Pseudopolymorphism in hy­droxy­benzo­phenones: the dihydrate of 2,2',4,4'-tetra­hydroxy­benzophenone

A dihydrate pseudopolymorph of bis­(2,4-dihy­droxy­phenyl)methanone, C₁₃H₁₀O₅·2H₂O, (I), was obtained during polymorphism screening of hy­droxy­benzophenone derivatives. This structure, in which the mol­ecule sits on a twofold axis, was compared with the known anhydrous form of (I) [Schlemper (1982). Acta Cryst. B38, 554-559]. The role of water in the crystal assembly was established on the basis of the known monohydrate pseudopolymorph of 3,4-dihy­droxy­benzo­phen­one [Landre, Souza, Corrêa, Martins & Doriguetto (2010). Acta Cryst. C66, o463-o465].

S1. Comment

To increase our knowledge of polymorphism in molecular compounds and pharmaceuticals (Legendre et al., 2012; Bonfilio et al., 2012; Martins, Bocelli et al., 2009; Martins, Paparidis et al., 2009; Martins, Doriguetto & Ellena, 2010; Martins, Legendre et al., 2010; Martins, Dos Santos et al., 2011; Martins, Lima et al., 2011; Landre et al., 2010; Corrêa et al. 2006; Doriguetto et al. 2004), we have studied 2,2',4,4'-tetrahydroxybenzophenone. Hydroxybenzophenones are found in sun-screening compounds in a variety of plastics and synthetic fabrics, due to their absorption bands in the near-UV (Furukawa et al., 1995; Ito et al., 1994; Onishi et al., 1987). They have also presented anti-inflammatory and antioxidant activity (Doriguetto et al., 2007). Structural relationships and the role of water in crystal assembly have been established on the basis of the anhydrous (Cox et al., 2008) and monohydrate (Landre et al., 2010) forms of 3,4-dihydroxybenzophenone. In the present study, a monoclinic dihydrate pseudopolymorph of 2,2',4,4'-tetrahydroxybenzophenone in space group C2/c, (I), is reported and compared with its known anhydrous form [space group P1, cell parameters a = 9.950 (2) Å, b = 12.479 (2) Å, c = 9.334 (1) Å, α = 98.80 (1)°, β = 93.22 (1)° γ = 72.45 (1)°, V = 1091.9 ų; Schlemper (1982)].

In the chosen asymmetric unit, the molecule (Fig. 1) sits on a twofold axis at (1/2, y, 1/4), with the carbonyl group C7═O1 residing on the symmetry element. The two solvent water molecules per molecule of (I) are related by symmetry.

The extended least-squares plane through the aromatic ring (r.m.s = 0.0216 Å; ring A in Fig. 1) also nearly incorporates the exocyclic atoms O1, O2, O3 and C7, which deviate from the plane by -0.055 (2), 0.328 (2), 0.115 (2) and 0.042 (2) Å, respectively. The least-squares planes through rings A and B form an angle of 35.36 (7)°. This value is smaller than those observed in 2,2',4-trihydroxybenzophenone [44.74 (6)°; Doriguetto et al., 2007] and 3,4-dihydroxybenzophenone [56.3 (4)°; Landre et al., 2010]. This angle represents a compromise between steric hindrance involving the 6- and 6'-positions, which mitigates for a larger angle, and the combination of the intramolecular hydrogen bonding to the carbonyl group and the presence of the OH group at the 4-position, which mitigate toward smaller dihedral angles. Comparing these three different benzophenones, it is possible to conclude that the angle between the rings is smaller in (I) than in 2,2',4-trihydroxybenzophenone, due to its extra OH at the 4'-position. The largest dihedral angle observed, that in 3,4-dihydroxybenzophenone, is due to the absence of an acceptor-bifurcated intramolecular hydrogen bond and of conjugation effects involving hydroxy groups para to the carbonyl fragment. However, when the angle between the rings in (I) is compared with that in its anhydrous form (Schlemper, 1982), it is possible to conclude, as expected, that the molecular shape does not necessarily manifest itself in a predictable manner in the crystal structure in terms of only intramolecular forces. The two benzophenone molecules present in the asymmetric unit of the anhydrous form of (I) have angles between rings A and B of 41.7 and 43.5°, which are similar to the value observed in 2,2',4-trihydroxybenzophenone (Doriguetto et al., 2007). Therefore, the deviation from planarity of the two-ring system in hydroxybenzophenones is the result of a delicate balance between a range of intra- and intermolecular forces. From the present study and that reported by Landre et al. (2010), the solvent water molecule appears to play an important role in both the packing and the molecular shape of the hydroxybenzophenone.

