Aspects of crystal engineering arising from packing behavior of functional mono para-substituted trityl compounds

Article abstract of DOI:10.1039/c5ce00871a

Four trityl compounds differing both in the functional group (OH, OMe, NH₂) at the specific trityl carbon and a para substituent, being bromine or phenyl at one of the phenyl groups, have been prepared and structurally studied by means of singl

Full text of DOI:10.1039/c5ce00871a

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Aspects of crystal engineering arising from
packing behavior of functional mono
Cite this: DOI: 10.1039/c5ce00871a
para-substituted trityl compounds†
Ingo Knepper,a Wilhelm Seichter,a Konstantinos Skobridis,b Vassiliki Theodoroub
a
*
and Edwin Weber
Four trityl compounds differing both in the functional group (OH, OMe, NH2) at the specific trityl carbon
and a para substituent, being bromine or phenyl at one of the phenyl groups, have been prepared and
structurally studied by means of single crystal X-ray diffraction and making use of Hirshfeld surface analysis.
Compared to the structures of corresponding prototypes and analogues, specific interaction modes and
packing motifs including cluster aggregates as well as non-cluster type structures depending on the substi-
tution and involving polymorphism were found, opening potential trend prediction with reference to crystal
engineering being useful in this compound class.
Received 4th May 2015,
Accepted 15th July 2015
DOI: 10.1039/c5ce00871a
www.rsc.org/crystengcomm
Here we report the X-ray crystal structures of four specific
trityl compounds (1–4, Fig. 1). Although being in close struc-
Introduction
Aside from their important property to be a parent substance
of the well known class of triphenylmethane dyes,1 trityl com-
pounds are also useful agents for functional group protection
in the synthesis of alcohols and amines.2,3 In other respects,
the basic compound triphenylmethanol has been shown to
selectively enclathrate methanol and DMSO in its crystal lat-
tice4 while more bulkily substituted triphenylmethanol deriva-
tives and analogous triarylmethanols demonstrate corre-
sponding inclusion formation with other guest solvents.5
Conversely, triphenylmethane derivatives as the guest were
found to be inclusion-complexed with crown compounds6,7
and, as a further subject, the packing modes of trityl alcohols
have been studied in dependency of specific para substitution
involving different halogen atoms.8,9 In all these latter struc-
tures, O–H⋯π10 and halogen⋯π11,12 interactions have proven
to dominate the crystal lattices while conventional O–H⋯O
hydrogen bonding13 is prevented from steric reason. However,
in most of the previous cases, the trityl alcohols are symmetri-
cally para substituted compound examples and corresponding
tritylamines are rarely described in the literature.14–16
tural relation, they systematically differ both in the main
functional group (hydroxyl, methoxy, amino) and the para
substituent (bromo, phenyl) being present at one of the phe-
nyl units. Based on a comparative discussion of the structural
results, including previous findings and making use of
Hirshfeld surface analysis,17 conclusions can be drawn that
can be helpful for future aspects of crystal engineering involv-
ing this interesting field of compounds.18–20 Moreover, previ-
ous findings in the context have shown that different melting
behavior of corresponding compounds are rather frequent
indicating the potential existence of polymorphous
structures,21–24 which is another inviting point of consider-
ation for carrying out this study.
a Institut für Organische Chemie, Technische Universität Bergakademie Freiberg,
Leipziger Str. 29, D-09596 Freiberg, Sachsen, Germany.
E-mail: edwin.weber@chemie.tu-freiberg.de
b Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
† CCDC 1062479–1062483. Overlay scheme of molecular conformation (Sup 1)
and crystallographic data. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c5ce00871a
Fig. 1 Chemical formula structures of the compounds studied.
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Results and discussion
Synthesis and X-ray structural study
non-covalent interactions in the crystal structures are listed
in Table 3. Perspective views of the molecular structures
including atom labelling and ring specification as well as illus-
trations of the packing structures are presented in Fig. 2–8.
Crystallization of the bromo substituted triarylmethanol 1
from a solvent mixture of n-hexane and diethyl ether (9 : 1)
yields colorless plates of the monoclinic space group P21/c
with two crystallographically independent molecules in the
asymmetric unit. The perspective view of the molecular struc-
ture is presented in Fig. 2a. The unsubstituted arene rings of
the molecules are arranged nearly orthogonal to one another
showing interplanar angles of 87.2(1) and 82.3IJ1)°, respec-
tively. The conformation of the molecule is stabilized by a rel-
atively short intramolecular C–H⋯O interaction10 ijdIJH⋯C)
2.34, 2.30 Å]. Contrary to expectations, the crystal structure
The compounds 1–4, studied in this paper, were synthesized
using respectively approaching described methods (1–4)21,25
or following standard preparative procedures (2, 3)26,27 and
are given in the experimental section. The crystal structures
of the compounds were performed using an X-ray diffraction
technique. Crystallographic data, experimental parameters
and selected details of the refinement calculations are sum-
marized in Table 1. Because of the high content of aromatic
units, the geometric features of the molecules can be
expressed by a set of dihedral angles between the arene rings.
