4-Iodo­quinoline

Nearly planar mol­ecules of the title compound, C₉H₆IN, are packed in inclined stacks along the short crystallographic b axis and mol­ecules in adjacent stacks are packed to form anti­parallel zigzag chains. Short inter­molecular N...I contacts [3.131 (3) Å] are observed between mol­ecules in adjacent stacks. A network of C—H...π hydrogen bonds [2.821 (5) and 3.083 (3) Å] between mol­ecules in adjacent stacks is also present. These motif-generating inter­actions, including the weak C—H...π inter­actions, are of relevance in crystal engineering and design.

S1. Comment

Information on the molecular packing of aromatic compounds in crystal structures is of importance for understanding solid-state properties and the influence of molecular structure on molecular packing (Kitaigorodskii, 1973). Halogen–nitrogen interactions have been considered as secondary motif-generating interactions (Desiraju & Harlow, 1989) and could play a useful role in crystal engineering and design. We report here the structure of 4-iodoquinoline, (I), which exhibits the typical herring-bone type structure known for many planar aromatic hydrocarbons (Desiraju & Gavezzotti, 1989, and references therein) and substituted aromatic compounds, e.g. 2,3-diodonaphthalene (Novak, 2007). Short intermolecular N···I [3.131 (3) Å] and C—H···π [2.821 (5) and 3.083 (3) Å] contacts are present between molecules in adjacent stacks and form a zigzag network of hydrogen bonds.

Compound (I) crystallizes in the monoclinic centrosymmetric space group P2₁/n. Fig. 1 shows the asymmetric unit and the atom-numbering scheme. Selected bond lengths and angles are given in Table 1.

Bond lengths and angles for the aromatic rings in (I) are within the ranges reported for substituted quinolines (Harlow et al., 1976; Das et al., 1990; Singh et al., 2008) and those calculated for quinoline (Dewar & Gleicher, 1966). The C—I bond length of 2.110 (4) Å is close to that observed in 4-iodopyridine [2.100 (5)Å; Ahrens & Jones, 1999]. These authors also report a mean value for the C—I bond of 2.090 Å based on entries in the Cambridge Structural Database (CSD, Version?; Allen, 2002) for 39 C—I bonds in substituted benzenes. A comparison of the values of the bond angles around the ring N atom, namely C1—N—C5, N—C1—C2 and N1—C5—C4 in (I) [117.3, 124.3 and 122.9°, respectively] with those for another 4-substituted quinoline, 1,4-bis-(4-quinolyl)-1,3-butadiyne (117.04, 124.3 and 123.0°, respectively; Singh et al., 2008) indicates a negligible influence of these substituent groups on the bond angles around the ring N atom. Furthermore, it is noteworthy that the two aromatic rings are not entirely coplanar, their ring planes being joined together at the C4—C5 bond edge at an angle of 1.40 (24)°. The I atom is out of the pseudo-molecular plane by about 2.6°. Bond angle values of 117.9 (3) and 122.3 (3)° for C2—C3—I1 and C4—C3—I1, respectively, suggest a significant peri interaction between the C—I and C9—H bonds.

Fig. 2 shows the contents of the unit cell, viewed approximately along the crystallographic c axis. Molecules of (I) are packed in the centrosymmetric space group in parallel inclined stacks along the crystallographic b axis. Planar molecules within a stack are separated by 4.353 Å, indicating weak π–π interactions between adjacent molecules within the stack. Molecules in adjacent stacks are packed to form an antiparallel zigzag chain of molecules. The molecular planes in adjacent stacks form an angle of about 69°, forming a herring-bone type structure, as shown in Fig. 3 and often observed for planar aromatic compounds. The dipolar nature of the layers of the large I atoms seems to cause the molecules to form stacks inclined with the stack axis to reduce atom–atom repulsive interactions, thereby increasing the distance between the planar molecules.

Two types of short intermolecular contacts are present. A short intermolecular N···Iⁱ [symmetry code: (i) 1/2 + x, 1/2 - y, 1/2 + z] contact of 3.131 (3) Å is observed between the N and I atoms of molecules in adjacent stacks, as shown in Fig. 2. The C—I···N geometry is nearly linear, with an angle of 171°. A short N···I contact of 2.988 (5) Å has been observed in 4-iodopyridine (Ahrens & Jones, 1999). Only a limited number of crystal structures with N···I contacts of less than 3.3 Å have been reported to date, as was observed by Ahrens & Jones. An exceptionally short N···I contact of 2.712 (2) Å was reported recently for a morpholine-β-iodophenylacetylene complex (Batsanov & Howard, 2000). Short N···I contacts have also been observed in the crystal structures of an aggregate of 1-iodoperfluoroheptane and tetramethylenediamine (Fontana et al., 2002), some diiodobenzothiaadiazoles (Tomura et al., 2002) and 4,5-diiodo[1,2,5]thiadiazolotetrathiafulvalene (Tomura & Yamashita, 2004). These short contacts could be induced by the weak Lewis acidity of the I atoms due to polarization of the C—I bond. These short N···I contacts lead to the formation of a motif with an antiparallel zigzag arrangement of molecules along the crystallographic a axis, as shown in Fig. 2. Such antiparallel zigzag motifs, as well parallel linear array motifs, have been observed in the crystal structures of 4-halobenzonitriles (Desiraju & Harlow, 1989). 4-Iodopyridine, in contrast, crystallizes in a polar space group and forms a parallel linear array of molecules along the polar c axis.

