N,N'-Bis(2-hydroxy­benzyl­idene)pentane-1,5-diamine

In the title potential O,N,N',O'-tetra­dentate Schiff base ligand {systematic name: 2,2'-[pentane-1,5-diylbis(nitrilo­methyl­idyne)]diphenol}, C₁₉H₂₂N₂O₂, the mutual orientation of the three planar fragments determines the conformation of the mol­ecule. The dihedral angles between the planes of the two salicyl­idene groups and the plane of the central extended pentane chain are 78.4 (2) and 62.0 (3)°, and the angle between the terminal ring planes is 55.4 (1)°. Strong intra­molecular O-H...N hydrogen bonds close almost-planar six-membered rings, and the O-H bonds are elongated as a result of hydrogen-bond formation.

S1. Comment

Much effort has been devoted in recent years to the design and synthesis of salicylaldimines and their metal complexes displaying binding properties toward deoxyribonucleic acid (DNA), with the aim of developing novel therapeutic agents which prevent the growth and replication of cancerous cells (Silvestri et al., 2007). Among the chemical moieties which have been used as part of chemotherapeutic agents are biogenic polyamines (Karigiannis & Papaioannou, 2000). The incorporation of biogenic polyamine fragments with flexibility and strong affinity for nucleic acids can prompt the emergence of new architectures with novel physicochemical properties and potential applications in technology and pharmaceutics. It seemed, therefore, to be of interest for us to synthesize the new salicylaldimine system derived from cadaverine, a biogenic amine.

The conformation of the title compound, (I), and its analogues can be described by the mutual orientation of three approximately planar fragments, A, B and C (Fig. 1): two salicylidene groups, for which the maximum deviations from the least-squares plane through nine atoms are 0.018 (3) Å for fragment A and 0.067 (3) Å for fragment B, and the central pentane chain (C), which adopts the exended conformation and is planar to within 0.044 (2) Å. The corresponding dihedral angles are: A/C 78.4 (2), B/C 62.0 (3) and A/B 55.4 (1)°. It should be noted that the conformation is not symmetrical. For fragment A, atom N8 is almost coplanar with the plane of the pentane chain [N8—C9—C10—C11 torsion angle 177.1 (3)°], while atom N14 is displaced by almost 1.5 Å [N14—C13—C12—C11 = 68.0 (4)°] from this plane.

In the analogues of (I) with different aliphatic chain lengths, two conformations are observed, depending on the even or odd number of atoms in the chain. This is related to the symmetry of the molecule, which is also a function of the number of atoms in the aliphatic chain. For the even-numbered aliphatic chains, the molecule can be centrosymmetric, with the centre of symmetry situated at the middle of the central C—C bond. In this case, due to the symmetry, the terminal ring planes have to be exactly parallel. This symmetry is realised in the analogues of (I) with n = 2 (Bresciani Pahor et al., 1978; in this case the symmetry is only approximate), n = 4 (Kennedy & Reglinski, 2001), n = 6 (Sheikhshoaie & Sharif, 2006) and n = 10 (Yu, 2006). The same symmetry is also observed for a dioxo-derivative of the n = 8 compound, 2,2-[3,6-dioxa-1,8-octanediylbis(nitrilomethylidene)]bisphenol (Etemadi et al., 2004).

When the number of C atoms in the chain is odd, the molecule cannot be centrosymmetric, and this is the case for (I), as well as for the molecule with n = 1, which lies on a twofold axis (Novitchi et al., 2002), and n = 3 (Elderman et al., 1991), with the molecule on a general position.

Interestingly, despite the different conformations, in three `intermediate-length' cases (n = 4, 5 and 6), the shape of the unit cell is similar. In particular, the b axes, which are parallel to the twofold screw axes for n = 4 and n = 6, are almost equal (ca 5.7 Å). In the case of (I), a pseudo 2₁ axis can be found along b (Fig. 2).

Short intramolecular O—H···N hydrogen bonds serve to close the almost planar six-membered rings [maximum deviations of 0.03 (3) and 0.06 (3) Å for fragments A and B, respectively]. The H atoms involved in these bonds (H1 and H17) are significantly displaced towards acceptor N atoms; the refined O—H distances are long in comparison with typical values. The reliability of these results is demonstrated by the difference Fourier maps (Fig. 3) calculated for a model without these H atoms.

