The effect of Cl...π interactions on the conformations of 4-chloro-5-(2-phenoxyethoxy)phthalonitrile and 4-chloro-5-[2- (pentafluorophenoxy)ethoxy]phthalonitrile

Article abstract of DOI:10.1107/S0108270111008675

4-Chloro-5-(2-phen-oxy-eth-oxy)phthalonitrile, C₁₆H ₁₁ClN₂O₂, (I), and 4-chloro-5-[2-(penta-fluoro- phen-oxy)eth-oxy]phthalo-nitrile, C₁₆H6ClF₅N ₂O₂, (II), show differ

Full text of DOI:10.1107/S0108270111008675

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
which includes noncovalent ꢀ-interactions between lone-pair
electrons of electronegative atoms (F, Cl, Br, O, S and N) and
perfluorobenzene derivatives (Quin˜onero et al., 2002). These
studies of quadrupole moments and electrostatic interactions
prompted us to compare them with the crystal structures of
fluorinated compounds, which also show several unique elec-
trostatic interactions in the crystalline state (Hori et al., 2007;
Hori & Naganuma, 2010), e.g. the arene–perfluoroarene
interaction (Patrick & Prosser, 1960; Williams, 1993) and C—
HÁ Á ÁF interactions (Desiraju, 1996; Thalladi et al., 1998). In
this paper, we discuss the halogen–ꢀ interaction, classified as
an anion–ꢀ interaction, between the pentafluorophenoxy
group and Cl atoms in 4-chloro-5-[2-(pentafluorophenoxy)-
ethoxy]phthalonitrile, (II), in order to understand fluorine-
substitution effects, given that no halogen–ꢀ interactions are
observed in the nonfluorinated compound 4-chloro-5-(2-
phenoxyethoxy)phthalonitrile, (I).
ISSN 0108-2701
The effect of ClÁ Á Áp interactions on
the conformations of 4-chloro-
5-(2-phenoxyethoxy)phthalonitrile
and 4-chloro-5-[2-(pentafluoro-
phenoxy)ethoxy]phthalonitrile
Akiko Hori,a,b* Yuta Inouea and Hidetaka Yugea
aSchool of Science, Kitasato University, Kitasato 1-15-1, Minami-ku, Sagamihara,
Kanagawa 252-0373, Japan, and bPRESTO, JST, Honcho 4-1-8, Kawaguchi, Saitama,
Japan
Correspondence e-mail: hori@kitasato-u.ac.jp
Received 2 February 2011
Accepted 7 March 2011
Online 12 April 2011
4-Chloro-5-(2-phenoxyethoxy)phthalonitrile, C16H11ClN2O2,
(I), and 4-chloro-5-[2-(pentafluorophenoxy)ethoxy]phthalo-
nitrile, C16H6ClF5N2O2, (II), show different types of electro-
static interaction. In (I), the phenoxy and phthalonitrile
(benzene-1,2-dicarbonitrile) moieties are well separated in an
open conformation and intermolecular C—HÁ Á Áꢀ interactions
are observed in the crystal packing. On the other hand, in (II),
the pentafluorophenoxy moiety interacts closely with the Cl
atom to form a folded conformation containing an intra-
molecular halogen–ꢀ interaction.
The molecular conformations of (I) and (II) are different
(Fig. 1), viz. open in (I) and folded in (II), and the folded
structure of (II) shows an apparently attractive interaction
between atom Cl1 and the pentafluorophenoxy moiety (ring
Comment
˚
B). The Cl1Á Á ÁCgB distance in (II) is 3.7253 (12) A, where
The anion–ꢀ interaction has been found and discussed as one
of the most interesting topics regarding electrostatic inter-
actions in the last decade. The provocative title of a paper,
‘Anion–ꢀ interactions: do they exist?’, which was a theoretical
study of the interaction reported by Quin˜onero et al. (2002),
attracted the interest of many chemists (Schottel et al., 2008).
Since ꢀ-conjugated molecules show remarkable electrostatic
interactions because of their quadrupole moments (i.e. nega-
tive charge of the aromatic centre), benzene molecules show
cation–ꢀ, C—HÁ Á Áꢀ and the sliding conformation of ꢀ–ꢀ
interactions (Doerksenm & Thakkar, 1999). On the other
hand, fluorinated compounds such as hexafluorobenzene have
the opposite quadrupole moment (i.e. positive charge of the
aromatic centre induced by the surrounding F atoms) and
show the opposite electrostatic interactions, e.g. anionÁ Á ÁC6F6
(anion–ꢀ), CFÁ Á ÁC6F6 (CF–ꢀ) and the sliding conformation of
C6F6Á Á ÁC6F6 (ꢀ–ꢀ) interactions. Several papers then demon-
strated the existence of anion–ꢀ interactions between anion
sources and aromatic moieties (Demeshko et al., 2004; de
Hoog et al., 2004; Berryman et al., 2006; Dawson et al., 2010),
CgB is the centroid of ring B. The aromatic rings (A and B) in
each compound are linked by the ethane-1,2-diyldioxy group,
and significant conformational differences of trans–gauche–
trans and trans–gauche–gauche conformations are observed in
the C5—O1—C9—C10—O2—C11 groups of (I) and (II),
respectively. The C9—C10—O2—C11 torsion angles in (I) and
(II) are trans [À173.89 (10)ꢀ] and gauche [À77.06 (18)ꢀ],
respectively. The thermodynamically unfavourable gauche–
gauche conformation is realised in (II) because of the intra-
molecular interaction between atom Cl1 and ring B. The O1—
C9—C10—O2 torsion angles have the same gauche config-
uration, viz. 75.96 (13)ꢀ in (I) and 71.99 (17)ꢀ in (II), and the
C5—O1—C9—C10 torsion angles are trans, viz. 171.51 (11)ꢀ
in (I) and À179.93 (13)ꢀ in (II). The dihedral angle between
the aromatic rings (A and B) of (II) is 68.75 (4)ꢀ, which is
smaller than the corresponding angle in (I) [70.89 (5)ꢀ]. The
˚
C4—Cl1 bond distance of 1.7256 (16) A in (II) is slightly
˚
longer than that of 1.7168 (14) A in (I), although the C10—O2
bond in (II) is longer than that in (I) [1.454 (2) versus
˚
1.4309 (16) A]. The C N bond distances in (I) and (II) are
o154 # 2011 International Union of Crystallography
doi:10.1107/S0108270111008675
Acta Cryst. (2011). C67, o154–o156

