Crystal structure of (E)-2,6-di-tert-butyl-4-{[2-(2,4-di-nitro-phen-yl)hydrazinylidene]meth-yl}phenol.

The essential part (including all the non-hydrogen atoms except two methyl carbons) of the mol-ecule of the title compound, C21H26N4O5, lies on a mirror plane, which bis-ects the t-butyl groups. The conformation of the C=N bond of this Schiff base compound is E, and there is an intra-molecular N-H⋯O hydrogen bond present, forming an S(6) ring motif. In the crystal, mol-ecules are linked via O-H⋯O hydrogen bonds, forming zigzag chains propagating along the a-axis direction. There are no other significant inter-molecular contacts present.

Chemical context

Sterically hindered phenol anti-oxidants are widely used in polymers and lubricants. They can protect polymers by increasing both their process stability and their long-term stability against oxidative degradation (Yamazaki & Seguchi, 1997 ▸; Silin et al., 1999 ▸). Hydrazones and Schiff bases have attracted much attention for their excellent biological properties, especially for their potential pharmacological and anti­tumor properties (Küçükgüzel et al., 2006 ▸; Khattab, 2005 ▸; Karthikeyan et al., 2006 ▸; Okabe et al., 1993 ▸). 2,4-Di­nitro­phenyl­hydrazine is frequently used as a reagent for the characterization of aldehydes and ketones (Furniss et al., 1999 ▸). Its derivatives are widely used as dyes (Guillaumont & Nakamura, 2000 ▸). They are also found to have versatile coordin­ating abilities towards different metal ions (Raj & Kurup, 2007 ▸). The present work is a part of an ongoing structural study of Schiff bases and their utilization in the synthesis of quinoxaline derivatives (Faizi et al., 2016a ▸), fluorescence sensors (Faizi et al., 2016b ▸) and coordination compounds (Faizi & Prisyazhnaya, 2015 ▸). We report herein on the synthesis and crystal structure of the title Schiff base compound with a sterically hindered phenol group.

Structural commentary

The mol­ecular structure of the title compound is shown in Fig. 1 ▸. All the non-hydrogen atoms except C16 and C19 lie on a crystallographic mirror plane at y = : the complete tert-butyl groups are generated by mirror symmetry. The conformation of the C7=N1 bond of this Schiff base compound is E, and there is an intra­molecular N2—H2⋯O1 hydrogen bond present, forming an S(6) ring motif (Fig. 1 ▸ and Table 1 ▸). The N1—N2 bond length is 1.385 (6) Å and the N1=C7 bond length is 1.278 (7) Å. The bond distances and angles in the title compound are comparable to those found in a closely related structure (Fun et al., 2013 ▸).

Figure 1

The mol­ecular structure of the title compound, with atom labelling [symmetry code: (i) x, −y + , z]. Displacement ellipsoids are drawn at the 30% probability level. The intra­molecular N—H⋯O hydrogen bond is shown as a dashed line (see Table 1 ▸)

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H2⋯O1	0.86	1.96	2.583 (8)	129
O5—H5O⋯O1i	0.82 (2)	2.28 (5)	2.782 (7)	120 (4)

Symmetry code: (i) .

Supra­molecular features

In the crystal, mol­ecules are linked by O—H⋯O hydrogen bonds, forming zigzag chains propagating along the a-axis direction (Fig. 2 ▸ and Table 1 ▸). There are no other significant inter­molecular contacts present.

Figure 2

A view of the zigzag chains in the crystal structure of the title compound. The hydrogen bonds are shown as dashed lines (see Table 1 ▸). For clarity, only the H atoms involved in hydrogen bonding have been included.

Database survey

There are very few examples of similar compounds in the literature. To the best of our knowledge, the recent report (Bhardwaj & Singh, 2015 ▸) of a similar compound with an hy­droxy group in the ortho position, capable of visual and reversible sensing of cyanide in DMSO solution, has not been characterized crystallographically. A search of the Cambridge Structural Database (CSD, Version 5.37, update May 2016; Groom et al., 2016 ▸) revealed the structure of one very similar compound, viz. 1-(2,4-di­nitro­phen­yl)-2-[(E)-2,4,5-tri­meth­oxy­benzyl­idene]hydrazine (II) (Fun et al., 2013 ▸), in which the 4-phenol group in the title compound is replaced by a trimeth­oxy group. In (II), the dihedral angle between the two benzene rings is 3.15 (11)°, compared to 0° in the title compound, owing to the mirror symmetry.