Related literature

For related literature, see: Bresciani Pahor, Calligaris, Nardin & Randaccio (1978); Elderman et al. (1991); Etemadi et al. (2004); Karigiannis & Papaioannou (2000); Kennedy & Reglinski (2001); Novitchi et al. (2002); Sheikhshoaie & Sharif (2006); Silvestri et al. (2007); Yu (2006).

S2. Experimental

To a solution of salicylaldehyde (0.4 mmol) in ethanol (30 ml), cadaverine (0.1 mmol) in methanol (30 ml) was added dropwise over a period of 30 min with stirring. The reaction was carried out for 72 h under an argon atmosphere. The solution volume was then reduced to 5 ml by rotary evaporation and the remaining solution was left to stand in the freezer. After 7 d, yellow crystals of (I) suitable for X-ray diffraction analysis were isolated.

S3. Refinement

The H atoms of the hydroxy groups were found in a difference Fourier map (cf. Fig. 3) and their positional and isotropic displacement parameters were refined [O—H = 1.00 (7) Å Please check added text]. The other H atoms were placed in idealized positions and refined as riding, with C—H = 0.95–0.99 Å [Please check added text] and with U_iso(H) = 1.2U_eq(C). Since the molecule is not chiral and lacks any heavy atoms, Friedel pairs were merged before the refinement.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Stereochemical Workstation Operation Manual (Siemens, 1989) and ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecule of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. The three fragments are denoted A, B and C.
	Fig. 2. The crystal packing of (I), as seen approximately along the c direction.
	Fig. 3. The difference Fourier maps calculated for a model without H atoms involved in intramolecular hydrogen bonds: (a) H1 and (b) H17. Solid lines indicate positive values and dashedlines indicate negative values. Contour level 0.04 e Å^-3.

2,2'-[pentane-1,5-diylbis(nitrilomethylidyne)]diphenol

Crystal data

C19H22N2O2	F(000) = 332
Mr = 310.39	Dx = 1.248 Mg m^−3
Monoclinic, Pc	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P -2yc	Cell parameters from 5004 reflections
a = 16.3631 (18) Å	θ = 2.3–24.0°
b = 5.6428 (5) Å	µ = 0.08 mm^−1
c = 9.1251 (8) Å	T = 100 K
β = 101.418 (10)°	Block, colourless
V = 825.88 (14) Å^3	0.45 × 0.3 × 0.2 mm
Z = 2

