4'-Iodo-2,2':6',2''-terpyridine

In the nearly planar title compound, C₁₅H₁₀IN₃, the three pyridine rings exhibit transoid conformations about the inter­annular C-C bonds. Very weak C-H...N and C-H...I inter­actions link the mol­ecules into ribbons. Significant [pi]-[pi] stacking between mol­ecules from different ribbons completes a three-dimensional framework of inter­molecular inter­actions. Four different packing motifs are observed among the known structures of simple 4'-substituted ter­pyridines.

S1. Comment

Much effort has been devoted in recent years to the design and synthesis of terpyridines and their metal complexes, which display binding properties conducive to supramolecular chemistry (Hoogenboom & Schubert, 2006). Such materials also have applications in the conversion of solar energy in dye-sensitized solar cells (Kalyanasundaram, 2006). Derivatives of 2,2':6',2''-terpyridines (tpy) can be linked together by spacers. Metal-coordinated tpy ligands with spacers at the 4'-position provide a means of influencing directionality and linear communication, meaning that electronic communication can occur along the coordination axis. The functionalization of tpy at this position is thus of particular importance. For that purpose, the title 4'-iodo derivative of tpy, (I), may play a crucial role since it can be used as a precursor for the preparation of stannyl or boronic acid compounds, which are used in Stille or Suzuki cross-coupling reactions, respectively. This paper describes the crystal structure of (I) and compares it with the structures of related 4'-substituted tpy derivatives.

In terpyridine derivatives, the three pyridine rings are usually close to being coplanar. For example, the interplanar angles between the terminal rings and the central ring in 4'-ethoxy-5,5''-dimethyl-2,2':6',2''-terpyridine are 4.32 (13) and 11.38 (11)° (Fallahpour et al., 1999a). In 4'-amino-2,2':6',2''-terpyridine, however, the interplanar angles between the two terminal rings and the central ring are 11.24 (15) and 20.71 (11)°, as a result of hydrogen-bond formation (Fallahpour et al., 1999b). In contrast, in 2,2':6',2''-terpyridine 1,1'-dioxide, the two pyridine N-oxide ring planes are almost perpendicular to one another, with an interplanar angle of 87.68 (10)°, while the angle between the plane of the central pyridine N-oxide ring and that of the terminal pyridine ring is 38.46 (10)°. The interplanar angle between the terminal pyridine N-oxide ring and the terminal pyridine ring is 70.98 (11)° (Fallahpour & Neuburger, 2001).

The molecule of (I) (Fig. 1), with unremarkable bond lengths and angles, has the expected nearly planar transoid conformation of the three pyridine rings and pseudo-C_s symmetry, with an r.m.s. fit of the atoms of the two halves of the molecule of 0.16 Å. The angles between the planes of the terminal pyridine rings containing atoms N8 and N14 and the plane of the central ring are 15.1 (2) and 9.4 (2)°, respectively. The angle between the planes of the terminal rings is 12.8 (2)°.

The mean plane of the molecule is nearly parallel to the (100) plane and, in the crystal packing, the molecules are distributed in slightly corrugated layers, which lie parallel to the same plane. There are only two intermolecular distances that are shorter than the sum of the van der Waals radii of any atom pair, although these are only marginally shorter than this limit (<0.06 Å). A very weak intermolecular C—H···N interaction (Table 1) links molecules related by a translation of one unit cell into extended chains, which run parallel to the [001] direction and which can be described by a graph-set motif of C(9) (Bernstein et al., 1995). Within the (100) plane, pairs of parallel chains are crosslinked by weak C—H···I interactions to give a ladder-like arrangement, where the C—H···I interactions are the rungs of the ladder and the C—H···N interactions form the ladder uprights (Fig. 2). Within each segment of the ladder structure, an asymmetric ring motif can be discerned, made up of one C—H···N and two C—H···I interactions. This ring motif can be described by a binary graph set of R³₃(19). Essentially, one terminal pyridine ring acts as a single acceptor, the other terminal ring acts as a donor for both types of interaction, and the central ring is involved in one acceptor interaction via the I atom. There are no significant intermolecular interactions between adjacent ladders in the same plane.

