4-[4-(Di­methyl­amino)­benzyl­idene­amino]-3,5-bis(2-pyridyl)-4H-1,2,4-triazole

The title compound, C₂₁H₁₉N₇, is a poly­pyridine ligand that is suitable for assembling complex metal systems capable of photoinduced electron transfer. The solid-state structure has been determined at room temperature by single-crystal X-ray diffraction. The mol­ecule is not flat and both the bis­(pyridyl)­triazole and the benzyl­id­ene­amine fragments show significant distortions from planarity.

S1. Comment

The design of new polypyridine ligands carrying redox-active sites is an important research field, since these species can be used to build up multicomponent systems for photoinduced electron transfer upon metal coordination (Venturi et al., 1998). Within this field, the structural organization of the multicomponent arrays is of extreme interest, since many factors that determine the rate constants of the electron-transfer process are connected to geometric parameters. Bis(pyridyl)triazole ligands have proved to be well suited in this context, and many luminescent and redox-active Ru^II and Os^II complexes based on this class of ligands have been reported (Balzani et al., 1996; Giuffrida et al., 1996; Serroni et al., 1996; Di Pietro et al., 2002).

We report here the synthesis and the crystal structure of a new ligand, (I), based on the bis(pyridyl)triazole coordinating subunit and bearing a dimethylamino moiety as the redox-active component. The coordinating and redox-active subunits are connected by an aromatic spacer, which controls the distance between the sites and allows suitable electronic coupling.

(scheme 1 - molecular skeleton)

In the crystal state, the bis(pyridyl)triazole fragment of the ligand is not flat, and the C3/N4/C4–C7 and C8/N9/C10–C13 pyridyl rings make dihedral angles of 40.16 (6) and 22.78 (7)°, respectively, with the triazole mean plane. The different rotations of the two rings are mainly due to the more important hydrogen-bonding interactions of the disordered ortho-CH group on the C8/N9/C10–C13 ring with either atom N2 or atom N5, depending on positions of the disordered N atoms in the ring (see Table 1). However, the C2—C3 and C1—-C8 bonds have almost the same length, both being slightly shorter than the typical single-bond value, and confirm the absence of important conjugation effects. An almost flat disposition of the three rings has been observed in similar 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole derivatives (Mernari et al., 1998; Sueur et al., 1991), in which the C_tri—C_pyr single-bond lengths are comparable to the present values despite the coplanar arrangement. However, the triazole ring has the same planar geometry in all the similar fragments reported in the Cambridge Structural Database (CSD; Allen et al., 1991) and shows comparable bond lengths and angle values.

Despite the possible large electronic delocalization, the 4-(dimethylamino)benzylideneamino substituent is not planar, as evidenced by the torsion angles involving the N5═C14 double bond. The methyleneamino N1—N5═C14—C15 system is slightly distorted from planarity [the torsion angle is −174.5 (1)°] and its mean plane forms dihedral angles of 62.7 (1) and 21.1 (1)° with the planes of the triazole and phenyl rings, respectively. The N5═C14 bond is significantly shorter than the corresponding bonds in the conjugated C1═N2—N3═C2 system of the triazole ring [mean value 1.365 (3) Å], while the C14—C15 distance is not significantly shorter than a typical Csp²—Csp² single bond, as expected. However, comparable bond-length values have been observed in the flat conformation of the same fragment in a similar compound (Akkurt & Hiller, 1993), which confirms that the reduced delocalization is not caused by the distortion from planarity.

S2. Experimental

An excess of SOCl₂ (2 ml) was added to C₆H₁₀(COOH)₂ (200 mg) dissolved in benzene (25 ml). After 30 min of reflux, the solution was distilled to eliminate the excess of SOCl₂. The isolated species C₆H₁₀C(O)Cl was added to a solution of 4(dimethylamino)benzoic acid (383.2 mg, 2.32 mmol) in benzene (50 ml; all reagents by Aldrich). After 1 h of reflux, the reaction mixture was cooled to room temperature, and the white precipitate was filtered off, washed 10 times with Et₂O and recrystallized from EtOH/Et₂O (1:2%, v/v) (yield 82%). Analysis calculated for C₂₁H₁₉N₇ (369.43): C 68.28, H 5.18, N 26.54%; found: C 67.99, H 5.24, N 26.77%.

