3,4-Lutidine

The crystal structure of 3,4-lutidine (3,4-di­methyl­pyridine, C₇H₉N), has been determined at 150 (2) K following in situ crystal growth from the liquid. In space group C2/c, there are four independent mol­ecules in the asymmetric unit, linked into dimers via C—H...N interactions.

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.053
• wR factor = 0.135
• Data-to-parameter ratio = 19.1

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

As part of a study devoted to improving the techniques for determining the crystal structures of substances that are liquids at room temperature, we have reported previously the crystal structures of 2,6-lutidine (Bond et al., 2001), 3,5-lutidine (Bond & Davies, 2002a) and 2,5-lutidine (Bond & Davies, 2002b). We report here the crystal structure of 3,4-lutidine, (I), determined at 150 (2) K following in situ crystal growth from the liquid.

Compound (I) crystallizes in the monoclinic space group C2/c with four independent molecules in the asymmetric unit (Fig. 1). Within the asymmetric unit, molecules are linked into dimers via C—H···N interactions (Table 1). In the structures of the other lutidines reported to date, molecules are linked into linear chains via C—H···N interactions involving the H atom at the 4-position; this interaction is clearly prohibited in (I). Two orientations may be envisaged for dimerization in which a centrosymmetric motif would result: either both molecules interact through the H atoms at their 2-positions, or both interact through the H atoms at their 6-positions. The observed dimer involves one molecule of (I) interacting through H at the 2-position and one interacting through H at the 6-position, giving rise to an asymmetric motif (point symmetry 1). In both independent dimers within the asymmetric unit, the interaction C6—H6···N1 is significantly shorter and closer to linear than the C2—H2···N1 interaction (Table 1). This is not obviously an intra-dimer effect and may be a result of inter-dimer interactions between methyl substituents. The dimers may be considered to form layers parallel to (001), with the planes through the dimer units lying alternately parallel to (110) and (110) in adjacent layers (Figs. 2 and 3).

S2. Experimental

The sample (99%) was obtained from the Aldrich company and used without further purification. The crystal was grown in a 0.3 mm glass capillary tube at ca 235 K (a temperature only slightly less than the melting point of the solid in the capillary) using a technique described earlier (Davies & Bond, 2001). Once grown, the crystal was cooled to 150 (2) K for data collection. The length of the cylindrical crystal was not estimated, but it exceeded the diameter of the collimator (0.35 mm).

S3. Refinement

H atoms were placed geometrically and refined with isotropic displacement parameters, with common parameters assigned to chemically equivalent H atoms (one parameter for all methyl H atoms, four parameters in total). Each methyl group was allowed to rotate about its local threefold axis.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Sheldrick, 1993) and CAMERON (Watkin et al., 1996); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The asymmetric unit and atom-labelling scheme in (I), showing displacement ellipsoids (C/N atoms) at the 50% probability level (XP; Sheldrick, 1993). Independent molecules are denoted by the suffixes A, B, C and D.
	Fig. 2. Projection on to (001) of a single layer in (I), showing dimers linked by C—H···N interactions orientated parallel to (110) (CAMERON; Watkin et al., 1996).
	Fig. 3. Projection on to (001) of the entire structure of (I), showing layers of dimers oriented alternately parallel to (110) and (110) (CAMERON; Watkin et al., 1996).