The molecules are stacked perpendicular to the (100) plane such that the planes of overlapping rings are almost parallel, but adjacent molecules in the stack appear as if they are rotated alternately about an axis almost perpendicular to the plane of the central pyridine ring by approximately 120° with respect to one another [Fig. 3; in reality this is a glide operation, which yields a reflection in a plane parallel to (010)]. This means that the central pyridine rings stack with potential π–π interactions, the centroid–centroid distance being 3.813 (3) Å, while one of the terminal pyridine rings in each molecule also partakes in weak π–π stacking, with a centroid–centroid distance of 3.972 (3) Å, although adjacent ring planes are inclined at an angle of about 21°. In contrast, the other terminal pyridine ring stacks in an alternating fashion with the I atom of the molecule below it, to give centroid···I distances of 3.738 (2) and 3.754 (2) Å. The combination of the ladder-generating C—H···X (X = N or I) interactions with the π–π and I···π interactions generates a three-dimensional framework; adjacent ladders in the π–π stacks are offset from one another, thereby creating a brickwork stacking pattern of ladders.

The crystal structures of the 4'-bromo and 4'-chloro analogues of (I) are known (Clegg & Scott, 2005; Beves et al., 2006). The molecules are slightly flatter than that of (I), the angles between the terminal pyridine ring planes and that of the central pyridine ring being 8.0 (1) and 5.4 (1)° for the chloro derivative and 5.1 (1) and 5.6 (1)° for the bromo derivative. These two structures are isomorphous, but although the structure of (I) has the same space group, the unit-cell dimensions differ markedly. Thus, (I) is not isomorphous with the chloro and bromo analogues, which is manifested in the quite different packing arrangements of the molecules. Unlike in (I), the molecules of the chloro and bromo analogues stack exactly on top of one another without a 120° rotation, as they are related by one unit-cell translation along the short b axis. According to Beves et al. (2006), the molecules are π-stacked, although the planes of the molecules are tilted somewhat with respect to the stacking axis direction. In addition, these two analogues do not exhibit any C—H···X (X = N or halogen) or halogen–π interactions, so the intermolecular interactions only form one-dimensional motifs. The lack of isomorphism between the structure of (I) and those of the other 4'-halo–tpy derivatives must be related to the influence of the bulkier I atom on the packing efficiency of the molecules.

The stacking motifs of adjacent molecules in (I) and related derivatives show four main patterns. Infinite stacks with alternating 120° rotation of adjacent molecules within the stack are formed in (I) and 4'-azido-2,2':6',2''-terpyridine (Fallahpour et al., 1999c). Infinite stacks with exact superposition of the molecules are present in the 4'-bromo and 4'-chloro analogues of (I), as described above, as well as in the orthorhombic polymorph of unsubstituted 2,2':6',2''-terpyridine itself (Bessel et al., 1992). The third motif involves just pairs of molecules, perfectly superimposed but not propagating beyond the pair. This motif is seen in the monoclinic polymorph of unsubstituted 2,2':6',2''-terpyridine (Boves et al., 2005). The fourth motif also involves just pairs of molecules, but this time they are related by a centre of inversion, so that all pyridine rings are sufficiently offset so as to preclude any possibility of π–π interactions. This is much like superimposing a `Y' on an upside-down `Y'. This motif is displayed by 4'-amino-2,2':6',2''-terpyridine (Fallahpour et al., 1999b) and 4'-dimethylamino-2,2':6',2''-terpyridine (Constable et al., 1992).

Related literature

For related literature, see: Bernstein et al. (1995); Bessel et al. (1992); Beves et al. (2006); Boves et al. (2005); Clegg & Scott (2005); Constable et al. (1992); Coudret (1996); Fallahpour & Neuburger (2001); Fallahpour et al. (1999a, 1999b, 1999c); Hoogenboom & Schubert (2006); Kalyanasundaram (2006); Sauer et al. (1999).

S2. Experimental

The title compound was prepared from 4'-amino-2,2':6',2''-terpyridine (Fallahpour et al., 1999b) according to the standard procedure of Coudret (1996) (yield 70%, m.p. 399–400 K). The spectroscopic data have been reported by Sauer et al. (1999). Crystals of (I) were grown by slow evaporation of a warm dichloromethane solution of the compound.

S3. Refinement

H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms [C—H = 0.95 Å and U_iso(H) = 1.2U_eq(C)].