S3. Refinement

Reflection intensities were evaluated by profile fitting of a 96-step peak scan among 2θ shells (Diamond, 1969) and were then corrected for Lorentz and polarization effects. Standard uncertainties were estimated from counting statistics. No absorption correction was applied. The structure was solved by direct methods and completed by a combination of full-matrix least-squares technique and Fourier map. In one 2-pyridyl fragment, it was not possible to identify the N atom in one of the two ortho positions, and it was necessary to treat the ring as the overlap of two rotated conformations, with the occupancy of N split on both ortho-positions of the ring. All non-H atoms were refined anisotropically. H atoms were located in idealized positions and allowed to ride on their parent C atoms, with isotropic displacement parameters related to the refined values of the corresponding parent atoms. In the last Fourier maps, the electron-density residuals were not significant.

Computing details

Data collection: P3/V (Siemens, 1989); cell refinement: P3/V; data reduction: SHELXTL-Plus (Siemens, 1990); program(s) used to solve structure: SIR93 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XPW (Siemens, 1996); software used to prepare material for publication: PARST97 (Nardelli, 1995) and SHELXL97.

Figures

Fig. 1. A perspective view, showing the atomic numbering scheme of the asymmetric unit. Dashed C—H bonds represent the two conformations of the disordered pyridyl ring, in which the methyl group is interchanged with the N atom. Displacement ellipsoids are drawn at the 50% probability level, while the H-atom size is arbitrary.

(4-Dimethylamino-benzylidene)-(3,5-bis(2-Pyridyl)-1,2,4-triazol-4-yl)amine

Crystal data

C21H19N7	F(000) = 1552
Mr = 369.43	The attempt to change the s.p. from C2/c into the non-standard I2/a gave no improvement into the refined model quality.
Monoclinic, C2/c	Dx = 1.276 Mg m^−3
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 26.300 (4) Å	Cell parameters from 31 reflections
b = 9.469 (2) Å	θ = 6.3–13.6°
c = 17.440 (2) Å	µ = 0.08 mm^−1
β = 117.69 (1)°	T = 298 K
V = 3846 (1) Å^3	Regular prism, colourless
Z = 8	0.20 × 0.19 × 0.10 mm

Data collection

Siemens P4 diffractometer	Rint = 0.010
Radiation source: sealed tube	θmax = 25.1°, θmin = 2.3°
Graphite monochromator	h = −7→31
ω–2θ scans	k = −1→11
4041 measured reflections	l = −20→18
3413 independent reflections	3 standard reflections every 197 reflections
2023 reflections with I > 2σ(I)	intensity decay: 0.0%

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)] = 0.032	H-atom parameters constrained
wR(F^2) = 0.076	w = 1/[σ^2(Fo^2) + (0.044P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.79	(Δ/σ)max = 0.004
3413 reflections	Δρmax = 0.14 e Å^−3
255 parameters	Δρmin = −0.14 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0011 (1)

