Crystal structure of 2-{(E)-[(2-hy­droxy­phen­yl)iminium­yl]meth­yl}-4-methyl­phenolate

The title compound, C₁₄H₁₃NO₂, exists as a zwitterion in the solid state, with the H atom of the phenol group transferred to the imine N atom. The dihedral angle between the planes of the benzene rings is 10.13 (9)°. Intra­molecular N—H...O hydrogen bond generate S(6) and S(5) loops. In the crystal, mol­ecules are connected by O—H...O hydrogen bonds, generating C(9) chains propagating in the [010] direction.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.050
• wR factor = 0.130
• Data-to-parameter ratio = 15.8

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......      0.974 Note
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600         51 Report
PLAT913_ALERT_3_C Missing # of Very Strong Reflections in FCF ....          1 Note

Alert level G
PLAT002_ALERT_2_G Number of Distance or Angle Restraints on AtSite          4 Note
PLAT172_ALERT_4_G The CIF-Embedded .res File Contains DFIX Records          2 Report
PLAT199_ALERT_1_G Reported _cell_measurement_temperature ..... (K)        293 Check
PLAT200_ALERT_1_G Reported   _diffrn_ambient_temperature ..... (K)        293 Check
PLAT309_ALERT_2_G Single Bonded Oxygen (C-O > 1.3 Ang) ...........         O1 Check
PLAT860_ALERT_3_G Number of Least-Squares Restraints .............          2 Note
PLAT910_ALERT_3_G Missing # of FCF Reflection(s) Below Th(Min) ...          1 Report
PLAT912_ALERT_4_G Missing # of FCF Reflections Above STh/L=  0.600         19 Note

   0 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   3 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   8 ALERT level G = General information/check it is not something unexpected

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

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S1. Chemical context

N-substituted imines, also known as Schiff bases represent one of the most widely used families of organic compounds. Schiff bases have been intensively used as synthetic inter­mediates and as ligands for coordinating transition and inner transition metal ions, and recently also for coordinating anions. Schiff base ligands may contain a variety of substituents with different electron-donating or electron-withdrawing groups, and therefore may have inter­esting chemical properties. They have attracted particular inter­est due to their biological activities acting as radiopharmaceuticals for cancer targeting.They have also been used as model systems for biological macromolecules . Besides the biological activity, solid-state thermochromism and photochromism are an another characteristic of these compounds leading to their application in various areas of materials science such as the control and measurement of radiation intensity, display systems and optical memory devices . Schiff bases derived from o-hy­droxy­aromatic aldehydes and ketones are excellent models for the study of keto-enol tautomerism both in solution and in the solid state (Blagus et al., 2010).

S2. Structural commentary

The structure of the title compound is as shown in Fig.1 is described in terms of three planar subunits,namely two terminal benzene rings and their substituents bridged by a C=N moiety. The molecule has adopted E-configuration about the C8—N1 double bond (1.301 (2)Å) with a C9—N1—C8—C4 torsion angle of 179.90 (16)°. The C4—C8 and N1—C9 bond distances [1.410 (2) and 1.404 (2)Å] confirm π-electron delocalisation between the phenyl rings. The N1—C8—C4[123.26 (15)°] is greater than the normal value of 120°. This may be due to inter­action of iminium H with phenolate O atom. The C6—C5—C4 [116.51 (15)°] is smaller than the normal value of 120° which is due to lengthening of the phenolate C5—O1 [1.304 (2)Å] bond. All other bond distances and bond angles are within the normal range (Eltayeb et al., 2010).

S3. Supra­molecular features

The iminium H atom is engaged in a strong intra­molecular hydrogen bond with the O atom of the phenolate (N⁺ —H···O ) to form a S(6) motif. The crystal structure is stabilised by both intra­molecular N1—H1···O1 and inter­molecular O2—H4···O1 hydrogen bonding linking the molecules into infinite one-dimensional chains as shown in the figure.2, table.2, extending along the b-axis of the unit cell.

S4. Synthesis and crystallization

o-Amino­phenol (5.45g, 0.01mole) was taken in 100mL round bottom flask. Salicyl­aldehyde (6.10g, 0.01mole) was added to the round bottom flask in methanol medium. The resulting mixture was refluxed for about 30 min. The resulting Schiff base was separated as orange crystals. The product was filtered, washed and recrystallized from methanol (M.P.134-135 ⁰C, Yield 75%). Single crystals of the compound were grown by slow evaporation method using ethanol as solvent at room temperature.

S5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1.

Related literature

For a related structure, see: Eltayeb et al. (2010). For background to Schiff bases and their applications, see: Blagus et al. (2010).