3,4-dimethylpyridine

Crystal data

C7H9N	Dx = 1.124 Mg m^−3
Mr = 107.15	Melting point: 261 K
Monoclinic, C2/c	Mo Kα radiation, λ = 0.7107 Å
a = 20.9006 (8) Å	Cell parameters from 9883 reflections
b = 20.6112 (9) Å	θ = 1.0–27.5°
c = 12.9921 (3) Å	µ = 0.07 mm^−1
β = 115.135 (2)°	T = 150 K
V = 5066.9 (3) Å^3	Cylinder, colourless
Z = 32	0.15 mm (radius)
F(000) = 1856

Data collection

Nonius KappaCCD diffractometer	Rint = 0.026
Radiation source: fine-focus sealed tube	θmax = 27.5°, θmin = 3.7°
Thin–slice ω and ϕ scans	h = 0→26
9752 measured reflections	k = 0→26
5740 independent reflections	l = −16→15
4041 reflections with I > 2σ(I)

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)] = 0.053	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.135	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0488P)^2 + 2.9233P] where P = (Fo^2 + 2Fc^2)/3
5740 reflections	(Δ/σ)max < 0.001
301 parameters	Δρmax = 0.20 e Å^−3
0 restraints	Δρmin = −0.16 e Å^−3

Special details

Experimental. Crystal grown in situ in a 0.30 mm Lindemann tube.