Synthesis and crystallization

A mixture of 3,5-di-tert-butyl-4-hy­droxy­benzaldehyde 0.100 g (0.427 mmol) and 2,4-di­nitro­phenyl­hydrazine (0.085 g, 0.427 mmol) in methanol was refluxed for 3 h in the presence of a catalytic amount of glacial acetic acid. After cooling, the red-coloured precipitate was washed with hot methanol several times, and then dried, giving a red-coloured shiny crystalline compound in high yield 170 g (96%). Yellow block-like crystals of the title compound (m.p. 372–373 K) were obtained by slow evaporation of a solution in di­chloro­methane and ethanol (5:1 v/v).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. The OH H atom was located in a difference Fourier map and refined with a distance restraint of 0.82 (2) Å with U iso(H) = 1.5U eq(O). The NH and C-bound H atoms were included in calculated positions and allowed to ride on the parent atoms: N—H = 0.86 Å, C—H = 0.93–0.96 Å with U iso(H) = 1.5U eq(C-meth­yl) and 1.2U eq(N,C) for other H atoms.

Table 2

Experimental details

Crystal data
Chemical formula	C21H26N4O5
M r	414.46
Crystal system, space group	Orthorhombic, P n m a
Temperature (K)	296
a, b, c (Å)	18.7651 (10), 6.9193 (4), 17.259 (1)
V (Å3)	2240.9 (2)
Z	4
Radiation type	Mo Kα
μ (mm−1)	0.09
Crystal size (mm)	0.22 × 0.15 × 0.11
Data collection
Diffractometer	STOE IPDS 2
Absorption correction	Integration (X-RED32; Stoe & Cie, 2002 ▸)
T min, T max	0.982, 0.994
No. of measured, independent and observed [I > 2σ(I)] reflections	14854, 2270, 912
R int	0.105
(sin θ/λ)max (Å−1)	0.606
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.071, 0.215, 0.96
No. of reflections	2270
No. of parameters	178
No. of restraints	2
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	0.39, −0.16

Computer programs: X-AREA and X-RED32 (Stoe & Cie, 2002 ▸), SHELXT (Sheldrick 2015a ▸), SHELXL2016/4 (Sheldrick, 2015b ▸), Mercury (Macrae et al., 2008 ▸), WinGX (Farrugia, 2012 ▸) and PLATON (Spek, 2009 ▸).

Crystal structure: contains datablock(s) I, Global. DOI: 10.1107/S2056989016020107/su5340sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016020107/su5340Isup2.hkl

CCDC reference: 1523249

Additional supporting information: crystallographic information; 3D view; checkCIF report

C21H26N4O5	Dx = 1.228 Mg m−3
Mr = 414.46	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pnma	Cell parameters from 6871 reflections
a = 18.7651 (10) Å	θ = 1.1–26.2°
b = 6.9193 (4) Å	µ = 0.09 mm−1
c = 17.259 (1) Å	T = 296 K
V = 2240.9 (2) Å3	Block, yellow
Z = 4	0.22 × 0.15 × 0.11 mm
F(000) = 880

STOE IPDS 2 diffractometer	2270 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	912 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.105
Detector resolution: 6.67 pixels mm-1	θmax = 25.5°, θmin = 1.6°
rotation method scans	h = −22→22
Absorption correction: integration (X-RED32; Stoe & Cie, 2002)	k = −8→8
Tmin = 0.982, Tmax = 0.994	l = −20→20
14854 measured reflections

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.071	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.215	w = 1/[σ2(Fo2) + (0.0904P)2] where P = (Fo2 + 2Fc2)/3
S = 0.96	(Δ/σ)max < 0.001
2270 reflections	Δρmax = 0.39 e Å−3
178 parameters	Δρmin = −0.16 e Å−3
2 restraints

