5-Di­methyl­amino-N,N-di­methyl-3-(4-pyridyl)-2,4-pentadieniminium tetra­fluoro­borate

The crystal structure of the title salt, C₁₄H₂₀N₃⁺·BF₄^-, shows that the pentamethinecyanine moiety of the cation is essentially planar and adopts an all-trans conformation. The plane of the pyridyl substituent makes a dihedral angle of 60.58 (9)° with the pentamethinecyanine plane.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• Disorder in solvent or counterion
• R factor = 0.056
• wR factor = 0.195
• Data-to-parameter ratio = 16.2

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



PLAT_302  Alert C Anion/Solvent disorder .......................      38.00 Perc.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

The title salt, (I), containing the relatively electron-poor 4-pyridyl substituent, was prepared in order to determine what effect (if any) the 4-pyridyl substitution at C3 would have on the conformation of the pentamethinecyanine moiety of the cation. The perchlorate salt analogue of (I) has been prepared (Hanke & Jutz, 1980), but a search of the Cambridge Structural Database (Allen & Kennard, 1993) showed that its structure had not been reported.

The crystal structure of (I) consists of discrete cations and tetrafluroborate anions, the latter being disordered over two sites. The pentamethinecyanine moiety of the cation (N1/C1—C5/N2) is essentially planar and adopts an all-trans conformation which makes a dihedral angle of 60.58 (9)° with the pyridine plane (Fig. 1). The planar terminal dimethylamino groups are rotated in opposite directions through 5.83 (12) and 6.69 (17)° out of the pentamethinecyanine plane. Bond lengths within the pentamethinecyanine fragment [C—C = 1.373 (3)–1.402 (3) Å; C—N = 1.311 (3) and 1.318 (3) Å] are similar to those reported in charge-density studies (Honda et al., 1986) for the parent perchlorate salt (II), indicating minimal perturbation of the pentamethinecyanine moiety by the (4-pyridyl) substituent at C3. Bond lengths within the pyridine fragment are normal; the C3—C34 bond length [1.486 (3) Å] linking the cyanine and pyridine moieties is entirely consistent with its being a Csp²—Csp² single bond. The cation dimensions and conformation are thus indicative of a lack of direct conjugative interaction between the two π systems. A coplanar arrangement of these two moieties would not be possible with the pentamethinecyanine fragment in the all-trans conformation because of severe steric interactions which would be present between the pyridine β-H atoms and the C1 and C5 H atoms of the cyanine moiety in the planar conformation. This situation is similar to that reported (Katoh et al., 1997) for the bis(pentamethinecyanine) salt (III) in which two electron-poor pentamethinecyanine units each have an all-trans conformation and are linked through their central C atoms; the cation has a conformation in which the two pentamethinecyanine moieties are mutually at right angles.

The ¹H NMR chemical shifts found for (I) in DMSO-d₆ are similar to those reported (Hanke & Jutz, 1980) for the perchlorate analogue. However, in the present case, two closely-spaced NMe signals were observed instead of one and coupling of the pyridine protons signals was resolved. In the case of the perchlorate salt, the latter signals were reported as broad multiplets. It is possible that the broadening was due to ion-pairing effects. Thus, when the spectrum of (I) was run in CDCl₃ [dilute solution due to low solubility of (I) in this solvent], two sets of pyridine signals were observed, while the remaining signals were unchanged. In the less polar solvent, tight ion pairing between the cations and tetrafluoroborate anions would be expected to occur. If the anion lies over one face of the pentamethinecyanine moiety, and migration of the anion between faces is slow on the NMR time scale, this would lead to discrimination between the two faces, and different environments for the α and β proton pairs of the pyridine moiety only.

S2. Experimental

The salt (I) was prepared as described (Hanke & Jutz, 1980) for the perchlorate analogue, except that NaBF₄ was used instead of NaClO₄. Crystallization from ethanol gave (I) as orange spars, m.p. 469.0–472.5 K. ¹H NMR (200 MHz, DMSO-d₆): δ = 3.10, 3.14 (each s, 6H, NMe), 6.07 (d, J = 12.2 Hz, 2H, C2—H+C4—H), 6.95 (d, J = 12.2 Hz, 2H, C1—H+C5—H), 7.28 (d, J_obs = 5.0 Hz, 2H, pyridine β-H) and 8.71 (d, J_obs = 5.0 Hz, 2H, pyridine α-H); (200 MHz, CDCl₃): δ = 3.19, 3.24 (each s, 6H, NMe), 6.28 (d, J = 12.2 Hz, 2H, C2—H+C4—H), 6.76 (d, J = 12.2 Hz, 2H, C1—H+C5—H), 7.26 (obscured by solvent peak, pyridine β-H), 7.34 (d, J_obs = 5.0 Hz, 1H, pyridine β-H), 8.71 (d, J_obs = 5.0 Hz, 1H, pyridine α-H) and 8.79 (d, J_obs = 5.0 Hz, 1H, pyridine α-H).