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	Occ. (<1)
N1	0.08976 (5)	1.06093 (13)	0.29330 (7)	0.0398 (3)
C1	0.05795 (6)	1.02098 (16)	0.20868 (8)	0.0390 (4)
N2	0.03231 (5)	1.13247 (13)	0.16159 (7)	0.0457 (3)
N3	0.04866 (5)	1.24847 (13)	0.21599 (8)	0.0466 (3)
C2	0.08303 (6)	1.20330 (16)	0.29491 (9)	0.0409 (4)
C3	0.11035 (6)	1.29603 (16)	0.37146 (9)	0.0436 (4)
N4	0.16527 (6)	1.26995 (15)	0.42673 (8)	0.0613 (4)
C4	0.19010 (8)	1.3577 (2)	0.49395 (12)	0.0782 (6)
H4	0.2284	1.3417	0.5333	0.094*
C5	0.16306 (10)	1.4694 (2)	0.50869 (13)	0.0835 (6)
H5	0.1823	1.5271	0.5569	0.1*
C6	0.10693 (9)	1.4945 (2)	0.45090 (13)	0.0772 (6)
H6	0.0874	1.5703	0.4589	0.093*
C7	0.07972 (7)	1.40657 (17)	0.38097 (11)	0.0576 (5)
H7	0.0415	1.4212	0.3409	0.069*
C8	0.05264 (6)	0.87696 (16)	0.17417 (9)	0.0414 (4)
C9	0.03719 (6)	0.86539 (16)	0.08822 (9)	0.0524 (5)	0.509 (14)
H9	0.0291	0.945	0.0533	0.063*	0.509 (14)
N9	0.03719 (6)	0.86539 (16)	0.08822 (9)	0.0524 (5)	0.491 (14)
C10	0.03394 (8)	0.7339 (2)	0.05535 (11)	0.0671 (5)
H10	0.0236	0.7236	−0.0031	0.08*
C11	0.04547 (8)	0.6165 (2)	0.10588 (12)	0.0709 (5)
H11	0.0438	0.527	0.0829	0.085*
C12	0.05956 (8)	0.6335 (2)	0.19098 (12)	0.0734 (5)
H12	0.0668	0.554	0.2258	0.088*
N13	0.06339 (7)	0.76390 (17)	0.22676 (9)	0.0611 (5)	0.509 (14)
C13	0.06339 (7)	0.76390 (17)	0.22676 (9)	0.0611 (5)	0.491 (14)
H13	0.073	0.7744	0.2849	0.073*	0.491 (14)
N5	0.12722 (5)	0.97417 (13)	0.36358 (7)	0.0464 (3)
C14	0.11254 (6)	0.96846 (16)	0.42368 (9)	0.0440 (4)
H14	0.0786	1.0117	0.4153	0.053*
C15	0.14722 (6)	0.89665 (16)	0.50438 (8)	0.0409 (4)
C16	0.12409 (6)	0.85994 (17)	0.55869 (9)	0.0481 (4)
H16	0.0862	0.8838	0.5427	0.058*
C17	0.15525 (7)	0.78974 (17)	0.63513 (9)	0.0496 (4)
H17	0.1379	0.7647	0.669	0.059*
C18	0.21295 (6)	0.75525 (16)	0.66298 (9)	0.0442 (4)
C19	0.23708 (6)	0.79526 (17)	0.60926 (9)	0.0490 (4)
H19	0.2755	0.7757	0.6263	0.059*
C20	0.20466 (6)	0.86270 (16)	0.53208 (9)	0.0465 (4)
H20	0.2215	0.8864	0.4973	0.056*
N6	0.24416 (6)	0.68529 (17)	0.73904 (8)	0.0641 (4)
C21	0.21881 (9)	0.6491 (3)	0.79370 (12)	0.1007 (8)
H21A	0.2466	0.6006	0.8442	0.151*
H21B	0.1862	0.589	0.7625	0.151*
H21C	0.2067	0.7337	0.811	0.151*
C22	0.30393 (8)	0.6556 (3)	0.76989 (13)	0.0988 (8)
H22A	0.3185	0.606	0.824	0.148*
H22B	0.3246	0.7426	0.7781	0.148*