organic compounds
Figure 2
A centrosymmetric pair of molecules of (I) linked through C—HÁ Á Áꢀ
interactions. The unit-cell outline and H atoms not involved in the motif
shown have been omitted for clarity. [Symmetry code: (i) Àx + 2, Ày + 1,
Àz + 1.]
aligned along the b axis and the F3Á Á ÁF4vi distance is short, at
˚
2.7756 (17) A [symmetry code: (vi) Àx, Ày, Àz + 1]. No ꢀ–ꢀ
stacking is observed in the crystal packing of (II).
In conclusion, the structures of (I) and (II) demonstrate that
ring fluorination is associated with the folded structure of (II)
through the halogen–ꢀ interaction. Since no strong inter-
molecular interactions are observed between the molecules in
either structure, the halogen–ꢀ interaction may be the domi-
nant driving force for the folding in (II).
Figure 1
The molecular structures of (a) (I) and (b) (II), both at 100 K, showing
the atom-labelling schemes. Displacement ellipsoids are drawn at the
50% probability level.
Experimental
˚
almost the same [C7 N1 = 1.1458 (19) A and C8 N2 =
Compounds (I) and (II) were prepared in one step using a general
procedure (Durmus¸ et al., 2009). Typically, K2CO3 (11 g, 81 mmol)
was added in portions over a period of 2 h to a dry dimethyl-
formamide solution (60 ml) of 4,5-dichlorophthalonitrile (4.0 g,
20 mmol) and 2-phenoxyethanol (5.1 ml, 40 mmol) under an N2
atmosphere. The reaction mixture was then stirred at 333 K for 2 d.
The mixture was evaporated to remove the solvent and the residue
was extracted with CHCl3. The product was further purified by
column chromatography (silica gel, CHCl3/MeOH) and recycled gas-
phase chromatography (CHCl3) to give (I) as a white powder.
Compound (II) was obtained from 2-(pentafluorophenoxy)ethanol
using the same procedure as for (I). Both compounds were crystal-
lized from CHCl3 by the vapour diffusion of MeOH to give colourless
crystals. Data for (I): yield 23%, m.p. 397–398 K; 1H NMR (400 MHz,
CDCl3, TMS): ꢁ 7.79 (s, Ar), 7.41 (s, Ar), 7.32 (t, J = 7.8 Hz, Ar), 7.01
(t, J = 7.8 Hz, Ar), 6.93 (d, J = 7.8 Hz, Ar), 4.54–4.51 (m, CH2), 4.44–
4.41 (m, CH2); EI–MS: 298 m/z (M+); elemental analysis calculated
for C16H11ClN2O2: C 64.3, H 3.7, N 9.4%; found: C 64.2, H 3.7, N
9.4%. Data for (II): yield 32%, m.p. 405–407 K; 1H NMR (400 MHz,
CDCl3, TMS): ꢁ 7.80 (s, Ar), 7.31 (s, Ar), 4.62–4.60 (m, CH2), 4.49–
4.47 (m, CH2); EI–MS: 388 m/z (M+); elemental analysis calculated
for C16H6ClF5N2O2: C 49.4, H 1.6, N 7.2%; found: C 49.4, H 1.5, N
7.1%.
˚
˚
1.144 (2) A for (I), and C7 N1 = 1.144 (2) A and C8 N2 =
˚
1.149 (2) A for (II)]. The C5—O1 bond distances are also the
˚
same, i.e. 1.3535 (16) and 1.3524 (18) A for (I) and (II),
respectively.
In the crystal structure of (I), no ꢀ–ꢀ stacking is observed,
but inversion-related pairs of molecules are linked by a C—
HÁ Á Áꢀ interaction (Fig. 2); atom H3 of ring A at (x, y, z)
interacts closely with a phenoxy group at (Àx + 2, Ày + 1,
Àz + 1) [symmetry code (i)]. The intermolecular Cl1Á Á ÁCl1i
˚
distance in the pair is short, at 3.274 (1) A. The formation of
the pair allows stabilization of the gauche configuration of
O1—C9—C10—O2 to give a trans–gauche–trans conforma-
tion in (I). Further, the H atoms in C10—H10A and C10—
H10B interact with rings Bii [symmetry code: (ii) Àx + 1, Ày,
Àz + 1] and Aiii [symmetry code: (iii) x, y À 1, z], respectively,
through C—HÁ Á Áꢀ interactions; H10AÁ Á ÁCgBii = 2.59 A
˚
iii
[C10Á Á ÁCgBii = 3.477 (2) A] and H10BÁ Á ÁCgA = 2.71 A
˚
˚
[C10Á Á ÁCgAiii = 3.492 (2) A]. Accordingly, the molecules are
˚
in a head-to-tail arrangement along the a axis and, further,
they form zigzag arrangements along the c axis.
In (II), the molecules are aligned parallel to the a axis. In
this direction, atom F5 in the pentafluorophenoxy group
interacts with ethoxy atom H9B of a neighbouring molecule
through a weak C—HÁ Á ÁF contact (Howard et al., 1996), with
Compound (I)
Crystal data
F5Á Á ÁH9Biv = 2.51 A [symmetry code: (iv) x À 1, y, z]. The
˚
3
˚
C16H11ClN2O2
Mr = 298.72
V = 1413.2 (10) A
Z = 4
F5Á Á ÁC5iv distance is also short, at 2.950 (2) A. Because the
˚
Monoclinic, P21=c
Mo Kꢃ radiation
ꢄ = 0.28 mmÀ1
T = 100 K
pentafluorophenoxy groups are aligned in the same direction,
the F substituents are located close to one another, with
˚
a = 9.808 (4) A
˚
b = 6.555 (3) A
v
F1Á Á ÁF5v = 2.8625 (15) A and F2Á Á ÁF4 = 2.8914 (17) A
˚
˚
˚
c = 22.018 (9) A
0.20 Â 0.10 Â 0.10 mm
ꢂ = 93.259 (4)ꢀ
[symmetry code: (v) x + 1, y, z]. Similarly, the molecules are
ꢁ
Acta Cryst. (2011). C67, o154–o156
Hori et al.
C16H11ClN2O2 and C16H6ClF5N2O2 o155

