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Volume 67 
Part 10 
Pages o387-o390  
October 2011  

Received 13 June 2011
Accepted 2 September 2011
Online 16 September 2011

Weak C-H...O hydrogen bonds in anisaldehyde, salicylaldehyde and cinnamaldehyde

aFaculty of Chemistry, University Duisburg-Essen, Universitätsstrasse 7, D-45117 Essen, Germany, and bSolid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India
Correspondence e-mail: roland.boese@uni-due.de

In situ cryocrystallization has been employed to grow single crystals of 4-methoxybenzaldehyde (anisaldehyde), C8H8O2, 2-hydroxybenzaldehyde (salicylaldehyde), C7H6O2, and (2E)-3-phenylprop-2-enal (cinnamaldehyde), C9H8O, all of which are liquids at room temperature. Several weak C-H...O interactions of the types Caryl-H...O, Cformyl-H...O and Csp3-H...O are present in these related crystal structures.

Comment

Experimental sophistication and developments in theoretical methodologies have improved the reliability of studies of weaker and lesser known intermolecular interactions (Desiraju & Steiner, 1999[Desiraju, G. R. & Steiner, T. (1999). The Weak Hydrogen Bond in Structural Chemistry and Biology. New York: Oxford University Press Inc.]). As a result, weakly bound complexes such as those involving C-H...O interactions are being extensively studied, and the nature and strength of these interactions are being assessed. The formyl C-H...O hydrogen bond in small-molecule aldehydes is one such example. Many simple aldehydes are liquids, so not many structural reports are available for these compounds. Even if solid, there are not many crystal structure determinations for aldehydes. [There are 37 simple aromatic aldehydes in the Cambridge Structural Database (CSD, Version 5.32, November 2010 update; Allen, 2002[Allen, F. H. (2002). Acta Cryst. B58, 380-388.]) with refcodes ANTHAL, AYOHAL, BARFOT, DEWLOH, DPEDAL, FATVUS, FAXXEI, FEDSAJ, FIXHIE, FIXHOK, FIYQOT, FOMZUD, FORBZA, HEQXOR, HODMAP, IHEMAJ, IHEMIR, IZALAW, JULZAR, KATKIA, KERKOI, LOSGOQ, MASBUD, NARZUC, OKUHEH, PHBALD10, RAJKOC, RAFJOC, SAZQIT, SOCHAT, SUNDUA, TEBBOR, WASLOS, XAMVUJ, XAMVEN, XAYCIJ and XIGWAM; four [alpha],[beta]-unsaturated aldehydes with refcodes JAZLAX, SIPKEH, WOBJOM and WOBJUS; and nine salicylaldehyde derivatives with refcodes KOYTOH, MAYWEO, NEJJOB, OVANIL, RAPLAW, XEVRUL, YIQYIH, YOMXOO and YOMXUU.] Therefore, we chose to investigate the nature and type of intermolecular interactions in the crystal structures of some very simple aldehydes.

[Scheme 1]