H22C	0.3087	0.5984	0.7283	0.148*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0427 (7)	0.0424 (8)	0.0320 (7)	0.0070 (6)	0.0155 (6)	0.0047 (6)
C1	0.0365 (8)	0.0465 (9)	0.0324 (8)	0.0012 (7)	0.0147 (7)	0.0030 (7)
N2	0.0462 (7)	0.0488 (8)	0.0388 (7)	0.0052 (7)	0.0170 (6)	0.0033 (7)
N3	0.0490 (8)	0.0473 (8)	0.0427 (7)	0.0082 (6)	0.0206 (6)	0.0051 (6)
C2	0.0418 (8)	0.0438 (9)	0.0397 (9)	0.0051 (7)	0.0210 (7)	0.0020 (7)
C3	0.0481 (10)	0.0419 (9)	0.0447 (9)	−0.0015 (8)	0.0248 (8)	0.0003 (7)
N4	0.0517 (9)	0.0679 (10)	0.0522 (8)	0.0005 (7)	0.0140 (7)	−0.0136 (8)
C4	0.0657 (12)	0.0828 (15)	0.0683 (12)	−0.0094 (11)	0.0160 (10)	−0.0210 (12)
C5	0.0849 (16)	0.0800 (15)	0.0832 (14)	−0.0249 (13)	0.0370 (12)	−0.0422 (12)
C6	0.0800 (14)	0.0589 (12)	0.1033 (15)	−0.0089 (11)	0.0517 (13)	−0.0291 (12)
C7	0.0570 (11)	0.0490 (10)	0.0689 (11)	−0.0023 (8)	0.0309 (9)	−0.0094 (9)
C8	0.0370 (8)	0.0469 (9)	0.0377 (8)	−0.0007 (7)	0.0152 (6)	0.0030 (8)
C9	0.0593 (9)	0.0551 (10)	0.0375 (8)	−0.0007 (8)	0.0180 (7)	−0.0013 (8)
N9	0.0593 (9)	0.0551 (10)	0.0375 (8)	−0.0007 (8)	0.0180 (7)	−0.0013 (8)
C10	0.0784 (13)	0.0681 (13)	0.0453 (10)	0.0003 (10)	0.0209 (9)	−0.0098 (10)
C11	0.0785 (13)	0.0509 (12)	0.0715 (13)	−0.0083 (10)	0.0250 (11)	−0.0151 (11)
C12	0.0903 (14)	0.0526 (12)	0.0714 (13)	−0.0049 (11)	0.0327 (11)	0.0132 (11)
N13	0.0790 (12)	0.0535 (11)	0.0499 (10)	−0.0027 (8)	0.0292 (8)	0.0054 (8)
C13	0.0790 (12)	0.0535 (11)	0.0499 (10)	−0.0027 (8)	0.0292 (8)	0.0054 (8)
N5	0.0530 (8)	0.0485 (8)	0.0335 (6)	0.0125 (6)	0.0166 (6)	0.0048 (6)
C14	0.0431 (9)	0.0469 (9)	0.0386 (8)	0.0021 (7)	0.0160 (7)	−0.0007 (7)
C15	0.0420 (9)	0.0454 (9)	0.0317 (7)	0.0025 (7)	0.0141 (7)	−0.0007 (7)
C16	0.0388 (8)	0.0623 (10)	0.0434 (8)	0.0092 (8)	0.0192 (7)	0.0033 (8)
C17	0.0514 (10)	0.0629 (11)	0.0413 (8)	0.0087 (8)	0.0274 (8)	0.0093 (8)
C18	0.0469 (9)	0.0470 (9)	0.0365 (8)	0.0068 (7)	0.0175 (7)	0.0022 (7)
C19	0.0381 (9)	0.0639 (11)	0.0445 (9)	0.0073 (8)	0.0187 (7)	0.0039 (8)
C20	0.0475 (9)	0.0568 (10)	0.0391 (8)	0.0007 (8)	0.0236 (7)	0.0032 (8)
N6	0.0587 (9)	0.0836 (11)	0.0484 (8)	0.0222 (8)	0.0235 (7)	0.0254 (8)
C21	0.0968 (16)	0.145 (2)	0.0669 (12)	0.0315 (15)	0.0433 (12)	0.0550 (14)
C22	0.0673 (13)	0.138 (2)	0.0786 (14)	0.0406 (14)	0.0233 (11)	0.0474 (14)