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
N1A	0.23300 (7)	0.60065 (6)	0.01432 (10)	0.0421 (3)
C2A	0.26063 (8)	0.64157 (7)	−0.03603 (12)	0.0394 (3)
H2A	0.2424	0.6398	−0.1166	0.048 (2)*
C3A	0.31361 (7)	0.68629 (7)	0.01988 (11)	0.0323 (3)
C4A	0.33999 (7)	0.68930 (7)	0.13817 (11)	0.0329 (3)
C5A	0.31180 (8)	0.64716 (7)	0.19112 (12)	0.0363 (3)
H5A	0.3287	0.6478	0.2715	0.050 (2)*
C6A	0.25910 (8)	0.60414 (7)	0.12734 (12)	0.0375 (3)
H6A	0.2406	0.5758	0.1657	0.047 (2)*
C7A	0.34097 (8)	0.72962 (8)	−0.04567 (13)	0.0432 (4)
H7AA	0.3154	0.7205	−0.1271	0.0730 (13)*
H7AB	0.3915	0.7215	−0.0214	0.0730 (13)*
H7AC	0.3338	0.7751	−0.0312	0.0730 (13)*
C8A	0.39661 (9)	0.73682 (8)	0.20617 (14)	0.0498 (4)
H8AA	0.4119	0.7284	0.2874	0.0730 (13)*
H8AB	0.3780	0.7811	0.1884	0.0730 (13)*
H8AC	0.4370	0.7320	0.1871	0.0730 (13)*
N1B	0.15531 (6)	0.49769 (6)	0.18226 (10)	0.0391 (3)
C2B	0.12057 (7)	0.48533 (7)	0.07082 (12)	0.0355 (3)
H2B	0.1335	0.5098	0.0206	0.048 (2)*
C3B	0.06718 (7)	0.43973 (7)	0.02281 (11)	0.0319 (3)
C4B	0.04803 (7)	0.40381 (6)	0.09667 (12)	0.0332 (3)
C5B	0.08360 (8)	0.41670 (7)	0.21207 (12)	0.0366 (3)
H5B	0.0717	0.3935	0.2647	0.050 (2)*
C6B	0.13596 (8)	0.46290 (7)	0.25080 (12)	0.0367 (3)
H6B	0.1595	0.4704	0.3304	0.047 (2)*
C7B	0.03213 (8)	0.43004 (8)	−0.10363 (12)	0.0437 (4)
H7BA	0.0531	0.4595	−0.1399	0.0730 (13)*
H7BB	−0.0185	0.4391	−0.1320	0.0730 (13)*
H7BC	0.0389	0.3851	−0.1216	0.0730 (13)*
C8B	−0.00871 (9)	0.35304 (8)	0.05216 (15)	0.0505 (4)
H8BA	−0.0152	0.3333	0.1157	0.0730 (13)*
H8BB	0.0051	0.3195	0.0121	0.0730 (13)*
H8BC	−0.0531	0.3731	−0.0004	0.0730 (13)*
N1C	0.47325 (7)	0.34998 (7)	−0.02172 (12)	0.0504 (4)
C2C	0.50067 (8)	0.39217 (8)	−0.07027 (13)	0.0449 (4)
H2C	0.4799	0.3939	−0.1510	0.048 (2)*
C3C	0.55689 (8)	0.43360 (7)	−0.01279 (12)	0.0369 (3)
C4C	0.58764 (7)	0.43149 (7)	0.10593 (12)	0.0363 (3)
C5C	0.56011 (8)	0.38758 (8)	0.15718 (13)	0.0421 (4)
H5C	0.5801	0.3844	0.2377	0.050 (2)*
C6C	0.50382 (8)	0.34839 (8)	0.09192 (14)	0.0458 (4)
H6C	0.4860	0.3189	0.1296	0.047 (2)*
C7C	0.58322 (9)	0.47896 (8)	−0.07719 (14)	0.0493 (4)
H7CA	0.5552	0.4729	−0.1590	0.0730 (13)*
H7CB	0.6330	0.4696	−0.0578	0.0730 (13)*
H7CC	0.5786	0.5239	−0.0566	0.0730 (13)*
C8C	0.64820 (9)	0.47483 (9)	0.17554 (14)	0.0517 (4)
H8CA	0.6614	0.4672	0.2565	0.0730 (13)*
H8CB	0.6341	0.5203	0.1572	0.0730 (13)*
H8CC	0.6886	0.4654	0.1585	0.0730 (13)*
N1D	0.39991 (7)	0.24523 (7)	0.14888 (11)	0.0498 (4)
C2D	0.36153 (8)	0.23333 (8)	0.03857 (13)	0.0429 (4)
H2D	0.3701	0.2598	−0.0142	0.048 (2)*
C3D	0.31041 (8)	0.18578 (7)	−0.00550 (12)	0.0378 (3)
C4D	0.29759 (8)	0.14682 (7)	0.07185 (13)	0.0401 (3)
C5D	0.33786 (9)	0.15837 (8)	0.18685 (13)	0.0452 (4)
H5D	0.3310	0.1326	0.2420	0.050 (2)*
C6D	0.38758 (9)	0.20700 (8)	0.22098 (13)	0.0479 (4)