Anisaldehyde (4-methoxybenzaldehyde), (I)[link], salicylaldehyde (2-hydroxybenzaldehyde), (II)[link], and cinnamaldehyde [(2E)-3-phenylprop-2-enal], (III)[link], are liquids with melting points of 272, 266 and 265.5 K, respectively. These compounds are widely used in the chemical industry as intermediates in the preparation of perfumes, flavouring agents, dyes, pharmaceuticals and agrochemicals. The interesting feature of these compounds is that they do not possess any strong hydrogen-bonding functionalities. In salicylaldehyde, the OH group is bound intramolecularly to the aldehyde C=O group. The possible intermolecular interactions in these three compounds are of the types Caryl-H...O, Cformyl-H...O, Csp2-H...O, Csp3-H...O, C-H...[pi] and [pi]-[pi]. The formyl C-H...O interaction is known to be very weak, owing to the poor electropositive character of the formyl H atom (Breneman & Wiberg, 1990[Breneman, C. M. & Wiberg, K. B. (1990). J. Comput. Chem. 11, 361-373.]; Williams, 1988[Williams, D. E. (1988). J. Comput. Chem. 9, 745-763.]). Despite this, short Cformyl-H...O contacts are frequently observed in the crystal structures of aliphatic aldehydes (Thakur et al., 2011[Thakur, T. S., Kirchner, M. T., Bläser, D., Boese, R. & Desiraju, G. R. (2011). Phys. Chem. Chem. Phys. 13, 14076-14091.]). The stabilizing nature of these Cformyl-H...O contacts has also been confirmed by computations on formaldehyde clusters; these calculations show a gradual increase in the electropositive nature of the formyl H atom on going from an isolated gas-phase environment to the crystal. X-ray crystallographic studies of aromatic aldehydes by Moorthy and Venugopalan also established that formyl C-H...O interactions are relevant to crystal packing (Moorthy et al., 2003[Moorthy, J. N., Natarajan, R., Mal, P., Dixit, S. & Venugopalan, P. (2003). Cryst. Growth Des. 3, 581-585.], 2004[Moorthy, J. N., Natarajan, R., Mal, P. & Venugopalan, P. (2004). New J. Chem. 28, 1416-1419.], 2005[Moorthy, J. N., Natarajan, R. & Venugopalan, P. (2005). J. Mol. Struct. 741, 107-114.]; Lo Presti et al., 2006[Lo Presti, L., Soave, R. & Destro, R. (2006). J. Phys. Chem. B, 110, 6405-6414.]). However, in the case of aromatic aldehydes, the Cformyl-H...O interactions have to compete with Caryl-H...O interactions involving a relatively more acidic H atom. With our ongoing interest in the study of C-H...O hydrogen bonds in aldehydes, we report here the crystal structures of (I)[link], (II)[link] and (III)[link] (Fig. 1[link]). Crystals were obtained in each case by means of in situ cryocrystallization.

Compound (I)[link] crystallizes in the space group P212121 with Z' = 1. The formyl and methoxy groups lie slightly out of the plane of the benzene ring by 4.3 (4) and -2.9 (3)°, respectively (torsion angles O1-C7-C1-C6 and C3-C4-O2-C8). The Caryl-Cformyl bond [1.455 (3) Å] is slightly shorter than a normal C-C single-bond distance (Allen et al., 1987[Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1-19.]). This is possibly a result of extended conjugation between the aldehyde group and the aromatic ring. There are several weak C-H...O hydrogen bonds (Table 1[link]). Molecules are arranged in zigzag chains along the c axis and are held together by weak Csp3-H...O hydrogen bonds between atom H8A of the methoxy group and the carbonyl O atom of a neighbouring molecule. The chains are stacked along the a axis via weak Csp3-H...[pi] interactions (Fig. 2[link]a). Molecules in adjacent chains (along the b axis) are held together by weak Caryl-H...O interactions, viz. C3-H3...O2i and C5-H5...O1ii (Fig. 2[link]b; symmetry codes as in Table 1[link]). The formyl H atom is not engaged in a directed intermolecular interaction (Ribeiro-Claro et al., 2002[Ribeiro-Claro, P. J. A., Drewbm, M. G. B. & Félixa, V. (2002). Chem. Phys. Lett. 356, 318-324.]).

Compound (II)[link] crystallizes in the space group P21/c with Z' = 1. The hydroxy group is intramolecularly hydrogen bonded to the formyl O atom (O2-H2...O1), as expected. A shorter Caryl-Cformyl bond [1.449 (2) Å] and a slightly elongated C=O bond [1.230 (2) Å] are observed. Molecules in (II)[link] are linked by weak Caryl-H...O hydrogen bonds (Table 2[link]): C3-H3 and C6-H6 interact with the carbonyl O atom (O1) and hydroxy O atom (O6), respectively, of different neighbouring molecules (Fig. 3[link]a). Additionally, a weak Cformyl-H...O interaction is also observed [C7-H7...O1(-x, -y + 1, -z + 1); Fig. 3[link]b].