S3. Refinement

H atoms were treated as riding atoms with C—H distances of 0.93 and 0.96 Å. All four methyl groups were allowed to rotate about their local threefold axis. The tetrafluoroborate ion is disordered by rotation about the B1—F1 bond over two sites with unequal occupancies [0.918 (5) and 0.082 (5)]. In the minor orientation, the three F atoms (F12, F13 and F14) were only allowed an overall isotropic vibration parameter; the geometry at B1 was restrained to be tetrahedral and an overall B—F distance was refined using a combination of DFIX and free-variable controls.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1992); cell refinement: SET4 and CELDIM (Enraf-Nonius, 1992); data reduction: HELENA in PLATON (Spek, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976) and PLATON (Spek, 2001); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. A view of (I) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Only the major component of the disordered tetrafluoroborate anion is shown

5-Dimethylamino-N,N-dimethyl-3-(4-pyridyl)-2,4-pentadieniminium tetrafluoroborate

Crystal data

C14H20N3^+·BF4^−	F(000) = 664
Mr = 317.14	Dx = 1.315 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.982 (2) Å	Cell parameters from 25 reflections
b = 10.492 (2) Å	θ = 9.1–11.2°
c = 19.950 (3) Å	µ = 0.11 mm^−1
β = 106.578 (19)°	T = 293 K
V = 1601.3 (6) Å^3	Needle, orange
Z = 4	0.38 × 0.34 × 0.20 mm

Data collection

Nonius CAD-4 diffractometer	Rint = 0.018
Radiation source: fine-focus sealed X-ray tube	θmax = 27.0°, θmin = 2.1°
Graphite monochromator	h = 0→10
θ/2θ scans	k = −13→0
3931 measured reflections	l = −25→24
3482 independent reflections	3 standard reflections every 120 min
2306 reflections with I > 2σ(I)	intensity decay: none

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)] = 0.057	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.195	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0995P)^2 + 0.6393P] where P = (Fo^2 + 2Fc^2)/3
3482 reflections	(Δ/σ)max = 0.009
215 parameters	Δρmax = 0.36 e Å^−3
13 restraints	Δρmin = −0.30 e Å^−3

Special details

Geometry. Mean-plane data from the final SHELXL97 refinement run:-

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

7.4886 (0.0031) x + 2.3601 (0.0157) y - 0.3101 (0.0396) z = 1.9387 (0.0012)

* -0.0594 (0.0013) N1 * 0.0288 (0.0015) C1 * 0.0258 (0.0018) C2 * 0.0054 (0.0016) C3 * 0.0662 (0.0018) C4 * -0.0425 (0.0015) C5 * -0.0244 (0.0013) N2

Rms deviation of fitted atoms = 0.0411

5.9988 (0.0056) x - 6.0519 (0.0072) y - 10.3986 (0.0124) z = 0.3414 (0.0029)

Angle to previous plane (with approximate e.s.d.) = 60.58 (9)

* 0.0160 (0.0013) C3 * 0.0163 (0.0018) N31 * -0.0035 (0.0018) C32 * -0.0108 (0.0018) C33 * -0.0040 (0.0017) C34 * -0.0163 (0.0018) C35 * 0.0024 (0.0017) C36

Rms deviation of fitted atoms = 0.0116

#######################################################################

7.4886 (0.0031) x + 2.3601 (0.0157) y - 0.3101 (0.0396) z = 1.9387 (0.0012)

* -0.0594 (0.0013) N1 * 0.0288 (0.0015) C1 * 0.0258 (0.0018) C2 * 0.0054 (0.0016) C3 * 0.0662 (0.0018) C4 * -0.0425 (0.0015) C5 * -0.0244 (0.0013) N2

Rms deviation of fitted atoms = 0.0411

7.5916 (0.0045) x + 2.7191 (0.0167) y - 2.1992 (0.0288) z = 1.9475 (0.0043)

Angle to previous plane (with approximate e.s.d.) = 5.83 (12)

