Crystal structure of a second monoclinic polymorph of 3-meth­­oxy­benzoic acid with Z′ = 1

A new polymorphic form of the title compound, C₈H₈O₃, is described in the centrosymmetric monoclinic space group P2₁/c with Z′ = 1 as compared to the first polymorph, which crystallizes with two conformers (Z′ = 2) in the asymmetric unit in the same space group. In the crystal of the second polymorph, inversion dimers linked by O—H⋯O hydrogen bonds occur and these are linked into zigzag chains, propagating along the b-axis direction by C—H⋯O links. The crystal structure also features a weak π–π inter­action, with a centroid-to-centroid distance of 3.8018 (6) Å. The second polymorph of the title compound is less stable than the reported first polymorph, as indicated by its smaller calculated lattice energy.

1. Chemical context

Meth­oxy­benzoic acid, also called anisic acid, consists of three isomers with mol­ecular formula C₈H₈O₃: the crystal structures of 2- and 4-meth­oxy­benzoic acids with Z′ = 1 have been reported (Parvez, 1987; Etter et al., 1988; Bryan, 1967; Colapietro & Domenicano, 1978; Fausto et al., 1997; Hathwar et al., 2011) and polymorphism has not been observed for these two isomers in the Cambridge Structural Database (CSD) (Version 5.39, last update August 2018; Groom et al., 2016) to date. In this article, we report a second polymorphic form (Iβ) of 3-meth­oxy­benzoic acid with Z′ = 1 and compare its properties with those of the previously reported first polymorphic form (Iα). Polymorph Iα crystallizes in the monoclinic space group P2₁/n with a = 13.8034 (17) Å, b = 5.0275 (5) Å, c = 21.446 (3) Å and β = 99.320 (13)° (Raffo et al., 2014; refcode EFINEO). The asymmetric unit of Iα consists of two mol­ecules with different conformations (Z′ = 2), which are connected into a homodimer through strong O—H⋯O hydrogen bonds. As described below, these two conformers (A and B) differ in the orientation of the meth­oxy group and its relative position from the —OH group. DFT calculations suggest that the A conformer of Iα is more energetically stable than the B conformer (Pereira Silva et al., 2015).

2. Structural commentary

The asymmetric unit of Iβ (Fig. 1) consists of a unique 3-meth­oxy­benzoic acid mol­ecule (Z′ = 1). The mol­ecule is almost planar with a maximum deviation of 0.107 (1) Å at atom O1. The mol­ecules of Iβ adopt a similar conformation (overlay r.m.s.d. = 0.052 Å) as compared to the conformer A of Iα (Raffo et al., 2014). The carboxyl group (O1/O2/C7/H1O2) of Iβ is close to coplanar with the attached phenyl ring (C1–C6) as indicated by the dihedral angle of 5.6 (7)°. The C8—O3—C3—C2 torsion angle of Iβ is −176.63 (7)° as compared to −176.75 (11) and −1.4 (2)° for conformers A and B, respectively, of Iα.

Figure 1 The mol­ecular structure of Iβ with 50% probability displacement ellipsoids.

3. Supra­molecular features

In the crystal of Iβ, two inversion-related mol­ecules are joined into a homodimer with an R₂²(8) graph-set motif via strong pairwise O—H⋯O hydrogen bonds (Fig. 2, Table 1). The homodimers are linked by weak C—H⋯O hydrogen bonds between two meth­oxy groups into zigzag chains with R₂²(6) graph-set motifs, which propagate along the b-axis direction. The [010] chains are stacked along the a axis into corrugated sheets parallel to the ab plane via weak π–π inter­actions with a centroid-to-centroid distance of 3.8018 (6) Å (symmetry codes: x − 1, y, z and x + 1, y, z) and slippage of 1.676 Å.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H1O2⋯O1^i	1.008 (19)	1.626 (19)	2.6295 (9)	173.3 (17)
C8—H8A⋯O3^ii	0.98	2.56	3.4016 (11)	144
Symmetry codes: (i) -x, -y+2, -z+2; (ii) -x, -y+1, -z+2.