Compound (III)[link] crystallizes in the space group P21/c with Z' = 1. The propenal fragment lies out of the plane of the benzene ring by -9.36 (18)° (torsion angle C2-C3-C11-C12), with a Caryl-Csp2 bond length of 1.4656 (16) Å. This indicates poor resonance between the propenal fragment and the aromatic ring. The molecules are arranged in linear chains arranged in a head-to-tail fashion via C14-H14...O1(x + 1, y, z + 1) hydrogen bonds (Table 3[link] and Fig. 4[link]). The carbonyl O atom has weak C-H...O interactions with one Caryl-H group (C13-H13 or C16-H16) from each of two adjacent chains. Despite the high acidity of the Csp2-H group relative to the Caryl-H groups, no Csp2-H...O hydrogen bonds (between the carbonyl O atom and aliphatic fragment) are observed. However, such interactions have been observed frequently in the crystal structures of some substituted cinnamaldehydes (CSD refcodes CUBNUJ, LUJTEQ, CUBJUJ and QODVAH).

[Figure 1]
Figure 1
The asymmetric units of the crystal structures of (I)[link], (II)[link] and (III)[link]. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2]
Figure 2
The crystal packing in (I)[link], with intermolecular interactions shown as thin lines. [Symmetry codes: (i) x + [{1\over 2}], -y + [{1\over 2}], -z + 1; (ii) -x + [{1\over 2}], -y + 1, z + [{1\over 2}]; (iii) -x + [{3\over 2}], -y, z - [{1\over 2}]; (iv) -x + [{1\over 2}], -y, z - [{1\over 2}]; (v) -x + 2, y + [{1\over 2}], -z + [{3\over 2}].]
[Figure 3]
Figure 3
(a) The crystal packing in (II)[link], viewed down the c axis, showing the layers formed by the Caryl-H...O interactions. (b) The Cformyl-H...O interactions between the molecules of adjacent layers. The interactions are shown as thin lines. [Symmetry codes: (i) -x + 1, y - [{1\over 2}], -z + [{3\over 2}]; (ii) -x + 2, y - [{1\over 2}], -z + [{3\over 2}]; (iii) -x, -y + 1, -z + 1.]
[Figure 4]
Figure 4
The crystal packing in (III)[link], with intermolecular interactions shown as thin lines. [Symmetry codes: (i) -x, -y + 1, -z; (ii) -x - 1, -y + 1, -z - 1; (iii) -x - 1, y + [{1\over 2}], -z - [{1\over 2}].]

Experimental

Crystallization was performed on the diffractometer using a miniature zone-melting procedure with focused IR laser radiation, according to Boese & Nussbaumer (1994[Boese, R. & Nussbaumer, M. (1994). Organic Crystal Chemistry, edited by D. W. Jones, pp. 20-37. Oxford University Press.]). The temperature of crystallization was 263 K for (I)[link], 253 K for (II)[link] (Fluka) and 248 K for (III)[link] (Fluka, 98%, lot No. 1222882 24005132). The first crystal of (I)[link] obtained was of low quality. Therefore, only a reduced set of frames was collected, but afterwards no better crystals could be obtained. For (I)-(III)[link], the low coverage of the reflection data resulted from the orientation of the cylindrical crystal and the chosen scan mode, both due to the in situ crystal-growing technique. Any other mounting of the crystal or different scan mode would lead to melting of the crystals.

