A second monoclinic polymorph of 4,4′-[butane-1,4-diylbis(nitrilo­methyl­idyne)]dibenzonitrile

Abstract

The asymmetric unit of the title Schiff base compound, C₂₀H₁₈N₄, contains one half-mol­ecule, lying across a crystallographic inversion centre and adopting an E configuration with respect to the C=N bonds. The imino group is coplanar with the benzene ring with a maximun deviation of 0.096 (1) Å for the N atom. Within the molecule, the planar units are parallel but extend in opposite directions from the methylene bridge. In the crystal structure, neighbouring mol­ecules are linked together by weak inter­molecular C—H⋯N hydrogen bonds involving the cyano N atoms, forming R ₂ ²(10) ring motifs.

Related literature

For general background, see: Casellato & Vigato (1977 ▶); Calligaris & Randaccio (1987 ▶). For related structures, see: Fun et al. (2008 ▶); Fun, Kia & Kargar (2008a ▶,b ▶); Fun & Kia (2008a ▶,b ▶). For bond-length data, see: Allen et al. (1987 ▶). For hydrogen-bond motifs, see: Bernstein et al. (1995 ▶).

Experimental

Crystal data

• C₂₀H₁₈N₄

• M _r = 314.38

• Monoclinic,

• a = 4.9958 (1) Å

• b = 14.8164 (2) Å

• c = 11.6633 (2) Å

• β = 97.310 (1)°

• V = 856.30 (3) ų

• Z = 2

• Mo Kα radiation

• μ = 0.07 mm⁻¹

• T = 100.0 (1) K

• 0.39 × 0.29 × 0.28 mm

Data collection

• Bruker SMART APEXII CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2005 ▶) T _min = 0.891, T _max = 0.979

• 18411 measured reflections

• 4473 independent reflections

• 3659 reflections with I > 2σ(I)

• R _int = 0.026

Refinement

• R[F ² > 2σ(F ²)] = 0.044

• wR(F ²) = 0.135

• S = 1.04

• 4473 reflections

• 109 parameters

• H-atom parameters constrained

• Δρ_max = 0.55 e Å⁻³

• Δρ_min = −0.26 e Å⁻³

Data collection: APEX2 (Bruker, 2005 ▶); cell refinement: SAINT (Bruker, 2005 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2003 ▶).

Supplementary Material

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

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H2A⋯N2i	0.93	2.52	3.4037 (11)	158

Symmetry code: (i) .

supplementary crystallographic information

Comment

The condensation of primary amines with carbonyl compounds yields Schiff base compounds (Casellato & Vigato, 1977); these are still one of the most prevalent mixed-donor ligands in coordination chemistry. In the past two decades, the syntheses, structures and properties of Schiff base complexes have stimulated much interest due to their noteworthy contributions in single molecule-based magnetism, materials science and the catalysis of many reactions such as carbonylation, hydroformylation, reduction, oxidation, epoxidation and hydrolysis (Casellato & Vigato 1977). In comparison to the Schiff base metal complexes, only a relatively small number of free Schiff base ligands have been characterized structurally (Calligaris & Randaccio, 1987). As an extension of our work (Fun et al., 2008; Fun, Kia & Kargar 2008a,b; Fun & Kia 2008a,b) on the structural characterization of Schiff base ligands, we reported herein the crystal structure of the title compound.

The asymmetric unit of the title compound contains one-half molecule (Fig. 1), lying across a crystallographic inversion centre and adopting E configurations with respect to the C═N bonds. The bond lengths (Allen et al., 1987) and angles are within normal ranges and are comparable with the related structure (Fun et al., 2008). The imino group is coplanar with the benzene ring, and the planar units are parallel but extend in opposite directions from the methylene bridge.

In the crystal structure, neighbouring molecules are linked together by weak intermolecular C-H···N hydrogen bonds (Table 1) involving the cyano N atoms, forming ten-membered rings with R₂²(10) ring motifs (Bernstein et al., 1995).

Experimental

The synthetic method has been described earlier (Fun, Kia & Kargar, 2008b). Single crystals suitable for X-ray analysis were obtained by evaporation of an ethanol solution at room temperature.

Refinement

H atoms were positioned geometrically, with C-H = 0.93 and 0.97 Å for aromatic and methylene H, respectively, and constrained to ride on their parent atoms with U_iso(H) = 1.2U_eq(C). The highest peak is located 0.68 Å from C5 atom.

