2,2′-(2,6-Pyridinedi­yl)diquinoline

The title mol­ecule, C₂₃H₁₅N₃, is a terpyridine derivative resulting from the Friedländer annulation between 2,6-diacetyl­pyridine and N,N′-bis­(2-amino­benz­yl)ethyl­ene­di­amine. The asymmetric unit contains one half-mol­ecule, the complete mol­ecule being generated by a mirror plane (one N atom and one C atom lie on the plane). The mol­ecule, although aromatic, is deformed from planarity as a result of crystal packing forces: mol­ecules are stacked along the short c axis, with a short separation of 3.605 (1) Å between the mean planes. The bent mol­ecular shape is reflected in the dihedral angle of 16.10 (5)° between the essentially planar quinoline groups. In addition to π...π inter­actions, the crystal structure features weak inter-stack C—H...N contacts involving atoms of the central pyridine rings which lie in a common crystallographic m plane.

Key indicators

• Single-crystal X-ray study
• T = 298 K, P = 0.0 kPa
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.041
• wR factor = 0.118
• Data-to-parameter ratio = 12.0

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT910_ALERT_3_C Missing # of FCF Reflections Below Th(Min) .....          1
PLAT480_ALERT_4_C Long H...A H-Bond Reported H1A    ..  N1      ..       2.72 Ang.

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   2 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
   1 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Thirty years after cisplatin was approved by the FDA for its use as a chemotherapy drug, studies regarding interactions between platinum-based complexes and basic sites in DNA remain actives. Recently, Bertrand et al. (2009) showed that Pt^II cationic complexes bearing 2,2':6',2"-terpyridine or a terpyridine derivative as ligand have the ability to platinate the human telomeric G-quadruplex. Interestingly, both the binding affinity and the platination activity seem to be determined by the extension of the aromatic surface of the terpyridine derivative. One of the ligands used in that work was 2,2'-(2,6-pyridinediyl)bis-quinoline, synthesized through the Friedländer condensation (Da Costa et al., 2009; Sridharan et al., 2009) between 2,6-diacetylpyridine and 2-nitrobenzaldehyde. We now report the crystal structure of this aromatic ligand.

The title terpyridine derivative was obtained as a by-product during the preparation of a macrocyclic ligand (see Experimental). More suitable synthesis are however available in the literature (Harris et al., 1969; Klassen et al., 1975; Bertrand et al., 2009). The molecule (Fig. 1) displays the crystallographic m symmetry, with atoms N1, C1 and H1A placed in the mirror planes normal to [010]. The molecular conformation observed in the solid-state is not suitable for coordination through the three N atoms: the quinoline N atoms are placed in a trans arrangement with respect to the central pyridine N atom, while a cis,cis conformation is required for the molecule to be a terdentate ligand. However, as invariably found in non-hindered terpyridine derivatives, aromatic fragments are free to rotate, for example about the C3—C4 bond in the case of the title molecule. Such a behavior has been reported, for example, for the coordination to Ru^II of a closely related terpyridine ligand, namely 2,6-bis(5,6,7,8-tetrahydroquinol-2-yl)pyridine (Sasaki et al., 1998).

Molecules are stacked along the short axis c, at a distance of 3.605 Å (separation between two mean planes passing through two neighboring molecules in the [001] direction, see Fig.2, inset). This short separation, although larger than that observed in graphite (ca. 3.36 Å), results in strong π···π interactions in the stacks, which, in turn, deform the molecules from planarity. The dihedral angle between the central pyridine ring and the quinoline substituent is 8.13 (8)°. The bent shape is also reflected in the dihedral angle between quinoline systems, 16.10 (5)° (Fig. 2, inset). Finally, the crystal structure is completed by weak intermolecular C—H···N contacts (Table 1 and Fig. 2), linking the stacks in the [100] direction.

Related literature

For the synthesis and the coordination behavior of the title molecule, see: Bertrand et al. (2009); Harris et al. (1969); Klassen et al. (1975). For a terpyridine derivative closely related to the title molecule, see: Sasaki et al. (1998). For the Friedländer condensation as a tool for the preparation of quinolines, see: Da Costa et al. (2009); Sridharan et al. (2009).

S2. Experimental

A mixture of 305 mg of 2,6-diacetylpyridine and 823 mg of Ce(NO₃)₃.6H₂O in methanol (25 ml) was refluxed for 30 min, followed by slow addition of a dissolution of N,N'-bis(2-aminobenzyl)ethylenediamine (530 mg in 25 ml methanol). The mixture was kept under these conditions for 3.5 h, and then cooled to room temperature, giving a red precipitate. After 1.5 month, the resulting solid was filtered, washed with cold methanol, diethyl ether, and air dried. Suitable single crystals were picked off from the solid. m.p. 495–497 K (lit. 500–501 K: Klassen et al., 1975).

S3. Refinement

All H atoms were placed in idealized positions, with C—H bond lengths fixed to 0.93 Å. Isotropic displacement parameters for H atoms were calculated from displacements of parent C atoms: U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS (Siemens, 1996); data reduction: XSCANS (Siemens, 1996); program(s) used to solve structure: SHELXTL-Plus (Sheldrick, 2008); program(s) used to refine structure: SHELXTL-Plus (Sheldrick, 2008); molecular graphics: SHELXTL-Plus (Sheldrick, 2008) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXTL-Plus (Sheldrick, 2008).

