2,4-Lutidine

The crystal structure of 2,4-lutidine (2,4-di­methyl­pyridine, C₇H₉N) has been determined at 150 (2) K, following in situ crystal growth from the liquid. In space group P2₁/n, the asymmetric unit comprises a whole mol­ecule. Molecules are linked via C—H...N interactions into chains that align to form polar sheets, and adjacent sheets are packed in an antiparallel arrangement.

Key indicators

• Powder X-ray study
• T = 150 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.055
• wR factor = 0.146
• Data-to-parameter ratio = 19.7

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level A:



DIFF_020  Alert A _diffrn_standards_interval_count and
          _diffrn_standards_interval_time are missing. Number of measurements
          between standards or time (min) between standards.

DIFF_022  Alert A _diffrn_standards_decay_% is missing
          Percentage decrease in standards intensity.


 Alert Level B:



ABSTM_02  Alert B The ratio of expected to reported Tmax/Tmin(RR') is < 0.75
          Tmin and Tmax reported:      0.653     1.000
          Tmin' and Tmax expected:      1.000     1.000
          RR' =      0.653
          Please check that your absorption correction is appropriate.


 Alert Level C:



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           28.86
         From the CIF: _reflns_number_total               1540
         TEST2: Reflns within _diffrn_reflns_theta_max
         Count of symmetry unique reflns         1676
         Completeness (_total/calc)             91.89%
          Alert C: < 95% complete


 2 Alert Level A = Potentially serious problem

 1 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

As part of a study devoted to improving techniques for determining the crystal structures of substances that are liquid at room temperature, we have reported previously the structures of four of the six lutidine (dimethylpyridine) isomers (Bond et al., 2001; Bond & Davies, 2002a,b,c). In each case, crystals of these low-melting materials were grown in situ from the liquid using a relatively simple `zone refinement' technique (Davies & Bond, 2001). Curiously, we had been unable to obtain a single-crystal of 2,4-lutidin,e (I), using this approach. A crystal of (I) was eventually grown by Boese's laser-assisted crystallization technique (Boese & Nussbaumer, 1994) using a sample held at 203 K in a 0.5 mm capillary. The crystal was cooled subsequently to 150 K for data collection.

In all of the lutidine isomers where the 4-position of the ring is unsubstituted, polar chains are formed via C4—H4···N interactions. In the 3,4-isomer, where the 4-position is substituted, dimers are formed via similar interactions from the 2- and 6-positions. In (I), where the 4-position is also substituted (Fig. 1), molecules are linked into chains along [010] via C—H···N interactions from the 3-position [H3···N1ⁱ = 2.75 Å and C3—H3···N1ⁱ = 166.8°; symmetry code: (i) 1/2 - x, 1/2 + y, 3/2 - z]. The fact that the 3-position is utilized in (I) would appear to be a consequence of effective packing of the methyl substituents between adjacent chains. The chains in (I) lie in sheets parallel to (100) (Fig. 2), and adjacent sheets are aligned in an antiparallel manner such that the crystal is not macroscopically polar (Fig. 3). Similar arrangements are observed in the 2,5- and 3,5-isomers.

S2. Experimental

The sample (99%) of (I) was obtained from the Aldrich company and used without further purification. A crystal was grown by Boese's laser-assisted crystallization technique (Boese & Nussbaumer, 1994) using a sample held at 203 K in a 0.5 mm capillary. The crystal was cooled subsequently to 150 K for data collection. The length of the cylindrical crystal was not measured, but it exceeded the diameter of the collimator (0.35 mm).

S3. Refinement

All H atoms were placed geometrically and refined with isotropic displacement parameters, with a common parameter assigned to all H atoms of the methyl groups, and a second parameter for H atoms attached to the ring (two displacement parameters in total). Each methyl group was allowed to rotate about its local threefold axis.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); 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 molecular unit of (I), showing displacement ellipsoids at 50% probability for non-H atoms.
	Fig. 2. Projection of (I) on to (100), showing molecules linked into chains via C—H···N interactions.
	Fig. 3. Projection of (I) on to (001), showing sheets aligned in an antiparallel manner.

2,4-dimethylpyridine

Crystal data

C7H9N	Dx = 1.113 Mg m^−3
Mr = 107.15	Melting point: 213 K
Monoclinic, P21/n	Mo Kα radiation, λ = 0.7107 Å
a = 7.4247 (8) Å	Cell parameters from 2543 reflections
b = 10.9401 (12) Å	θ = 2.5–28.9°
c = 8.2473 (9) Å	µ = 0.07 mm^−1
β = 107.342 (2)°	T = 150 K
V = 639.45 (12) Å^3	Cylinder, colourless
Z = 4	0.25 mm (radius)
F(000) = 232

Data collection

Bruker SMART APEX diffractometer equipped with Oxford Cryosystems cryostream and OHCD laser-assisted crystallisation device (Scientific Consulting, Essen, Germany)	1540 independent reflections
Radiation source: fine-focus sealed tube	1133 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.030
thin–slice ω scans	θmax = 28.9°, θmin = 3.7°
Absorption correction: multi-scan (SADABS; Sheldrick, 2001)	h = −9→9
Tmin = 0.653, Tmax = 1.000	k = −13→14
4515 measured reflections	l = −11→10

