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Acta Crystallogr Sect E Struct Rep Online. 2009 August 1; 65(Pt 8): o2001.
Published online 2009 July 25. doi:  10.1107/S1600536809029043
PMCID: PMC2977167

3-Fluoro­salicylaldoxime at 6.5 GPa


3-Fluoro­salicylaldoxime, C7H6FNO2, unlike many salicylaldoxime derivatives, forms a crystal structure containing hydrogen-bonded chains rather than centrosymmetric hydrogen-bonded ring motifs. Each chain inter­acts with two chains above and two chains below via π–π stacking contacts [shortest centroid–centroid distance = 3.295 (1) Å]. This structure at 6.5 GPa represents the final point in a single-crystal compression study.

Related literature

For salicylaldoximes with bulky side groups which more commonly form hydrogen-bonded chains, see: Koziol & Kosturkiewicz (1984 [triangle]); Maurin (1994 [triangle]). For salicylaldoximes without bulky side groups that form chains, see: Wood et al. (2007a [triangle],b [triangle]); Wood, Forgan, Parsons et al. (2006 [triangle]). For high pressure studies on salicyl­aldoximes, see: Wood et al. (2008 [triangle], 2009 [triangle]); Wood, Forgan, Henderson et al. (2006 [triangle]). For specialized equipment used in the high pressure study, see: Merrill & Bassett (1974 [triangle]); Piermarini et al. (1975 [triangle]).

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Object name is e-65-o2001-scheme1.jpg


Crystal data

  • C7H6FNO2
  • M r = 155.13
  • Orthorhombic, An external file that holds a picture, illustration, etc.
Object name is e-65-o2001-efi1.jpg
  • a = 6.156 (2) Å
  • b = 9.751 (3) Å
  • c = 8.6764 (18) Å
  • V = 520.8 (3) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 0.17 mm−1
  • T = 298 K
  • 0.15 × 0.12 × 0.10 mm

Data collection

  • Bruker APEXII diffractometer
  • Absorption correction: multi-scan (SADABS; Sheldrick, 2006 [triangle]) T min = 0.39, T max = 0.98
  • 2715 measured reflections
  • 333 independent reflections
  • 233 reflections with I > 2σ(I)
  • R int = 0.074


  • R[F 2 > 2σ(F 2)] = 0.036
  • wR(F 2) = 0.049
  • S = 0.94
  • 305 reflections
  • 106 parameters
  • 94 restraints
  • H atoms treated by a mixture of independent and constrained refinement
  • Δρmax = 0.16 e Å−3
  • Δρmin = −0.18 e Å−3

Data collection: APEX2 (Bruker, 2004 [triangle]); cell refinement: SAINT (Bruker, 2004 [triangle]); data reduction: SAINT; method used to solve structure: model taken from ambient pressure structure (Wood et al., 2007b [triangle]); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003 [triangle]); molecular graphics: Mercury (Macrae et al., 2008 [triangle]); software used to prepare material for publication: CRYSTALS.

Table 1
Hydrogen-bond geometry (Å, °)

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809029043/tk2511sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809029043/tk2511Isup2.hkl

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


We thank the Cambridge Crystallographic Data Centre, the University of Edinburgh and the EPSRC for funding.

supplementary crystallographic information


Hydrogen-bonded chain formation is more common for salicylaldoximes with bulky side-groups, e.g. Koziol & Kosturkiewicz (1984) & Maurin (1994). The structure of the title compound, 3-fluorosalicylaldoxime, (I), which has been previously reported at ambient-pressure/150 K (Wood et al., 2007a) is one of the exceptions to this trend along with salicylaldoxime-III (Wood, Forgan, Parsons et al., 2006) and 3-hydroxysalicylaldoxime (Wood et al., 2007b). Salicylaldoxime-I (Wood, Forgan, Henderson et al., 2006) and four of its 3-substituted derivatives (Wood et al., 2008), all of which form hydrogen-bonded dimers, have been studied under compression using a diamond-anvil high-pressure cell. This paper details the results of the continuation of the series to (I). The highest pressure structure is reported here but the ambient-pressure/ambient-temperature structure and further high pressure structures in between have been submitted to the CCDC as a private communication (Wood et al., 2009).

Compound (I) crystallizes with one molecule in the asymmetric unit in the space group Pna21 (Fig. 1). The molecule forms an intramolecular phenolic OH···N hydrogen bond [O5···N2 = 2.530 (7) Å] and an intermolecular oximic OH···O hydrogen bond [O1···O5 = 2.684 (8) Å] with a neighbouring molecule related by the 21 screw axis. These two interactions taken together form a secondary level C(5) chain running parallel to the crystallographic c axis.

The compression of the 3-fluorosalicylaldoxime structure is anisotropic (Fig. 2). It can be seen that the c-axis is the least compressible (decreases by 4.9% up to 6.5 GPa) and this direction also corresponds to the direction of the hydrogen-bonded chains in the crystal structure. The next least compressible direction is that of the crystallographic b axis (decreases by 7.8%), where the main interactions are H···F and H···H contacts between the chains. Finally, the direction that compresses the most up to 6.5 GPa (14.4%) is along the a axis which corresponds to the π-π stacking direction; closest contact = Cg()···Cg()i = 3.295 (1) Å for i: 0.5+x, 0.5-y, z.