Structure description

N-substituted imines, also known as Schiff bases represent one of the most widely used families of organic compounds. Schiff bases have been intensively used as synthetic inter­mediates and as ligands for coordinating transition and inner transition metal ions, and recently also for coordinating anions. Schiff base ligands may contain a variety of substituents with different electron-donating or electron-withdrawing groups, and therefore may have inter­esting chemical properties. They have attracted particular inter­est due to their biological activities acting as radiopharmaceuticals for cancer targeting.They have also been used as model systems for biological macromolecules . Besides the biological activity, solid-state thermochromism and photochromism are an another characteristic of these compounds leading to their application in various areas of materials science such as the control and measurement of radiation intensity, display systems and optical memory devices . Schiff bases derived from o-hy­droxy­aromatic aldehydes and ketones are excellent models for the study of keto-enol tautomerism both in solution and in the solid state (Blagus et al., 2010).

The structure of the title compound is as shown in Fig.1 is described in terms of three planar subunits,namely two terminal benzene rings and their substituents bridged by a C=N moiety. The molecule has adopted E-configuration about the C8—N1 double bond (1.301 (2)Å) with a C9—N1—C8—C4 torsion angle of 179.90 (16)°. The C4—C8 and N1—C9 bond distances [1.410 (2) and 1.404 (2)Å] confirm π-electron delocalisation between the phenyl rings. The N1—C8—C4[123.26 (15)°] is greater than the normal value of 120°. This may be due to inter­action of iminium H with phenolate O atom. The C6—C5—C4 [116.51 (15)°] is smaller than the normal value of 120° which is due to lengthening of the phenolate C5—O1 [1.304 (2)Å] bond. All other bond distances and bond angles are within the normal range (Eltayeb et al., 2010).

The iminium H atom is engaged in a strong intra­molecular hydrogen bond with the O atom of the phenolate (N⁺ —H···O ) to form a S(6) motif. The crystal structure is stabilised by both intra­molecular N1—H1···O1 and inter­molecular O2—H4···O1 hydrogen bonding linking the molecules into infinite one-dimensional chains as shown in the figure.2, table.2, extending along the b-axis of the unit cell.

For a related structure, see: Eltayeb et al. (2010). For background to Schiff bases and their applications, see: Blagus et al. (2010).

Synthesis and crystallization

o-Amino­phenol (5.45g, 0.01mole) was taken in 100mL round bottom flask. Salicyl­aldehyde (6.10g, 0.01mole) was added to the round bottom flask in methanol medium. The resulting mixture was refluxed for about 30 min. The resulting Schiff base was separated as orange crystals. The product was filtered, washed and recrystallized from methanol (M.P.134-135 ⁰C, Yield 75%). Single crystals of the compound were grown by slow evaporation method using ethanol as solvent at room temperature.

Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 1.

Computing details

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015) and PLATON (Spek, 2009).

Figures

	Fig. 1. ORTEP Plot of (I) drawn at 40% probability level
	Fig. 2. A perspective view of the one-dimensional infinite chain in the title compound, (I), showing N—H···O and O—H···O hydrogen-bnd interactions as dashed lines. H atoms not involved in the interactions have been omitted for the sake of clarity.

2-{(E)-[(2-Hydroxyphenyl)iminiumyl]methyl}-4-methylphenolate

Crystal data

C14H13NO2	Dx = 1.313 Mg m^−3
Mr = 227.25	Melting point: 355 K
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
a = 12.9474 (18) Å	Cell parameters from 500 reflections
b = 9.0660 (13) Å	θ = 5.0–50.0°
c = 19.583 (3) Å	µ = 0.09 mm^−1
V = 2298.7 (6) Å^3	T = 293 K
Z = 8	Block, colorless
F(000) = 960	0.3 × 0.25 × 0.20 mm

Data collection

Bruker APEXII CCD diffractometer	1810 reflections with I > 2σ(I)
Radiation source: graphite monochromator	Rint = 0.059
OMEGA–PHI scans	θmax = 27.6°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −16→16
Tmin = 0.875, Tmax = 1.000	k = −11→8
29481 measured reflections	l = −25→25
2583 independent reflections

Refinement

Refinement on F^2	2 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F^2 > 2σ(F^2)] = 0.050	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.130	w = 1/[σ^2(Fo^2) + (0.0467P)^2 + 1.0454P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max = 0.015
2583 reflections	Δρmax = 0.21 e Å^−3
163 parameters	Δρmin = −0.20 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

