Bis[4-(salicylideneamino)phenyl]methane

The crystal structure of the title Schiff base {systematic name: 2,2′-[methyl­ene­di-p-phenyl­ene­bis(nitrilo­methyl­idyne)]­diphenol}, C₂₇H₂₂N₂O₂, consists of intra­molecularly hydro­gen-bonded mol­ecules inter­linked by C—H...O hydrogen bonds [C...O = 3.426 (2) Å and C—H...O = 152.7 (17)°]. The mol­ecule is in the enol form and is located on a twofold axis. The central methane C atom of the diphenyl­methane motif is displaced from the aromatic ring planes. This effect is compared with previous results, which display an inverse correlation between the out-of-plane displacement and the C—C—C angle around the central methane C atom. In the title compound, the displacement is 0.124 (2) Å and the C—C—C angle is 110.18 (19)°.

S1. Comment

Bis-bidentate Schiff base ligands have attracted significant interest as building blocks in metallosupramolecular chemistry, especially for the synthesis of helicates (see, for example, Kruger et al., 2001; Yoshida & Ichikawa, 1997; Yoshida et al., 2000; Franceschi et al., 2001; Albrecht, 2001). The title compound, (I), has been shown to form helicate supramolecular complexes with transition metals of the form [M₂L₂] (Yoshida & Ichikawa, 1997; Yoshida et al., 2000; Kruger et al., 2001). Free N-salicylideneanilines are often thermochromic (Ogawa et al., 1998; Filarowski et al., 2002; Popović, et al., 2002; Ogawa & Harada, 2003), due to a temperature-dependent equilibrium between the keto–amine form and the enol–imino form.

The location of the H atoms showed unequivocally that (I) occurs in the enol-imino form in the crystalline state, in agreement with previous IR results (Kruger et al., 2001; Pui et al., 2001). This is also the form found in CHCl₃ solution (Yoshida et al., 2000; Kruger et al., 2001). The factors determining whether a given molecule will occur in the keto–amine or enol–imino form are manifold. It has been shown to depend on the substitution on the benzene rings (Filarowski et al., 2002; Popović et al., 2002) and intermolecular hydrogen bonding (Ogawa et al., 1998; Ogawa & Harada, 2003), and aggregation (packing) of the molecules plays an important role for the equilibrium in solution (Ogawa et al., 2001; Ogawa & Harada, 2003). It has been reported that (I) undergoes a colour change from yellow to red at 373 K (Zhu et al., 2001), but it is unclear whether this colour change is related to the keto–enol tautomerism.

The molecules of (I) are V-shaped, with atom C14 coinciding with a crystallographic twofold axis. The angle between the two symmetry-related C8–C13 benzene rings is 78.87 (5)°. The C2–C7 phenol ring (ring 1) is not coplanar with the C8–C13 benzene ring (ring 2), the interplanar angle being 12.99 (7)° (Fig. 1b, Table 1). The imino plane is almost coplanar with ring 1 [interplanar angle 1.66 (11)°]. It is, however, twisted significantly out of the plane of ring 2: the C1—N1—C8—C9 torsion angle differs significantly from 180° (Table 1) and the interplanar angle is 14.86 (13)°. This lack of coplanarity is presumably caused by steric hindrance between the H atoms on atoms C1 and C13. Indeed, the H1A···H13 distance [2.07 (3) Å] is significantly shorter than the sum of the van der Waals radii (2.40 Å; Reference?).

Surprisingly, atom C14 is significantly out of the mean plane of ring 2 [0.124 (2) Å]. In order to determine whether this phenomenon is particular to the structure of (I) or reflects a general effect, we examined the Cambridge Structural Database (CSD, Version 5.27 of November 2005, 355064 entries; Allen, 2002). Fig. 3 shows the search fragment, bisphenylmethane, together with the relation between the average distance of the methane C atom (C_m) to the planes of the benzene rings and the methane C—C_m—C bond angle. Below a given onset angle, there is an inverse linear correlation between the angle and displacement of the C_m atom out of the aromatic plane. The data with R < 0.05 (38 structures, 44 angles) were fitted to the relation d = d₀ + α(a-a_c) for a < a_c, and d = d₀ otherwise. The fit, with R² = 0.919, resulted in a_c = 112.1 (4)°, d₀ = 0.057 (6) Å and α = −0.048 (3) Å/degree. The value found in (I) (black diamond in Fig. 3) is in excellent agreement with the overall correlation. Structures of lesser quality, 0.05 < R < 0.10 (61 structures, 93 angles), show a larger spread than the lower R factor data set but the trends are similar. The displacement is towards the interior of the V shape formed by the two aromatic rings. This effect is likely to be related to π–π interactions between the two benzene rings. However, in (I) and several, but not all, of the CSD structures with significant out of plane displacements, the two benzene rings are not coplanar. This suggests that a more complicated mechanism may be responsible for the observed behaviour.