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

	x	y	z	Uiso*/Ueq
O1	0.3313 (3)	0.250000	0.5101 (4)	0.172 (3)
O2	0.2860 (3)	0.250000	0.3982 (3)	0.1219 (18)
O3	0.4249 (4)	0.250000	0.1717 (3)	0.1208 (19)
O4	0.5398 (4)	0.250000	0.1781 (3)	0.134 (2)
O5	0.7461 (2)	0.250000	0.8580 (3)	0.0968 (15)
H5O	0.738 (3)	0.250000	0.9045 (15)	0.145*
N1	0.5301 (3)	0.250000	0.5745 (3)	0.0688 (13)
N2	0.4674 (3)	0.250000	0.5319 (3)	0.0755 (14)
H2	0.426908	0.250000	0.555180	0.091*
N3	0.3381 (3)	0.250000	0.4404 (4)	0.0986 (19)
N4	0.4801 (5)	0.250000	0.2079 (4)	0.0960 (18)
C1	0.4705 (4)	0.250000	0.4537 (3)	0.0683 (16)
C2	0.4077 (3)	0.250000	0.4074 (4)	0.0738 (17)
C3	0.4119 (4)	0.250000	0.3273 (4)	0.0743 (17)
H3	0.370779	0.250000	0.297265	0.089*
C4	0.4780 (4)	0.250000	0.2928 (4)	0.0776 (17)
C5	0.5396 (4)	0.250000	0.3361 (4)	0.0778 (18)
H5A	0.583662	0.250000	0.311488	0.093*
C6	0.5360 (3)	0.250000	0.4143 (3)	0.0707 (16)
H6	0.578077	0.250000	0.442879	0.085*
C7	0.5207 (3)	0.250000	0.6478 (4)	0.0686 (16)
H7	0.474375	0.250000	0.666931	0.082*
C8	0.5798 (3)	0.250000	0.7027 (3)	0.0642 (15)
C9	0.6498 (3)	0.250000	0.6776 (3)	0.0677 (15)
H9	0.659076	0.250000	0.624701	0.081*
C10	0.7066 (3)	0.250000	0.7293 (3)	0.0666 (16)
C11	0.6887 (3)	0.250000	0.8089 (4)	0.0739 (17)
C12	0.6187 (3)	0.250000	0.8373 (3)	0.0663 (15)
C13	0.5656 (3)	0.250000	0.7812 (3)	0.0656 (15)
H13	0.518293	0.250000	0.797276	0.079*
C14	0.7841 (3)	0.250000	0.7007 (4)	0.0775 (18)
C15	0.7881 (4)	0.250000	0.6117 (4)	0.098 (2)
H15A	0.764903	0.136762	0.592106	0.146*
H15B	0.837191	0.250000	0.596024	0.146*
C16	0.8233 (2)	0.4334 (8)	0.7297 (3)	0.1114 (18)
H16A	0.797329	0.546218	0.713820	0.167*
H16B	0.870376	0.437202	0.708115	0.167*
H16C	0.826331	0.430459	0.785250	0.167*
C18	0.6013 (3)	0.250000	0.9242 (3)	0.0755 (18)
C19	0.6312 (3)	0.4323 (7)	0.9640 (2)	0.0973 (16)
H19A	0.679150	0.408097	0.980849	0.146*
H19B	0.602137	0.464417	1.007856	0.146*
H19C	0.631039	0.537943	0.927893	0.146*
C20	0.5207 (4)	0.250000	0.9375 (4)	0.102 (2)
H20A	0.500334	0.363387	0.914288	0.154*
H20B	0.511112	0.250000	0.991999	0.154*

	U11	U22	U33	U12	U13	U23
O1	0.081 (4)	0.362 (10)	0.073 (4)	0.000	0.007 (3)	0.000
O2	0.083 (4)	0.164 (5)	0.118 (4)	0.000	−0.024 (3)	0.000
O3	0.147 (5)	0.135 (5)	0.080 (4)	0.000	−0.034 (4)	0.000
O4	0.147 (5)	0.177 (6)	0.078 (4)	0.000	0.013 (4)	0.000
O5	0.077 (3)	0.136 (4)	0.078 (3)	0.000	−0.017 (3)	0.000
N1	0.072 (3)	0.078 (3)	0.056 (3)	0.000	0.000 (3)	0.000
N2	0.063 (3)	0.103 (4)	0.061 (3)	0.000	−0.005 (3)	0.000
N3	0.068 (4)	0.145 (6)	0.083 (4)	0.000	−0.009 (4)	0.000
N4	0.130 (6)	0.091 (4)	0.068 (4)	0.000	−0.009 (4)	0.000
C1	0.083 (4)	0.059 (4)	0.064 (4)	0.000	−0.008 (4)	0.000
C2	0.078 (5)	0.081 (4)	0.063 (4)	0.000	−0.010 (4)	0.000
C3	0.082 (5)	0.063 (4)	0.078 (5)	0.000	−0.022 (4)	0.000
C4	0.102 (5)	0.066 (4)	0.065 (4)	0.000	−0.007 (4)	0.000
C5	0.086 (5)	0.077 (4)	0.070 (4)	0.000	0.001 (4)	0.000
C6	0.072 (4)	0.079 (4)	0.061 (4)	0.000	−0.004 (3)	0.000
C7	0.067 (4)	0.069 (4)	0.069 (4)	0.000	0.003 (4)	0.000
C8	0.069 (4)	0.066 (4)	0.058 (4)	0.000	0.001 (3)	0.000
C9	0.077 (4)	0.068 (4)	0.058 (3)	0.000	−0.001 (4)	0.000
C10	0.069 (4)	0.068 (4)	0.063 (4)	0.000	0.003 (3)	0.000
C11	0.064 (4)	0.080 (4)	0.078 (4)	0.000	−0.016 (4)	0.000
C12	0.069 (4)	0.070 (4)	0.060 (4)	0.000	−0.011 (3)	0.000
C13	0.061 (4)	0.072 (4)	0.064 (4)	0.000	0.002 (3)	0.000
C14	0.075 (4)	0.076 (4)	0.082 (4)	0.000	0.001 (4)	0.000
C15	0.084 (5)	0.125 (6)	0.084 (5)	0.000	0.019 (4)	0.000
C16	0.086 (3)	0.122 (4)	0.126 (5)	−0.028 (3)	0.000 (3)	0.000 (4)
C18	0.076 (4)	0.090 (5)	0.061 (4)	0.000	−0.004 (3)	0.000
C19	0.115 (4)	0.109 (4)	0.068 (3)	−0.002 (3)	−0.002 (3)	−0.013 (3)
C20	0.089 (5)	0.147 (7)	0.071 (4)	0.000	0.017 (4)	0.000