Compound (I)[link]

Crystal data
  • C8H8O2

  • Mr = 136.14

  • Orthorhombic, P 21 21 21

  • a = 4.970 (4) Å

  • b = 9.034 (9) Å

  • c = 15.544 (14) Å

  • V = 697.9 (11) Å3

  • Z = 4

  • Mo K[alpha] radiation

  • [mu] = 0.09 mm-1

  • T = 203 K

  • 0.30 × 0.30 × 0.30 mm

Data collection
  • Siemens SMART three-axis goniometer with an APEXII area-detector system

  • 2015 measured reflections

  • 885 independent reflections

  • 705 reflections with I > 2[sigma](I)

  • Rint = 0.069

  • [theta]max = 24.0°

Refinement
  • R[F2 > 2[sigma](F2)] = 0.036

  • wR(F2) = 0.071

  • S = 0.94

  • 885 reflections

  • 92 parameters

  • H-atom parameters constrained

  • [Delta][rho]max = 0.12 e Å-3

  • [Delta][rho]min = -0.13 e Å-3

Table 1
Hydrogen-bond geometry (Å, °) for (I)[link]

D-H...A D-H H...A D...A D-H...A
C3-H3...O2i 0.96 2.75 3.603 (4) 149
C5-H5...O1ii 0.96 2.70 3.447 (4) 135
C8-H8A...O1iii 0.97 2.71 3.582 (4) 150
C8-H8B...O1iv 0.97 2.75 3.434 (4) 128
Symmetry codes: (i) [-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]; (ii) [x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]; (iii) [-x+{\script{3\over 2}}, -y, z-{\script{1\over 2}}]; (iv) [-x+{\script{1\over 2}}, -y, z-{\script{1\over 2}}].

Compound (II)[link]

Crystal data
  • C7H6O2

  • Mr = 122.12

  • Monoclinic, P 21 /c

  • a = 6.3945 (3) Å

  • b = 13.8939 (9) Å

  • c = 6.9172 (4) Å

  • [beta] = 103.262 (3)°

  • V = 598.17 (6) Å3

  • Z = 4

  • Mo K[alpha] radiation

  • [mu] = 0.10 mm-1

  • T = 233 K

  • 0.3 × 0.3 × 0.3 mm

Data collection
  • Siemens SMART three-axis goniometer with an APEXII area-detector system

  • 8643 measured reflections

  • 1853 independent reflections

  • 1002 reflections with I > 2[sigma](I)

  • Rint = 0.056

  • [theta]max = 36.2°

Refinement
  • R[F2 > 2[sigma](F2)] = 0.057

  • wR(F2) = 0.185

  • S = 1.00

  • 1853 reflections

  • 82 parameters

  • H-atom parameters constrained

  • [Delta][rho]max = 0.32 e Å-3

  • [Delta][rho]min = -0.18 e Å-3

Table 2
Hydrogen-bond geometry (Å, °) for (II)[link]

D-H...A D-H H...A D...A D-H...A
O2-H2...O1 1.07 1.61 2.6231 (18) 156
C3-H3...O1i 0.96 2.76 3.460 (2) 130
C7-H7...O1ii 0.96 2.73 3.443 (2) 132
C6-H6...O2iii 0.96 2.70 3.513 (2) 143
Symmetry codes: (i) [-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]; (ii) -x, -y+1, -z+1; (iii) x-1, y, z.

Compound (III)[link]

Crystal data
  • C9H8O

  • Mr = 132.15

  • Monoclinic, P 21 /c

  • a = 5.9626 (2) Å

  • b = 12.9977 (3) Å

  • c = 9.2522 (2) Å

  • [beta] = 94.282 (2)°

  • V = 715.04 (3) Å3

  • Z = 4

  • Mo K[alpha] radiation

  • [mu] = 0.08 mm-1

  • T = 173 K

  • 0.3 × 0.3 × 0.3 mm

Data collection
  • Siemens SMART three-axis goniometer with an APEXII area-detector system

  • 7349 measured reflections

  • 1775 independent reflections

  • 1648 reflections with I > 2[sigma](I)