The V-shaped molecules pack into chevron-like columns that extend along (010) (Fig. 2) via van der Waals contacts. These columns are connected to their inverted neighbour stack along the c axis by C—H···O hydrogen bonds between the enol O atom and the H atom on atom C1.

S2. Experimental

A sample of (I), synthesized by Franceschi & Floriani (2000), was kindly provided by Dr F. Franceschi of the Department of Chemistry of the École Polytechnique Fédérale de Lausanne, Switzerland. A plate-shaped yellow crystal with well developed faces was selected and mounted on a glass needle. The structure of (I) was determined using synchrotron radiation data collected at the Swiss–Norwegian Beam Line at the European Synchrotron Radiation Facility (ESRF), Grenoble, France.

S3. Refinement

All H atoms were clearly visible in the difference electron-density map. They were initially included in the riding model. Subsequent refinement including the H-atom positions led to significant reduction in residuals. Thus, the positions of all H atoms were refined freely in the final model. The atomic displacement parameters of the H atoms were constrained according to U_iso(H) = 1.2U_eq(C) or 1.5U_eq(O).

Computing details

Data collection: MAR345 Software (Marresearch, 2005); cell refinement: CrysAlis RED (Oxford Diffraction, 2000); data reduction: CrysAlis RED and XPREP (Siemens, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1996); software used to prepare material for publication: Please provide missing details.

Figures

	Fig. 1. The molecular structure of (I) and atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Dashed lines indicate the intramolecular O—H···N hydrogen bonds. (a) A projection of (I) onto the mean plane. The molecule is situated on a twofold axis (through atom C14). Unlabelled atoms are related to labelled atoms by the symmetry operator (1 − x, y, −z + 3/2). [Please check added text] (b) A view of (I), perpendicular to the least-squares plane of the C8–C13 aromatic ring. Note the twist of the molecule at N.
	Fig. 2. A packing diagram for (I), in projection along (010). The V shapes on the right-hand side indicate the orientation of the molecular shapes in the columns along (010) (i.e. perpendicular to the plane of view).
	Fig. 3. The relation between the C—Cm—C bond angle around the methylene group in diphenylmethane and the average distance between the methane C atom Cm and the aromatic ring planes, as extracted from the CSD. The search fragment is shown in the inset, with the C—Cm—C bond angle marked in bold. Closed solid squares represent CSD data with 0.05 < R < 0.10 and open circles are data with R < 0.05. The black diamond represents (I).

2,2'-[methylenedi-p-phenylenebis(nitrilomethylidyne)]diphenol

Crystal data

C27H22N2O2	Z = 4
Mr = 406.47	F(000) = 856
Monoclinic, C2/c	Dx = 1.319 Mg m^−3
Hall symbol: -C 2yc	Synchrotron radiation, λ = 0.80000 Å
a = 36.496 (7) Å	µ = 0.08 mm^−1
b = 4.6030 (9) Å	T = 293 K
c = 12.231 (2) Å	Platelet, yellow
β = 95.06 (3)°	0.40 × 0.15 × 0.05 mm
V = 2046.7 (7) Å^3

Data collection

MAR345 diffractometer	1820 reflections with I > 2σ(I)
Radiation source: bending magnet 1 at ESRF	Rint = 0.022
Si(111) double crystal monochromator with bent second crystal for sagittal focusing	θmax = 29.9°, θmin = 4.3°
Detector resolution: 6.667 pixels mm^-1	h = −44→45
ϕ scans	k = −5→5
5072 measured reflections	l = −15→15
1954 independent reflections

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)] = 0.056	Hydrogen site location: difference Fourier map
wR(F^2) = 0.168	Only H-atom coordinates refined
S = 1.12	w = 1/[σ^2(Fo^2) + (0.09P)^2 + 1.25P] where P = (Fo^2 + 2Fc^2)/3
1954 reflections	(Δ/σ)max < 0.001
174 parameters	Δρmax = 0.14 e Å^−3
0 restraints	Δρmin = −0.13 e Å^−3

Special details

Experimental. Diffraction data were collected in single-bunch mode using a MAR345 area detector and focusing optics. The latter consisted of a vertically collimating Rh-coated Si mirror followed by a Si(111) double crystal monochromator, where the second crystal is sagittally bent for horizontal focusing, and a second vertically focusing Rh-coated mirror. A total of 90 images were measured with 2° oscillations. Prior to data collection, it was verified on a test image that none of the symmetry elements of the crystal was parallel to the oscillation axis, thereby ensuring as complete a data set as possible (94.4% completeness). The degree of linear polarization was assumed to be 0.95 (Birkedal, 2000). The integrated intensities were scaled to correct for variations in the incident beam intensity and for orientation-dependent absorption of the sample mount.