Fig. 3 shows the compression of the π-π stacking contact geometry in comparison with equivalent interactions in other salicylaldoximes and with general stacking contacts found in the CSD. It can be seen that the compression follows the trend of the earlier oxime pressure studies (Wood et al., 2008) in that the interaction compresses to the edge of what is seen at ambient conditions in the CSD. In this experiment the crystal disintegrated when the pressure was increased further and this may be indicative that a destructive phase transition occurred.


All solvents and reagents were used as received from Aldrich and Fisher. 1H and 13C NMR were obtained using a Bruker AC250 spectrometer at ambient temperature. Chemical shifts (δ) are reported in p.p.m. relative to internal standards. Fast atom bombardment mass spectrometry (FABMS) was carried out using a Kratos MS50TC spectrometer with a thioglycerol matrix. Analytical data was obtained from the University of St Andrews Microanalytical Service.

KOH (0.674 g, 10.20 mmol) and NH2OH.HCl (0.709 g, 10.20 mmol) were dissolved in EtOH, mixed thoroughly and a white KCl precipitate removed by filtration. 3-Fluorosalicylaldehyde (1.000 g, 7.14 mmol) was added to the filtrate, and the mixture refluxed for 3 h. The solvent was removed in vacuo, the residue redissolved in CHCl3, washed with water three times, and dried over MgSO4. The solvent was removed in vacuo to yield the crude product as a white powder (0.980 g, 88.5%). A pale-yellow block suitable for X-ray diffraction was grown by slow evaporation of a hexane/chloroform solution. (Anal. Calc. for C7H6FNO2: C, 54.2; H, 3.9; N, 9.0. Found: C, 54.3; H, 3.5; N, 9.2%); 1H NMR (250 MHz, CDCl3): δ(H) (p.p.m.) 6.78 (dt, 1H, ArHb), 6.90 (dd, 1H, ArHa), 7.05 (m, 1H, ArHc), 8.16 (s, 1H, CHN); 13C NMR (63 MHz, CDCl3) δ(C) (p.p.m.) 118.0 (aromatic CH), 118.7 (aromatic C-CHN), 119.8 (aromatic CH), 126.0 (aromatic CH), 145.9 (aromatic C—F), 152.8 (ArCHN), 153.6 (aromatic C—OH); FABMS m/z 156 (MH)+, 70%.

The high-pressure experiments were carried out using a Merrill-Bassett diamond anvil cell (half-opening angle 40°), equipped with brilliant-cut diamonds with 600 µm culets and a tungsten gasket (Merrill & Bassett, 1974). A 1:1 mixture of n-pentane and isopentane was used as a hydrostatic medium. Due to the high volatility of the n-pentane/isopentane solution, the cell was cooled in dry-ice prior to loading. A small ruby chip was also loaded into the cell as the pressure calibrant, with the ruby fluorescence method being used to measure the pressure (Piermarini et al., 1975).

Following data collection, an absorption correction was applied using the program SADABS (Sheldrick, (2006). The Tmax/Tmin ratio is larger than calculated on the basis of the crystal dimensions. However, multi-scan procedures (such as SADABS used in the present study) correct for all systematic errors that lead to disparities in the intensities of equivalent data. It is likely that the larger than expected range of transmission is accounted for by crystal decay or absorption by the high pressure cell.


The hydrogen atoms were located in a Fourier difference map. The positional and isotropic displacement parameters were then refined subject to restraints [C—H = 0.93 (2) Å, O—H = 0.82 (2) Å and Uiso(H) = 1.5 Ueq(C or O)]. In subsequent cycles of least-squares refinement all the Uiso(H) values were fixed and the H-atoms attached to C were constrained to ride on their parent atoms. H1 and H5 were refined subject to distance restraints equal to 0.84 (5) Å.

In the absence of significant anomalous scattering effects, 316 Friedel pairs were averaged in the final refinement.

The crystal quality was beginning to deteriorate by this pressure and the number of reflections collected also dropped. In order to deal with this, global vibration and thermal similarity restraints were applied to the model.


Fig. 1.
Molecular structure of (I) with probability ellipsoids drawn at the 50% level, showing atom labelling.
Fig. 2.
Graph of the fractional variation of the lattice parameters (a, b and c) of (I) as a function of pressure (GPa). The cell lengths are displayed as red squares, green triangles and blue circles for a, b and c, respectively.
Fig. 3.
Graph of stacking distance (in Å) against stacking offset (in Å) for phenyl group stacking interactions in the CSD. The five previously published salicylaldoxime compression studies have been highlighted; salicylaldoxime (dark-blue), 3-chlorosalicylaldoxime ...