These parameters together with relevant torsion angles are
summarized in Table 2, while information regarding possible
Table 1 Crystallographic and structure refinement data of the compounds studied
Compound
1
2B
2C
3
4
Empirical formula
C
19H15OBr
C25H20
336.41
Triclinic
¯
P1
O
C25H20
O
C20H17OBr
C19H16NBr
Formula weight
Crystal system
Space group
339.22
Monoclinic
P21/c
336.41
Monoclinic
P21
353.25
Orthorhombic
Pna21
338.24
Monoclinic
P21/c
a/Å
b/Å
c/Å
α/°
10.7736(2)
15.2684(3)
18.6621(3)
90.0
104.275(1)
90.0
15.6058(3)
18.7804(4)
21.1189(4)
68.874(1)
74.947(1)
74.080(1)
5462.16IJ19)
12
8.9849(6)
5.7029(3)
17.1999IJ11)
90.0
99.978(4)
90.0
12.1520(3)
13.7838(3)
9.5790(3)
90.0
90.0
90.0
10.7837(2)
15.2773(4)
18.8871(4)
90.0
104.273(1)
90.0
β/°
γ/°
V/Å3
2975.05(9)
8
867.99(9)
2
1604.49(7)
4
3015.52IJ12)
8
Z
FIJ000)
1376
1.515
2.759
2136
1.227
0.073
356
1.287
0.077
720
1.462
2.561
1376
1.490
2.719
Dc/Mg m−3
μ/mm−1
Data collection
Temperature/K
No. of collected reflections
Within the θ-limit/°
90(2)
30 095
100(2)
100(2)
12 855
173(2)
8781
100(2)
59 570
107 343
1.2–28.1
−20/20, −24/24,
−27/27
1.8–29.2
−14/14, −20/20,
−25/25
2.3–30.1
−12/12, −8/8,
−24/24
2.6–28.4
−8/16, −14/18,
−12/7
1.7–28.6
−14/14, −20/20,
−25/25
Index ranges h, k,
l
No. of unique reflections
Rint
7905
0.0244
26 583
0.0314
4710
0.0222
3219
0.0185
7712
0.0223
Refinement calculations:
full-matrix least-squares on all
F
2 values
Weighting expression wa
ijσ2IJFo2) +
(0.0435P)2 +
1.4259P]−1
387
ijσ2IJFo2) +
(0.0595P)2 +
3.4661P]−1
1411
ijσ2IJFo2) +
(0.0561P)2 +
0.1424P]−1
240
ijσ2IJFo2) +
(0.0282P)2 +
0.3652P]−1
201
ijσ2IJFo2) +
(0.0428P)2 +
2.5837P]−1
395
No. of refined parameters
No. of F values used [I >
2σIJI)]
6551
17 994
4409
2913
6771
Final R-Indices
P
P
RIJ= |ΔF|/ |Fo|)
0.0292
0.0801
1.035
0.0521
0.1522
1.005
0.0358
0.0952
1.037
0.0231
0.0594
0.940
0.0272
0.0782
1.006
wR on F2
S (=Goodness of fit on F2)
Final Δρmax/Δρmin (e Å−3
KPI (%)
)
0.60/−0.92
0.65/−0.43
0.34/−0.19
0.45/−0.44
0.92/−0.64
69.8
67.7
71.4
68.6
69.7
Total potential solvent
accessible
Void volume/Å3
Void volume per unit cell/%
—
—
81.2
1.5
—
—
—
—
—
—
a
P = IJFo2 + 2Fc2)/3
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Table 3 Geometric parameters for hydrogen bond type contacts of the compounds studied
Atoms involved
Distance/Å
Angle/°
D–H⋯A
D–H
C–Br
D⋯A
H⋯A