* 0.0048 (0.0018) N1 * -0.0015 (0.0006) C11 * -0.0015 (0.0006) C12 * -0.0018 (0.0007) C1

Rms deviation of fitted atoms = 0.0028

#########################################################################

7.4886 (0.0031) x + 2.3601 (0.0157) y - 0.3101 (0.0396) z = 1.9387 (0.0012)

* -0.0594 (0.0013) N1 * 0.0288 (0.0015) C1 * 0.0258 (0.0018) C2 * 0.0054 (0.0016) C3 * 0.0662 (0.0018) C4 * -0.0425 (0.0015) C5 * -0.0244 (0.0013) N2

Rms deviation of fitted atoms = 0.0411

7.2706 (0.0059) x + 1.9358 (0.0159) y + 1.8738 (0.0352) z = 2.0549 (0.0061)

Angle to previous plane (with approximate e.s.d.) = 6.69 (17)

* -0.0086 (0.0019) N2 * 0.0027 (0.0006) C21 * 0.0027 (0.0006) C22 * 0.0032 (0.0007) C5

Rms deviation of fitted atoms = 0.0050

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
N1	0.3035 (2)	−0.17387 (18)	−0.05512 (9)	0.0492 (5)
N2	0.1476 (2)	0.36189 (17)	0.14546 (9)	0.0498 (5)
N31	0.2935 (3)	−0.1981 (2)	0.25025 (12)	0.0687 (6)
C1	0.3017 (3)	−0.1229 (2)	0.00465 (11)	0.0460 (5)
H1	0.3292	−0.1754	0.0438	0.055*
C2	0.2618 (3)	0.0037 (2)	0.01395 (10)	0.0460 (5)
H2	0.2446	0.0585	−0.0240	0.055*
C3	0.2459 (3)	0.05342 (19)	0.07643 (10)	0.0416 (5)
C4	0.2132 (3)	0.1838 (2)	0.08161 (11)	0.0462 (5)
H4	0.2117	0.2353	0.0435	0.055*
C5	0.1832 (3)	0.2406 (2)	0.13913 (10)	0.0437 (5)
H5	0.1884	0.1884	0.1773	0.052*
C11	0.3487 (4)	−0.3066 (2)	−0.06035 (14)	0.0655 (7)
H11A	0.3656	−0.3474	−0.0158	0.098*
H11B	0.4545	−0.3120	−0.0740	0.098*
H11C	0.2559	−0.3485	−0.0947	0.098*
C12	0.2575 (4)	−0.1003 (2)	−0.11992 (11)	0.0596 (6)
H12A	0.1396	−0.0699	−0.1293	0.089*
H12B	0.2672	−0.1535	−0.1578	0.089*
H12C	0.3355	−0.0291	−0.1152	0.089*
C21	0.1195 (4)	0.4114 (3)	0.20963 (13)	0.0647 (7)
H21A	0.1345	0.3440	0.2434	0.097*
H21B	0.0030	0.4449	0.1998	0.097*
H21C	0.2023	0.4780	0.2280	0.097*
C22	0.1389 (4)	0.4541 (2)	0.09001 (14)	0.0717 (8)
H22A	0.2544	0.4694	0.0861	0.108*
H22B	0.0903	0.5325	0.1008	0.108*
H22C	0.0663	0.4211	0.0465	0.108*
C32	0.1698 (4)	−0.2136 (2)	0.18975 (14)	0.0626 (7)
H32	0.0928	−0.2815	0.1858	0.075*
C33	0.1494 (3)	−0.1348 (2)	0.13284 (12)	0.0516 (5)
H33	0.0611	−0.1502	0.0918	0.062*
C34	0.2616 (3)	−0.03225 (19)	0.13724 (10)	0.0406 (5)
C35	0.3878 (3)	−0.0138 (2)	0.20049 (10)	0.0494 (5)
H35	0.4642	0.0550	0.2065	0.059*