Computing details

Data collection: COLLECT (Nonius, 2000); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2003).

Figures

	Fig. 1. A view of the molecule of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented by circles of arbitrary size.
	Fig. 2. A plane of molecules of (I), viewed down the a axis, showing the ladder-like structure formed by the shortest intermolecular C—H···N and C—H···I distances (dashed lines). [Symmetry codes: (i) -x + 1, -y + 1, z + 1/2; (ii) x, y, z + 1; (iii) -x + 1, -y + 1, z - 1/2; (iv) x, y, z - 1.]
	Fig. 3. The stacking of molecules of (I) along the a direction, showing the alternating positions of atom I1 and the consequent stacking of the phenyl rings.

4'-iodo-2,2':6',2''-terpyridine

Crystal data

C15H10IN3	F(000) = 696
Mr = 359.17	Dx = 1.844 Mg m^−3
Orthorhombic, Pna21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2n	Cell parameters from 15271 reflections
a = 7.4518 (2) Å	θ = 2.0–30.0°
b = 17.2432 (3) Å	µ = 2.46 mm^−1
c = 10.0691 (2) Å	T = 160 K
V = 1293.81 (5) Å^3	Prism, colourless
Z = 4	0.30 × 0.28 × 0.25 mm

Data collection

Nonius KappaCCD area-detector diffractometer	3713 independent reflections
Radiation source: Nonius FR590 sealed tube generator	3524 reflections with I > 2σ(I)
Horizontally mounted graphite crystal monochromator	Rint = 0.055
Detector resolution: 9 pixels mm^-1	θmax = 30.0°, θmin = 2.3°
ω scans with κ offsets	h = −10→10
Absorption correction: multi-scan (Blessing, 1995)	k = −24→24
Tmin = 0.448, Tmax = 0.544	l = −14→14
19500 measured reflections

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)] = 0.040	H-atom parameters constrained
wR(F^2) = 0.096	w = 1/[σ^2(Fo^2) + (0.0449P)^2 + 5.4428P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max = 0.001
3712 reflections	Δρmax = 0.79 e Å^−3
172 parameters	Δρmin = −1.87 e Å^−3
1 restraint	Absolute structure: Flack & Bernardinelli (1999, 2000), 1738 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.03 (3)

Special details

Experimental. Solvent used: dichloromethane Cooling Device: Oxford Cryosystems Cryostream 700 Crystal mount: glued on a glass fibre Mosaicity (°.): 0.547 (1) Frames collected: 260 Seconds exposure per frame: 13 Degrees rotation per frame: 1.9 Crystal-Detector distance (mm): 33.8

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.