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)] = 0.055	H-atom parameters constrained
wR(F^2) = 0.146	w = 1/[σ^2(Fo^2) + (0.0973P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.94	(Δ/σ)max < 0.001
1540 reflections	Δρmax = 0.20 e Å^−3
78 parameters	Δρmin = −0.31 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: 0.19 (2)

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
N1	0.14857 (14)	0.64758 (9)	0.65190 (14)	0.0394 (3)
C2	0.17370 (16)	0.76169 (10)	0.71317 (15)	0.0334 (3)
C3	0.19828 (16)	0.86006 (10)	0.61580 (15)	0.0345 (3)
H3	0.2174	0.9395	0.6643	0.050 (2)*
C4	0.19522 (16)	0.84361 (10)	0.44918 (15)	0.0353 (3)
C5	0.16838 (18)	0.72517 (11)	0.38610 (16)	0.0392 (4)
H5	0.1652	0.7086	0.2722	0.050 (2)*
C6	0.14654 (19)	0.63256 (11)	0.49059 (18)	0.0427 (4)
H6	0.1287	0.5521	0.4452	0.050 (2)*
C7	0.1742 (2)	0.77769 (13)	0.89345 (16)	0.0474 (4)
H7A	0.0635	0.7370	0.9102	0.103 (3)*
H7B	0.1702	0.8650	0.9186	0.103 (3)*
H7C	0.2892	0.7415	0.9696	0.103 (3)*
C8	0.2206 (2)	0.94818 (12)	0.33953 (18)	0.0545 (4)
H8A	0.2258	1.0252	0.4014	0.103 (3)*
H8B	0.1142	0.9503	0.2352	0.103 (3)*
H8C	0.3384	0.9371	0.3106	0.103 (3)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0418 (6)	0.0327 (6)	0.0468 (7)	0.0003 (4)	0.0178 (5)	0.0034 (4)
C2	0.0280 (6)	0.0379 (6)	0.0335 (6)	−0.0001 (4)	0.0080 (5)	0.0011 (5)
C3	0.0369 (6)	0.0295 (6)	0.0372 (7)	−0.0016 (4)	0.0112 (5)	−0.0030 (4)
C4	0.0361 (6)	0.0335 (6)	0.0396 (7)	0.0030 (4)	0.0162 (5)	0.0035 (5)
C5	0.0435 (7)	0.0416 (7)	0.0374 (7)	−0.0004 (5)	0.0194 (6)	−0.0057 (5)
C6	0.0506 (8)	0.0306 (6)	0.0537 (8)	−0.0033 (5)	0.0259 (6)	−0.0077 (5)
C7	0.0481 (8)	0.0594 (9)	0.0344 (7)	−0.0080 (6)	0.0121 (6)	0.0001 (6)
C8	0.0750 (10)	0.0434 (8)	0.0532 (9)	0.0039 (7)	0.0317 (8)	0.0127 (6)

Geometric parameters (Å, º)

N1—C6	1.3361 (17)	C5—H5	0.950
N1—C2	1.3388 (15)	C6—H6	0.950
C2—C3	1.3870 (16)	C7—H7A	0.980
C2—C7	1.4960 (17)	C7—H7B	0.980
C3—C4	1.3794 (17)	C7—H7C	0.980
C3—H3	0.950	C8—H8A	0.980
C4—C5	1.3884 (16)	C8—H8B	0.980
C4—C8	1.5045 (17)	C8—H8C	0.980
C5—C6	1.3706 (18)
C6—N1—C2	116.70 (10)	N1—C6—H6	117.7
N1—C2—C3	122.18 (12)	C5—C6—H6	117.7
N1—C2—C7	116.29 (11)	C2—C7—H7A	109.5
C3—C2—C7	121.52 (11)	C2—C7—H7B	109.5
C4—C3—C2	120.64 (10)	H7A—C7—H7B	109.5
C4—C3—H3	119.7	C2—C7—H7C	109.5
C2—C3—H3	119.7	H7A—C7—H7C	109.5
C3—C4—C5	116.93 (10)	H7B—C7—H7C	109.5
C3—C4—C8	122.13 (11)	C4—C8—H8A	109.5
C5—C4—C8	120.94 (11)	C4—C8—H8B	109.5
C6—C5—C4	119.01 (11)	H8A—C8—H8B	109.5
C6—C5—H5	120.5	C4—C8—H8C	109.5
C4—C5—H5	120.5	H8A—C8—H8C	109.5
N1—C6—C5	124.53 (11)	H8B—C8—H8C	109.5
C6—N1—C2—C3	−0.57 (18)	C2—C3—C4—C8	179.75 (12)
C6—N1—C2—C7	179.53 (10)	C3—C4—C5—C6	0.06 (17)
N1—C2—C3—C4	0.84 (18)	C8—C4—C5—C6	179.76 (12)
C7—C2—C3—C4	−179.26 (10)	C2—N1—C6—C5	0.05 (19)
C2—C3—C4—C5	−0.55 (17)	C4—C5—C6—N1	0.2 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3···N1^i	0.95	2.75	3.6822 (15)	167

Symmetry code: (i) −x+1/2, y+1/2, −z+3/2.