Figure 2 Partial crystal packing of Iβ. Dashed lines represent the hydrogen-bonds. Hydrogen atoms not involved in hydrogen bonding are omitted for clarity.

4. Hirshfeld surface analysis

The Hirshfeld surfaces mapped with normalized contact distance d_norm and the two-dimensional fingerprint plots for Iβ were generated using CrystalExplorer17.5 (Turner et al., 2017). The large and small red spots on the Hirshfeld surface mapped with d_norm (Fig. 3) correspond to the O2—H1O2⋯O1 and C8—H8A⋯O3 hydrogen bonds, respectively. The H⋯O distances are 1.09 and 0.16 Å shorter than the sum of van der Waals radii of H and O atoms (2.72 Å). The H⋯H contact is the most populated contact and contributes 42.3% of the total inter­molecular contacts, followed by H⋯O/O⋯H (32.9%), H⋯C/C⋯H (11.4%) and C⋯C (8.1%) contacts (Fig. 4). The tips of pseudo-mirrored sharp spikes at d_e + d_i ≃ 1.6 Å represent the shortest H⋯O/O⋯H contacts, corresponding to the O2—H1O2⋯O1 hydrogen-bond. The absence of significant C—H⋯π inter­action in the crystal structure of Iβ is indicated by the absence of characteristic `wings' in the fingerprint plot of H⋯C/C⋯H contacts. The C⋯C contacts include the weak π–π inter­action, which appears as a unique `triangle' focused at d_e ≃ d_i ≃ 1.8 Å. The π–π inter­action is illustrated as a unique pattern of red and blue `triangles' on the shape-index surface and a flat region on the curvedness surface of the phenyl ring (see supporting Figures S1 and S2).

Figure 3 The Hirshfeld surface mapped over dnorm of the central mol­ecule of Iβ hydrogen bonded to two neighbouring mol­ecules.

Figure 4 The two-dimensional fingerprint plots of Iβ for different inter­molecular contacts giving their percentages of contribution to the Hirshfeld surface. di and de are the distances from the Hirshfeld surface to the nearest atom inter­ior and exterior, respectively, to the surface.

5. Lattice energy calculation

The lattice energies of polymorphs Iα and Iβ were calculated using PIXEL software (Gavezzotti, 2003) at default settings. The calculated lattice energy of Iα (107.5 kJ mol⁻¹) is larger than that of Iβ (98.5 kJ mol⁻¹) and this comparison is in agreement with the report of Pereira Silva et al. (2015), in which Iα is more stable than Iβ under ambient conditions.

6. Database survey

For the structure of 2-meth­oxy­benzoic acid (refcodes FUFBOX and FUFBOX01, respectively), see: Parvez (1987) and Etter et al. (1988). For the structure of 4-meth­oxy­benzoic acid (refcodes ANISIC, ANISIC01, ANISIC02 and ANISIC04, respectively), see: Bryan (1967), Colapietro & Domenicano (1978), Fausto et al. (1997) and Hathwar et al. (2011). For the previous structure of 3-meth­oxy­benzoic acid (refcodes EFINEO and EFINEO01, respectively), see: Raffo et al. (2014) and Pereira Silva et al. (2015).

7. Synthesis and crystallization

Single crystals of Iβ were obtained from an unsuccessful attempt of co-crystallization between 3-meth­oxy­benzoic acid and hexa­methyl­ene­tetra­mine. Colourless plate-like crystals were obtained from slow evaporation of a methano­lic mixture of 3-meth­oxy­benzoic acid and hexa­methyl­ene­tetra­mine in equimolar ratio at room temperature.

8. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The O-bound H atom was located from the difference-Fourier map and refined freely [O2—H1O2 = 1.01 (2) Å]. The remaining H atoms were positioned geometrically [C—H = 0.95 and 0.98 Å] and refined using a riding model with U_iso(H) = 1.2 or 1.5U_eq(C). A rotating group model (AFIX 137) was applied to the methyl group.