Data collection

Kuma KM4 CCD four-circle diffractometer	1484 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.033
Graphite monochromator	θmax = 28.2°, θmin = 3.6°
Detector resolution: 8.1929 pixels mm^-1	h = −21→20
ω scans	k = −7→7
8735 measured reflections	l = −12→12
1868 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)] = 0.063	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.113	H atoms treated by a mixture of independent and constrained refinement
S = 1.15	w = 1/[σ^2(Fo^2) + (0.01P)^2 + 0.9022P] where P = (Fo^2 + 2Fc^2)/3
1868 reflections	(Δ/σ)max = 0.001
216 parameters	Δρmax = 0.36 e Å^−3
2 restraints	Δρmin = −0.25 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
C1	0.6136 (3)	−0.3963 (8)	1.0580 (5)	0.0284 (10)
O1	0.5394 (2)	−0.4934 (6)	0.9954 (4)	0.0374 (8)
H1	0.509 (4)	−0.370 (13)	0.926 (8)	0.08 (2)*
C2	0.6654 (3)	−0.5159 (8)	1.1735 (5)	0.0331 (11)
H2	0.6486	−0.6640	1.2072	0.040*
C3	0.7412 (3)	−0.4194 (9)	1.2391 (5)	0.0373 (11)
H3	0.7758	−0.5008	1.3192	0.045*
C4	0.7677 (3)	−0.2056 (10)	1.1901 (5)	0.0387 (11)
H4	0.8205	−0.1423	1.2350	0.046*
C5	0.7167 (3)	−0.0856 (8)	1.0758 (5)	0.0332 (10)
H5	0.7345	0.0615	1.0424	0.040*
C6	0.6386 (3)	−0.1786 (8)	1.0082 (5)	0.0268 (9)
C7	0.5854 (3)	−0.0465 (9)	0.8896 (5)	0.0311 (10)
H7	0.6039	0.1009	0.8577	0.037*
N8	0.5136 (2)	−0.1280 (8)	0.8277 (4)	0.0365 (10)
C9	0.4629 (3)	0.0083 (11)	0.7050 (6)	0.0457 (14)
H9A	0.4404	−0.1003	0.6216	0.055*
H9B	0.4988	0.1262	0.6678	0.055*
C10	0.3923 (3)	0.1336 (8)	0.7537 (5)	0.0327 (9)
H10A	0.4146	0.2360	0.8405	0.039*
H10B	0.3548	0.0152	0.7860	0.039*
C11	0.3429 (3)	0.2840 (8)	0.6292 (5)	0.0353 (9)
H11A	0.3818	0.3880	0.5886	0.042*
H11B	0.3152	0.1788	0.5475	0.042*
C12	0.2775 (3)	0.4361 (8)	0.6801 (5)	0.0338 (9)
H12A	0.2399	0.3322	0.7241	0.041*
H12B	0.3055	0.5445	0.7596	0.041*
C13	0.2258 (3)	0.5808 (8)	0.5570 (5)	0.0336 (10)
H13A	0.1907	0.6941	0.6000	0.040*
H13B	0.2627	0.6723	0.5042	0.040*
N14	0.1725 (2)	0.4217 (7)	0.4515 (4)	0.0296 (8)
C15	0.0976 (3)	0.4839 (8)	0.3955 (4)	0.0278 (9)
H15	0.0761	0.6274	0.4270	0.033*
C16	0.0450 (3)	0.3362 (8)	0.2837 (5)	0.0254 (9)
