Structural comparisons between methyl-ated and unmethyl-ated nitro-phenyl lophines

Article abstract of DOI:10.1107/S0108270109022203

The lophine derivative 2-(2-nitro-phen-yl)-4,5-diphenyl-1H-imidazole, C₂₁H₁₅N₃O₂, (I), crystallized from ethanol as a sol-vent-free crystal and from acetonitrile as the monosolvate, C₂₁H₁₅N

Full text of DOI:10.1107/S0108270109022203

organic compounds
˚
Acta Crystallographica Section C
Crystal Structure
hydrogen bonded to imidazole [OÁ Á ÁN = 2.823 (4) A] but
has no effect on the packing of molecules in the unit cell.
Communications
ISSN 0108-2701
Comment
Recently, heterocyclic imidazole derivatives have attracted
considerable attention because of their unique linear and
nonlinear optical properties (Santos et al., 2001). Lophine
(2,4,5-triphenyl-1H-imidazole) is an attractive fluorescence
and chemiluminescence compound. The chemiluminescence
properties of lophine were reported for the first time by
Radziszewski (1877), who showed that it emits yellow light
when it reacts with oxygen in the presence of a strong base.
The chemistry of lophine derivatives has a long history in
relation to important physicochemical phenomena such as
chemiluminescence through its oxidation and photo-, piezo-
and thermochromic properties (Zimmerman et al., 1961;
Maeda & Hayashi, 1969, 1970). Only a few imidazole ana-
logues or nitro derivatives of lophine are known (Inouye &
Sakaino, 1985, 1986, 2000; Sakaino, Fujii et al., 1990; Sakaino,
Shimizu et al., 1990; Kaftory et al., 1998; Bu et al., 2003). The
spectral properties of lophine derivatives are of interest: the
colour change is dependent on the solvation in the crystal and
in different derivatives. We have recently synthesized various
Structural comparisons between
methylated and unmethylated nitro-
phenyl lophines
Diana Yanover and Menahem Kaftory*
Schulich Faculty of Chemistry, Technion – Israel Institute of Technology, Haifa
32000, Israel
Correspondence e-mail: kaftory@tx.technion.ac.il
Received 2 March 2009
Accepted 10 June 2009
Online 7 July 2009
The lophine derivative 2-(2-nitrophenyl)-4,5-diphenyl-1H-
imidazole, C21H15N3O2, (I), crystallized from ethanol as a
solvent-free crystal and from acetonitrile as the monosolvate,
C21H15N3O2ÁC2H3N, (II). Crystallization of 2-(4-nitrophenyl)-
4,5-diphenyl-1H-imidazole from methanol yielded the me-
thanol monosolvate, C21H15N3O2ÁCH4O, (III). Three lophine
derivatives of methylated imidazole, namely, 1-methyl-2-(2-
nitrophenyl)-4,5-diphenyl-1H-imidazole methanol solvate,
C22H17N3O2ÁCH4O, (IV), 1-methyl-2-(3-nitrophenyl)-4,5-
diphenyl-1H-imidazole, C22H17N3O2, (V), and 1-methyl-2-(4-
nitrophenyl)-4,5-diphenyl-1H-imidazole, C22H17N3O2, (VI),
were recrystallized from methanol, acetonitrile and ethanol,
respectively, but only (IV) produced a solvate. Compounds
(III) and (IV) each crystallize with two independent molecules
in the asymmetric unit. Five imidazole molecules in the six
crystals differ in their molecular conformations by rotation of
the aromatic rings with respect to the central imidazole ring.
In the absence of a methyl group on the imidazole [com-
pounds (I)–(III)], the rotation angles are not strongly affected
by the position of the nitro group [44.8 (2) and 45.5 (1)ꢀ in (I)
and (II), respectively, and 15.7 (2) and 31.5 (1)ꢀ in the two
molecules of (III)]. However, the rotation angle is strongly
affected by the presence of a methyl group on the imidazole
[compounds (IV)–(VI)], and the position of the nitro group
(ortho, meta or para) on a neighbouring benzene ring; values
of the rotation angle range from 26.0 (1) [in (VI)] to 85.2 (1)ꢀ
[in (IV)]. This group repulsion also affects the outer N—C—N
bond angle. The packing of the molecules in (I), (II) and (III)
is determined by hydrogen bonding. In (I) and (II), molecules
form extended chains through N—HÁ Á ÁN hydrogen bonds
lophine derivatives to study their spectral properties with the
aim of understanding the relationship between molecular and
crystal structures and colour change (Fridman, Kaftory,
Eichen et al., 2007; Fridman, Kaftory & Speiser, 2007; Fridman
et al., 2008). In order to examine the effect of the ability of the
imidazole ring to form hydrogen bonds on the crystal colour,
we have prepared lophine derivatives with nitrophenyl at
position 7 of the imidazole (for notation see scheme), as well
as compounds where the N—H hydrogen-donor ability in
imidazole is blocked by replacing the H atom with a methyl
group. We present here a comparison between the molecular
and crystal structures of six lophine o-, m- and p-nitrophenyl
derivatives (Figs. 1–6).
˚
˚
[with an NÁ Á ÁN distance of 2.944 (5) A in (I) and 2.920 (3) A
in (II)], while in (III) the chain is formed with a methanol
solvent molecule as the mediator between two imidazole rings,
˚
with OÁ Á ÁN distances of 2.788 (4)–2.819 (4) A. In the absence
of the imidazole N—H H-atom donor, the packing of
molecules (IV)–(VI) is determined by weaker intermolecular
interactions. The methanol solvent molecule in (IV) is
Acta Cryst. (2009). C65, o365–o370
doi:10.1107/S0108270109022203
# 2009 International Union of Crystallography o365

