3-Fluoro­salicylaldoxime

In contrast with many salicylaldoxime derivatives, which form crystal structures based on hydrogen-bonded ring motifs, 3-fluoro­salicylaldoxime, C₇H₆FNO₂, forms hydrogen-bonded chains. Each chain inter­acts with two chains above and two chains below via π–π stacking contacts [centroid–centroid distance = 3.6353 (1) Å].

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.037
• wR factor = 0.095
• Data-to-parameter ratio = 9.3

checkCIF/PLATON results

No syntax errors found



Alert level B
ABSTM02_ALERT_3_B  The ratio of expected to reported Tmax/Tmin(RR') is < 0.75
            Tmin and Tmax reported:      0.500     0.980
            Tmin(prime) and Tmax expected:      0.953     0.975
            RR(prime) =      0.522
            Please check that your absorption correction is appropriate.
PLAT061_ALERT_3_B Tmax/Tmin Range Test RR' too Large .............       0.52

Alert level C
PLAT431_ALERT_2_C Short Inter HL..A Contact  F6     ..  N2      ..       3.01 Ang.

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           30.33
           From the CIF: _reflns_number_total                981
           Count of symmetry unique reflns         1061
           Completeness (_total/calc)             92.46%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured         0
           Fraction of Friedel pairs measured     0.000
           Are heavy atom types Z>Si present         no
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          3

   0 ALERT level A = In general: serious problem
   2 ALERT level B = Potentially serious problem
   1 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

3-Fluoro-salicylaldoxime (I) crystallizes with one molecule in the asymmetric unit in the space group Pna2₁. The molecule forms an intramolecular phenolic OH···N hydrogen bond [O5···N2 = 2.586 (3) Å] (Figure 1) and an intermolecular oximic OH···O hydrogen bond [O1···O5 = 2.815 (2) 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 (Figure 2).

Each chain interacts with two chains above and two chains below via π-π stacking contacts in which the C-atoms in one ring lie 3.357 (2) to 3.583 (2) Å from the plane of the other ring. The dihedral angle between the two phenyl planes is 3.91 (7)°. The molecule also forms three close contacts involving the fluoro group C9H9···F6 [C9···F6 = 3.304 (3) Å], O5H5···F6 [O5···F6 = 3.034 (2) Å] and N2···F6 [N2···F6 = 3.011 (2) Å] (Figure 3).

Related literature

Chain formation is characteristic of salicylaldoximes bearing large substituents [e.g. Cambridge Structural Database (Allen, 2002) refcodes HEPKET10 (Koziol & Kosturkiewicz, 1984) and HELBOP (Maurin, 1994)]. The structures of 3-fluorosalicylaldoxime (this work), one of the polymorphs of salicylaldoxime [designated phase III by Wood et al. (2006)] and 3-hydroxysalicylaldoxime (Wood et al., 2007) are exceptions to this rule.

S2. Experimental

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 parts per million (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 hr. The solvent was removed in vacuo, and the residue redissolved in CHCl₃, washed with water 3 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, ArH_b), 6.90 (dd, 1H, ArH_a), 7.05 (m, 1H, ArH_c), 8.16 (s, 1H, CHN); ¹³C NMR (63 MHz, CDCl₃) δ(C) (p.p.m.) 118.0 (1 C, aromatic CH), 118.7 (1 C, aromatic C-CHN), 119.8 (1 C, aromatic CH), 126.0 (1 C, aromatic CH), 145.9 (1 C, aromatic C—F), 152.8 (1 C, ArCHN), 153.6 (1 C, aromatic C—OH); FABMS m/z 156 (MH)+, 70%.

Following data collection (see Table 1) an absorption correction was applied using the program SADABS. T_max/T_min is larger than calculated on the basis of the crystal dimensions. However, multi-scan procedures (such as SADABS) correct for all systematic errors that lead to disparities in the intensities of equivalent data. It is possible that the larger than expected range of transmission is accounted for by crystal decay or absorption by the mounting fibre.

S3. Refinement

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 U_iso(H) = 1.5 U_eq(C or O)]. In subsequent cycles of least squares all the U_iso(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.

Computing details

Data collection: SMART (Siemens, 1993); cell refinement: SAINT; data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: DIAMOND (Brandenburg, 2004); software used to prepare material for publication: CRYSTALS.

Figures

	Fig. 1. Molecular structure of I with probability ellipsoids drawn at the 50% level.
	Fig. 2. H-bonded chain formation in the crystal structure of I.
	Fig. 3. Packing of C(5) chains in the crystal structure of I showing π-π stacking interactions. This view is along the chains shown in Fig. 2.