O1—N3	1.209 (7)	C9—H9	0.9300
O2—N3	1.219 (7)	C10—C11	1.415 (8)
O3—N4	1.210 (7)	C10—C14	1.536 (8)
O4—N4	1.232 (8)	C11—C12	1.401 (8)
O5—C11	1.370 (7)	C12—C13	1.390 (8)
O5—H5O	0.816 (19)	C12—C18	1.536 (8)
N1—C7	1.278 (7)	C13—H13	0.9300
N1—N2	1.385 (6)	C14—C15	1.538 (9)
N2—C1	1.352 (7)	C14—C16	1.549 (6)
N2—H2	0.8600	C14—C16i	1.549 (6)
N3—C2	1.424 (8)	C15—H15A	0.96
N4—C4	1.466 (8)	C15—H15B	0.96
C1—C6	1.405 (8)	C15—H15Ai	0.96
C1—C2	1.422 (8)	C16—H16A	0.9600
C2—C3	1.385 (8)	C16—H16B	0.9600
C3—C4	1.374 (8)	C16—H16C	0.9600
C3—H3	0.9300	C18—C20	1.530 (9)
C4—C5	1.376 (9)	C18—C19	1.542 (5)
C5—C6	1.352 (8)	C18—C19i	1.542 (5)
C5—H5A	0.9300	C19—H19A	0.9600
C6—H6	0.9300	C19—H19B	0.9600
C7—C8	1.458 (8)	C19—H19C	0.9600
C7—H7	0.9300	C20—H20A	0.96
C8—C13	1.380 (7)	C20—H20B	0.96
C8—C9	1.383 (8)	C20—H20Ai	0.96
C9—C10	1.390 (8)
C11—O5—H5O	118 (4)	C12—C11—C10	124.2 (6)
C7—N1—N2	114.1 (5)	C13—C12—C11	115.4 (5)
C1—N2—N1	119.6 (5)	C13—C12—C18	121.9 (5)
C1—N2—H2	120.2	C11—C12—C18	122.7 (5)
N1—N2—H2	120.2	C8—C13—C12	123.0 (6)
O1—N3—O2	120.6 (6)	C8—C13—H13	118.5
O1—N3—C2	119.7 (6)	C12—C13—H13	118.5
O2—N3—C2	119.7 (6)	C10—C14—C15	111.5 (5)
O3—N4—O4	124.2 (7)	C10—C14—C16	110.2 (3)
O3—N4—C4	119.5 (8)	C15—C14—C16	107.4 (4)
O4—N4—C4	116.3 (7)	C10—C14—C16i	110.2 (3)
N2—C1—C6	121.3 (6)	C15—C14—C16i	107.4 (4)
N2—C1—C2	121.8 (6)	C16—C14—C16i	110.0 (6)
C6—C1—C2	117.0 (5)	C14—C15—H15A	109.3
C3—C2—C1	120.9 (6)	C14—C15—H15B	109.2
C3—C2—N3	116.9 (6)	H15A—C15—H15B	109.6
C1—C2—N3	122.3 (6)	C14—C15—H15Ai	109.3 (4)
C4—C3—C2	118.9 (6)	H15A—C15—H15Ai	109.7
C4—C3—H3	120.5	H15B—C15—H15Ai	109.6
C2—C3—H3	120.5	C14—C16—H16A	109.5
C3—C4—C5	121.5 (6)	C14—C16—H16B	109.5
C3—C4—N4	117.2 (7)	H16A—C16—H16B	109.5
C5—C4—N4	121.3 (7)	C14—C16—H16C	109.5
C6—C5—C4	120.1 (7)	H16A—C16—H16C	109.5
C6—C5—H5A	120.0	H16B—C16—H16C	109.5
C4—C5—H5A	120.0	C20—C18—C12	110.9 (5)
C5—C6—C1	121.7 (6)	C20—C18—C19	107.1 (4)
C5—C6—H6	119.2	C12—C18—C19	110.9 (3)
C1—C6—H6	119.2	C20—C18—C19i	107.1 (4)
N1—C7—C8	122.6 (6)	C12—C18—C19i	110.9 (3)