The other type of short intermolecular contacts observed in the crystal structure of (I) are weak C—H···π hydrogen bonds (Nishio, 2004), which are shown in Fig. 4. Short intermolecular contacts of 2.821 (5) and 3.083 (3) Å are observed for C7—H7···C7ⁱⁱ and C7—H7···C6ⁱⁱ [symmetry code: (ii) 3/2 - x, -1/2 + y, 1/2 - z], respectively, between the benzene rings of molecules of (I) in adjacent stacks. These hydrogen bonds are almost linear, with respective C7—H7···C7ⁱⁱ and C7—H7···C6ⁱⁱ bond angles of 170.2 and 161.2°. This results in a zigzag network of hydrogen bonds in the crystallographic b-axis direction. The hydrogen-bond network and the N···I bond network are quite isolated from each other and generate independent packing motifs.

S2. Experimental

4-Iodoquinoline was prepared from 4-chloroquinolinehydrochloride by treatment with sodium iodide (Wolf et al., 2003). Suitable X-ray quality rectangular crystals of (I) were grown by crystallization from an ethyl acetatate–hexane solvent system [Solvent ratio?] (m.p. 362- 363 K). X-ray crystallographic data were collected from a single-crystal sample with dimensions 0.35 × 0.30 × 0.30 mm.

S3. Refinement

All H atoms were positioned geometrically and treated using a riding model, with C—H = 0.93 Å and with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: ARGUS (Enraf–Nonius, 1977); cell refinement: ARGUS (Enraf–Nonius, 1977); data reduction: maXus (Enraf–Nonius, 1977); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLUTO (Motherwell & Clegg, 1978) and ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. A drawing of (I), with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The unit-cell contents of (I), viewed approximately along the c axis. Dashed lines show intermolecular N···I contacts [3.131 (3) Å for N1···I1^i; symmetry code: (i) 1/2 + x, 1/2 - y, 1/2 + z.]
	Fig. 3. A space-filling representation of the herring-bone packing of (I).
	Fig. 4. A packing diagram, viewed along the c axis. Dotted lines show the C—H···π short contacts for C7—H7···C7^ii [2.821 (5) Å] and C7—H7···C6^ii [3.083 (3) Å]. [Symmetry code: (ii) 3/2 - x, -1/2 + y, 1/2 - z.]

4-Iodoquinoline

Crystal data

C9H6IN	F(000) = 480
Mr = 255.05	Dx = 2.036 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 14.1973 (17) Å	Cell parameters from 25 reflections
b = 4.3526 (4) Å	θ = 9.9–14.2°
c = 14.9151 (14) Å	µ = 3.78 mm^−1
β = 115.484 (8)°	T = 293 K
V = 832.01 (15) Å^3	Block, colourless
Z = 4	0.35 × 0.30 × 0.30 mm

Data collection

Enraf–Nonius MACH3 diffractometer	1267 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.025
Graphite monochromator	θmax = 25.0°, θmin = 1.7°
ω/q scans	h = 0→16
Absorption correction: ψ scan (North et al., 1968)	k = 0→5
Tmin = 0.352, Tmax = 0.397	l = −17→15
1528 measured reflections	3 standard reflections every 3600 min
1465 independent reflections	intensity decay: <3

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)] = 0.031	H-atom parameters constrained
wR(F^2) = 0.075	w = 1/[σ^2(Fo^2) + (0.0507P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.11	(Δ/σ)max < 0.001
1465 reflections	Δρmax = 1.06 e Å^−3
101 parameters	Δρmin = −1.08 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0159 (11)

