
C4—C3—C2	118.4 (3)	H8A—C8—H8C	109.5
C4—C3—H3	120.8	H8B—C8—H8C	109.5
C2—C3—H3	120.8	O4—C9—H9A	109.5
C5—C4—C3	123.1 (3)	O4—C9—H9B	109.5
C5—C4—H4	118.5	H9A—C9—H9B	109.5
C3—C4—H4	118.5	O4—C9—H9C	109.5
C4—C5—C6	118.9 (3)	H9A—C9—H9C	109.5
C4—C5—H5	120.6	H9B—C9—H9C	109.5
C6—C5—H5	120.6
C8—O3—C2—C1	−172.8 (3)	C9—O4—C6—C5	−7.4 (5)
C8—O3—C2—C3	5.7 (5)	C2—C1—C6—O4	178.5 (3)
C6—C1—C2—O3	178.9 (2)	C7—C1—C6—O4	−2.0 (4)
C7—C1—C2—O3	−0.6 (4)	C2—C1—C6—C5	0.4 (4)
C6—C1—C2—C3	0.3 (4)	C7—C1—C6—C5	179.9 (3)
C7—C1—C2—C3	−179.2 (3)	C4—C5—C6—O4	−178.6 (3)
O3—C2—C3—C4	−179.2 (3)	C4—C5—C6—C1	−0.8 (5)
C1—C2—C3—C4	−0.8 (5)	C2—C1—C7—O2	114.4 (3)
C2—C3—C4—C5	0.4 (6)	C6—C1—C7—O2	−65.0 (3)
C3—C4—C5—C6	0.3 (6)	C2—C1—C7—O1	−66.0 (3)
C9—O4—C6—C1	174.7 (3)	C6—C1—C7—O1	114.5 (3)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O1i	0.77 (4)	1.87 (4)	2.632 (4)	168 (5)
O2—H2···O2i	0.79 (5)	1.83 (5)	2.618 (4)	173 (5)

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯O1i	0.77 (4)	1.87 (4)	2.632 (4)	168 (5)
O2—H2⋯O2i	0.79 (5)	1.83 (5)	2.618 (4)	173 (5)

Symmetry code: (i) .