  • Rint = 0.023

  • [theta]max = 31.8°

Refinement
  • R[F2 > 2[sigma](F2)] = 0.050

  • wR(F2) = 0.125

  • S = 1.06

  • 1775 reflections

  • 92 parameters

  • H-atom parameters constrained

  • [Delta][rho]max = 0.28 e Å-3

  • [Delta][rho]min = -0.17 e Å-3

Table 3
Hydrogen-bond geometry (Å, °) for (III)[link]

D-H...A D-H H...A D...A D-H...A
C13-H13...O1i 0.96 2.81 3.5982 (18) 140
C14-H14...O1ii 0.96 2.63 3.304 (2) 128
C16-H16...O1iii 0.96 2.73 3.3880 (17) 126
Symmetry codes: (i) -x, -y+1, -z; (ii) x+1, y, z+1; (iii) [x+1, -y+{\script{1\over 2}}, z+{\script{1\over 2}}].

H atoms of the methoxy group were idealized with tetrahedral angles in a combined rotating and rigid-group refinement, with C-H = 0.97 Å and Uiso(H) = 1.5Ueq(C). All other C-bound H atoms were refined using a riding model starting from idealized geometries, with C-H = 0.96 Å and Uiso(H) = 1.2Ueq(C). The hydroxy H-atom position in (II)[link] was taken from a Fourier map and also refined as a riding atom, with Uiso(H) = 1.5Ueq(O).

For all compounds, data collection: APEX2 (Bruker, 2006[Bruker (2006). APEX2 (Version 2.0-2) and SAINT (Version 7.34A). Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: APEX2; data reduction: SAINT (Bruker, 2006[Bruker (2006). APEX2 (Version 2.0-2) and SAINT (Version 7.34A). Bruker AXS Inc., Madison, Wisconsin, USA.]); program(s) used to solve structure: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXTL; molecular graphics: Mercury (Macrae et al., 2008[Macrae, C. F., Bruno, I. J., Chisholm, J. A., Edgington, P. R., McCabe, P., Pidcock, E., Rodriguez-Monge, L., Taylor, R., van de Streek, J. & Wood, P. A. (2008). J. Appl. Cryst. 41, 466-470.]); software used to prepare material for publication: publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).


Supplementary data for this paper are available from the IUCr electronic archives (Reference: FG3222 ). Services for accessing these data are described at the back of the journal.


Acknowledgements

TST thanks the Indian Institute of Science for a postdoctoral fellowship. MTK, DB and RB thank the DFG (grant No. FOR-618). GRD thanks the DST for the award of a J. C. Bose fellowship.

References

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Allen, F. H., Kennard, O., Watson, D. G., Brammer, L., Orpen, A. G. & Taylor, R. (1987). J. Chem. Soc. Perkin Trans. 2, pp. S1-19.
Boese, R. & Nussbaumer, M. (1994). Organic Crystal Chemistry, edited by D. W. Jones, pp. 20-37. Oxford University Press.
Breneman, C. M. & Wiberg, K. B. (1990). J. Comput. Chem. 11, 361-373.  [CrossRef] [ChemPort] [ISI]
Bruker (2006). APEX2 (Version 2.0-2) and SAINT (Version 7.34A). Bruker AXS Inc., Madison, Wisconsin, USA.
Desiraju, G. R. & Steiner, T. (1999). The Weak Hydrogen Bond in Structural Chemistry and Biology. New York: Oxford University Press Inc.
Lo Presti, L., Soave, R. & Destro, R. (2006). J. Phys. Chem. B, 110, 6405-6414.  [CSD] [CrossRef] [PubMed] [ChemPort]
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Moorthy, J. N., Natarajan, R. & Venugopalan, P. (2005). J. Mol. Struct. 741, 107-114.  [ChemPort]
Ribeiro-Claro, P. J. A., Drewbm, M. G. B. & Félixa, V. (2002). Chem. Phys. Lett. 356, 318-324.  [ChemPort]
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Acta Cryst (2011). C67, o387-o390   [ doi:10.1107/S0108270111035840 ]