Another important conformational difference between the anhydrous and hydrated forms of (I) is the para-hydroxy H-atom orientations. In (I) (Fig. 1), both para-hydroxy O—H bonds are oriented anti to the C7—O1 group. In the anhydrous form, one of the two molecules present in the asymmetric unit has both O—H bonds at the 4- and 4'-positions syn to the bond analogous to C7—O1. The second molecule in the anhydrous form has one para-position O—H bond syn to C7—O1 and the other anti to it. Thus, the orientation of the hydroxy H atoms in hydroxybenzophenone is a result of crystal packing forces or intermolecular bonding motifs, with the water in the structure once again playing an important role in this intramolecular feature.

The intramolecular geometry of (I) was also analysed using Mogul (Bruno et al., 2004), a knowledge base of molecular geometry derived from the Cambridge Structural Database (CSD; Allen, 2002). This analysis revealed that the C1—C7 single bond is shorter than the average value [mean = 1.49 (2) Å and C1—C7 = 1.4644 (16) Å], while the C7═O1 double bond is longer than expected [mean = 1.23 (2) and C7═O1 = 1.260 (2) Å]. This geometric feature is due to a resonance phenomenon caused by conjugation between C7═O1 and rings A and B. The small O1—C7—C1—C2 torsion angle [-18.33 (14)°] corroborates this conjugation. Therefore, resonance-assisted hydrogen bonds (RAHBs) (Gilli et al., 1989) occur around the carbonyl and both ortho-hydroxy groups. The intramolecular hydrogen-bond geometry (Table 1) agrees well with that found by Schlemper (~2.6 Å) for the anhydrous form.

The packing of (I) is governed by an infinite planar two-dimensional network in the (201) plane, stabilized by intermolecular hydrogen bonds (Fig. 2). There are no direct hydrogen bonds between molecules of (I); all three intermolecular hydrogen bonds involve water (O4 in Fig. 2, Table 1). These interactions bridge the para-OH group of one molecule (O3, Fig. 2) and the ortho-OH group (O2ⁱⁱ) of the molecule related by a translation of [010] (symmetry code defined in the caption of Fig. 2). The aggregation in (201) includes R₆⁵(22) and R₄⁴(12) assemblies (Fig. 2) [see Bernstein et al. (1995) for nomenclature of hydrogen-bond motifs]. The two-dimensional networks parallel to (201) are themselves connected along the [001] direction via π–π interactions (Fig. 3), completing the three-dimensional network. The centroids of the aromatic rings are 3.703 (1) Å apart, with a substantial slippage of 1.374 Å, which indicates that these π–π interactions are weak.

Related literature

For related literature, see: Allen (2002); Bernstein et al. (1995); Bonfilio et al. (2012); Bruno et al. (2004); Corrêa et al. (2006); Cox et al. (2008); Doriguetto et al. (2004, 2007); Furukawa et al. (1995); Gilli et al. (1989); Ito et al. (1994); Landre et al. (2010); Legendre et al. (2012); Martins, Bocelli, Bonfilio, Araújo, Lima, Neves, Veloso, Doriguetto & Ellena (2009); Martins, Doriguetto & Ellena (2010); Martins, Dos Santos, Coelho, Barbosa, Dias, Fracca, Neves, Stringheta & Doriguetto (2011); Martins, Legendre, Honorato, Ayala, Doriguetto & Ellena (2010); Martins, Lima, Azarias, Abreu, Neves, Legendre, Andrade, Oliveira, Ellena & Doriguetto (2011); Martins, Paparidis, Doriguetto & Ellena (2009); Onishi et al. (1987); Schlemper (1982).

S2. Experimental

Colourless prismatic crystals of (I) were obtained from a water–methanol solution (1:1 v/v) by slow evaporation at room temperature.

S3. Refinement

Phenyl H atoms were observed in a difference Fourier synthesis but were refined using a riding model, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C). Hydroxy H atoms were located by difference Fourier synthesis and refined with free coordinates and with U_iso(H) = 1.5U_eq(O).Water H atoms were placed in positions located in a difference Fourier map, and then the water molecule was refined as a rigid group with U_iso(H) = 1.5U_eq(O4). Two reflections (110 and 111) were omitted from the refinement because their intensities appeared to be significantly reduced behind the shadow of the beam-stop.