Figures

	Fig. 1. The structure of the title compound, with displacement ellipsoids at the 30% probability level for non-H atoms. Non-labeled atoms are generated by symmetry code x, 1/2-y, z.
	Fig. 2. A part of the crystal structure, viewed down c axis. Dashed lines represent non-bonding intermolecular contacts. The inset shows a part of a stack along [001]. Two least-squares planes are represented (red), which were computed using all atoms in each selected molecule (Macrae et al., 2008).

2,2'-(2,6-Pyridinediyl)diquinoline

Crystal data

C23H15N3	Dx = 1.358 Mg m^−3
Mr = 333.38	Melting point = 495–497 K
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 100 reflections
a = 11.960 (2) Å	θ = 5.5–11.7°
b = 34.509 (6) Å	µ = 0.08 mm^−1
c = 3.9509 (5) Å	T = 298 K
V = 1630.7 (5) Å^3	Plate, orange
Z = 4	0.40 × 0.20 × 0.10 mm
F(000) = 696

Data collection

Siemens P4 diffractometer	Rint = 0.031
Radiation source: X-ray	θmax = 25.1°, θmin = 2.4°
Graphite monochromator	h = −14→14
ω scans	k = −41→41
5603 measured reflections	l = −4→4
1469 independent reflections	2 standard reflections every 48 reflections
1032 reflections with I > 2σ(I)	intensity decay: 1%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.041	H-atom parameters constrained
wR(F^2) = 0.118	w = 1/[σ^2(Fo^2) + (0.0614P)^2 + 0.1644P] where P = (Fo^2 + 2Fc^2)/3
S = 1.02	(Δ/σ)max < 0.001
1469 reflections	Δρmax = 0.16 e Å^−3
122 parameters	Δρmin = −0.11 e Å^−3
0 restraints	Extinction correction: SHELXTL-Plus, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 constraints	Extinction coefficient: 0.0069 (16)
Primary atom site location: structure-invariant direct methods

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

	x	y	z	Uiso*/Ueq
N1	0.05056 (13)	0.2500	0.0324 (4)	0.0465 (5)
C1	−0.15745 (18)	0.2500	−0.2714 (6)	0.0572 (6)
H1A	−0.2280	0.2500	−0.3703	0.069*
C2	−0.10509 (12)	0.28415 (5)	−0.1980 (4)	0.0539 (4)
H2A	−0.1388	0.3077	−0.2506	0.065*
C3	−0.00108 (11)	0.28327 (4)	−0.0443 (4)	0.0465 (4)
C4	0.05844 (12)	0.32017 (4)	0.0278 (4)	0.0468 (4)
N5	0.00977 (10)	0.35190 (4)	−0.0808 (3)	0.0522 (4)
C6	0.06408 (13)	0.38627 (4)	−0.0411 (4)	0.0522 (4)
C7	0.01369 (16)	0.42018 (5)	−0.1667 (5)	0.0667 (5)
H7A	−0.0563	0.4188	−0.2686	0.080*
C8	0.06583 (19)	0.45476 (5)	−0.1410 (5)	0.0752 (6)
H8A	0.0319	0.4769	−0.2279	0.090*
C9	0.17008 (19)	0.45757 (5)	0.0147 (5)	0.0762 (6)
H9A	0.2049	0.4816	0.0326	0.091*
C10	0.22110 (16)	0.42554 (5)	0.1402 (5)	0.0660 (5)
H10A	0.2907	0.4278	0.2437	0.079*
C11	0.16971 (13)	0.38897 (4)	0.1153 (4)	0.0528 (4)
C12	0.21698 (13)	0.35438 (4)	0.2379 (4)	0.0555 (4)
H12A	0.2859	0.3549	0.3468	0.067*
C13	0.16215 (12)	0.32044 (4)	0.1973 (4)	0.0511 (4)
H13A	0.1925	0.2975	0.2804	0.061*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0355 (9)	0.0555 (11)	0.0484 (10)	0.000	0.0022 (8)	0.000
C1	0.0364 (11)	0.0734 (16)	0.0619 (14)	0.000	−0.0071 (11)	0.000
C2	0.0404 (8)	0.0637 (10)	0.0576 (10)	0.0072 (7)	−0.0014 (7)	−0.0021 (8)
C3	0.0361 (7)	0.0586 (9)	0.0448 (8)	0.0043 (7)	0.0045 (6)	−0.0018 (7)
C4	0.0395 (8)	0.0554 (9)	0.0456 (8)	0.0054 (7)	0.0048 (7)	−0.0030 (7)
N5	0.0442 (7)	0.0569 (8)	0.0555 (8)	0.0078 (6)	0.0016 (6)	−0.0002 (7)
C6	0.0506 (9)	0.0563 (10)	0.0498 (9)	0.0089 (8)	0.0066 (7)	−0.0027 (8)
C7	0.0688 (11)	0.0654 (11)	0.0659 (11)	0.0147 (9)	0.0013 (9)	0.0016 (9)
C8	0.0985 (16)	0.0599 (12)	0.0672 (12)	0.0145 (11)	0.0066 (12)	0.0053 (10)
C9	0.0981 (16)	0.0617 (11)	0.0687 (13)	−0.0086 (11)	0.0121 (11)	−0.0025 (10)
C10	0.0672 (11)	0.0673 (11)	0.0635 (11)	−0.0064 (10)	0.0044 (9)	−0.0083 (9)
C11	0.0522 (9)	0.0561 (10)	0.0501 (9)	0.0020 (7)	0.0060 (8)	−0.0062 (8)
C12	0.0443 (8)	0.0648 (11)	0.0575 (10)	0.0031 (8)	−0.0032 (7)	−0.0078 (8)
C13	0.0426 (8)	0.0545 (9)	0.0561 (9)	0.0077 (7)	−0.0033 (7)	−0.0043 (7)