C36	0.3987 (4)	−0.0986 (3)	0.25434 (12)	0.0625 (7)
H36	0.4853	−0.0853	0.2962	0.075*
B1	0.3106 (3)	0.1668 (2)	0.37692 (11)	0.0590 (7)
F1	0.2062 (2)	0.13381 (19)	0.31236 (9)	0.0938 (6)
F2	0.4698 (3)	0.1104 (3)	0.39202 (14)	0.1248 (13)	0.918 (5)
F3	0.2298 (4)	0.1316 (4)	0.42561 (14)	0.1420 (14)	0.918 (5)
F4	0.3280 (4)	0.29452 (18)	0.38245 (16)	0.1267 (13)	0.918 (5)
F12	0.4433 (18)	0.2401 (19)	0.3687 (4)	0.101 (7)*	0.082 (5)
F13	0.376 (3)	0.0601 (6)	0.4128 (5)	0.101 (7)*	0.082 (5)
F14	0.2162 (12)	0.233 (2)	0.4114 (6)	0.101 (7)*	0.082 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0584 (11)	0.0492 (10)	0.0425 (9)	0.0009 (8)	0.0183 (8)	−0.0048 (8)
N2	0.0618 (11)	0.0421 (10)	0.0459 (10)	0.0054 (8)	0.0161 (8)	0.0013 (8)
N31	0.0935 (17)	0.0622 (13)	0.0594 (13)	0.0108 (12)	0.0361 (12)	0.0184 (10)
C1	0.0524 (12)	0.0485 (12)	0.0388 (10)	0.0020 (9)	0.0160 (9)	−0.0011 (9)
C2	0.0562 (12)	0.0465 (11)	0.0361 (10)	0.0018 (10)	0.0143 (9)	0.0041 (8)
C3	0.0448 (10)	0.0428 (11)	0.0372 (9)	−0.0003 (9)	0.0115 (8)	0.0018 (8)
C4	0.0584 (13)	0.0431 (11)	0.0380 (10)	0.0002 (9)	0.0153 (9)	0.0040 (8)
C5	0.0478 (11)	0.0410 (11)	0.0419 (10)	0.0006 (9)	0.0123 (9)	0.0044 (8)
C11	0.0806 (17)	0.0556 (14)	0.0628 (15)	0.0082 (13)	0.0244 (13)	−0.0095 (12)
C12	0.0818 (17)	0.0616 (15)	0.0404 (11)	−0.0013 (13)	0.0255 (11)	−0.0054 (10)
C21	0.0826 (18)	0.0567 (14)	0.0601 (14)	0.0129 (13)	0.0288 (13)	−0.0065 (12)
C22	0.105 (2)	0.0480 (14)	0.0655 (16)	0.0155 (14)	0.0294 (15)	0.0156 (12)
C32	0.0819 (17)	0.0470 (13)	0.0694 (16)	−0.0043 (12)	0.0384 (14)	0.0056 (11)
C33	0.0617 (13)	0.0453 (12)	0.0509 (12)	−0.0026 (10)	0.0211 (10)	−0.0002 (10)
C34	0.0491 (11)	0.0394 (10)	0.0370 (9)	0.0054 (8)	0.0179 (8)	0.0010 (8)
C35	0.0531 (12)	0.0545 (13)	0.0416 (11)	0.0011 (10)	0.0152 (9)	0.0040 (9)
C36	0.0672 (15)	0.0764 (17)	0.0436 (12)	0.0133 (13)	0.0153 (11)	0.0130 (12)
B1	0.0675 (17)	0.0479 (14)	0.0597 (16)	−0.0004 (13)	0.0150 (13)	−0.0053 (12)
F1	0.0918 (12)	0.1004 (14)	0.0806 (12)	0.0026 (10)	0.0105 (9)	−0.0291 (10)
F2	0.0929 (17)	0.155 (3)	0.1112 (19)	0.0495 (17)	0.0042 (13)	−0.0369 (17)
F3	0.153 (3)	0.182 (3)	0.1065 (19)	−0.034 (2)	0.0625 (18)	0.0211 (18)
F4	0.155 (3)	0.0539 (12)	0.151 (2)	−0.0137 (14)	0.0111 (19)	−0.0174 (13)

Geometric parameters (Å, º)