N1—C7—H7	118.7	C19—C18—C19i	109.8 (5)
C8—C7—H7	118.7	C18—C19—H19A	109.5
C13—C8—C9	119.4 (6)	C18—C19—H19B	109.5
C13—C8—C7	119.4 (6)	H19A—C19—H19B	109.5
C9—C8—C7	121.2 (5)	C18—C19—H19C	109.5
C8—C9—C10	121.8 (6)	H19A—C19—H19C	109.5
C8—C9—H9	119.1	H19B—C19—H19C	109.5
C10—C9—H9	119.1	C18—C20—H20A	109.3
C9—C10—C11	116.2 (6)	C18—C20—H20B	109.5
C9—C10—C14	121.4 (5)	H20A—C20—H20B	109.6
C11—C10—C14	122.4 (5)	C18—C20—H20Ai	109.3 (5)
O5—C11—C12	121.4 (6)	H20A—C20—H20Ai	109.6
O5—C11—C10	114.4 (6)	H20B—C20—H20Ai	109.6
C7—N1—N2—C1	180.000 (1)	C7—C8—C9—C10	180.000 (1)
N1—N2—C1—C6	0.000 (1)	C8—C9—C10—C11	0.000 (2)
N1—N2—C1—C2	180.000 (1)	C8—C9—C10—C14	180.000 (1)
N2—C1—C2—C3	180.000 (1)	C9—C10—C11—O5	180.000 (1)
C6—C1—C2—C3	0.000 (1)	C14—C10—C11—O5	0.000 (1)
N2—C1—C2—N3	0.000 (1)	C9—C10—C11—C12	0.000 (2)
C6—C1—C2—N3	180.000 (1)	C14—C10—C11—C12	180.000 (1)
O1—N3—C2—C3	180.000 (1)	O5—C11—C12—C13	180.000 (1)
O2—N3—C2—C3	0.000 (1)	C10—C11—C12—C13	0.000 (2)
O1—N3—C2—C1	0.000 (1)	O5—C11—C12—C18	0.000 (2)
O2—N3—C2—C1	180.000 (1)	C10—C11—C12—C18	180.000 (2)
C1—C2—C3—C4	0.000 (1)	C9—C8—C13—C12	0.000 (2)
N3—C2—C3—C4	180.000 (1)	C7—C8—C13—C12	180.000 (1)
C2—C3—C4—C5	0.000 (1)	C11—C12—C13—C8	0.000 (2)
C2—C3—C4—N4	180.000 (1)	C18—C12—C13—C8	180.000 (2)
O3—N4—C4—C3	0.000 (1)	C9—C10—C14—C15	0.000 (2)
O4—N4—C4—C3	180.000 (1)	C11—C10—C14—C15	180.000 (1)
O3—N4—C4—C5	180.000 (1)	C9—C10—C14—C16	119.2 (4)
O4—N4—C4—C5	0.000 (1)	C11—C10—C14—C16	−60.8 (4)
C3—C4—C5—C6	0.000 (1)	C9—C10—C14—C16i	−119.2 (4)
N4—C4—C5—C6	180.000 (1)	C11—C10—C14—C16i	60.8 (4)
C4—C5—C6—C1	0.000 (1)	C13—C12—C18—C20	0.000 (2)
N2—C1—C6—C5	180.000 (1)	C11—C12—C18—C20	180.000 (2)
C2—C1—C6—C5	0.000 (1)	C13—C12—C18—C19	−118.8 (4)
N2—N1—C7—C8	180.000 (1)	C11—C12—C18—C19	61.2 (4)
N1—C7—C8—C13	180.000 (1)	C13—C12—C18—C19i	118.8 (4)
N1—C7—C8—C9	0.000 (2)	C11—C12—C18—C19i	−61.2 (4)
C13—C8—C9—C10	0.000 (2)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···O1	0.86	1.96	2.583 (8)	129
O5—H5O···O1ii	0.82 (2)	2.28 (5)	2.782 (7)	120 (4)