Figures

Fig. 1.

The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level [symmetry code: (A) -x, 1 - y, -z].

Fig. 2.

A partial packing diagram viewed down the a axis, showing R22(10) ring motifs. Hydrogen bonds are shown as dashed lines.

Crystal data

C20H18N4	F000 = 332
Mr = 314.38	Dx = 1.219 Mg m−3
Monoclinic, P21/n	Mo Kα radiation λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 6822 reflections
a = 4.9958 (1) Å	θ = 2.2–39.9º
b = 14.8164 (2) Å	µ = 0.08 mm−1
c = 11.6633 (2) Å	T = 100.0 (1) K
β = 97.310 (1)º	Block, yellow
V = 856.30 (3) Å3	0.39 × 0.29 × 0.28 mm
Z = 2

Data collection

Bruker SMART APEXII CCD area-detector diffractometer	4473 independent reflections
Radiation source: fine-focus sealed tube	3659 reflections with I > 2σ(I)
Monochromator: graphite	Rint = 0.026
T = 100.0(1) K	θmax = 37.5º
φ and ω scans	θmin = 2.8º
Absorption correction: multi-scan(SADABS; Bruker, 2005)	h = −8→8
Tmin = 0.891, Tmax = 0.979	k = −24→25
18411 measured reflections	l = −19→18

Refinement

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.044	H-atom parameters constrained
wR(F2) = 0.135	w = 1/[σ2(Fo2) + (0.0727P)2 + 0.1307P] where P = (Fo2 + 2Fc2)/3
S = 1.04	(Δ/σ)max < 0.001
4473 reflections	Δρmax = 0.55 e Å−3
109 parameters	Δρmin = −0.26 e Å−3
Primary atom site location: structure-invariant direct methods	Extinction correction: none

Special details

Experimental. The low-temperature data was collected with the Oxford Cyrosystem Cobra low-temperature attachment.

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.

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 > 2sigma(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
N1	0.01080 (11)	0.32548 (4)	0.04403 (5)	0.01925 (11)
N2	1.09394 (17)	−0.03532 (5)	0.17351 (7)	0.03381 (17)
C1	0.40142 (14)	0.18220 (4)	0.04338 (6)	0.01953 (12)
H1A	0.3066	0.1973	−0.0279	0.023*
C2	0.59829 (14)	0.11593 (5)	0.04968 (6)	0.02080 (12)
H2A	0.6360	0.0866	−0.0169	0.025*
C3	0.74003 (13)	0.09356 (4)	0.15748 (6)	0.01898 (11)
C4	0.68642 (13)	0.13779 (5)	0.25771 (6)	0.02032 (12)
H4A	0.7827	0.1231	0.3288	0.024*
C5	0.48772 (13)	0.20402 (4)	0.25021 (5)	0.01888 (11)
H5A	0.4503	0.2335	0.3168	0.023*
C6	0.34401 (12)	0.22663 (4)	0.14350 (5)	0.01610 (11)
C7	0.13465 (12)	0.29707 (4)	0.13917 (5)	0.01716 (11)
H7A	0.0919	0.3215	0.2080	0.021*
C8	−0.19246 (13)	0.39541 (4)	0.05029 (6)	0.02132 (12)
H8A	−0.1937	0.4135	0.1301	0.026*
H8B	−0.3694	0.3715	0.0221	0.026*
C9	−0.13397 (12)	0.47738 (4)	−0.02174 (6)	0.01933 (12)
H9A	−0.1314	0.4587	−0.1013	0.023*
H9B	−0.2785	0.5209	−0.0204	0.023*
C10	0.93805 (15)	0.02262 (5)	0.16554 (6)	0.02439 (14)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
N1	0.0200 (2)	0.0161 (2)	0.0217 (2)	0.00380 (17)	0.00313 (18)	0.00211 (17)
N2	0.0380 (4)	0.0346 (4)	0.0290 (3)	0.0179 (3)	0.0052 (3)	0.0058 (3)
C1	0.0237 (3)	0.0179 (2)	0.0164 (2)	0.0047 (2)	0.00064 (19)	0.00065 (19)
C2	0.0249 (3)	0.0188 (3)	0.0187 (3)	0.0055 (2)	0.0026 (2)	0.0003 (2)
C3	0.0188 (2)	0.0166 (2)	0.0215 (3)	0.00276 (18)	0.00223 (19)	0.00326 (19)
C4	0.0197 (2)	0.0220 (3)	0.0185 (3)	0.0020 (2)	−0.00060 (19)	0.0026 (2)
C5	0.0199 (2)	0.0200 (3)	0.0163 (2)	0.00113 (19)	0.00059 (18)	−0.00036 (19)
C6	0.0173 (2)	0.0140 (2)	0.0168 (2)	0.00002 (17)	0.00157 (17)	0.00093 (17)
C7	0.0183 (2)	0.0148 (2)	0.0187 (2)	0.00041 (17)	0.00331 (18)	−0.00005 (18)
C8	0.0179 (2)	0.0180 (2)	0.0289 (3)	0.00373 (19)	0.0065 (2)	0.0041 (2)
C9	0.0152 (2)	0.0177 (2)	0.0252 (3)	0.00334 (17)	0.00291 (19)	0.0039 (2)
C10	0.0252 (3)	0.0242 (3)	0.0238 (3)	0.0065 (2)	0.0032 (2)	0.0043 (2)