D–H⋯A
Symmetry
C–Br⋯Br
C⋯Br
Br⋯Br
C–Br⋯Br
1
OIJ1)–HIJ1)⋯CIJ14A)b
OIJ1A)–HIJ1A)⋯CIJ12)b
CIJ8)–HIJ8)⋯OIJ1)
1 − x, 1 − y, 2 − z
−x, 1 − y, 2 − z
x, y, z
x, y, z
x, y, z
0.83(1)
0.83(1)
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
1.898(2)
1.902(2)
3.428(2)
3.230(2)
2.689(2)
2.660(2)
3.669(2)
3.674(2)
3.544(3)
3.639(2)
3.590(2)
3.600(2)
3.634(2)
4.245(2)
5.613(2)
2.670(2)
2.492(2)
2.34
2.30
2.75
2.78
2.86
2.73
2.86
2.88
2.78
3.869(2)
3.869(2)
153.2(2)
148.5(2)
101
102
164
157
130
160
135
133
150
87.9(2)
151.4(2)
CIJ18A)–HIJ18A)⋯OIJ1A)
CIJ5)–HIJ5)⋯OIJ1A)
CIJ3A)–HIJ3A)⋯OIJ1)
CIJ14)–HIJ14)⋯centroidIJCA)a
CIJ15)–HIJ15)⋯CIJ6)b
CIJ6A)–HIJ6A)⋯CIJ16)b
CIJ9A)–HIJ9A)⋯CIJ18)b
CIJ11A)–HIJ11A)⋯CIJ3A)b
CIJ4)–BrIJ1)⋯BrIJ1A)
CIJ4A)–BrIJ1A)⋯BrIJ1)
x, 1 + y, z
1 − x, 1 − y, 2 − z
1 − x, 1 − y, 2 − z
1 − x, 1 − y, 2 − z
−x, 0.5 + y, 1.5 − z
−x, 2 − y, 2 − z
1 − x, −0.5 + y, 2.5 − z
1 − x, 0.5 + y, 2.5 − z
2B
OIJ1)–HIJ1)⋯OIJ1B)
x, y, −1 + z
x, y, z
x, y, 1 + z
x, y, z
x, y, z
0.84
0.84
0.84
0.84
0.84
0.84
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
2.929(2)
2.737(2)
2.790(2)
2.743(2)
2.735(2)
2.741(2)
3.639(3)
3.678(3)
3.553(3)
3.592(3)
3.595(3)
3.663(3)
3.565(3)
3.683(3)
3.663(3)
3.532(3)
2.724(2)
3.456(3)
3.633(3)
3.570(3)
3.682(3)
3.535(3)
3.563(3)
3.673(3)
3.632(3)
2.712(2)
3.671(3)
3.669(3)
3.482(3)
3.660(3)
2.17
2.02
2.09
1.99
2.00
1.96
2.70
2.86
2.85
2.82
2.84
2.76
2.72
2.89
2.76
2.62
2.39
2.72
2.85
2.81
2.86
2.71
2.75
2.90
2.83
2.37
2.78
2.84
2.75
2.82
151
143
141
150
147
155
172
145
132
139
137
160
149
142
160
161
101
134
141
138
146
146
145
139
143
101
157
146
134
148
OIJ1A)–HIJ1A)⋯OIJ1)
OIJ1B)–HIJ1B)⋯OIJ1A)
OIJ1C)–HIJ1C)⋯OIJ1D)
OIJ1D)–HIJ1D)⋯OIJ1E)
OIJ1E)–HIJ1E)⋯OIJ1C)
CIJ3)–HIJ3)⋯centroidIJBA)a
CIJ8)–HIJ8)⋯CIJ22E)b
x, y, z
1 − x, −y, −z
1 − x, −y, 1 − z
1 − x, 1 − y, 1 − z
1 − x, −y, 1 − z
2 − x, −y, −z
x, y, z
CIJ23)–HIJ23)⋯CIJ5B)b
CIJ5A)–HIJ5A)⋯CIJ5B)b
CIJ10A)–HIJ10A)⋯CIJ22C)b
CIJ22A)–HIJ22A)⋯centroidIJCC)a
CIJ3B)–HIJ3B)⋯CIJ4)b
x, y, 1 + z
CIJ4B)–HIJ4B)⋯CIJ24A)b
CIJ9B)–HIJ9B)⋯centroidIJB)a
CIJ15B)–HIJ15B)⋯OIJ1A)
CIJ12C)–HIJ12C)⋯OIJ1C)
CIJ5C)–HIJ5C)⋯centroidIJAE)a
CIJ8C)–HIJ8C)⋯CIJ22B)b
CIJ24C)–HIJ24C)⋯CIJ18)b
CIJ2D)–HIJ2D)⋯CIJ9D)b
CIJ5D)–HIJ5D)⋯CIJ10C)b
CIJ8D)–HIJ8D)⋯CIJ18D)b
CIJ19D)–HIJ19D)⋯CIJ3D)b
CIJ21D)–HIJ21D)⋯CIJ25E)b
CIJ2E)–HIJ2E)⋯OIJ1E)
CIJ2E)–HIJ2E)⋯CIJ6D)b
CIJ4E)–HIJ4E)⋯CIJ16B)b