organic compounds
For both compounds, data collection: APEX2 (Bruker, 2006); cell
refinement: SAINT (Bruker, 2006); data reduction: SAINT;
program(s) used to solve structure: SHELXS97 (Sheldrick, 2008);
program(s) used to refine structure: SHELXL97 (Sheldrick, 2008);
molecular graphics: SHELXTL (Sheldrick, 2008); software used to
prepare material for publication: SHELXTL.
Data collection
Bruker APEXII CCD
diffractometer
Absorption correction: empirical
(using intensity measurements)
(SADABS; Sheldrick, 1996)
Tmin = 0.947, Tmax = 0.973
15329 measured reflections
3228 independent reflections
2744 reflections with I > 2ꢅ(I)
Rint = 0.029
This work was supported in part by a Kitasato University
Research Grant for Young Researchers.
Refinement
R[F2 > 2ꢅ(F2)] = 0.035
wR(F2) = 0.087
S = 1.04
190 parameters
H-atom parameteÀrs3 constrained
˚
Áꢆmax = 0.46 e A
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GD3379). Services for accessing these data are
described at the back of the journal.
À3
˚
3228 reflections
Áꢆmin = À0.56 e A
Compound (II)
References
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˚
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˚
a = 5.8272 (13) A
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˚
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˚
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ꢁ
o156 Hori et al. C16H11ClN2O2 and C16H6ClF5N2O2
Acta Cryst. (2011). C67, o154–o156