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

	x	y	z	Uiso*/Ueq
I1	0.34425 (3)	0.559690 (13)	0.39444 (6)	0.01972 (9)
N1	0.4181 (5)	0.7922 (2)	0.6643 (4)	0.0135 (6)
N8	0.3567 (6)	0.8850 (3)	0.3472 (5)	0.0174 (10)
N14	0.5254 (5)	0.6454 (2)	0.9086 (5)	0.0198 (8)
C2	0.3750 (6)	0.7977 (3)	0.5350 (4)	0.0142 (8)
C3	0.3506 (6)	0.7337 (3)	0.4524 (5)	0.0171 (8)
H3	0.3195	0.7396	0.3615	0.021*
C4	0.3740 (6)	0.6607 (2)	0.5088 (4)	0.0135 (7)
C5	0.4212 (6)	0.6536 (2)	0.6412 (4)	0.0156 (8)
H5	0.4404	0.6041	0.6801	0.019*
C6	0.4397 (6)	0.7210 (2)	0.7153 (4)	0.0140 (7)
C7	0.3595 (7)	0.8778 (4)	0.4813 (5)	0.0170 (11)
C9	0.3459 (6)	0.9560 (3)	0.2967 (6)	0.0208 (10)
H9	0.3452	0.9612	0.2028	0.025*
C10	0.3356 (6)	1.0230 (3)	0.3725 (5)	0.0197 (12)
H10	0.3314	1.0726	0.3315	0.024*
C11	0.3315 (7)	1.0156 (3)	0.5119 (5)	0.0213 (9)
H11	0.3213	1.0600	0.5674	0.026*
C12	0.3426 (7)	0.9417 (3)	0.5658 (6)	0.0217 (10)
H12	0.3389	0.9346	0.6593	0.026*
C13	0.4838 (6)	0.7162 (2)	0.8607 (4)	0.0142 (8)
C15	0.5594 (7)	0.6399 (3)	1.0357 (5)	0.0231 (10)
H15	0.5885	0.5902	1.0702	0.028*
C16	0.5559 (7)	0.7025 (3)	1.1246 (4)	0.0206 (9)
H16	0.5833	0.6954	1.2159	0.025*
C17	0.5116 (7)	0.7748 (3)	1.0754 (5)	0.0211 (9)
H17	0.5068	0.8187	1.1324	0.025*
C18	0.4738 (6)	0.7819 (3)	0.9398 (5)	0.0188 (8)
H18	0.4421	0.8307	0.9027	0.023*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
I1	0.02336 (13)	0.01637 (12)	0.01942 (13)	−0.00224 (8)	−0.0028 (2)	−0.00483 (16)
N1	0.0160 (16)	0.0137 (16)	0.0108 (15)	−0.0010 (13)	0.0029 (13)	0.0015 (12)
N8	0.020 (2)	0.0143 (19)	0.018 (2)	−0.0098 (15)	−0.0003 (15)	−0.0005 (17)
N14	0.0304 (17)	0.0203 (14)	0.009 (2)	−0.0005 (13)	−0.0020 (17)	−0.0015 (17)
C2	0.0095 (16)	0.0147 (18)	0.018 (2)	−0.0005 (14)	0.0018 (14)	0.0019 (15)
C3	0.023 (2)	0.0137 (19)	0.0144 (19)	0.0030 (16)	−0.0002 (16)	0.0015 (15)
C4	0.0120 (17)	0.0113 (17)	0.0171 (19)	−0.0011 (14)	0.0001 (15)	−0.0007 (15)
C5	0.0162 (19)	0.0131 (17)	0.0175 (19)	−0.0009 (15)	−0.0007 (15)	0.0026 (15)
C6	0.0138 (18)	0.0144 (18)	0.0138 (18)	−0.0023 (15)	−0.0033 (15)	0.0001 (14)
C7	0.014 (2)	0.021 (2)	0.015 (2)	0.0002 (17)	0.0020 (17)	0.0086 (19)
C9	0.019 (2)	0.028 (3)	0.016 (2)	0.0014 (18)	−0.0114 (17)	0.007 (2)
C10	0.0216 (19)	0.0189 (18)	0.018 (3)	−0.0003 (14)	−0.0044 (16)	0.0039 (17)
C11	0.026 (2)	0.015 (2)	0.023 (2)	0.0004 (17)	−0.0033 (18)	−0.0019 (17)
C12	0.026 (3)	0.020 (2)	0.019 (3)	−0.0005 (17)	−0.0072 (18)	−0.0004 (18)
C13	0.0117 (16)	0.0185 (18)	0.012 (2)	0.0022 (14)	−0.0020 (12)	0.0013 (13)
C15	0.025 (2)	0.020 (2)	0.023 (2)	0.0012 (18)	−0.0082 (19)	−0.0008 (18)
C16	0.027 (2)	0.024 (2)	0.0113 (17)	−0.0015 (18)	−0.0006 (16)	−0.0001 (16)
C17	0.030 (3)	0.022 (2)	0.0115 (18)	0.001 (2)	0.0003 (18)	−0.0018 (16)
C18	0.021 (2)	0.0202 (19)	0.0151 (17)	0.0057 (17)	0.0000 (16)	0.0021 (15)

Geometric parameters (Å, º)