CIJ9E)–HIJ9E)⋯centroidIJBD)a
CIJ24E)–HIJ24E)⋯CIJ22C)b
−1 + x, y, 1 + z
1 − x, −y, 1 − z
x, y, 1 + z
x, y, z
2 − x, 1 − y, 1 − z
2 − x, 1 − y, 1 − z
x, y, z
1 − x, 1 − y, 1 − z
2 − x, 1 − y, 1 − z
1 − x, 1 − y, 1 − z
1 − x, 1 − y, 1 − z
x, y, z
x, y, z
x, y, z
x, y, z
2 − x, 1 − y, 1 − z
x, y, z
2C
OIJ1)–HIJ1)⋯CIJ11)b
CIJ6)–HIJ6)⋯OIJ1)
CIJ15)–HIJ15)⋯OIJ1)
CIJ4)–HIJ4)⋯centroidIJC)a
CIJ9)–HIJ9)⋯CIJ1)b
CIJ11)–HIJ11)⋯CIJ10)b
x, −1 + y, z
0.85(2)
0.95
0.84
0.95
0.95
3.398(2)
3.371(2)
2.805(2)
3.704(2)
3.619(2)
3.725(2)
2.62(10)
2.53
2.47
2.92
2.77
153(2)
148
101
140
149
x, 1 + y, z
x, y, z
−1 + x, y, z
−x, 0.5 + y, 1 − z
1 − x, 0.5 + y, 1 − z
0.95
2.89
147
3
CIJ8)–HIJ8)⋯CIJ15)b
1 − x, 2 − y, −z
0.95
0.95
3.705(3)
3.594(3)
2.85
2.75
150
149
CIJ16)–HIJ16)⋯centroidIJB)a
0.5 − x, 0.5 + y, −0.5 + z
4
NIJ1)–HIJ1A)⋯centroidIJAA)a
NIJ1)–HIJ2A)⋯CIJ14A)b
NIJ1A)–HIJ1AA)⋯CIJ8)b
NIJ1A)–HIJ1AB)⋯centroidIJA)a
−x, 1 − y, 2 − z
−x, 1 − y, 2 − z
1 − x, 1 − y, 2 − z
1 − x, 1 − y, 2 − z
0.89(1)
0.89(1)
0.88(1)
0.89(1)
3.518(3)
3.363(3)
3.579(3)
3.649(3)
2.682(2)
2.582(2)
2.799(2)
2.826(2)
157(2)
148(2)
148(2)
156
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Table 3 (continued)
Atoms involved
Distance/Å
Angle/°
D–H⋯A
D–H
C–Br
D⋯A
H⋯A
D–H⋯A
Symmetry
C–Br⋯Br
C⋯Br
Br⋯Br
C–Br⋯Br
CIJ6)–HIJ6)⋯NIJ1)
x, y, z
x, y, z
x, y, z
x, y, z
−x, −0.5 + y, 1.5 − z
−x, 1 − y, 2 − z
−x, 1 − y, 2 − z
1 − x, 2 − y, 2 − z
1 − x, −0.5 + y, 2.5 − z
1 − x, 0.5 + y, 2.5 − z
0.95
0.95
0.95
0.95
0.95
0.95
0.95
0.95
2.785(3)
2.741(3)
2.799(3)
2.773(3)
3.650(3)
3.637(3)
3.698(3)
3.618(3)
5.622(3)
4.251(3)
2.45
2.35
2.47
2.40
2.86
2.79
2.95
2.70
101
104
100
103
141
149
136
163
CIJ12)–HIJ12)⋯NIJ1)
CIJ2A)–HIJ2AA)⋯NIJ1A)
CIJ18A)–HIJ18A)⋯NIJ1A)
CIJ14)–HIJ14)⋯CIJ15A)b
CIJ17)–HIJ17)⋯CIJ3)b
CIJ18)–HIJ18)⋯centroidIJCA)a
CIJ9A)–HIJ9A)⋯CIJ6A)b
CIJ4)–BrIJ1)⋯BrIJ1A)
1.901(2)
1.900(2)
3.856(2)
3.856(2)
153.5(2)
88.4(2)
CIJ4A)–BrIJ1A)⋯BrIJ1)
a
Means centre of the aromatic ring. 1: Ring CA: CIJ13A)⋯CIJ18A). 2: Ring B: CIJ7)⋯CIJ12); ring C: CIJ14)⋯CIJ19); ring BA: CIJ7A)⋯CIJ12A); ring CC:
CIJ14C)⋯CIJ19C); ring BD: CIJ7D)⋯CIJ12D); ring AE: CIJ1E)⋯CIJ6E). 3, 4: Ring A: CIJ1)⋯CIJ6); ring B: CIJ7)⋯CIJ12); ring AA: CIJ1A)⋯CIJ6A); ring CA:
CIJ13A)⋯CIJ18A). b To achieve reasonable hydrogen bond geometries, individual atoms instead of ring centroids were choosen as acceptors.