Table 2
Experimental details

Crystal data
Chemical formula	C8H8O3
Mr	152.14
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	100
a, b, c (Å)	3.8018 (4), 15.6027 (16), 11.9755 (12)
β (°)	90.889 (2)
V (Å^3)	710.28 (13)
Z	4
Radiation type	Mo Kα
μ (mm^−1)	0.11
Crystal size (mm)	0.56 × 0.22 × 0.12
Data collection
Diffractometer	Bruker SMART APEXII DUO CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2009)
Tmin, Tmax	0.881, 0.987
No. of measured, independent and observed [I > 2σ(I)] reflections	9395, 2550, 2049
Rint	0.023
(sin θ/λ)max (Å^−1)	0.758
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.038, 0.113, 1.04
No. of reflections	2550
No. of parameters	105
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å^−3)	0.40, −0.27
Computer programs: APEX2 and SAINT (Bruker, 2009), SHELXS2013 and SHELXTL (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015), PLATON (Spek, 2009) and publCIF (Westrip, 2010).

Supporting information

Computing details

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS2013 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: PLATON (Spek, 2009) and publCIF (Westrip, 2010).

3-Methoxybenzoic acid

Crystal data

C8H8O3	F(000) = 320
Mr = 152.14	Dx = 1.423 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 3.8018 (4) Å	Cell parameters from 3889 reflections
b = 15.6027 (16) Å	θ = 2.6–32.4°
c = 11.9755 (12) Å	µ = 0.11 mm^−1
β = 90.889 (2)°	T = 100 K
V = 710.28 (13) Å^3	Plate, colourless
Z = 4	0.56 × 0.22 × 0.12 mm

Data collection

Bruker SMART APEXII DUO CCD diffractometer	2550 independent reflections
Radiation source: fine-focus sealed tube	2049 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
φ and ω scans	θmax = 32.6°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −5→5
Tmin = 0.881, Tmax = 0.987	k = −21→23
9395 measured reflections	l = −18→17

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: mixed
R[F^2 > 2σ(F^2)] = 0.038	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.113	w = 1/[σ^2(Fo^2) + (0.0616P)^2 + 0.1229P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max = 0.001
2550 reflections	Δρmax = 0.40 e Å^−3
105 parameters	Δρmin = −0.27 e Å^−3
0 restraints

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.