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

	x	y	z	Uiso*/Ueq
H1	0.6541 (13)	0.138 (3)	0.2650 (11)	0.063 (7)*
H4	0.5002 (18)	0.378 (3)	0.1982 (14)	0.099 (9)*
N1	0.71804 (10)	0.16956 (16)	0.25537 (7)	0.0328 (3)
C8	0.78912 (12)	0.1022 (2)	0.29051 (8)	0.0345 (4)
H8	0.8579	0.1254	0.2819	0.041*
O1	0.58630 (9)	0.00525 (16)	0.31990 (7)	0.0465 (4)
C9	0.73191 (11)	0.2767 (2)	0.20440 (8)	0.0315 (4)
O2	0.55197 (9)	0.31121 (17)	0.20963 (7)	0.0494 (4)
C14	0.64308 (12)	0.3480 (2)	0.18036 (9)	0.0350 (4)
C5	0.66350 (13)	−0.0477 (2)	0.35492 (9)	0.0358 (4)
C10	0.82779 (13)	0.3143 (2)	0.17751 (9)	0.0389 (4)
H10	0.8872	0.2685	0.1937	0.047*
C4	0.76708 (12)	−0.0042 (2)	0.34097 (8)	0.0335 (4)
C2	0.83378 (15)	−0.1684 (2)	0.42880 (10)	0.0451 (5)
C13	0.65167 (14)	0.4516 (2)	0.12897 (9)	0.0415 (5)
H13	0.5928	0.4982	0.1124	0.050*
C6	0.64951 (14)	−0.1513 (2)	0.40786 (9)	0.0441 (5)
H6	0.5830	−0.1815	0.4191	0.053*
C11	0.83474 (14)	0.4189 (2)	0.12694 (10)	0.0462 (5)
H11	0.8990	0.4445	0.1094	0.055*
C3	0.84905 (13)	−0.0673 (2)	0.37804 (9)	0.0418 (5)
H3	0.9163	−0.0390	0.3676	0.050*
C7	0.73159 (15)	−0.2085 (2)	0.44311 (9)	0.0461 (5)
H7	0.7190	−0.2763	0.4778	0.055*
C12	0.74692 (16)	0.4864 (2)	0.10209 (9)	0.0457 (5)
H12	0.7520	0.5554	0.0671	0.055*
C1	0.92146 (18)	−0.2371 (3)	0.46830 (12)	0.0691 (7)
H1A	0.9742	−0.2687	0.4372	0.104*
H1B	0.8963	−0.3205	0.4935	0.104*
H1C	0.9497	−0.1658	0.4994	0.104*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0232 (6)	0.0327 (9)	0.0425 (8)	−0.0010 (6)	−0.0004 (6)	−0.0013 (6)
C8	0.0243 (7)	0.0355 (11)	0.0437 (9)	−0.0001 (7)	−0.0016 (7)	−0.0035 (8)
O1	0.0253 (6)	0.0571 (10)	0.0572 (8)	−0.0049 (6)	−0.0043 (5)	0.0051 (7)
C9	0.0267 (8)	0.0304 (10)	0.0372 (8)	−0.0001 (7)	−0.0005 (6)	−0.0027 (7)
O2	0.0249 (6)	0.0582 (10)	0.0651 (9)	0.0050 (6)	0.0004 (6)	0.0148 (7)
C14	0.0271 (8)	0.0381 (11)	0.0398 (9)	0.0005 (7)	−0.0008 (7)	−0.0029 (8)
C5	0.0305 (8)	0.0360 (11)	0.0410 (9)	−0.0041 (7)	0.0000 (7)	−0.0059 (8)
C10	0.0281 (8)	0.0410 (12)	0.0477 (10)	0.0032 (7)	0.0011 (7)	−0.0013 (8)
C4	0.0289 (8)	0.0332 (10)	0.0383 (8)	−0.0017 (7)	−0.0016 (7)	−0.0022 (7)
C2	0.0450 (10)	0.0474 (13)	0.0429 (10)	0.0017 (9)	−0.0054 (8)	0.0043 (9)
C13	0.0381 (9)	0.0443 (12)	0.0423 (10)	0.0050 (8)	−0.0062 (8)	0.0023 (8)
C6	0.0378 (9)	0.0485 (13)	0.0459 (10)	−0.0095 (8)	0.0057 (8)	0.0001 (9)
C11	0.0377 (10)	0.0494 (13)	0.0516 (11)	−0.0049 (9)	0.0109 (8)	0.0016 (9)
C3	0.0288 (8)	0.0483 (13)	0.0482 (10)	0.0004 (8)	−0.0034 (7)	0.0044 (9)
C7	0.0528 (11)	0.0463 (13)	0.0392 (9)	−0.0045 (9)	0.0019 (8)	0.0038 (9)
C12	0.0516 (11)	0.0447 (13)	0.0408 (9)	−0.0021 (9)	0.0033 (9)	0.0053 (9)
C1	0.0560 (13)	0.085 (2)	0.0662 (14)	0.0045 (12)	−0.0112 (11)	0.0278 (14)

Geometric parameters (Å, º)