H6D	0.4145	0.2136	0.3002	0.047 (2)*
C7D	0.27101 (9)	0.17719 (9)	−0.13189 (13)	0.0547 (4)
H7DA	0.2880	0.2089	−0.1707	0.0730 (13)*
H7DB	0.2204	0.1838	−0.1546	0.0730 (13)*
H7DC	0.2789	0.1332	−0.1528	0.0730 (13)*
C8D	0.24239 (10)	0.09446 (9)	0.03272 (18)	0.0620 (5)
H8DA	0.2429	0.0712	0.0989	0.0730 (13)*
H8DB	0.2525	0.0640	−0.0165	0.0730 (13)*
H8DC	0.1957	0.1140	−0.0098	0.0730 (13)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1A	0.0428 (7)	0.0406 (7)	0.0423 (7)	−0.0108 (6)	0.0175 (6)	−0.0042 (5)
C2A	0.0423 (8)	0.0411 (8)	0.0346 (7)	−0.0047 (7)	0.0162 (6)	−0.0016 (6)
C3A	0.0312 (7)	0.0299 (7)	0.0379 (7)	0.0023 (6)	0.0165 (6)	0.0034 (6)
C4A	0.0290 (7)	0.0285 (7)	0.0380 (7)	0.0010 (6)	0.0112 (6)	0.0015 (5)
C5A	0.0392 (8)	0.0351 (8)	0.0336 (7)	0.0000 (6)	0.0145 (6)	0.0020 (6)
C6A	0.0404 (8)	0.0340 (8)	0.0414 (8)	−0.0057 (6)	0.0206 (6)	0.0022 (6)
C7A	0.0441 (9)	0.0427 (9)	0.0477 (9)	−0.0017 (7)	0.0243 (7)	0.0071 (7)
C8A	0.0455 (9)	0.0462 (10)	0.0473 (9)	−0.0138 (8)	0.0097 (7)	0.0005 (7)
N1B	0.0366 (7)	0.0401 (7)	0.0396 (7)	−0.0025 (6)	0.0152 (5)	−0.0012 (5)
C2B	0.0374 (8)	0.0360 (8)	0.0378 (7)	−0.0001 (6)	0.0204 (6)	0.0050 (6)
C3B	0.0314 (7)	0.0312 (7)	0.0349 (7)	0.0054 (6)	0.0159 (6)	0.0030 (5)
C4B	0.0325 (7)	0.0265 (7)	0.0423 (8)	0.0022 (6)	0.0174 (6)	0.0018 (6)
C5B	0.0432 (8)	0.0337 (7)	0.0381 (8)	0.0061 (6)	0.0223 (6)	0.0086 (6)
C6B	0.0376 (8)	0.0384 (8)	0.0319 (7)	0.0054 (6)	0.0126 (6)	0.0002 (6)
C7B	0.0432 (8)	0.0507 (10)	0.0361 (8)	0.0043 (7)	0.0156 (6)	−0.0003 (7)
C8B	0.0507 (10)	0.0434 (9)	0.0594 (10)	−0.0119 (8)	0.0254 (8)	−0.0024 (7)
N1C	0.0469 (8)	0.0502 (8)	0.0525 (8)	−0.0143 (7)	0.0197 (6)	−0.0051 (6)
C2C	0.0431 (9)	0.0489 (9)	0.0392 (8)	−0.0055 (7)	0.0142 (7)	−0.0005 (7)
C3C	0.0342 (7)	0.0330 (8)	0.0446 (8)	0.0016 (6)	0.0179 (6)	0.0020 (6)
C4C	0.0325 (7)	0.0330 (7)	0.0429 (8)	0.0006 (6)	0.0155 (6)	−0.0030 (6)
C5C	0.0423 (8)	0.0445 (9)	0.0404 (8)	−0.0006 (7)	0.0184 (7)	0.0012 (6)
C6C	0.0463 (9)	0.0430 (9)	0.0528 (9)	−0.0068 (7)	0.0257 (7)	0.0025 (7)
C7C	0.0494 (10)	0.0475 (9)	0.0535 (9)	−0.0023 (8)	0.0244 (8)	0.0088 (8)
C8C	0.0463 (9)	0.0494 (10)	0.0522 (10)	−0.0108 (8)	0.0140 (8)	−0.0054 (8)
N1D	0.0521 (8)	0.0485 (8)	0.0500 (8)	−0.0098 (7)	0.0228 (6)	−0.0029 (6)
C2D	0.0478 (9)	0.0405 (8)	0.0461 (9)	−0.0027 (7)	0.0253 (7)	0.0053 (7)
C3D	0.0351 (8)	0.0371 (8)	0.0415 (8)	0.0051 (7)	0.0165 (6)	0.0020 (6)
C4D	0.0368 (8)	0.0339 (8)	0.0540 (9)	0.0016 (7)	0.0236 (7)	0.0019 (6)
C5D	0.0545 (10)	0.0434 (9)	0.0481 (9)	0.0044 (8)	0.0317 (8)	0.0100 (7)
C6D	0.0519 (10)	0.0516 (10)	0.0396 (8)	0.0004 (8)	0.0188 (7)	−0.0042 (7)
C7D	0.0517 (10)	0.0616 (11)	0.0432 (9)	0.0057 (9)	0.0129 (7)	0.0006 (8)
C8D	0.0549 (11)	0.0496 (11)	0.0827 (13)	−0.0127 (9)	0.0304 (10)	0.0006 (9)