C17	0.0739 (3)	0.1168 (8)	0.2413 (4)	0.0267 (9)
O17	0.1500 (2)	0.0338 (6)	0.3046 (3)	0.0335 (7)
H17	0.186 (4)	0.165 (11)	0.400 (7)	0.067 (19)*
C18	0.0243 (3)	−0.0141 (8)	0.1298 (5)	0.0313 (10)
H18	0.0443	−0.1598	0.0985	0.038*
C19	−0.0544 (3)	0.0656 (10)	0.0634 (5)	0.0386 (12)
H19	−0.0881	−0.0265	−0.0126	0.046*
C20	−0.0842 (3)	0.2768 (9)	0.1066 (6)	0.0386 (11)
H20	−0.1384	0.3303	0.0612	0.046*
C21	−0.0346 (3)	0.4115 (8)	0.2171 (5)	0.0306 (10)
H21	−0.0553	0.5569	0.2476	0.037*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.025 (2)	0.029 (2)	0.031 (2)	−0.0022 (19)	0.0072 (18)	−0.0018 (17)
O1	0.0334 (19)	0.0325 (17)	0.0444 (19)	−0.0096 (15)	0.0029 (15)	0.0004 (15)
C2	0.035 (3)	0.031 (2)	0.034 (2)	0.002 (2)	0.010 (2)	0.0076 (19)
C3	0.035 (3)	0.044 (3)	0.032 (2)	0.009 (2)	0.003 (2)	0.005 (2)
C4	0.028 (2)	0.044 (3)	0.041 (3)	−0.004 (2)	0.001 (2)	−0.007 (2)
C5	0.028 (3)	0.029 (2)	0.043 (3)	−0.001 (2)	0.0082 (19)	−0.003 (2)
C6	0.025 (2)	0.027 (2)	0.029 (2)	−0.0001 (18)	0.0081 (17)	−0.0011 (18)
C7	0.027 (2)	0.035 (2)	0.033 (2)	0.0039 (19)	0.0115 (18)	0.0086 (19)
N8	0.031 (2)	0.048 (2)	0.030 (2)	0.0078 (18)	0.0059 (16)	0.0085 (17)
C9	0.032 (3)	0.065 (4)	0.040 (3)	0.013 (2)	0.008 (2)	0.017 (2)
C10	0.031 (2)	0.036 (2)	0.0306 (19)	0.0002 (18)	0.0045 (16)	−0.0007 (17)
C11	0.031 (2)	0.041 (2)	0.033 (2)	0.005 (2)	0.0065 (17)	−0.0018 (18)
C12	0.032 (2)	0.037 (2)	0.031 (2)	0.0013 (19)	0.0015 (17)	−0.0014 (18)
C13	0.032 (2)	0.034 (2)	0.032 (2)	0.000 (2)	0.0022 (17)	−0.0079 (19)
N14	0.026 (2)	0.034 (2)	0.0288 (18)	0.0003 (16)	0.0040 (14)	−0.0056 (15)
C15	0.030 (2)	0.029 (2)	0.026 (2)	−0.0024 (18)	0.0091 (17)	−0.0027 (17)
C16	0.025 (2)	0.023 (2)	0.028 (2)	−0.0023 (18)	0.0053 (17)	0.0022 (17)
C17	0.030 (2)	0.024 (2)	0.027 (2)	−0.0011 (18)	0.0066 (18)	0.0030 (16)
O17	0.0319 (18)	0.0338 (17)	0.0340 (16)	0.0085 (14)	0.0046 (14)	−0.0012 (14)
C18	0.038 (3)	0.028 (2)	0.029 (2)	−0.005 (2)	0.0080 (19)	−0.0021 (18)
C19	0.036 (3)	0.042 (3)	0.036 (2)	−0.010 (2)	0.002 (2)	0.001 (2)
C20	0.026 (2)	0.040 (3)	0.046 (3)	−0.005 (2)	−0.002 (2)	0.007 (2)
C21	0.027 (3)	0.026 (2)	0.039 (3)	0.0031 (19)	0.0067 (19)	0.0048 (19)