organic compounds
Figure 1
The molecular structure of (I), showing displacement ellipsoids at the
50% probability level and H atoms as small spheres of arbitrary radii
(Farrugia, 1999).
Figure 3
The molecular structures of molecules (IIIa) and (IIIb), showing
displacement ellipsoids at the 50% probability level and H atoms as
small spheres of arbitrary radii (Farrugia, 1999). The methanol solvent
molecule is not shown.
Figure 2
The molecular structure of (II), showing displacement ellipsoids at the
50% probability level and H atoms as small spheres of arbitrary radii
(Farrugia, 1999). The acetonitrile solvent molecule is not shown.
Comparison of the bond lengths in the imidazole rings of (I)
˚
to (IV) reveals the following ranges: N1—C7 1.350–1.375 A,
˚
N2—C7 1.317–1.333 A, N1—C8 1.377–1.395 A, N2—C9
˚
˚
˚
1.369–1.383 A and C8—C9 1.374–1.377 A. Statistical calcula-
tion of the related bond lengths in the imidazole rings in 56
lophine derivatives taken from the Cambridge Structural
Database (CSD, Version 1.11 of 2009; Allen, 2002) provided
corresponding average values of 1.353 (8), 1.333 (7),
˚
1.370 (16), 1.386 (7) and 1.375 (8) A, respectively.
The conformation of the molecules differs by rotation of the
phenyl rings with respect to the central imidazole. The
conformation is affected by the presence or absence of a bulky
group [an H atom in (I)–(III) and a methyl group in (IV)–
(VI)], and is also dependent on the position of the nitro group
(ortho, meta or para) on the phenyl ring at position 7 of the
imidazole with respect to the H atom or methyl group. An
overlay of the molecules in the six crystals [only one of the two
Figure 4
The molecular structure of (IV), showing displacement ellipsoids at the
50% probability level and H atoms as small spheres of arbitrary radii
(Farrugia, 1999). The methanol solvent molecule is not shown.
ꢁ
o366 Yanover and Kaftory
Six solvates of C21H15N3O2 and C22H17N3O2
Acta Cryst. (2009). C65, o365–o370