I1—C4	2.100 (4)	C9—C10	1.386 (8)
N1—C6	1.340 (5)	C9—H9	0.9500
N1—C2	1.344 (6)	C10—C11	1.410 (7)
N8—C9	1.328 (7)	C10—H10	0.9500
N8—C7	1.356 (7)	C11—C12	1.388 (7)
N14—C15	1.308 (7)	C11—H11	0.9500
N14—C13	1.349 (5)	C12—H12	0.9500
C2—C3	1.393 (6)	C13—C18	1.387 (6)
C2—C7	1.487 (7)	C15—C16	1.402 (7)
C3—C4	1.391 (6)	C15—H15	0.9500
C3—H3	0.9500	C16—C17	1.382 (7)
C4—C5	1.384 (6)	C16—H16	0.9500
C5—C6	1.388 (6)	C17—C18	1.400 (6)
C5—H5	0.9500	C17—H17	0.9500
C6—C13	1.503 (5)	C18—H18	0.9500
C7—C12	1.398 (8)
C6—N1—C2	117.7 (4)	C9—C10—C11	118.3 (4)
C9—N8—C7	117.8 (6)	C9—C10—H10	120.9
C15—N14—C13	117.3 (4)	C11—C10—H10	120.9
N1—C2—C3	123.6 (4)	C12—C11—C10	118.1 (5)
N1—C2—C7	115.8 (4)	C12—C11—H11	121.0
C3—C2—C7	120.5 (4)	C10—C11—H11	121.0
C4—C3—C2	117.1 (4)	C11—C12—C7	119.4 (5)
C4—C3—H3	121.4	C11—C12—H12	120.3
C2—C3—H3	121.4	C7—C12—H12	120.3
C5—C4—C3	120.3 (4)	N14—C13—C18	123.2 (4)
C5—C4—I1	118.8 (3)	N14—C13—C6	116.7 (4)
C3—C4—I1	120.9 (3)	C18—C13—C6	120.1 (4)
C4—C5—C6	117.9 (4)	N14—C15—C16	124.5 (5)
C4—C5—H5	121.0	N14—C15—H15	117.8
C6—C5—H5	121.0	C16—C15—H15	117.8
N1—C6—C5	123.3 (4)	C17—C16—C15	118.0 (4)
N1—C6—C13	116.8 (4)	C17—C16—H16	121.0
C5—C6—C13	119.9 (4)	C15—C16—H16	121.0
N8—C7—C12	122.2 (6)	C16—C17—C18	118.5 (4)
N8—C7—C2	116.6 (6)	C16—C17—H17	120.8
C12—C7—C2	121.2 (5)	C18—C17—H17	120.8
N8—C9—C10	124.1 (5)	C13—C18—C17	118.5 (4)
N8—C9—H9	117.9	C13—C18—H18	120.8
C10—C9—H9	117.9	C17—C18—H18	120.8
C6—N1—C2—C3	0.5 (6)	C7—N8—C9—C10	−0.7 (8)
C6—N1—C2—C7	−177.6 (4)	N8—C9—C10—C11	−1.8 (7)
N1—C2—C3—C4	−0.4 (7)	C9—C10—C11—C12	1.6 (7)
C7—C2—C3—C4	177.6 (4)	C10—C11—C12—C7	0.7 (7)
C2—C3—C4—C5	−0.7 (6)	N8—C7—C12—C11	−3.3 (8)
C2—C3—C4—I1	−179.3 (3)	C2—C7—C12—C11	179.0 (5)
C3—C4—C5—C6	1.6 (6)	C15—N14—C13—C18	−0.7 (7)
I1—C4—C5—C6	−179.8 (3)	C15—N14—C13—C6	−178.2 (4)
C2—N1—C6—C5	0.5 (6)	N1—C6—C13—N14	−172.7 (4)
C2—N1—C6—C13	−178.7 (4)	C5—C6—C13—N14	8.1 (6)
C4—C5—C6—N1	−1.5 (7)	N1—C6—C13—C18	9.7 (6)
C4—C5—C6—C13	177.6 (4)	C5—C6—C13—C18	−169.5 (4)
C9—N8—C7—C12	3.2 (9)	C13—N14—C15—C16	−0.2 (8)
C9—N8—C7—C2	−178.9 (4)	N14—C15—C16—C17	0.8 (8)
N1—C2—C7—N8	165.6 (5)	C15—C16—C17—C18	−0.5 (8)
C3—C2—C7—N8	−12.6 (7)	N14—C13—C18—C17	1.0 (7)
N1—C2—C7—C12	−16.6 (7)	C6—C13—C18—C17	178.5 (4)
C3—C2—C7—C12	165.3 (5)	C16—C17—C18—C13	−0.4 (7)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C15—H15···I1^i	0.95	3.17	3.793 (5)	125
C17—H17···N8^ii	0.95	2.69	3.526 (6)	147

Symmetry codes: (i) −x+1, −y+1, z+1/2; (ii) x, y, z+1.