Geometric parameters (Å, º)

N1—C3^i	1.3383 (16)	C7—C8	1.350 (2)
N1—C3	1.3383 (16)	C7—H7A	0.9300
C1—C2	1.3658 (18)	C8—C9	1.394 (3)
C1—C2^i	1.3658 (18)	C8—H8A	0.9300
C1—H1A	0.9300	C9—C10	1.357 (2)
C2—C3	1.385 (2)	C9—H9A	0.9300
C2—H2A	0.9300	C10—C11	1.407 (2)
C3—C4	1.486 (2)	C10—H10A	0.9300
C4—N5	1.3123 (18)	C11—C12	1.407 (2)
C4—C13	1.410 (2)	C12—C13	1.352 (2)
N5—C6	1.3615 (19)	C12—H12A	0.9300
C6—C7	1.407 (2)	C13—H13A	0.9300
C6—C11	1.410 (2)
C3^i—N1—C3	118.13 (17)	C6—C7—H7A	119.6
C2—C1—C2^i	119.3 (2)	C7—C8—C9	120.52 (18)
C2—C1—H1A	120.3	C7—C8—H8A	119.7
C2^i—C1—H1A	120.3	C9—C8—H8A	119.7
C1—C2—C3	119.07 (15)	C10—C9—C8	120.48 (18)
C1—C2—H2A	120.5	C10—C9—H9A	119.8
C3—C2—H2A	120.5	C8—C9—H9A	119.8
N1—C3—C2	122.20 (14)	C9—C10—C11	120.57 (18)
N1—C3—C4	118.07 (13)	C9—C10—H10A	119.7
C2—C3—C4	119.69 (13)	C11—C10—H10A	119.7
N5—C4—C13	122.69 (14)	C12—C11—C10	124.15 (16)
N5—C4—C3	116.09 (13)	C12—C11—C6	117.07 (14)
C13—C4—C3	121.21 (13)	C10—C11—C6	118.78 (15)
C4—N5—C6	118.54 (13)	C13—C12—C11	119.96 (14)
N5—C6—C7	118.67 (15)	C13—C12—H12A	120.0
N5—C6—C11	122.39 (14)	C11—C12—H12A	120.0
C7—C6—C11	118.92 (15)	C12—C13—C4	119.27 (14)
C8—C7—C6	120.72 (18)	C12—C13—H13A	120.4
C8—C7—H7A	119.6	C4—C13—H13A	120.4
C2^i—C1—C2—C3	−1.4 (3)	C6—C7—C8—C9	−0.8 (3)
C3^i—N1—C3—C2	0.1 (3)	C7—C8—C9—C10	0.5 (3)
C3^i—N1—C3—C4	−177.46 (10)	C8—C9—C10—C11	0.0 (3)
C1—C2—C3—N1	0.6 (3)	C9—C10—C11—C12	179.83 (16)
C1—C2—C3—C4	178.17 (16)	C9—C10—C11—C6	−0.3 (3)
N1—C3—C4—N5	173.63 (14)	N5—C6—C11—C12	−1.3 (2)
C2—C3—C4—N5	−4.0 (2)	C7—C6—C11—C12	179.88 (15)
N1—C3—C4—C13	−5.2 (2)	N5—C6—C11—C10	178.75 (14)
C2—C3—C4—C13	177.17 (14)	C7—C6—C11—C10	0.0 (2)
C13—C4—N5—C6	3.0 (2)	C10—C11—C12—C13	−178.88 (16)
C3—C4—N5—C6	−175.81 (13)	C6—C11—C12—C13	1.2 (2)
C4—N5—C6—C7	178.05 (14)	C11—C12—C13—C4	0.8 (2)
C4—N5—C6—C11	−0.7 (2)	N5—C4—C13—C12	−3.1 (2)
N5—C6—C7—C8	−178.24 (16)	C3—C4—C13—C12	175.65 (14)
C11—C6—C7—C8	0.6 (2)

Symmetry code: (i) x, −y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C1—H1A···N1^ii	0.93	2.72	3.641 (3)	169

Symmetry code: (ii) x−1/2, −y+1/2, −z−1/2.