N1—C8	1.301 (2)	C2—C3	1.367 (3)
N1—C9	1.404 (2)	C2—C7	1.400 (3)
N1—H1	0.895 (16)	C2—C1	1.508 (3)
C8—C4	1.410 (2)	C13—C12	1.377 (3)
C8—H8	0.9300	C13—H13	0.9300
O1—C5	1.304 (2)	C6—C7	1.369 (3)
C9—C10	1.391 (2)	C6—H6	0.9300
C9—C14	1.401 (2)	C11—C12	1.380 (3)
O2—C14	1.353 (2)	C11—H11	0.9300
O2—H4	0.932 (17)	C3—H3	0.9300
C14—C13	1.381 (3)	C7—H7	0.9300
C5—C6	1.410 (3)	C12—H12	0.9300
C5—C4	1.424 (2)	C1—H1A	0.9600
C10—C11	1.374 (3)	C1—H1B	0.9600
C10—H10	0.9300	C1—H1C	0.9600
C4—C3	1.407 (2)
C8—N1—C9	127.59 (14)	C12—C13—C14	120.40 (17)
C8—N1—H1	113.3 (15)	C12—C13—H13	119.8
C9—N1—H1	119.1 (15)	C14—C13—H13	119.8
N1—C8—C4	123.26 (15)	C7—C6—C5	121.52 (17)
N1—C8—H8	118.4	C7—C6—H6	119.2
C4—C8—H8	118.4	C5—C6—H6	119.2
C10—C9—C14	119.50 (16)	C10—C11—C12	120.41 (17)
C10—C9—N1	123.55 (15)	C10—C11—H11	119.8
C14—C9—N1	116.95 (14)	C12—C11—H11	119.8
C14—O2—H4	111.4 (18)	C2—C3—C4	122.59 (17)
O2—C14—C13	123.12 (15)	C2—C3—H3	118.7
O2—C14—C9	117.36 (16)	C4—C3—H3	118.7
C13—C14—C9	119.52 (15)	C6—C7—C2	122.30 (18)
O1—C5—C6	122.24 (16)	C6—C7—H7	118.9
O1—C5—C4	121.25 (16)	C2—C7—H7	118.9
C6—C5—C4	116.51 (16)	C13—C12—C11	120.12 (18)
C11—C10—C9	120.02 (16)	C13—C12—H12	119.9
C11—C10—H10	120.0	C11—C12—H12	119.9
C9—C10—H10	120.0	C2—C1—H1A	109.5
C3—C4—C8	119.13 (15)	C2—C1—H1B	109.5
C3—C4—C5	119.91 (16)	H1A—C1—H1B	109.5
C8—C4—C5	120.96 (15)	C2—C1—H1C	109.5
C3—C2—C7	117.15 (17)	H1A—C1—H1C	109.5
C3—C2—C1	122.77 (18)	H1B—C1—H1C	109.5
C7—C2—C1	120.08 (18)
C9—N1—C8—C4	179.90 (16)	O2—C14—C13—C12	178.77 (18)
C8—N1—C9—C10	8.4 (3)	C9—C14—C13—C12	−0.9 (3)
C8—N1—C9—C14	−171.45 (17)	O1—C5—C6—C7	178.47 (18)
C10—C9—C14—O2	−177.89 (16)	C4—C5—C6—C7	−1.0 (3)
N1—C9—C14—O2	2.0 (2)	C9—C10—C11—C12	−0.6 (3)
C10—C9—C14—C13	1.8 (3)	C7—C2—C3—C4	0.1 (3)
N1—C9—C14—C13	−178.31 (16)	C1—C2—C3—C4	179.5 (2)
C14—C9—C10—C11	−1.1 (3)	C8—C4—C3—C2	178.41 (19)
N1—C9—C10—C11	179.06 (17)	C5—C4—C3—C2	−1.3 (3)
N1—C8—C4—C3	−177.72 (17)	C5—C6—C7—C2	−0.2 (3)
N1—C8—C4—C5	2.0 (3)	C3—C2—C7—C6	0.7 (3)
O1—C5—C4—C3	−177.76 (17)	C1—C2—C7—C6	−178.8 (2)
C6—C5—C4—C3	1.7 (3)	C14—C13—C12—C11	−0.8 (3)
O1—C5—C4—C8	2.5 (3)	C10—C11—C12—C13	1.5 (3)
C6—C5—C4—C8	−177.99 (17)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H4···O1^i	0.93 (2)	1.65 (2)	2.5756 (18)	176 (3)
N1—H1···O2	0.90 (2)	2.32 (2)	2.6598 (19)	102 (2)
N1—H1···O1	0.90 (2)	1.84 (2)	2.5933 (19)	141 (2)

Symmetry code: (i) −x+1, y+1/2, −z+1/2.