Geometric parameters (Å, °)

N1—C7	1.2714 (8)	C4—H4A	0.9300
N1—C8	1.4590 (8)	C5—C6	1.3962 (9)
N2—C10	1.1548 (9)	C5—H5A	0.9300
C1—C2	1.3851 (9)	C6—C7	1.4740 (8)
C1—C6	1.4015 (9)	C7—H7A	0.9300
C1—H1A	0.9300	C8—C9	1.5260 (9)
C2—C3	1.4019 (9)	C8—H8A	0.9700
C2—H2A	0.9300	C8—H8B	0.9700
C3—C4	1.3955 (10)	C9—C9i	1.5249 (13)
C3—C10	1.4382 (9)	C9—H9A	0.9700
C4—C5	1.3906 (9)	C9—H9B	0.9700
C7—N1—C8	117.13 (6)	C1—C6—C7	121.58 (5)
C2—C1—C6	120.53 (6)	N1—C7—C6	121.92 (6)
C2—C1—H1A	119.7	N1—C7—H7A	119.0
C6—C1—H1A	119.7	C6—C7—H7A	119.0
C1—C2—C3	119.30 (6)	N1—C8—C9	110.76 (5)
C1—C2—H2A	120.3	N1—C8—H8A	109.5
C3—C2—H2A	120.3	C9—C8—H8A	109.5
C4—C3—C2	120.75 (6)	N1—C8—H8B	109.5
C4—C3—C10	119.48 (6)	C9—C8—H8B	109.5
C2—C3—C10	119.75 (6)	H8A—C8—H8B	108.1
C5—C4—C3	119.36 (6)	C9i—C9—C8	112.85 (7)
C5—C4—H4A	120.3	C9i—C9—H9A	109.0
C3—C4—H4A	120.3	C8—C9—H9A	109.0
C4—C5—C6	120.49 (6)	C9i—C9—H9B	109.0
C4—C5—H5A	119.8	C8—C9—H9B	109.0
C6—C5—H5A	119.8	H9A—C9—H9B	107.8
C5—C6—C1	119.57 (6)	N2—C10—C3	178.58 (8)
C5—C6—C7	118.86 (5)
C6—C1—C2—C3	0.04 (10)	C2—C1—C6—C5	0.30 (10)
C1—C2—C3—C4	−0.57 (10)	C2—C1—C6—C7	−179.71 (6)
C1—C2—C3—C10	177.78 (6)	C8—N1—C7—C6	−179.98 (5)
C2—C3—C4—C5	0.76 (10)	C5—C6—C7—N1	174.67 (6)
C10—C3—C4—C5	−177.60 (6)	C1—C6—C7—N1	−5.31 (10)
C3—C4—C5—C6	−0.41 (10)	C7—N1—C8—C9	124.91 (7)
C4—C5—C6—C1	−0.12 (10)	N1—C8—C9—C9i	−62.65 (9)
C4—C5—C6—C7	179.90 (6)

Symmetry codes: (i) −x, −y+1, −z.

Hydrogen-bond geometry (Å, °)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2A···N2ii	0.93	2.52	3.4037 (11)	158

Symmetry codes: (ii) −x+2, −y, −z.