lacks conventional hydrogen bonding.13 Instead, the hydroxy
hydrogen of the molecules is used for the formation of a O–
H⋯π contact10 to the bromophenyl ring of an adjacent mole-
cule ijO–H⋯CIJarene) 2.64 Å, 156.0°; 2.46 Å, 153.6°] resulting in
the creation of supramolecular strands, the structure of
which is shown in Fig. 3. Interstrand association is accom-
plished by a close network of weak C–H⋯π contacts28,29
ijdIJH⋯CIJaryl)) 2.73–2.88 Å] and C–Br⋯Br–C interactions of the
type II geometry30,31 (θ1 = 151.4°, θ2 = 87.9°).
Å3 per unit cell (~1.5% of the cell volume). By way of contrast,
neither conventional intramolecular nor intermolecular
hydrogen bonds are observed in the previously reported struc-
ture of 2A.33 The crystal of this polymorph is composed of iso-
lated molecules with only weak C–H⋯π contacts ijdIJH⋯C)
2.80–2.92 Å] acting between them to form molecular strings.
In the course of our crystal growing experiments we
noticed that crystals of 2 obtained from diethyl ether existing
in the monoclinic space group P21 with one molecule in the
asymmetric unit represent another new polymorph 2C
(Fig. 2c). The twist angle between the aromatic rings of the
biphenyl element is 4.0IJ1)°. Remarkably, the packing of mole-
cules as well as the pattern of intermolecular non-covalent
bonding of this polymorph are also fundamentally different
from that of the aforementioned structures of 2A and 2B. As
illustrated in Fig. 5, the crystal is constructed of supramolec-
ular strands running along the b-axis. Within a given strand,
the molecules are connected by C–H⋯O hydrogen bonding
ijdIJH⋯C) 2.53 Å]. The hydroxy hydrogen of the molecule par-
ticipates in O–H⋯π hydrogen bond formation ijdIJH⋯π)
2.62(1) Å, ∠O–H⋯π 153IJ2)°] between the molecules of adja-
cent strands. Interstand association is completed by weak C–
H⋯π contacts ijdIJH⋯π) 2.77–2.92 Å, ∠C–H⋯π 140–149°].
Crystallization of the methyl ether derivative of 1, that is
3, from methanol yields colorless rods of the orthorhombic
space group Pna21 with one molecule in the asymmetric part
of the unit cell (Fig. 6a). The pair of phenyl rings are oriented
at 70.1IJ1)° to one another, while these rings are inclined at
angles of 81.0(1) and 61.4IJ1)° with respect to the plane of the
bromophenyl ring. As the molecule 3 lacks a strong hydrogen
donor, the crystal structure is characterized by poor molecu-
lar association. A view of the packing structure along the crys-
tallographic c-axis (Fig. 7) reveals that neither the ether oxy-
gen nor the bromine atoms participate in molecular cross-
linking, Hence, interactions between the molecules are
restricted to weak C–H⋯π contacts only.