Computing details

Data collection: COLLECT (Nonius, 1999); cell refinement: HKL SCALEPACK (Otwinowski & Minor 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); 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 publication routines (Farrugia, 1999).

Figures

	Fig. 1. The molecular structure of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Dashed lines indicate hydrogen bonds. [Symmetry code: (i) -x + 1, y, -z + 1/2.]
	Fig. 2. The packing of (I), projected onto (201). Hydrogen bonds are shown as dashed lines. [Symmetry codes: (i) -x + 1, y, -z + 1/2; (ii) x, y - 1, z; (iii) -x + 1/2, y - 1/2, -z - 1/2; (iv) -x + 1/2, y + 1/2, -z - 1/2; (v) x, y + 1, z; (vi) -x + 1, y + 1, -z + 1/2; (vii) x + 1/2, y + 1/2, z + 1.]
	Fig. 3. The aromatic rings of (I), linked along the [001] direction via π–π interactions. H atoms have been omitted for clarity. Centroid-to-centroid (Cg···Cg) separations are shown as dashed lines. [Symmetry codes: (i) -x + 1, y, -z + 1/2; (viii) -x + 1, -y + 1, -z; (ix) x, -y + 1, z + 1/2.]

bis(2,4-dihydroxyphenyl)methanone dihydrate

Crystal data

C13H10O5·2H2O	F(000) = 592
Mr = 282.24	Dx = 1.466 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 7662 reflections
a = 15.1394 (4) Å	θ = 2.9–26.0°
b = 7.7629 (3) Å	µ = 0.12 mm^−1
c = 11.0690 (4) Å	T = 295 K
β = 100.628 (2)°	Prism, colourless
V = 1278.57 (8) Å^3	0.05 × 0.05 × 0.05 mm
Z = 4

Data collection

Nonius KappaCCD area-detector diffractometer	981 reflections with I > 2σ(I)
Radiation source: Enraf Nonius FR590	Rint = 0.051
Graphite monochromator	θmax = 26.0°, θmin = 3.4°
Detector resolution: 9 pixels mm^-1	h = −18→18
CCD rotation images, thick slices scans	k = −9→9
7103 measured reflections	l = −12→13
1240 independent 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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.126	H atoms treated by a mixture of independent and constrained refinement
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0728P)^2 + 0.4275P] where P = (Fo^2 + 2Fc^2)/3
1240 reflections	(Δ/σ)max < 0.001
101 parameters	Δρmax = 0.14 e Å^−3
0 restraints	Δρmin = −0.15 e Å^−3

Special details

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 > 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
C1	0.44815 (8)	0.48865 (19)	0.14427 (12)	0.0359 (4)
C2	0.37980 (9)	0.57568 (18)	0.06271 (13)	0.0373 (4)
C3	0.32772 (9)	0.49145 (19)	−0.03477 (12)	0.0401 (4)
H3	0.281	0.5494	−0.0847	0.048*
C4	0.34478 (9)	0.32128 (19)	−0.05843 (12)	0.0377 (4)
C5	0.41609 (10)	0.23521 (19)	0.01498 (13)	0.0407 (4)
H5	0.4296	0.1222	−0.0029	0.049*
C6	0.46581 (9)	0.31833 (19)	0.11319 (13)	0.0396 (4)
H6	0.5132	0.2599	0.1614	0.048*
C7	0.5	0.5795 (3)	0.25	0.0375 (5)
O1	0.5	0.74181 (18)	0.25	0.0469 (4)
O2	0.36230 (8)	0.74570 (14)	0.07727 (11)	0.0489 (4)
O3	0.29250 (8)	0.24425 (15)	−0.15537 (10)	0.0486 (3)
H2A	0.4087 (16)	0.785 (3)	0.139 (2)	0.073*
H3A	0.3047 (14)	0.133 (3)	−0.1561 (19)	0.073*
O4	0.33177 (8)	−0.08554 (14)	−0.16605 (11)	0.0553 (4)
H4A	0.3321	−0.127	−0.0971	0.083*
H4B	0.3007	−0.1431	−0.225	0.083*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0361 (7)	0.0369 (8)	0.0324 (7)	0.0013 (5)	0.0008 (6)	0.0006 (5)
C2	0.0405 (7)	0.0335 (8)	0.0369 (7)	0.0040 (5)	0.0044 (6)	0.0026 (5)
C3	0.0394 (7)	0.0392 (8)	0.0377 (8)	0.0051 (6)	−0.0038 (6)	0.0034 (6)
C4	0.0394 (7)	0.0387 (8)	0.0324 (7)	−0.0022 (6)	−0.0003 (5)	0.0016 (6)
C5	0.0453 (8)	0.0356 (8)	0.0383 (7)	0.0050 (6)	−0.0003 (6)	−0.0011 (6)
C6	0.0383 (7)	0.0402 (8)	0.0371 (7)	0.0063 (6)	−0.0016 (6)	0.0019 (6)
C7	0.0392 (10)	0.0363 (11)	0.0360 (10)	0	0.0043 (8)	0
O1	0.0568 (9)	0.0363 (8)	0.0423 (8)	0	−0.0048 (7)	0
O2	0.0573 (7)	0.0360 (6)	0.0465 (6)	0.0103 (5)	−0.0087 (5)	−0.0021 (4)
O3	0.0556 (7)	0.0398 (6)	0.0419 (6)	0.0007 (5)	−0.0138 (5)	−0.0021 (5)
O4	0.0650 (8)	0.0420 (7)	0.0507 (7)	−0.0015 (5)	−0.0105 (6)	−0.0027 (5)