N1—C1	1.311 (3)	C35—C36	1.378 (3)
N1—C11	1.450 (3)	C35—H35	0.93
N1—C12	1.460 (3)	C36—H36	0.93
C1—C2	1.390 (3)	C11—H11A	0.96
C1—H1	0.93	C11—H11B	0.96
C2—C3	1.390 (3)	C11—H11C	0.96
C2—H2	0.93	C12—H12A	0.96
C3—C4	1.402 (3)	C12—H12B	0.96
C3—C34	1.486 (3)	C12—H12C	0.96
C4—C5	1.373 (3)	C21—H21A	0.96
C4—H4	0.93	C21—H21B	0.96
C5—H5	0.93	C21—H21C	0.96
N2—C5	1.318 (3)	C22—H22A	0.96
N2—C21	1.457 (3)	C22—H22B	0.96
N2—C22	1.456 (3)	C22—H22C	0.96
N31—C32	1.333 (4)	B1—F1	1.364 (2)
N31—C36	1.328 (4)	B1—F2	1.356 (2)
C32—C33	1.376 (3)	B1—F3	1.361 (2)
C32—H32	0.93	B1—F4	1.348 (2)
C33—C34	1.386 (3)	B1—F12	1.356 (3)
C33—H33	0.93	B1—F13	1.351 (3)
C34—C35	1.385 (3)	B1—F14	1.350 (3)
C1—N1—C11	121.7 (2)	N2—C21—H21C	109.5
C1—N1—C12	121.63 (19)	H21A—C21—H21C	109.5
C11—N1—C12	116.69 (19)	H21B—C21—H21C	109.5
C5—N2—C22	122.24 (19)	N2—C22—H22A	109.5
C5—N2—C21	121.33 (19)	N2—C22—H22B	109.5
C22—N2—C21	116.4 (2)	H22A—C22—H22B	109.5
C36—N31—C32	116.3 (2)	N2—C22—H22C	109.5
N1—C1—C2	125.0 (2)	H22A—C22—H22C	109.5
N1—C1—H1	117.5	H22B—C22—H22C	109.5
C2—C1—H1	117.5	N31—C32—C33	123.8 (2)
C3—C2—C1	124.14 (19)	N31—C32—H32	118.1
C3—C2—H2	117.9	C33—C32—H32	118.1
C1—C2—H2	117.9	C32—C33—C34	119.5 (2)
C2—C3—C4	119.94 (18)	C32—C33—H33	120.3
C2—C3—C34	119.80 (18)	C34—C33—H33	120.3
C4—C3—C34	120.26 (17)	C35—C34—C33	117.05 (19)
C5—C4—C3	124.46 (19)	C35—C34—C3	121.93 (19)
C5—C4—H4	117.8	C33—C34—C3	121.02 (18)
C3—C4—H4	117.8	C36—C35—C34	119.2 (2)
N2—C5—C4	126.38 (19)	C36—C35—H35	120.4
N2—C5—H5	116.8	C34—C35—H35	120.4
C4—C5—H5	116.8	N31—C36—C35	124.2 (2)
N1—C11—H11A	109.5	N31—C36—H36	117.9
N1—C11—H11B	109.5	C35—C36—H36	117.9
H11A—C11—H11B	109.5	F2—B1—F1	112.3 (2)
N1—C11—H11C	109.5	F3—B1—F1	108.6 (2)
H11A—C11—H11C	109.5	F4—B1—F1	110.5 (2)
H11B—C11—H11C	109.5	F2—B1—F3	109.1 (2)
N1—C12—H12A	109.5	F4—B1—F2	110.3 (2)
N1—C12—H12B	109.5	F4—B1—F3	105.7 (3)
H12A—C12—H12B	109.5	F12—B1—F1	108.5 (3)
N1—C12—H12C	109.5	F13—B1—F1	109.2 (3)
H12A—C12—H12C	109.5	F14—B1—F1	109.5 (3)
H12B—C12—H12C	109.5	F13—B1—F12	109.8 (3)
N2—C21—H21A	109.5	F14—B1—F12	109.8 (3)
N2—C21—H21B	109.5	F14—B1—F13	110.1 (3)
H21A—C21—H21B	109.5
C11—N1—C1—C2	179.2 (2)	N31—C32—C33—C34	−0.3 (4)
C12—N1—C1—C2	−1.7 (3)	C32—C33—C34—C35	−1.2 (3)
N1—C1—C2—C3	174.3 (2)	C32—C33—C34—C3	178.8 (2)
C1—C2—C3—C4	177.1 (2)	C2—C3—C34—C35	120.9 (2)
C1—C2—C3—C34	−3.7 (3)	C4—C3—C34—C35	−59.9 (3)
C2—C3—C4—C5	175.2 (2)	C2—C3—C34—C33	−59.1 (3)
C3—C4—C5—N2	−178.2 (2)	C4—C3—C34—C33	120.1 (2)
C4—C5—N2—C21	−179.5 (2)	C33—C34—C35—C36	1.7 (3)
C34—C3—C4—C5	−4.0 (3)	C3—C34—C35—C36	−178.2 (2)
C22—N2—C5—C4	−1.2 (4)	C32—N31—C36—C35	−0.7 (4)
C36—N31—C32—C33	1.3 (4)	C34—C35—C36—N31	−0.8 (4)