organic compounds
Figure 5
The molecular structure of (V), showing displacement ellipsoids at the
50% probability level and H atoms as small spheres of arbitrary radii
(Farrugia, 1999).
independent molecules of (III) and (VI) is shown] is shown in
Figs. 7(a) and 7(b), and the rotation angles of the phenyl rings
are given in Table 1. The main difference between the
conformations of molecules (I) and (III) is the rotation of the
phenyl ring at position 7. The rotation angles in (I) and (II) are
44.8 (7) and 45.5 (4)ꢀ, respectively, compared with 15.7 (5) and
31.5 (6)ꢀ in molecules (IIIa) and (IIIb), respectively. This
difference can be explained by the larger repulsion of the nitro
group in the ortho position compared with that in the para
position. In the presence of a methyl group, the rotation angle
decreases in the following sequence: o-nitro in (IV) [85.2 (1)ꢀ]
> m-nitro in (V) [36.0 (1)ꢀ] > p-nitro in (VI) [26.0 (1)ꢀ in (VIa)
and 30.8 (1)ꢀ in (VIb)]. It should be noted that the confor-
mations of the two crystallographically independent molecules
in (VI) are different with respect to the rotation of the phenyl
rings in positions 8 and 9 (see notation in the scheme). The
effect of the methyl group is also seen in the angles C1—C7—
N1 and C1—C7—N2, where the angle is larger on the side
with the methyl group: 124.7 (3) and 123.2 (3)ꢀ in (IV),
126.1 (2) and 122.6 (2)ꢀ in (V), 126.9 (2) and 122.2 (2)ꢀ in
(VIa), and 125.8 (2) and 123.2 (2)ꢀ in (VIb), respectively. In
the absence of the methyl group [compounds (I)–(III)] the
opposite relation between values of the equivalent bond
angles is observed: 123.2 (3) and 126.1 (3)ꢀ in (I), 122.9 (2) and
125.2 (2)ꢀ (o-nitro group) in (II), 124.4 (3) and 125.2 (3)ꢀ in
(IIIa), and 124.1 (3) and 125.3 (3)ꢀ (p-nitro group) in (IIIb).
The molecular packing is similar in compounds (I)–(III) as
they all form folded chains comprising molecules bonded to
each other by hydrogen bonds. However, while in the crystals
of (I) and (II) the molecules are connected to each other
through N—HÁ Á ÁN hydrogen bonds (Figs. 8 and 9, respec-
tively), in (III) a mediator molecule, viz. methanol, forms
hydrogen bonds between each pair of molecules of (III). The
geometry of the hydrogen bonds is given in Table 2. A similar
chain formation by hydrogen bonds has been observed in five
other lophine derivatives (Seethalakshmi et al., 2006; Inouye
Figure 6
The molecular structures of molecules (VIa) and (VIb), showing
displacement ellipsoids at the 50% probability level and H atoms as
small spheres of arbitrary radii (Farrugia, 1999).
& Sakaino, 1986; Thuer et al., 2004; Liu et al., 2005; Thiru-
valluvar et al., 2007). While the methanol solvent molecule in
(III) has a specific role in the packing arrangement as
described above, the role of the acetonitrile molecules in
solvate (II) is to occupy lattice voids. In the absence of the
imidazole N—H H-atom donor, the packing of molecules in
(IV)–(VI) is determined by much weaker intermolecular
interactions, such as weak C—HÁ Á ÁO hydrogen bonds
between the O atoms of the nitro group and aromatic H atoms
(Table 2). The methanol solvent molecule in (IV), although
˚
hydrogen bonded to the imidazole [O33Á Á ÁN2 = 2.823 (4) A],
does not play any significant role in the unit-cell packing.
Differential scanning calorimetry (DSC) thermographs (see
Figs. s1 and s2 in the supplementary material) show that the
ꢁ
Acta Cryst. (2009). C65, o365–o370
Yanover and Kaftory
Six solvates of C21H15N3O2 and C22H17N3O2 o367

organic compounds
Figure 7
Overlay of molecules (a) of (I)–(III) (red, green and blue, respectively, in
the electronic version of the paper) and (b) of (IV)–(VI) (red, green and
blue, respectively, in the electronic version of the paper). Only one
molecule [(IIIa) and (VIa)] is shown for compounds (III) and (VI).
Figure 9
1
2
Hydrogen-bonding in (II). [Symmetry code: (ii) À + x, y, 32 À z.]
Figure 8
1
2
Hydrogen-bonding in (I). [Symmetry code: (i) x, Ày, + z.]
solvent molecules are removed at 394 and 377 K for (II) and
(III), respectively. Upon removal of acetonitrile from (II)
there is no change in the crystal colour, whereas removal of
the methanol from (III) changes the crystal colour from light
yellow to red. It is therefore suggested that the change of
colour is a result of the change in the hydrogen bonding. This
assumption needs further investigation.
Experimental
Benzil (1 mmol), the appropriate benzaldehyde (1 mmol) and
ammonium acetate (1.2 g) were dissolved in boiling glacial acetic acid
(16 ml) and refluxed for 5–24 h. On completion of the reaction, the
reaction mixture was poured into ice water, washed with NaHCO3
and then washed several times with ethyl acetate. The combined
extracts were dried over MgSO4. The purification was carried out by
flash column chromatography. Compound (I) crystallized solvent-
free from ethanol and from acetonitrile as monosolvate (II);
Figure 10
Hydrogen-bonding in (III). The bold numbers 1–4 refer to the hydrogen
bonds as they are listed for (III) in Table 2.
compounds (III) and (IV) both crystallized from methanol as
monosolvates; compound (V) crystallized from acetonitrile and
compound (VI) from ethanol.
ꢁ
o368 Yanover and Kaftory
Six solvates of C21H15N3O2 and C22H17N3O2
Acta Cryst. (2009). C65, o365–o370

