N,N′-Bis(3-hydr­oxy-4-methoxy­benzyl­idene)hydrazine

The title compound, C₁₆H₁₆N₂O₄, was synthesized by the reaction of 3-hydr­oxy-4-methoxy­benzaldehyde with hydrazine hydrate. The mol­ecule possesses a crystallographically imposed centre of symmetry. An intra­molecular O—H...O hydrogen bond promotes planarity of the mol­ecular backbone. In the crystal structure, inter­molecular O—H...N and C—H...O hydrogen bonds stabilize the crystal packing.

Key indicators

• Single-crystal X-ray study
• T = 294 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.037
• wR factor = 0.103
• Data-to-parameter ratio = 13.7

checkCIF/PLATON results

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Alert level C
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          1
              C16 H16 N2 O4

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

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

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S1. Comment

Recently, a number of azine compounds containing both a diimine linkage and N—N bonding have been investigated in terms of their crystallography and coordination chemistry (Zheng et al., 2005; Kundu et al., 2005; Kesslen & Euler, 1999; Armstrong et al., 1998; Xu et al., 1997). We report here the crystal structure of the title compound, (I), where two 3-hydroxy-4-methoxybenzylidene units are directly linked through the imine N atoms.

The molecule of (I) possesses a crystallographically imposed centre of symmetry at the mid-point of the N—N bond (Fig. 1). The N—N bond length of 1.412 (2) Å (Table 1) is somewhat longer than that observed in related azine compounds (Xu et al., 2005; Liu et al., 2004; Şengül et al., 2004). The C═N—N angle [112.82 (15)°] is similar to that in N,N'-bis(4-chlorobenzylidene)hydrazine (Zheng et al., 2005) but significantly smaller than the ideal sp² value of 120°, as a consequence of repulsion between the nitrogen lone pairs and the adjacent C═N bond. An intramolecular O—H···O hydrogen bond (Table 2) provides planarity of the molecular backbone, with an r.m.s deviation of 0.034 (6) Å.

In the crystal structure, intermolecular O—H···N and C—H···O hydrogen bonds (Table 2) stabilize the crystal packing (Fig. 2).

S2. Experimental

The title compound was synthesized by the reaction of 3-hydroxy-4-methoxybenzaldehyde with hydrazine hydrate in refluxing ethanol (Liu et al., 2004). Single crystals suitable for X-ray analysis were obtained by slow evaporation of a tetrahydrofuran solution.

S3. Refinement

All H atoms were located in a difference Fourier map. C-bound H atoms were refined as riding, with C—H = 0.93–0.96 Å and U_iso(H) = 1.2U_eq(C). Atom H1 was refined isotropically, with O1—H1 = 0.85 (1) Å.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of (I), showing the intramolecular hydrogen bonds (dashed lines) and with displacement ellipsoids at the 30% probability level. The suffix A corresponds to symmetry operation (−1 − x, 1 − y, 1 − z).
	Fig. 2. The crystal packing of (I), viewed approximately down the a axis, showing the intermolecular hydrogen-bonded (dashed lines) extended network.

N,N'-Bis(3-hydroxy-4-methoxybenzylidene)hydrazine

Crystal data

C16H16N2O4	F(000) = 316
Mr = 300.31	Dx = 1.339 Mg m^−3
Monoclinic, P21/c	Melting point = 538–539 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 5.6858 (12) Å	Cell parameters from 1595 reflections
b = 10.018 (2) Å	θ = 2.6–26.1°
c = 13.902 (3) Å	µ = 0.10 mm^−1
β = 109.841 (4)°	T = 294 K
V = 744.8 (3) Å^3	Block, light yellow
Z = 2	0.30 × 0.22 × 0.16 mm

Data collection

Bruker SMART CCD area-detector diffractometer	1523 independent reflections
Radiation source: fine-focus sealed tube	1065 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.026
ϕ and ω scans	θmax = 26.4°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −5→7
Tmin = 0.946, Tmax = 0.980	k = −12→10
4096 measured reflections	l = −17→15