Geometric parameters (Å, º)

N1A—C6A	1.3335 (18)	N1C—C6C	1.337 (2)
N1A—C2A	1.3393 (19)	N1C—C2C	1.338 (2)
C2A—C3A	1.386 (2)	C2C—C3C	1.386 (2)
C2A—H2A	0.950	C2C—H2C	0.950
C3A—C4A	1.3963 (19)	C3C—C4C	1.397 (2)
C3A—C7A	1.5047 (19)	C3C—C7C	1.506 (2)
C4A—C5A	1.3855 (19)	C4C—C5C	1.385 (2)
C4A—C8A	1.501 (2)	C4C—C8C	1.498 (2)
C5A—C6A	1.382 (2)	C5C—C6C	1.381 (2)
C5A—H5A	0.950	C5C—H5C	0.950
C6A—H6A	0.950	C6C—H6C	0.950
C7A—H7AA	0.980	C7C—H7CA	0.980
C7A—H7AB	0.980	C7C—H7CB	0.980
C7A—H7AC	0.980	C7C—H7CC	0.980
C8A—H8AA	0.980	C8C—H8CA	0.980
C8A—H8AB	0.980	C8C—H8CB	0.980
C8A—H8AC	0.980	C8C—H8CC	0.980
N1B—C6B	1.3328 (18)	N1D—C6D	1.330 (2)
N1B—C2B	1.3399 (18)	N1D—C2D	1.335 (2)
C2B—C3B	1.388 (2)	C2D—C3D	1.382 (2)
C2B—H2B	0.950	C2D—H2D	0.950
C3B—C4B	1.3985 (19)	C3D—C4D	1.398 (2)
C3B—C7B	1.5010 (19)	C3D—C7D	1.502 (2)
C4B—C5B	1.387 (2)	C4D—C5D	1.389 (2)
C4B—C8B	1.501 (2)	C4D—C8D	1.502 (2)
C5B—C6B	1.375 (2)	C5D—C6D	1.375 (2)
C5B—H5B	0.950	C5D—H5D	0.950
C6B—H6B	0.950	C6D—H6D	0.950
C7B—H7BA	0.980	C7D—H7DA	0.980
C7B—H7BB	0.980	C7D—H7DB	0.980
C7B—H7BC	0.980	C7D—H7DC	0.980
C8B—H8BA	0.980	C8D—H8DA	0.980
C8B—H8BB	0.980	C8D—H8DB	0.980
C8B—H8BC	0.980	C8D—H8DC	0.980
C6A—N1A—C2A	116.38 (12)	C6C—N1C—C2C	115.92 (13)
N1A—C2A—C3A	125.25 (13)	N1C—C2C—C3C	125.53 (14)
N1A—C2A—H2A	117.4	N1C—C2C—H2C	117.2
C3A—C2A—H2A	117.4	C3C—C2C—H2C	117.2
C2A—C3A—C4A	117.43 (12)	C2C—C3C—C4C	117.56 (13)
C2A—C3A—C7A	120.62 (12)	C2C—C3C—C7C	120.61 (14)
C4A—C3A—C7A	121.95 (13)	C4C—C3C—C7C	121.83 (14)
C5A—C4A—C3A	117.79 (13)	C5C—C4C—C3C	117.43 (13)
C5A—C4A—C8A	120.81 (13)	C5C—C4C—C8C	121.08 (14)
C3A—C4A—C8A	121.40 (13)	C3C—C4C—C8C	121.49 (14)
C6A—C5A—C4A	120.21 (13)	C6C—C5C—C4C	120.42 (14)
C6A—C5A—H5A	119.9	C6C—C5C—H5C	119.8
C4A—C5A—H5A	119.9	C4C—C5C—H5C	119.8
N1A—C6A—C5A	122.94 (13)	N1C—C6C—C5C	123.13 (15)
N1A—C6A—H6A	118.5	N1C—C6C—H6C	118.4
C5A—C6A—H6A	118.5	C5C—C6C—H6C	118.4