Geometric parameters (Å, º)

N1—C2	1.362 (2)	C11—H11	0.93
N1—C1	1.369 (2)	C12—N13	1.366 (2)
N1—N5	1.423 (1)	C12—H12	0.93
C1—N2	1.315 (2)	N5—C14	1.275 (2)
C1—C8	1.471 (2)	C14—C15	1.443 (2)
N2—N3	1.383 (2)	C14—H14	0.93
N3—C2	1.318 (2)	C15—C16	1.3867 (19)
C2—C3	1.476 (2)	C15—C20	1.3932 (19)
C3—N4	1.3350 (19)	C16—C17	1.3694 (19)
C3—C7	1.377 (2)	C16—H16	0.93
N4—C4	1.334 (2)	C17—C18	1.400 (2)
C4—C5	1.364 (3)	C17—H17	0.93
C4—H4	0.93	C18—N6	1.364 (2)
C5—C6	1.367 (3)	C18—C19	1.406 (2)
C5—H5	0.93	C19—C20	1.371 (2)
C6—C7	1.372 (2)	C19—H19	0.93
C6—H6	0.93	C20—H20	0.93
C7—H7	0.93	N6—C22	1.433 (2)
C8—N13	1.351 (2)	N6—C21	1.435 (2)
C8—C9	1.3631 (19)	C21—H21A	0.96
C9—C10	1.357 (2)	C21—H21B	0.96
C9—H9	0.93	C21—H21C	0.96
C10—C11	1.362 (2)	C22—H22A	0.96
C10—H10	0.93	C22—H22B	0.96
C11—C12	1.362 (2)	C22—H22C	0.96
C2—N1—C1	106.0 (1)	C11—C12—H12	119
C2—N1—N5	126.8 (1)	N13—C12—H12	119
C1—N1—N5	126.9 (1)	C8—N13—C12	117.27 (14)
N2—C1—N1	109.3 (1)	C14—N5—N1	112.3 (1)
N2—C1—C8	124.42 (12)	N5—C14—C15	121.7 (1)
N1—C1—C8	126.27 (13)	N5—C14—H14	119.1
C1—N2—N3	107.7 (1)	C15—C14—H14	119.1
C2—N3—N2	107.6 (1)	C16—C15—C20	117.03 (13)
N3—C2—N1	109.4 (1)	C16—C15—C14	120.35 (13)
N3—C2—C3	124.11 (14)	C20—C15—C14	122.61 (14)
N1—C2—C3	126.46 (13)	C17—C16—C15	122.19 (14)
N4—C3—C7	123.42 (14)	C17—C16—H16	118.9
N4—C3—C2	116.86 (14)	C15—C16—H16	118.9
C7—C3—C2	119.67 (14)	C16—C17—C18	120.84 (14)
C4—N4—C3	116.29 (15)	C16—C17—H17	119.6
N4—C4—C5	124.29 (19)	C18—C17—H17	119.6
N4—C4—H4	117.9	N6—C18—C17	121.07 (14)
C5—C4—H4	117.9	N6—C18—C19	121.67 (14)
C4—C5—C6	118.34 (18)	C17—C18—C19	117.26 (13)
C4—C5—H5	120.8	C20—C19—C18	120.83 (14)
C6—C5—H5	120.8	C20—C19—H19	119.6
C5—C6—C7	119.25 (18)	C18—C19—H19	119.6
C5—C6—H6	120.4	C19—C20—C15	121.82 (14)
C7—C6—H6	120.4	C19—C20—H20	119.1
C6—C7—C3	118.41 (16)	C15—C20—H20	119.1
C6—C7—H7	120.8	C18—N6—C22	121.31 (15)
C3—C7—H7	120.8	C18—N6—C21	120.42 (15)
N13—C8—C9	122.97 (15)	C22—N6—C21	118.09 (14)