3-fluorosalicylaldoxime

Crystal data

C7H6FNO2	F(000) = 320
Mr = 155.13	Dx = 1.527 Mg m^−3
Orthorhombic, Pna21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2n	Cell parameters from 2462 reflections
a = 7.0497 (3) Å	θ = 3–30°
b = 10.5161 (4) Å	µ = 0.13 mm^−1
c = 9.1022 (4) Å	T = 150 K
V = 674.79 (5) Å^3	Block, pale yellow
Z = 4	0.36 × 0.34 × 0.19 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer	840 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.034
ω scans	θmax = 30.3°, θmin = 3.0°
Absorption correction: multi-scan (SADABS; Sheldrick, 2006)	h = −9→9
Tmin = 0.50, Tmax = 0.98	k = −14→14
5425 measured reflections	l = −11→12
981 independent reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.037	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.095	w = 1/[σ^2(F^2) + (0.05P)^2], where P = [max(Fo^2,0) + 2Fc^2]/3
S = 1.00	(Δ/σ)max = 0.000100
981 reflections	Δρmax = 0.24 e Å^−3
106 parameters	Δρmin = −0.22 e Å^−3
3 restraints

Special details

Experimental. Used Oxford Cryosystems low temperature device. Data collection strategy optimized with COSMO.

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

	x	y	z	Uiso*/Ueq
O1	0.4921 (3)	0.18525 (14)	0.8860 (2)	0.0413
N2	0.4610 (3)	0.17539 (15)	0.7354 (2)	0.0308
C3	0.4249 (3)	0.28150 (17)	0.6744 (3)	0.0291
C4	0.3910 (3)	0.28594 (19)	0.5162 (2)	0.0269
C5	0.3791 (3)	0.17354 (18)	0.4329 (3)	0.0257
O5	0.3996 (2)	0.05548 (13)	0.4920 (2)	0.0309
C6	0.3441 (3)	0.18391 (19)	0.2834 (3)	0.0300
F6	0.3325 (2)	0.07390 (12)	0.2058 (2)	0.0401
C7	0.3223 (3)	0.2981 (2)	0.2124 (3)	0.0328
C8	0.3356 (3)	0.4092 (2)	0.2956 (3)	0.0327
C9	0.3695 (3)	0.4030 (2)	0.4445 (3)	0.0295
H1	0.520 (5)	0.111 (3)	0.909 (4)	0.0609*
H3	0.4159	0.3549	0.7269	0.0344*
H5	0.426 (4)	0.063 (3)	0.579 (3)	0.0455*
H7	0.3001	0.2989	0.1116	0.0381*
H8	0.3191	0.4887	0.2494	0.0387*
H9	0.3797	0.4761	0.4983	0.0346*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0687 (12)	0.0326 (8)	0.0228 (7)	0.0036 (8)	−0.0049 (7)	0.0006 (6)
N2	0.0405 (10)	0.0290 (8)	0.0228 (9)	−0.0002 (7)	−0.0001 (7)	−0.0011 (6)
C3	0.0360 (10)	0.0231 (8)	0.0280 (10)	−0.0005 (8)	0.0018 (8)	−0.0042 (7)
C4	0.0282 (10)	0.0256 (9)	0.0268 (10)	−0.0002 (7)	0.0019 (8)	0.0000 (7)
C5	0.0300 (9)	0.0229 (9)	0.0242 (9)	0.0009 (7)	0.0024 (8)	0.0000 (7)
O5	0.0462 (9)	0.0225 (6)	0.0241 (6)	0.0008 (6)	0.0000 (6)	−0.0008 (5)
C6	0.0328 (11)	0.0306 (10)	0.0268 (11)	0.0021 (7)	0.0003 (8)	−0.0045 (8)
F6	0.0606 (9)	0.0332 (6)	0.0266 (6)	0.0058 (5)	−0.0048 (6)	−0.0086 (5)
C7	0.0370 (11)	0.0379 (11)	0.0235 (8)	0.0050 (8)	0.0004 (9)	0.0033 (8)
C8	0.0345 (11)	0.0299 (9)	0.0336 (10)	0.0036 (7)	0.0005 (9)	0.0075 (8)
C9	0.0331 (9)	0.0237 (9)	0.0316 (9)	0.0018 (7)	0.0001 (8)	−0.0012 (7)

Geometric parameters (Å, º)

O1—N2	1.392 (2)	O5—H5	0.82 (3)
O1—H1	0.83 (3)	C6—F6	1.358 (2)
N2—C3	1.272 (2)	C6—C7	1.372 (3)
C3—C4	1.460 (3)	C7—C8	1.395 (3)
C3—H3	0.911	C7—H7	0.931
C4—C5	1.407 (3)	C8—C9	1.378 (3)
C4—C9	1.401 (3)	C8—H8	0.943
C5—O5	1.361 (2)	C9—H9	0.915
C5—C6	1.387 (3)
N2—O1—H1	102 (3)	C5—C6—F6	116.98 (19)
O1—N2—C3	113.33 (16)	C5—C6—C7	123.4 (2)
N2—C3—C4	119.43 (17)	F6—C6—C7	119.62 (18)
N2—C3—H3	121.9	C6—C7—C8	118.0 (2)
C4—C3—H3	118.6	C6—C7—H7	119.4
C3—C4—C5	120.97 (18)	C8—C7—H7	122.6
C3—C4—C9	120.34 (19)	C7—C8—C9	120.4 (2)
C5—C4—C9	118.70 (18)	C7—C8—H8	119.4
C4—C5—O5	123.17 (17)	C9—C8—H8	120.1
C4—C5—C6	118.26 (19)	C4—C9—C8	121.2 (2)
O5—C5—C6	118.57 (19)	C4—C9—H9	118.8
C5—O5—H5	108.9 (19)	C8—C9—H9	120.0