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

	x	y	z	Uiso*/Ueq
O1	0.20200 (18)	0.96657 (4)	0.88546 (5)	0.02247 (16)
O2	−0.04494 (18)	0.88699 (4)	1.01876 (5)	0.02142 (16)
H1O2	−0.091 (5)	0.9451 (12)	1.0523 (16)	0.068 (5)*
O3	0.17686 (17)	0.58676 (4)	0.92170 (5)	0.01959 (15)
C1	0.2204 (2)	0.81461 (6)	0.86862 (7)	0.01512 (16)
C2	0.1573 (2)	0.73618 (6)	0.91952 (7)	0.01515 (16)
H2A	0.0504	0.7341	0.9906	0.018*
C3	0.2516 (2)	0.66069 (5)	0.86565 (7)	0.01517 (16)
C4	0.4082 (2)	0.66360 (6)	0.76109 (7)	0.01698 (17)
H4A	0.4738	0.6121	0.7245	0.020*
C5	0.4674 (2)	0.74261 (6)	0.71099 (7)	0.01847 (18)
H5A	0.5727	0.7447	0.6396	0.022*
C6	0.3755 (2)	0.81821 (6)	0.76329 (7)	0.01759 (17)
H6A	0.4169	0.8718	0.7283	0.021*
C7	0.1244 (2)	0.89573 (6)	0.92491 (7)	0.01636 (17)
C8	0.2877 (2)	0.50822 (6)	0.87173 (7)	0.01985 (18)
H8A	0.2229	0.4601	0.9198	0.030*
H8B	0.5434	0.5091	0.8628	0.030*
H8C	0.1726	0.5017	0.7984	0.030*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0301 (3)	0.0151 (3)	0.0223 (3)	−0.0001 (2)	0.0063 (2)	0.0011 (2)
O2	0.0285 (3)	0.0176 (3)	0.0184 (3)	0.0009 (2)	0.0077 (2)	−0.0004 (2)
O3	0.0254 (3)	0.0134 (3)	0.0202 (3)	0.0012 (2)	0.0073 (2)	0.0000 (2)
C1	0.0147 (3)	0.0151 (4)	0.0156 (3)	0.0003 (3)	0.0006 (2)	−0.0005 (3)
C2	0.0151 (3)	0.0165 (4)	0.0139 (3)	0.0002 (3)	0.0018 (2)	−0.0004 (3)
C3	0.0146 (3)	0.0150 (4)	0.0159 (3)	0.0000 (3)	0.0013 (2)	0.0001 (3)
C4	0.0161 (3)	0.0190 (4)	0.0160 (3)	0.0008 (3)	0.0025 (3)	−0.0026 (3)
C5	0.0175 (4)	0.0231 (4)	0.0149 (4)	−0.0005 (3)	0.0035 (3)	−0.0001 (3)
C6	0.0182 (4)	0.0183 (4)	0.0164 (4)	−0.0009 (3)	0.0023 (3)	0.0021 (3)
C7	0.0164 (3)	0.0170 (4)	0.0157 (3)	0.0006 (3)	0.0008 (3)	0.0001 (3)
C8	0.0217 (4)	0.0141 (4)	0.0238 (4)	0.0017 (3)	0.0033 (3)	−0.0029 (3)

Geometric parameters (Å, º)

O1—C7	1.2394 (10)	C3—C4	1.3956 (12)
O2—C7	1.3110 (10)	C4—C5	1.3909 (12)
O2—H1O2	1.01 (2)	C4—H4A	0.9500
O3—C3	1.3666 (10)	C5—C6	1.3829 (12)
O3—C8	1.4301 (10)	C5—H5A	0.9500
C1—C2	1.3896 (12)	C6—H6A	0.9500
C1—C6	1.4019 (11)	C8—H8A	0.9800
C1—C7	1.4823 (12)	C8—H8B	0.9800
C2—C3	1.3925 (12)	C8—H8C	0.9800
C2—H2A	0.9500
C7—O2—H1O2	109.8 (11)	C6—C5—H5A	119.4
C3—O3—C8	116.94 (7)	C4—C5—H5A	119.4
C2—C1—C6	120.52 (8)	C5—C6—C1	119.09 (8)
C2—C1—C7	120.47 (7)	C5—C6—H6A	120.5
C6—C1—C7	119.01 (8)	C1—C6—H6A	120.5
C1—C2—C3	119.62 (7)	O1—C7—O2	122.85 (8)
C1—C2—H2A	120.2	O1—C7—C1	121.76 (7)
C3—C2—H2A	120.2	O2—C7—C1	115.39 (7)
O3—C3—C2	115.43 (7)	O3—C8—H8A	109.5
O3—C3—C4	124.26 (7)	O3—C8—H8B	109.5
C2—C3—C4	120.31 (8)	H8A—C8—H8B	109.5
C5—C4—C3	119.34 (8)	O3—C8—H8C	109.5
C5—C4—H4A	120.3	H8A—C8—H8C	109.5
C3—C4—H4A	120.3	H8B—C8—H8C	109.5
C6—C5—C4	121.13 (8)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1O2···O1^i	1.008 (19)	1.626 (19)	2.6295 (9)	173.3 (17)
C8—H8A···O3^ii	0.98	2.56	3.4016 (11)	144

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

 

Footnotes

‡Thomson Reuters ResearcherID: F-8816-2012.

§Thomson Reuters ResearcherID: A-5525-2009.