N13—C8—C1	120.44 (13)	N6—C21—H21A	109.5
C9—C8—C1	116.59 (13)	N6—C21—H21B	109.5
C10—C9—C8	117.80 (15)	H21A—C21—H21B	109.5
C10—C9—H9	121.1	N6—C21—H21C	109.5
C8—C9—H9	121.1	H21A—C21—H21C	109.5
C9—C10—C11	121.60 (16)	H21B—C21—H21C	109.5
C9—C10—H10	119.2	N6—C22—H22A	109.5
C11—C10—H10	119.2	N6—C22—H22B	109.5
C10—C11—C12	118.34 (17)	H22A—C22—H22B	109.5
C10—C11—H11	120.8	N6—C22—H22C	109.5
C12—C11—H11	120.8	H22A—C22—H22C	109.5
C11—C12—N13	121.99 (17)	H22B—C22—H22C	109.5
C2—N1—C1—N2	−1.20 (16)	N1—C1—C8—C9	−157.01 (13)
N5—N1—C1—N2	−174.92 (12)	N13—C8—C9—C10	−1.6 (2)
C2—N1—C1—C8	178.70 (14)	C1—C8—C9—C10	177.73 (14)
N5—N1—C1—C8	5.0 (2)	C8—C9—C10—C11	0.2 (3)
N1—C1—N2—N3	1.41 (15)	C9—C10—C11—C12	1.1 (3)
C8—C1—N2—N3	−178.49 (13)	C10—C11—C12—N13	−1.2 (3)
C1—N2—N3—C2	−1.08 (16)	C9—C8—N13—C12	1.5 (2)
N2—N3—C2—N1	0.33 (17)	C1—C8—N13—C12	−177.78 (15)
N2—N3—C2—C3	179.03 (13)	C11—C12—N13—C8	−0.1 (3)
C1—N1—C2—N3	0.50 (17)	C2—N1—N5—C14	66.65 (19)
N5—N1—C2—N3	174.25 (12)	C1—N1—N5—C14	−120.89 (15)
C1—N1—C2—C3	−178.15 (14)	N1—N5—C14—C15	−174.5 (1)
N5—N1—C2—C3	−4.4 (2)	N5—C14—C15—C16	−163.16 (15)
N3—C2—C3—N4	−137.81 (15)	N5—C14—C15—C20	17.7 (2)
N1—C2—C3—N4	40.7 (2)	C20—C15—C16—C17	−1.9 (2)
N3—C2—C3—C7	39.6 (2)	C14—C15—C16—C17	178.92 (14)
N1—C2—C3—C7	−141.88 (16)	C15—C16—C17—C18	1.8 (2)
C7—C3—N4—C4	0.2 (2)	C16—C17—C18—N6	−179.97 (16)
C2—C3—N4—C4	177.58 (15)	C16—C17—C18—C19	−0.2 (2)
C3—N4—C4—C5	0.0 (3)	N6—C18—C19—C20	178.51 (15)
N4—C4—C5—C6	−0.4 (3)	C17—C18—C19—C20	−1.3 (2)
C4—C5—C6—C7	0.6 (3)	C18—C19—C20—C15	1.2 (2)
C5—C6—C7—C3	−0.3 (3)	C16—C15—C20—C19	0.4 (2)
N4—C3—C7—C6	−0.1 (3)	C14—C15—C20—C19	179.56 (15)
C2—C3—C7—C6	−177.37 (16)	C17—C18—N6—C22	−176.99 (17)
N2—C1—C8—N13	−157.77 (15)	C19—C18—N6—C22	3.2 (3)
N1—C1—C8—N13	22.3 (2)	C17—C18—N6—C21	−1.9 (3)
N2—C1—C8—C9	22.9 (2)	C19—C18—N6—C21	178.31 (17)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C9—H9···N2	0.93	2.57	2.864 (2)	99
C13—H13···N5	0.93	2.38	2.959 (2)	120