Crystallization of the biphenyl containing alcohol 2 from
¯
CHCl3 yields colorless crystals of the space group P1 with the
asymmetric part of the unit cell comprising six independent
molecules (Z = 12, Z′ = 6). Crystal structures featuring large
values of Z′, particularly in connection with polymorphism,
have received increasing interest in the last years being
discussed in a topical review article.32 In the present struc-
ture, the molecules are assembled to form two trimers
(Fig. 2b), each of them held together by a cyclic array of O–
H⋯O hydrogen bonds ijdIJO⋯O) 2.735IJ3)–2.928IJ3) Å] and
weak C–H⋯O ijdIJH⋯O) 2.37–2.38 Å] as well as C–H⋯π con-
tacts ijdIJH⋯C) 2.72–2.84 Å]. The conformation of a trimer is
such that its molecules are oriented in one direction with a
nearly parallel alignment of their biphenyl axes. As is evident
from geometric parameters (Table 2), the conformations of
the molecules significantly deviate, which in particular can
be seen from tilt angles between aromatic rings of the biphe-
nyl units ranging from 22.9(1) to 44.6IJ1)° (Sup 1). It should
be noted at this point that a known crystal structure of 2 (2A)
reported by Ferguson et al.33 exists in the non-
centrosymmetric orthorhombic space group P212121 (Z = 4, Z′
= 1), so that the present crystal structure represents a second
polymorph (2B) of this compound. The difference in space
group symmetries of the polymorphs suggests fundamental
differences regarding the packing structures and modes of
molecular association. In the present crystal structure, the
molecules of adjacent trimers adopt an antiparallel arrange-
ment (Fig. 4) thus allowing close packing and formation of
multiple C–H⋯π-interactions. Nevertheless, the crystal of 2B
contains solvent accessible lattice voids with a volume of 81.2
The compound 4, being the amine analogue of 1, crystal-
lizes from n-hexane as colorless plates of the monoclinic
space group P21/c with two independent molecules in the
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Fig. 2 Illustration of the molecular structures of 1 (a) and of the polymorphs 2B, 2C (b, c) including numbering of relevant atoms and ring
specification. Thermal ellipsoids are drawn at 50% probability level. Grey ellipsoids represent hetero atoms. Broken lines represent C–H⋯O and O–
H⋯O hydrogen bonds.
asymmetric unit (Fig. 6b). The molecules markedly deviate in
their conformations as can be seen from the dihedral angles
of 53.8(1) and 70.7IJ1)° formed between the unsubstituted aro-
matic rings. The bond lengths CIJaryl)–CIJsp3) and C–N are
1.537IJ2)–1.542IJ2) and 1.479IJ2)/1.484IJ2) Å and agree well with
those found in the crystal structures of the polymorphic
forms of plain triphenylmethylamine.22–24 The coordination
behavior of the amine 4 resembles that of the alcohol 1, i.e.
the strong hydrogen donors are involved in weak N–H⋯π
contacts ijdIJH⋯π) 2.62–2.83 Å] giving rise to the formation of
supramolecular strands (Fig. 8). Owing to the similarity of
cell parameters between 1 and 4 the packing of molecules in
the respective crystal structures is essentially of the same
kind. More strictly speaking, in 4 one of the unsubstituted
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molecules (labelled as 1 and 2 in Fig. 9) which are very simi-
lar. Due to the high content of hydrogen atoms in the crystal
structure, the 2D-fingerprint plots are dominated by H⋯H
interactions comprising 58.4 and 56.6% of the surface,
respectively (peak 1). Peak 2 represents C⋯H interactions
(including C–H⋯π and O–H⋯π contacts) which comprise
38.0 and 40.7% of the surface. Br⋯H interactions (de + di ≈
3.0 Å, peak 3) make up 17.2 and 14.1% of the Hirshfeld sur-
face. The bright streak along the diagonal (de = di ≈ 1.9 Å)
indicate the presence of weak Br⋯Br contacts. The sum (de +
di) = 2.30 Å for H⋯H interactions as well as the diffuse pat-
tern of points at the upper right region of the plots (de ≈ 2.6,
di ≈ 2.75 Å) indicate that the packing is moderately efficient.
The lattice energy calculated for 1 is −133.9 kJ mol−1.
Polymorph 2A, derived from the CSD (Refcode YUHGOX),
and polymorph 2C crystallize with one molecule in the asym-
metric unit of the cell. Their 2D-fingerprint plots (Fig. 10)
exhibit similarities which are reflected by nearly identical
values for the different kinds of interactions, in which H⋯H
contacts make up 58.4/56.6%, C⋯H interactions 38.0/40.7%
and O⋯H interactions 3.1/3.1%. Nevertheless, the plots dis-
play differences. The fingerprint plot of 2A reveals a diffuse
blue tail of points at the upper right (di = 2.4–2.8 Å), which
indicates a non-optimal packing of molecules. The plot of
polymorph 2C is characterized by two sharp features (de + di
= 2.5 Å) which, apart from CH⋯π bonding, represent O–
H⋯π contacts, the latter being absent in polymorph 2A. The
structural similarities of the polymorphs are reflected by
nearly identical lattice energies of −165.5 (2A) and −169.9 kJ
mol−1 (2C).