Geometric parameters (Å, º)

C1—C6	1.404 (2)	C5—C6	1.365 (2)
C1—C2	1.4134 (19)	C5—H5	0.93
C1—C7	1.4644 (16)	C6—H6	0.93
C2—O2	1.3616 (17)	C7—O1	1.260 (2)
C2—C3	1.378 (2)	C7—C1^i	1.4644 (16)
C3—C4	1.380 (2)	O2—H2A	0.93 (3)
C3—H3	0.93	O3—H3A	0.88 (2)
C4—O3	1.3498 (17)	O4—H4A	0.8278
C4—C5	1.396 (2)	O4—H4B	0.8559
C6—C1—C2	116.34 (12)	C6—C5—C4	119.41 (14)
C6—C1—C7	123.43 (12)	C6—C5—H5	120.3
C2—C1—C7	120.11 (14)	C4—C5—H5	120.3
O2—C2—C3	117.18 (12)	C5—C6—C1	122.56 (12)
O2—C2—C1	121.55 (13)	C5—C6—H6	118.7
C3—C2—C1	121.26 (13)	C1—C6—H6	118.7
C2—C3—C4	120.17 (12)	O1—C7—C1^i	118.79 (9)
C2—C3—H3	119.9	O1—C7—C1	118.79 (9)
C4—C3—H3	119.9	C1^i—C7—C1	122.42 (18)
O3—C4—C3	118.16 (12)	C2—O2—H2A	105.4 (13)
O3—C4—C5	121.85 (14)	C4—O3—H3A	110.3 (14)
C3—C4—C5	119.96 (13)	H4A—O4—H4B	114.1
C6—C1—C2—O2	−174.01 (13)	C3—C4—C5—C6	3.0 (2)
C7—C1—C2—O2	2.2 (2)	C4—C5—C6—C1	0.1 (2)
C6—C1—C2—C3	6.3 (2)	C2—C1—C6—C5	−4.6 (2)
C7—C1—C2—C3	−177.48 (11)	C7—C1—C6—C5	179.28 (13)
O2—C2—C3—C4	176.80 (13)	C6—C1—C7—O1	157.60 (11)
C1—C2—C3—C4	−3.5 (2)	C2—C1—C7—O1	−18.33 (14)
C2—C3—C4—O3	−179.53 (13)	C6—C1—C7—C1^i	−22.40 (11)
C2—C3—C4—C5	−1.3 (2)	C2—C1—C7—C1^i	161.67 (14)
O3—C4—C5—C6	−178.86 (14)

Symmetry code: (i) −x+1, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2A···O1	0.94 (2)	1.71 (2)	2.556 (1)	150 (2)
O3—H3A···O4	0.88 (2)	1.75 (2)	2.636 (2)	176 (2)
O4—H4A···O2^ii	0.83	2.14	2.954 (2)	167
O4—H4B···O3^iii	0.86	1.95	2.797 (2)	167

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