Crystal data

C7H6FNO2F(000) = 320
Mr = 155.13Dx = 1.978 Mg m3
Orthorhombic, Pna21Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2nCell parameters from 779 reflections
a = 6.156 (2) Åθ = 3–24°
b = 9.751 (3) ŵ = 0.17 mm1
c = 8.6764 (18) ÅT = 298 K
V = 520.8 (3) Å3Block, pale-yellow
Z = 40.15 × 0.12 × 0.10 mm

Data collection

Bruker APEXII diffractometer233 reflections with I > 2σ(I)
graphiteRint = 0.074
ω scansθmax = 27.0°, θmin = 3.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 2006)h = −6→6
Tmin = 0.39, Tmax = 0.98k = −10→10
2715 measured reflectionsl = −10→10
333 independent reflections


Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.036 Method, part 1, Chebychev polynomial, (Watkin, 1994, Prince, 1982) [weight] = 1.0/[A0*T0(x) + A1*T1(x) ··· + An-1]*Tn-1(x)] where Ai are the Chebychev coefficients listed below and x = F /Fmax Method = Robust Weighting (Prince, 1982) W = [weight] * [1-(deltaF/6*sigmaF)2]2 Ai are 12.4 13.8 4.45 -0.254
wR(F2) = 0.049(Δ/σ)max < 0.001
S = 0.94Δρmax = 0.16 e Å3
305 reflectionsΔρmin = −0.18 e Å3
106 parametersExtinction correction: Larson (1970), Equation 22
94 restraintsExtinction coefficient: 119.189
Primary atom site location: structure-invariant direct methods

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

O10.4779 (9)0.1918 (6)0.9058 (5)0.0268
N20.4588 (11)0.1849 (7)0.7440 (5)0.0247
C30.4049 (11)0.3001 (7)0.6852 (7)0.0191
C40.3841 (12)0.3034 (7)0.5185 (6)0.0157
C50.3721 (11)0.1828 (9)0.4328 (5)0.0143
O50.3858 (9)0.0571 (5)0.4956 (5)0.0214
C60.3455 (12)0.1950 (9)0.2755 (6)0.0201
F60.3356 (7)0.0740 (5)0.1972 (4)0.0265
C70.3246 (12)0.3167 (8)0.2001 (7)0.0185
C80.3431 (12)0.4332 (8)0.2861 (6)0.0189
C90.3738 (11)0.4309 (8)0.4436 (6)0.0183
H50.392 (14)0.059 (7)0.594 (4)0.0321*
H10.546 (15)0.114 (6)0.929 (7)0.0400*

Atomic displacement parameters (Å2)

O10.037 (5)0.032 (5)0.0119 (13)0.002 (2)0.0009 (19)0.003 (2)
N20.035 (6)0.028 (4)0.0109 (15)−0.001 (3)0.001 (2)0.008 (3)
C30.017 (5)0.022 (4)0.0176 (17)0.000 (3)0.001 (3)0.001 (2)
C40.010 (4)0.020 (2)0.0176 (18)0.001 (2)−0.002 (3)0.0018 (16)
C50.004 (4)0.020 (2)0.0189 (19)0.000 (2)0.000 (3)0.0014 (16)
O50.023 (4)0.022 (2)0.019 (2)0.0014 (19)0.003 (2)0.0014 (18)
C60.022 (6)0.020 (2)0.019 (2)0.000 (3)−0.001 (3)−0.0035 (16)
F60.035 (3)0.023 (2)0.0215 (17)0.0051 (16)0.001 (2)−0.0071 (18)
C70.017 (5)0.024 (3)0.015 (2)0.002 (2)0.002 (3)−0.0008 (18)
C80.022 (5)0.017 (3)0.018 (2)0.000 (2)0.001 (3)0.004 (2)
C90.022 (5)0.016 (3)0.017 (2)0.005 (2)0.002 (3)−0.003 (2)

Geometric parameters (Å, °)

O1—N21.410 (6)O5—H50.86 (4)
O1—H10.89 (4)C6—F61.363 (9)
N2—C31.278 (9)C6—C71.361 (9)
C3—C41.452 (8)C7—C81.365 (10)
C4—C51.394 (9)C8—C91.380 (8)
C4—C91.404 (10)C8—H80.938
C5—O51.345 (9)C9—H90.932
C5—C61.380 (7)
N2—O1—H1103 (4)C5—C6—F6115.1 (7)
O1—N2—C3112.2 (7)C5—C6—C7124.2 (7)
N2—C3—C4116.2 (7)F6—C6—C7120.8 (5)
N2—C3—H3123.1C6—C7—C8117.1 (6)
C3—C4—C5121.2 (6)C8—C7—H7121.3
C3—C4—C9119.0 (6)C7—C8—C9122.6 (8)
C5—C4—C9119.8 (5)C7—C8—H8118.8
C4—C5—O5123.3 (4)C9—C8—H8118.6
C4—C5—C6117.5 (7)C4—C9—C8118.6 (7)
O5—C5—C6119.1 (7)C4—C9—H9121.4
C5—O5—H5113 (5)C8—C9—H9119.9

Hydrogen-bond geometry (Å, °)

O1—H1···O5i0.89 (7)1.81 (6)2.684 (8)165 (7)
O5—H5···N20.85 (4)1.84 (6)2.530 (7)137 (6)

Symmetry codes: (i) −x+1, −y, z+1/2.


Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: TK2511).


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