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.103	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0456P)^2 + 0.1273P] where P = (Fo^2 + 2Fc^2)/3
1523 reflections	(Δ/σ)max < 0.001
111 parameters	Δρmax = 0.12 e Å^−3
1 restraint	Δρmin = −0.18 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.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq
O1	0.0710 (2)	0.88695 (12)	0.79780 (7)	0.0602 (4)
H1	0.186 (3)	0.9442 (17)	0.8247 (14)	0.088 (7)*
O2	0.3775 (2)	1.00468 (12)	0.71810 (8)	0.0647 (4)
N1	−0.4169 (2)	0.54375 (11)	0.53530 (8)	0.0468 (3)
C1	−0.2847 (3)	0.61183 (14)	0.49583 (10)	0.0455 (4)
H1A	−0.3016	0.5970	0.4278	0.059 (5)*
C2	−0.1074 (3)	0.71255 (13)	0.55342 (10)	0.0407 (4)
C3	−0.1002 (3)	0.75316 (13)	0.65066 (10)	0.0403 (4)
H3	−0.2081	0.7147	0.6802	0.046 (4)*
C4	0.0659 (3)	0.84964 (14)	0.70261 (10)	0.0395 (3)
C5	0.2262 (3)	0.90923 (14)	0.65841 (11)	0.0438 (4)
C6	0.2204 (3)	0.86946 (17)	0.56329 (12)	0.0570 (5)
H6	0.3282	0.9083	0.5338	0.069 (5)*
C7	0.0538 (3)	0.77149 (16)	0.51091 (12)	0.0549 (4)
H7	0.0507	0.7451	0.4464	0.071 (5)*
C8	0.5390 (4)	1.0770 (2)	0.67879 (16)	0.0731 (6)
H8A	0.6500	1.0162	0.6622	0.113 (9)*
H8B	0.6349	1.1396	0.7292	0.113 (8)*
H8C	0.4417	1.1243	0.6183	0.110 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0820 (9)	0.0624 (8)	0.0341 (6)	−0.0261 (6)	0.0169 (6)	−0.0125 (5)
O2	0.0696 (8)	0.0634 (7)	0.0583 (7)	−0.0317 (6)	0.0179 (6)	−0.0157 (6)
N1	0.0591 (8)	0.0357 (7)	0.0322 (6)	−0.0073 (6)	−0.0018 (6)	−0.0032 (5)
C1	0.0585 (10)	0.0373 (8)	0.0310 (7)	0.0004 (7)	0.0026 (6)	−0.0034 (6)
C2	0.0472 (8)	0.0339 (7)	0.0344 (7)	0.0022 (6)	0.0050 (6)	−0.0019 (6)
C3	0.0466 (9)	0.0355 (7)	0.0344 (7)	−0.0036 (6)	0.0082 (6)	0.0018 (6)
C4	0.0486 (8)	0.0352 (7)	0.0287 (7)	0.0010 (6)	0.0052 (6)	−0.0002 (6)
C5	0.0433 (8)	0.0393 (8)	0.0426 (8)	−0.0048 (6)	0.0065 (6)	−0.0037 (6)
C6	0.0598 (11)	0.0637 (11)	0.0542 (10)	−0.0142 (8)	0.0280 (8)	−0.0099 (8)
C7	0.0671 (11)	0.0581 (10)	0.0425 (9)	−0.0073 (8)	0.0225 (8)	−0.0138 (7)
C8	0.0586 (11)	0.0615 (12)	0.0947 (16)	−0.0213 (10)	0.0201 (12)	−0.0051 (11)

Geometric parameters (Å, º)

O1—C4	1.3659 (17)	C3—C4	1.3727 (19)
O1—H1	0.855 (10)	C3—H3	0.9301
O2—C5	1.3631 (17)	C4—C5	1.394 (2)
O2—C8	1.417 (2)	C5—C6	1.371 (2)
N1—C1	1.269 (2)	C6—C7	1.387 (2)
N1—N1^i	1.413 (2)	C6—H6	0.9300
C1—C2	1.459 (2)	C7—H7	0.9299
C1—H1A	0.9300	C8—H8A	0.9600
C2—C7	1.381 (2)	C8—H8B	0.9600
C2—C3	1.3987 (19)	C8—H8C	0.9600
C4—O1—H1	111.6 (14)	O2—C5—C6	126.49 (14)
C5—O2—C8	118.80 (13)	O2—C5—C4	113.82 (12)
C1—N1—N1^i	112.82 (15)	C6—C5—C4	119.70 (13)
N1—C1—C2	122.33 (13)	C5—C6—C7	120.05 (15)
N1—C1—H1A	118.8	C5—C6—H6	120.0
C2—C1—H1A	118.8	C7—C6—H6	120.0
C7—C2—C3	118.89 (13)	C2—C7—C6	120.83 (14)
C7—C2—C1	119.77 (13)	C2—C7—H7	119.6
C3—C2—C1	121.32 (14)	C6—C7—H7	119.6
C4—C3—C2	120.18 (14)	O2—C8—H8A	109.4
C4—C3—H3	119.9	O2—C8—H8B	109.5
C2—C3—H3	119.9	H8A—C8—H8B	109.5
O1—C4—C3	119.14 (14)	O2—C8—H8C	109.5
O1—C4—C5	120.51 (12)	H8A—C8—H8C	109.5
C3—C4—C5	120.35 (13)	H8B—C8—H8C	109.5
N1^i—N1—C1—C2	177.44 (14)	O1—C4—C5—O2	−0.6 (2)
N1—C1—C2—C7	171.79 (14)	C3—C4—C5—O2	178.98 (12)
N1—C1—C2—C3	−9.5 (2)	O1—C4—C5—C6	179.27 (14)
C7—C2—C3—C4	−0.3 (2)	C3—C4—C5—C6	−1.1 (2)
C1—C2—C3—C4	−178.99 (13)	O2—C5—C6—C7	−179.35 (15)
C2—C3—C4—O1	−179.49 (13)	C4—C5—C6—C7	0.7 (2)
C2—C3—C4—C5	0.9 (2)	C3—C2—C7—C6	−0.1 (2)
C8—O2—C5—C6	3.4 (2)	C1—C2—C7—C6	178.65 (14)
C8—O2—C5—C4	−176.71 (15)	C5—C6—C7—C2	−0.2 (3)

Symmetry code: (i) −x−1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2	0.86 (1)	2.20 (2)	2.6405 (17)	112 (2)
O1—H1···N1^ii	0.86 (1)	2.18 (2)	2.9365 (16)	147 (2)
C7—H7···O1^iii	0.93	2.49	3.391 (2)	164

Symmetry codes: (ii) −x, y+1/2, −z+3/2; (iii) x, −y+3/2, z−1/2.