The polymorph 2B refers to the structure with Z′ = 6. We
therefore computed Hirshfeld surfaces choosing each individ-
ual molecule in turn as a target and obtained six distinct fin-
gerprint plots (Fig. 11). Each fingerprint plot displays three
characteristic patterns labelled 1–3 for molecule 3. The plots
are similar in that they all indicate a large proportion for
H⋯H interactions varying from 57.0 to 63.6%, followed by
C⋯H interactions (32.2–39.1%) and O–H⋯O hydrogen bonds
(2.8–3.4%), the latter appearing as a pair of spikes, the upper
left (de > di) corresponding with the hydrogen bond donor,
the lower one (de < di) with the hydrogen bond acceptor. The
values for de + di are in the range between 1.95 and 2.15 Å.
Peak 1 of the plots represents H⋯H interactions with some
of them showing anomalous short distances near 2.0 Å which
suggests a tight packing of molecules. Compared with 2A and
2C, the increased content of H⋯H interactions which is
accompanied by a decrease of C⋯H interactions may be
attributed to completely different packing modes which in 2B
includes compact trimers of O–H⋯O bonded molecules.
Obviously, the unique alignment of the biphenyl parts within
the trimers enhances the degree of C–H⋯π interactions. They
are visible in the 2D-fingerprint plots as “wings” (peak 2). It
should be noted here, that O–H⋯O hydrogen bonds have a
structure directing effect, although they represent only a
small proportion of the Hirshfeld surfaces. Furthermore, we
see in some of the fingerprint plots (molecules 1–3) a rather
Fig. 3 Structure of the supramolecular strand of 1 with labelling of
relevant atoms. The oxygens are displayed as dotted, the bromine
atoms as cross-hatched circles. Broken double lines represent O–H⋯π
interactions.
arene rings and the bromophenyl ring of each molecule act
as acceptors for hydrogen bonding. Interstrand association is
realized by C–Br⋯Br–C contacts of type-II geometry [θ1
=
153.5°; CIJ7)–BrIJ1)⋯BrIJ2) θ2 = 91.0°] and arene–arene interac-
tions [C–H⋯π 2.70–2.86 Å, 141–163°].
Hirshfeld surface analysis
Hirshfeld surfaces17 represent an effective way to gain insight
in the packing behavior of molecules in the crystalline
state.34 In order to visualize quantitatively the different types
of intermolecular interactions (hydrogen bonding, halogen-
based interactions, C–H⋯π contacts, etc.) two-dimensional
fingerprint plots,35 derived from Hirshfeld surfaces, were pre-
pared by using the CrystalExplorer program (version 3.1).36 In
these plots the distance de (distance of the Hirshfeld surface
from the nearest nucleus outside the surface) is plotted
against di (the corresponding distance to the nearest nucleus
inside the surface).
For the structure 1, there are two crystallographically inde-
pendent molecules in the asymmetric part of the unit cell.
Thus, we have produced two fingerprint plots for the
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Fig. 4 Packing diagram of 2B. The hydrogen atoms of the aromatic units are omitted for clarity. The oxygens are displayed as dotted circles.
Broken lines represent hydrogen bond type interactions.
diffuse collection of points at larger values for de and di, indi-
cating that parts of the Hirshfeld surface of the molecules
are without close contacts indicating the presence of voids in
the crystal lattice. Unfortunately, we could not compute the
lattice energy for polymorph 2B, because the number of
atoms exceeded the limit allowed by the program OPIX
(Gavezotti).37
The structure 3 bears resemblance to the structure of 1 in
that the only strong features are H⋯H (52.8%) and C⋯H
contacts (24.9%). The fingerprint plot of the molecule
(Fig. 12) is characterized by two “wings” (de + di ≈ 2.7 Å)
which can be ascribed to C–H⋯π interactions. The lattice
energy is computed to −130.1 kJ mol−1.
The 2D-fingerprint plots for the two independent mole-
cules of the amine 4 (Z′ = 2) (Fig. 13) show proportions of
51.4 and 46.6% for H⋯H interactions. C⋯H represent 31.5
and 33.3% of the Hirshfeld surface, respectively. The C–H⋯π
and N–H⋯π interactions in the crystal structure appear as
distinct “wings” at the upper left and lower right region of
the plot. The Br⋯H interactions also have a relatively signifi-
cant contribution to the total Hirshfeld surfaces comprising
14.3 and 17.0%, respectively. Similar to the crystal structure
of 1, Br⋯Br contacts are clearly visible as a bright streak (de
= di ≈ 1.9 Å). The lattice energy of the structure amounts to
−137.0 kJ mol−1.