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 > 2Σ(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
I1	0.252868 (18)	0.19189 (7)	0.065384 (18)	0.04610 (17)
N1	0.5425 (2)	0.4702 (10)	0.3835 (2)	0.0498 (9)
C1	0.4633 (4)	0.3018 (12)	0.3761 (3)	0.0532 (12)
H1	0.4617	0.2334	0.4346	0.064*
C2	0.3803 (3)	0.2174 (11)	0.2858 (3)	0.0479 (10)
H2	0.3261	0.0956	0.2851	0.057*
C3	0.3803 (3)	0.3162 (9)	0.1994 (3)	0.0384 (9)
C4	0.4640 (3)	0.4969 (9)	0.2017 (3)	0.0355 (9)
C5	0.5433 (3)	0.5719 (10)	0.2968 (3)	0.0404 (9)
C6	0.6272 (4)	0.7592 (11)	0.3043 (4)	0.0548 (12)
H6	0.6787	0.8117	0.3666	0.066*
C7	0.6334 (4)	0.8636 (12)	0.2214 (4)	0.0606 (13)
H7	0.6887	0.9895	0.2274	0.073*
C8	0.5573 (4)	0.7842 (12)	0.1267 (4)	0.0583 (13)
H8	0.5637	0.8518	0.0704	0.070*
C9	0.4741 (3)	0.6084 (11)	0.1169 (3)	0.0464 (10)
H9	0.4233	0.5609	0.0538	0.056*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.0401 (2)	0.0452 (2)	0.0379 (2)	−0.00058 (11)	0.00236 (14)	−0.00469 (11)
N1	0.0418 (18)	0.060 (3)	0.0351 (18)	0.0060 (18)	0.0049 (14)	−0.0024 (17)
C1	0.053 (3)	0.064 (3)	0.035 (2)	0.006 (2)	0.012 (2)	0.003 (2)
C2	0.044 (2)	0.053 (3)	0.040 (2)	0.0004 (19)	0.0127 (19)	0.0008 (19)
C3	0.0317 (19)	0.039 (2)	0.035 (2)	0.0052 (16)	0.0051 (15)	−0.0042 (16)
C4	0.0336 (17)	0.034 (2)	0.0339 (18)	0.0094 (15)	0.0096 (14)	−0.0021 (15)
C5	0.0328 (18)	0.036 (2)	0.041 (2)	0.0068 (18)	0.0056 (15)	−0.0049 (19)
C6	0.038 (2)	0.052 (3)	0.062 (3)	0.0033 (19)	0.010 (2)	−0.009 (2)
C7	0.042 (2)	0.052 (3)	0.085 (4)	−0.001 (2)	0.025 (2)	0.001 (3)
C8	0.060 (3)	0.056 (3)	0.067 (3)	0.010 (2)	0.035 (3)	0.014 (2)
C9	0.045 (2)	0.045 (3)	0.045 (2)	0.005 (2)	0.0152 (18)	0.000 (2)

Geometric parameters (Å, º)

I1—C3	2.110 (4)	C4—C5	1.419 (5)
N1—C1	1.307 (6)	C5—C6	1.407 (6)
N1—C5	1.371 (5)	C6—C7	1.355 (7)
C1—C2	1.405 (7)	C6—H6	0.9300
C1—H1	0.9300	C7—C8	1.404 (8)
C2—C3	1.358 (6)	C7—H7	0.9300
C2—H2	0.9300	C8—C9	1.361 (7)
C3—C4	1.414 (5)	C8—H8	0.9300
C4—C9	1.418 (5)	C9—H9	0.9300
C1—N1—C5	117.3 (3)	N1—C5—C4	122.9 (4)
N1—C1—C2	124.3 (4)	C6—C5—C4	119.5 (4)
N1—C1—H1	117.9	C7—C6—C5	120.4 (4)
C2—C1—H1	117.9	C7—C6—H6	119.8
C3—C2—C1	119.0 (4)	C5—C6—H6	119.8
C3—C2—H2	120.5	C6—C7—C8	120.8 (5)
C1—C2—H2	120.5	C6—C7—H7	119.6
C2—C3—C4	119.8 (4)	C8—C7—H7	119.6
C2—C3—I1	117.9 (3)	C9—C8—C7	120.2 (4)
C4—C3—I1	122.3 (3)	C9—C8—H8	119.9
C3—C4—C9	125.2 (3)	C7—C8—H8	119.9
C3—C4—C5	116.7 (3)	C8—C9—C4	120.9 (4)
C9—C4—C5	118.2 (4)	C8—C9—H9	119.6
N1—C5—C6	117.5 (4)	C4—C9—H9	119.6
C5—N1—C1—C2	0.6 (7)	C9—C4—C5—N1	−178.4 (4)
N1—C1—C2—C3	−0.5 (7)	C3—C4—C5—C6	−178.0 (4)
C1—C2—C3—C4	1.0 (6)	C9—C4—C5—C6	1.7 (6)
C1—C2—C3—I1	−178.8 (3)	N1—C5—C6—C7	179.0 (4)
C2—C3—C4—C9	178.6 (4)	C4—C5—C6—C7	−1.1 (7)
I1—C3—C4—C9	−1.5 (5)	C5—C6—C7—C8	−0.9 (7)
C2—C3—C4—C5	−1.7 (5)	C6—C7—C8—C9	2.2 (7)
I1—C3—C4—C5	178.2 (3)	C7—C8—C9—C4	−1.5 (7)
C1—N1—C5—C6	178.6 (4)	C3—C4—C9—C8	179.3 (4)
C1—N1—C5—C4	−1.3 (6)	C5—C4—C9—C8	−0.4 (6)
C3—C4—C5—N1	1.9 (6)