organic compounds
Compound (I)
Compound (IV)
Crystal data
Crystal data
3
3
˚
V = 1752.6 (7) A
Z = 4
˚
V = 2017.8 (7) A
Z = 4
C21H15N3O2
Mr = 341.36
Monoclinic, Cc
C22H17N3O2ÁCH4O
Mr = 387.43
Monoclinic, P21=c
Mo Kꢁ radiation
ꢂ = 0.09 mmÀ1
T = 293 K
0.59 Â 0.37 Â 0.08 mm
Mo Kꢁ radiation
ꢂ = 0.09 mmÀ1
T = 293 K
0.09 Â 0.02 Â 0.02 mm
˚
˚
a = 5.8130 (10) A
a = 10.521 (2) A
˚
b = 19.769 (4) A
˚
b = 15.003 (3) A
˚
˚
c = 23.243 (5) A
c = 9.056 (2) A
ꢀ = 111.49 (3)ꢀ
ꢀ = 95.480 (3)ꢀ
Data collection
Data collection
Nonius KappaCCD diffractometer
6192 measured reflections
1533 independent reflections
943 reflections with I > 2ꢃ(I)
Rint = 0.083
Nonius KappaCCD diffractometer
11012 measured reflections
3292 independent reflections
1604 reflections with I > 2ꢃ(I)
Rint = 0.084
Refinement
Refinement
R[F2 > 2ꢃ(F2)] = 0.043
wR(F2) = 0.090
S = 0.88
1533 reflections
236 parameters
2 restraints
H-atom parameteÀrs3 constrained
R[F2 > 2ꢃ(F2)] = 0.059
wR(F2) = 0.150
S = 0.91
263 parameters
H-atom parameteÀrs3 constrained
˚
˚
Áꢄmax = 0.12 e A
Áꢄmax = 0.15 e A
À3
À3
˚
˚
Áꢄmin = À0.13 e A
3292 reflections
Áꢄmin = À0.24 e A
Compound (V)
Compound (II)
Crystal data
3
˚
V = 1802.6 (6) A
Z = 4
Crystal data
C22H17N3O2
Mr = 355.39
3
˚
V = 4075.2 (15) A
Z = 8
Mo Kꢁ radiation
ꢂ = 0.08 mmÀ1
T = 293 K
C21H15N3O2ÁC2H3N
Monoclinic, P21=c
Mo Kꢁ radiation
ꢂ = 0.09 mmÀ1
T = 293 K
0.08 Â 0.03 Â 0.01 mm
Mr = 382.41
Orthorhombic, Pbca
˚
a = 16.242 (3) A
˚
b = 9.583 (2) A
˚
a = 9.111 (2) A
b = 18.830 (4) A
˚
c = 23.754 (5) A
˚
c = 11.615 (2) A
˚
ꢀ = 94.36 (2)ꢀ
0.50 Â 0.09 Â 0.05 mm
Data collection
Data collection
Nonius KappaCCD diffractometer
10123 measured reflections
3139 independent reflections
1975 reflections with I > 2ꢃ(I)
Rint = 0.055
Nonius KappaCCD diffractometer
6703 measured reflections
3584 independent reflections
1506 reflections with I > 2ꢃ(I)
Rint = 0.080
Refinement
Refinement
R[F2 > 2ꢃ(F2)] = 0.056
wR(F2) = 0.154
S = 1.09
244 parameters
H-atom parameteÀrs3 constrained
R[F2 > 2ꢃ(F2)] = 0.047
wR(F2) = 0.106
S = 0.81
263 parameters
H-atom parameteÀrs3 constrained
˚
Áꢄmax = 0.26 e A
˚
Áꢄmax = 0.15 e A
À3
˚
À3
3139 reflections
Áꢄmin = À0.21 e A
˚
3584 reflections
Áꢄmin = À0.16 e A
Compound (VI)
Compound (III)
Crystal data
Crystal data
C22H17N3O2
Mr = 355.39
Triclinic, P1
ꢅ = 109.63 (3)ꢀ
V = 1788.2 (10) A
Z = 4
Mo Kꢁ radiation
ꢂ = 0.09 mmÀ1
T = 293 K
3
3
˚
V = 3884.8 (12) A
Z = 8
Mo Kꢁ radiation
ꢂ = 0.09 mmÀ1
T = 293 K
˚
C21H15N3O2ÁCH4O
Mr = 373.40
Monoclinic, P21=c
˚
˚
a = 11.855 (2) A
˚
˚
a = 11.728 (2) A
b = 12.384 (2) A
˚
c = 14.791 (3) A
b = 11.365 (2) A
˚
c = 29.241 (6) A
0.20 Â 0.20 Â 0.05 mm
ꢁ = 111.95 (3)ꢀ
ꢀ = 99.56 (3)ꢀ
0.50 Â 0.05 Â 0.05 mm
ꢀ = 94.62 (2)ꢀ
Data collection
Data collection
Nonius KappaCCD diffractometer
22154 measured reflections
6747 independent reflections
2718 reflections with I > 2ꢃ(I)
Rint = 0.105
Nonius KappaCCD diffractometer
14497 measured reflections
6250 independent reflections
4081 reflections with I > 2ꢃ(I)
Rint = 0.091
Refinement
Refinement
R[F2 > 2ꢃ(F2)] = 0.067
wR(F2) = 0.156
S = 0.88
505 parameters
H-atom parameteÀrs3 constrained
R[F2 > 2ꢃ(F2)] = 0.044
wR(F2) = 0.130
S = 0.89
489 parameters
H-atom parameteÀrs3 constrained
˚
˚
Áꢄmax = 0.17 e A
Áꢄmax = 0.16 e A
À3
À3
˚
˚
6747 reflections
Áꢄmin = À0.18 e A
6248 reflections
Áꢄmin = À0.19 e A
ꢁ
Acta Cryst. (2009). C65, o365–o370
Yanover and Kaftory
Six solvates of C21H15N3O2 and C22H17N3O2 o369