Geometric parameters (Å, º)

C1—O1	1.351 (5)	C11—H11A	0.9900
C1—C2	1.389 (6)	C11—H11B	0.9900
C1—C6	1.398 (6)	C12—C13	1.506 (6)
O1—H1	1.00 (7)	C12—H12A	0.9900
C2—C3	1.378 (7)	C12—H12B	0.9900
C2—H2	0.9500	C13—N14	1.470 (5)
C3—C4	1.386 (7)	C13—H13A	0.9900
C3—H3	0.9500	C13—H13B	0.9900
C4—C5	1.378 (7)	N14—C15	1.279 (6)
C4—H4	0.9500	C15—C16	1.459 (6)
C5—C6	1.406 (6)	C15—H15	0.9500
C5—H5	0.9500	C16—C21	1.389 (6)
C6—C7	1.454 (6)	C16—C17	1.407 (6)
C7—N8	1.285 (6)	C17—O17	1.349 (5)
C7—H7	0.9500	C17—C18	1.383 (6)
N8—C9	1.471 (6)	O17—H17	1.20 (6)
C9—C10	1.495 (6)	C18—C19	1.385 (7)
C9—H9A	0.9900	C18—H18	0.9500
C9—H9B	0.9900	C19—C20	1.375 (8)
C10—C11	1.517 (5)	C19—H19	0.9500
C10—H10A	0.9900	C20—C21	1.389 (7)
C10—H10B	0.9900	C20—H20	0.9500
C11—C12	1.514 (6)	C21—H21	0.9500
O1—C1—C2	119.0 (4)	C12—C11—H11B	109.0
O1—C1—C6	121.0 (4)	C10—C11—H11B	109.0
C2—C1—C6	120.0 (4)	H11A—C11—H11B	107.8
C1—O1—H1	106 (4)	C13—C12—C11	113.9 (3)
C3—C2—C1	119.9 (4)	C13—C12—H12A	108.8
C3—C2—H2	120.1	C11—C12—H12A	108.8
C1—C2—H2	120.1	C13—C12—H12B	108.8
C2—C3—C4	121.1 (4)	C11—C12—H12B	108.8
C2—C3—H3	119.5	H12A—C12—H12B	107.7
C4—C3—H3	119.5	N14—C13—C12	109.3 (3)
C5—C4—C3	119.4 (5)	N14—C13—H13A	109.8
C5—C4—H4	120.3	C12—C13—H13A	109.8
C3—C4—H4	120.3	N14—C13—H13B	109.8
C4—C5—C6	120.7 (4)	C12—C13—H13B	109.8
C4—C5—H5	119.7	H13A—C13—H13B	108.3
C6—C5—H5	119.7	C15—N14—C13	119.4 (4)
C1—C6—C5	119.0 (4)	N14—C15—C16	120.6 (4)
C1—C6—C7	121.5 (4)	N14—C15—H15	119.7
C5—C6—C7	119.6 (4)	C16—C15—H15	119.7
N8—C7—C6	120.3 (4)	C21—C16—C17	119.0 (4)
N8—C7—H7	119.8	C21—C16—C15	120.2 (4)
C6—C7—H7	119.8	C17—C16—C15	120.7 (4)
C7—N8—C9	118.4 (4)	O17—C17—C18	119.2 (4)
N8—C9—C10	111.9 (4)	O17—C17—C16	121.3 (4)
N8—C9—H9A	109.2	C18—C17—C16	119.5 (4)
C10—C9—H9A	109.2	C17—O17—H17	112 (3)
N8—C9—H9B	109.2	C17—C18—C19	120.5 (5)
C10—C9—H9B	109.2	C17—C18—H18	119.7
H9A—C9—H9B	107.9	C19—C18—H18	119.7
C9—C10—C11	111.8 (3)	C20—C19—C18	120.5 (5)
C9—C10—H10A	109.3	C20—C19—H19	119.7
C11—C10—H10A	109.3	C18—C19—H19	119.7
C9—C10—H10B	109.3	C19—C20—C21	119.5 (5)
C11—C10—H10B	109.3	C19—C20—H20	120.2
H10A—C10—H10B	107.9	C21—C20—H20	120.2
C12—C11—C10	113.1 (3)	C20—C21—C16	120.9 (4)
C12—C11—H11A	109.0	C20—C21—H21	119.6
C10—C11—H11A	109.0	C16—C21—H21	119.6
O1—C1—C2—C3	−179.8 (4)	C10—C11—C12—C13	−178.1 (4)
C6—C1—C2—C3	0.2 (7)	C11—C12—C13—N14	68.4 (5)
C1—C2—C3—C4	−1.1 (8)	C12—C13—N14—C15	140.7 (4)
C2—C3—C4—C5	1.2 (8)	C13—N14—C15—C16	176.3 (4)
C3—C4—C5—C6	−0.4 (8)	N14—C15—C16—C21	−176.3 (4)
O1—C1—C6—C5	−179.4 (4)	N14—C15—C16—C17	3.5 (6)
C2—C1—C6—C5	0.6 (6)	C21—C16—C17—O17	−178.7 (4)
O1—C1—C6—C7	1.2 (7)	C15—C16—C17—O17	1.5 (6)
C2—C1—C6—C7	−178.8 (4)	C21—C16—C17—C18	3.0 (6)
C4—C5—C6—C1	−0.5 (7)	C15—C16—C17—C18	−176.8 (4)
C4—C5—C6—C7	178.9 (4)	O17—C17—C18—C19	179.5 (4)
C1—C6—C7—N8	0.1 (7)	C16—C17—C18—C19	−2.1 (7)
C5—C6—C7—N8	−179.3 (4)	C17—C18—C19—C20	0.5 (7)
C6—C7—N8—C9	−178.2 (4)	C18—C19—C20—C21	0.4 (8)
C7—N8—C9—C10	−105.4 (5)	C19—C20—C21—C16	0.5 (8)
N8—C9—C10—C11	177.1 (4)	C17—C16—C21—C20	−2.2 (7)
C9—C10—C11—C12	−173.1 (4)	C15—C16—C21—C20	177.7 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···N8	1.00 (7)	1.64 (7)	2.552 (5)	148 (6)
O17—H17···N14	1.20 (6)	1.55 (6)	2.555 (5)	136 (5)
C13—H13A···O17^i	0.99	2.60	3.533 (6)	156

Symmetry code: (i) x, −y+1, z+1/2.