C3A—C7A—H7AA	109.5	C3C—C7C—H7CA	109.5
C3A—C7A—H7AB	109.5	C3C—C7C—H7CB	109.5
H7AA—C7A—H7AB	109.5	H7CA—C7C—H7CB	109.5
C3A—C7A—H7AC	109.5	C3C—C7C—H7CC	109.5
H7AA—C7A—H7AC	109.5	H7CA—C7C—H7CC	109.5
H7AB—C7A—H7AC	109.5	H7CB—C7C—H7CC	109.5
C4A—C8A—H8AA	109.5	C4C—C8C—H8CA	109.5
C4A—C8A—H8AB	109.5	C4C—C8C—H8CB	109.5
H8AA—C8A—H8AB	109.5	H8CA—C8C—H8CB	109.5
C4A—C8A—H8AC	109.5	C4C—C8C—H8CC	109.5
H8AA—C8A—H8AC	109.5	H8CA—C8C—H8CC	109.5
H8AB—C8A—H8AC	109.5	H8CB—C8C—H8CC	109.5
C6B—N1B—C2B	116.15 (13)	C6D—N1D—C2D	116.07 (14)
N1B—C2B—C3B	125.28 (13)	N1D—C2D—C3D	125.55 (14)
N1B—C2B—H2B	117.4	N1D—C2D—H2D	117.2
C3B—C2B—H2B	117.4	C3D—C2D—H2D	117.2
C2B—C3B—C4B	117.39 (12)	C2D—C3D—C4D	117.38 (13)
C2B—C3B—C7B	120.51 (12)	C2D—C3D—C7D	120.31 (14)
C4B—C3B—C7B	122.11 (13)	C4D—C3D—C7D	122.31 (14)
C5B—C4B—C3B	117.51 (13)	C5D—C4D—C3D	117.46 (14)
C5B—C4B—C8B	121.53 (13)	C5D—C4D—C8D	120.97 (14)
C3B—C4B—C8B	120.95 (13)	C3D—C4D—C8D	121.57 (15)
C6B—C5B—C4B	120.41 (13)	C6D—C5D—C4D	120.10 (14)
C6B—C5B—H5B	119.8	C6D—C5D—H5D	119.9
C4B—C5B—H5B	119.8	C4D—C5D—H5D	119.9
N1B—C6B—C5B	123.26 (13)	N1D—C6D—C5D	123.42 (15)
N1B—C6B—H6B	118.4	N1D—C6D—H6D	118.3
C5B—C6B—H6B	118.4	C5D—C6D—H6D	118.3
C3B—C7B—H7BA	109.5	C3D—C7D—H7DA	109.5
C3B—C7B—H7BB	109.5	C3D—C7D—H7DB	109.5
H7BA—C7B—H7BB	109.5	H7DA—C7D—H7DB	109.5
C3B—C7B—H7BC	109.5	C3D—C7D—H7DC	109.5
H7BA—C7B—H7BC	109.5	H7DA—C7D—H7DC	109.5
H7BB—C7B—H7BC	109.5	H7DB—C7D—H7DC	109.5
C4B—C8B—H8BA	109.5	C4D—C8D—H8DA	109.5
C4B—C8B—H8BB	109.5	C4D—C8D—H8DB	109.5
H8BA—C8B—H8BB	109.5	H8DA—C8D—H8DB	109.5
C4B—C8B—H8BC	109.5	C4D—C8D—H8DC	109.5
H8BA—C8B—H8BC	109.5	H8DA—C8D—H8DC	109.5
H8BB—C8B—H8BC	109.5	H8DB—C8D—H8DC	109.5

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C6A—H6A···N1B	0.95	2.48	3.368 (2)	156
C2B—H2B···N1A	0.95	2.83	3.630 (2)	143
C6C—H6C···N1D	0.95	2.45	3.339 (2)	156
C2D—H2D···N1C	0.95	2.88	3.661 (2)	140