organic compounds
Table 1
SHELXS97 (Sheldrick, 2008); program(s) used to refine structure:
SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for
Windows (Farrugia, 1999); software used to prepare material for
publication: SHELXL97.
Comparison of phenyl ring (Ph) rotation (ꢀ) with respect to the imidazole
ring.
Ph rotation at
position 2
Ph rotation at
position 4
Ph rotation at
position 5
This research was supported by the Fund for the Promotion
of Research at Technion and the Technion VPR Fund.
(I)
(II)
(IIIa)
(IIIb)
(IV)
(V)
44.8 (2)
45.5 (1)
15.7 (2)
31.5 (1)
85.2 (1)
30.5 (1)
26.0 (1)
30.8 (1)
45.0 (2)
41.0 (2)
37.4 (2)
30.9 (2)
69.5 (1)
65.5 (1)
54.5 (1)
81.1 (1)
34.3 (2)
33.1 (1)
46.5 (2)
35.3 (2)
24.3 (2)
24.2 (1)
25.8 (2)
12.5 (2)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GG3195). Additional figures are also available.
Services for accessing these data are described at the back of the journal.
(VIa)
(VIb)
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D—HÁ Á ÁA
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2.942 (5) 165
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N1a—H1aÁ Á ÁO3a
0.86
0.86
0.82
0.82
1.96
1.95
1.98
1.98
2.819 (4) 175
2.788 (4) 166
2.791 (4) 171
2.792 (4) 169
N1b—H1bÁ Á ÁO3biii
O3a—H3OaÁ Á ÁN2biii
O3b—H3ObÁ Á ÁN2a
(IV)
(V)
C18—H18Á Á ÁO2iv
C4—H4Á Á ÁO1v
0.96
0.96
0.96
2.56
2.48
3.426 (4) 150
3.148 (3) 127
(VI)
C12a—H12aÁ Á ÁO1avi
2.66
2.63
2.69
2.58
3.544 (3) 154
3.258 (3) 124
3.241 (3) 118
3.431 (3) 148
C14b—H14bÁ Á ÁO2bvii 0.96
C18b—H18bÁ Á ÁO1avi
0.96
0.96
C19b—H19bÁ Á ÁO1bvi
Symmetry codes: (i) x, Ày, 12 + z; (ii) À x, y, À z; (iii) 1 À x, À + y, À z; (iv) 1 À x,
1
2
3
2
1
1
2
2
5
1 À y, 1 À z; (v) x, À y, 12 + z; (vi) x, À1 + y, À1 + z; (vi) x, y, À1 + z.
2
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˚
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˚
˚
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808.
N—H = 0.86 A and O—H = 0.82 A, and with Uiso(H) = 1.2Ueq(C, N
or O).
For all compounds, data collection: COLLECT (Nonius, 2000); cell
refinement: DENZO HKL-2000 (Otwinowski & Minor, 1997); data
reduction: DENZO HKL-2000; program(s) used to solve structure:
ꢁ
o370 Yanover and Kaftory
Six solvates of C21H15N3O2 and C22H17N3O2
Acta Cryst. (2009). C65, o365–o370