Birkedal, H. (2000). PhD thesis, University of Lausanne, Switzerland.

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	0.36000 (5)	−0.0015 (4)	1.03239 (11)	0.0643 (5)
H1	0.3750 (8)	0.135 (7)	0.988 (3)	0.096*
N1	0.38758 (4)	0.2842 (3)	0.87619 (12)	0.0385 (4)
C1	0.36495 (5)	0.1510 (4)	0.80768 (14)	0.0372 (4)
H1A	0.3650 (6)	0.180 (5)	0.7287 (17)	0.045*
C2	0.33803 (5)	−0.0529 (4)	0.84262 (14)	0.0364 (4)
C3	0.33650 (5)	−0.1219 (4)	0.95443 (16)	0.0447 (5)
C4	0.31002 (7)	−0.3174 (5)	0.9847 (2)	0.0601 (6)
H4	0.3103 (7)	−0.358 (6)	1.063 (2)	0.072*
C5	0.28598 (6)	−0.4440 (5)	0.9057 (2)	0.0597 (6)
H5	0.2688 (7)	−0.581 (6)	0.927 (2)	0.072*
C6	0.28759 (6)	−0.3830 (5)	0.7952 (2)	0.0537 (6)
H6	0.2706 (7)	−0.467 (5)	0.740 (2)	0.064*
C7	0.31352 (5)	−0.1893 (4)	0.76485 (18)	0.0465 (5)
H7	0.3147 (6)	−0.139 (5)	0.6886 (19)	0.056*
C8	0.41373 (5)	0.4826 (4)	0.84031 (14)	0.0355 (4)
C9	0.44218 (6)	0.5668 (4)	0.91650 (16)	0.0442 (5)
H9	0.4426 (6)	0.496 (5)	0.9895 (19)	0.053*
C10	0.46934 (6)	0.7534 (4)	0.88853 (17)	0.0465 (5)
H10	0.4891 (7)	0.804 (5)	0.939 (2)	0.056*
C11	0.46882 (5)	0.8690 (4)	0.78316 (15)	0.0383 (4)
C12	0.43968 (5)	0.7934 (4)	0.70847 (16)	0.0432 (5)
H12	0.4371 (6)	0.878 (5)	0.6330 (18)	0.052*
C13	0.41257 (5)	0.6015 (4)	0.73512 (15)	0.0419 (5)
H13	0.3913 (6)	0.554 (5)	0.6829 (18)	0.050*
C14	0.5000	1.0572 (6)	0.7500	0.0459 (7)
H14	0.4925 (6)	1.191 (5)	0.6891 (19)	0.055*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0777 (11)	0.0796 (12)	0.0353 (7)	−0.0241 (9)	0.0028 (7)	0.0018 (7)
N1	0.0397 (8)	0.0371 (8)	0.0394 (8)	−0.0008 (6)	0.0073 (7)	−0.0002 (6)
C1	0.0401 (10)	0.0375 (9)	0.0346 (9)	0.0005 (7)	0.0059 (8)	−0.0002 (7)
C2	0.0358 (9)	0.0343 (9)	0.0394 (9)	0.0029 (7)	0.0058 (7)	0.0008 (7)
C3	0.0478 (11)	0.0452 (10)	0.0421 (10)	−0.0006 (8)	0.0089 (9)	0.0007 (8)
C4	0.0685 (15)	0.0605 (13)	0.0542 (13)	−0.0081 (11)	0.0216 (12)	0.0097 (10)
C5	0.0500 (12)	0.0500 (12)	0.0818 (16)	−0.0093 (10)	0.0211 (12)	0.0024 (11)
C6	0.0394 (10)	0.0484 (11)	0.0722 (14)	−0.0048 (8)	−0.0012 (10)	−0.0033 (10)
C7	0.0450 (10)	0.0421 (10)	0.0516 (11)	−0.0009 (8)	0.0003 (9)	0.0022 (8)
C8	0.0370 (9)	0.0323 (8)	0.0378 (9)	0.0014 (6)	0.0063 (7)	−0.0009 (7)
C9	0.0495 (11)	0.0452 (10)	0.0376 (9)	−0.0064 (8)	0.0023 (8)	0.0002 (8)
C10	0.0472 (11)	0.0451 (11)	0.0465 (10)	−0.0080 (8)	−0.0005 (9)	−0.0038 (8)
C11	0.0372 (9)	0.0266 (8)	0.0522 (10)	0.0045 (6)	0.0111 (8)	−0.0037 (7)
C12	0.0445 (10)	0.0432 (10)	0.0426 (10)	0.0035 (8)	0.0083 (8)	0.0069 (8)
C13	0.0391 (10)	0.0463 (10)	0.0400 (10)	−0.0025 (8)	0.0018 (8)	0.0030 (8)
C14	0.0458 (15)	0.0280 (12)	0.0655 (17)	0.000	0.0139 (14)	0.000

Geometric parameters (Å, º)

O1—C3	1.344 (3)	C7—H7	0.97 (2)
O1—H1	1.02 (3)	C8—C9	1.388 (3)
N1—C1	1.280 (2)	C8—C13	1.395 (2)
N1—C8	1.418 (2)	C9—C10	1.377 (3)
C1—C2	1.450 (2)	C9—H9	0.95 (2)
C1—H1A	0.97 (2)	C10—C11	1.393 (3)
C2—C7	1.396 (3)	C10—H10	0.94 (2)
C2—C3	1.410 (3)	C11—C12	1.384 (3)
C3—C4	1.395 (3)	C11—C14^i	1.514 (2)
C4—C5	1.376 (4)	C11—C14	1.514 (2)
C4—H4	0.97 (3)	C12—C13	1.386 (3)
C5—C6	1.386 (4)	C12—H12	1.00 (2)
C5—H5	0.94 (3)	C13—H13	0.99 (2)
C6—C7	1.375 (3)	C14—H14	0.99 (2)
C6—H6	0.95 (3)
C3—O1—H1	102.4 (18)	C9—C8—N1	117.13 (16)
C1—N1—C8	121.26 (15)	C13—C8—N1	124.84 (17)
N1—C1—C2	122.14 (16)	C10—C9—C8	121.29 (18)
N1—C1—H1A	121.7 (13)	C10—C9—H9	119.8 (14)
C2—C1—H1A	116.1 (13)	C8—C9—H9	118.9 (14)
C7—C2—C3	118.80 (17)	C9—C10—C11	121.1 (2)
C7—C2—C1	120.03 (17)	C9—C10—H10	121.4 (14)
C3—C2—C1	121.16 (17)	C11—C10—H10	117.4 (14)
O1—C3—C4	119.41 (19)	C12—C11—C10	117.49 (17)
O1—C3—C2	121.19 (17)	C12—C11—C14^i	121.27 (15)
C4—C3—C2	119.4 (2)	C10—C11—C14^i	121.16 (16)
C5—C4—C3	120.0 (2)	C12—C11—C14	121.27 (15)
C5—C4—H4	124.0 (16)	C10—C11—C14	121.16 (16)
C3—C4—H4	115.9 (16)	C11—C12—C13	121.85 (18)
C4—C5—C6	121.3 (2)	C11—C12—H12	121.2 (13)
C4—C5—H5	119.2 (15)	C13—C12—H12	117.0 (13)
C6—C5—H5	119.4 (15)	C12—C13—C8	120.16 (19)
C7—C6—C5	118.9 (2)	C12—C13—H13	121.8 (12)
C7—C6—H6	119.4 (15)	C8—C13—H13	118.0 (13)
C5—C6—H6	121.6 (15)	C11—C14—C11^i	110.17 (19)
C6—C7—C2	121.5 (2)	C11—C14—H14	113.1 (13)
C6—C7—H7	120.6 (14)	C11^i—C14—H14	108.7 (13)
C2—C7—H7	117.9 (14)	H14—C14—H14^i	103 (3)
C9—C8—C13	118.02 (17)
C9—C8—N1—C1	−165.97 (17)	O1—C3—C2—C1	−0.2 (3)
C1—N1—C8—C9	−165.97 (17)	C10—C11—C14—C11^i	82.96 (16)
C2—C1—N1—C8	179.92 (15)

Symmetry code: (i) −x+1, y, −z+3/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···N1	1.02 (3)	1.63 (3)	2.595 (2)	155 (3)
C1—H1A···O1^ii	0.97 (2)	2.53 (2)	3.426 (2)	152.7 (17)

Symmetry code: (ii) x, −y, z−1/2.