Comparative reflection and conclusions
Based on the above discussion and including previous struc-
tural results of appropriate compounds of comparison,
remarks can be made and conclusions drawn as follows. Con-
sidering the construction mode observed in the crystal struc-
ture of the prototype tritylalcohol (Ph3OH), molecular tetra-
mers with the hydroxyl groups forming a pyramidal motif of
O–H⋯O hydrogen bonds are found.38 Though behaving in a
special manner, conventional hydrogen bonding is taking a
main effect in this crystal. By way of contrast, the crystal
structure of 1 shows O–H⋯π bonded molecular strands inter-
linked via weak Br⋯Br interactions. Thus, compared to the
prototype just one single bromo substituent as in 1 induces
loss of conventional hydrogen bonding between OH groups
which in the main may be attributed to effects of molecular
packing possibly supported by the opening of a specific
Br⋯Br interaction. A similar way of acting is reported for the
tribromo and triiodo derivatives of tritylalcohol in their crys-
tal structures that are characterized by O–H⋯π bonded
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Fig. 5 Packing diagram of 2C. The oxygen atoms are displayed as dotted circles. Broken lines represent C–H⋯O hydrogen bonds, broken double
lines O/C–H⋯π type interactions.
molecular chains with the halogens being here involved in
Hal⋯π instead of Hal⋯Hal contacts.39 Even more puzzling
facts have been found for the biphenyl derivative 2 of which
we succeeded to crystallize two polymorphous structures (2B
from CHCl3, 2C from n-hexane/diethyl ether, 9 : 1) differing
from that of the known polymorph (2A) obtained from nitro-
methane.33 While in 2A the crystal structure is only stabilized
by weak C–H⋯π interactions, surprisingly enough, in the
polymorphous crystal of 2B the molecules are assembled to
O–H⋯O bonded trimers which are further stabilized by C–
H⋯O and C–H⋯π contacts. Hence, 2B behaves similarly to
the unsubstituted prototype compound in O–H⋯O bonded
cluster formation though giving rise to trimer instead of tet-
ramer clustered building units typical of the prototype. This
may be due to the spatial demand of the additional phenyl
86.1 (2A), 77.5 (2B) and 82.4 J g−1 (2C) have been determined.
Actually, the temperature difference between the polymorphs
2A and 2C is very small, which can be explained by structural
similarities.
It stands to reason that the methyl ether analogous com-
pound 3 can not form corresponding OH involved interac-
tions. However, Hal⋯Hal contacts typical of 1 are also absent
in 3 while only weak C–H⋯π interactions, comparable to 2A
determine the crystal structure. Two polymorphic crystal
structures are also known for the parent compound of 4, i.e.
the unsubstituted triphenylmethylamine. One is composed of
N–H⋯N bonded molecular dimers with the amino hydrogens
disordered over two positions23,24 whereas in the other poly-
morph, molecules are interlinked by weak N–H⋯π contacts
to 2D supramolecular aggregates.15 On the other side, a
molecular organization analogous to that of 1 is found in the
crystal structure of the corresponding amine 4 with both
amino hydrogens being involved in chain formation via N–
H⋯π interaction. So, following the relation of O–H⋯O to O–
H⋯π interactions in the tritylalcohols, interchangeability of
N–H⋯N for N–H⋯π contacts, according to substitution and
polymorphism obviously is also a characteristic feature in the
crystal formation of the tritylamines.
substituent in 2B, but enabling as
a secondary effect
favourable weak intermolecular contacts in the packing. As
opposed to 2B, in the polymorphous structure 2C the mole-
cules are assembled to C–H⋯O bonded strands which are
connected by O–H⋯π hydrogen bonding interactions and
weak C–H⋯π contacts to a three-dimensional supramolecular
network. Hence grown from different solvents, 2 can be
obtained as crystals 2A–2C showing distinctly different
modes of intermolecular interactions. Considering the ther-
mal behavior of the polymorphs, a detailed investigation has
been performed by differential scanning calorimetry (DSC).
The onset temperatures for the melting of 135.3 °C (2A),
105.0 °C (2B) and 134.6 °C (2C) as well as enthalpy values of
In summary, the impression is given that compounds
involving both trityl alcohols and amines rather sensitively
respond to substitution or change of substituent as well as
the solvent used for crystallization in the formation of an
appropriate crystal structure. Therefore, to exert control on a
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Fig. 6 Illustration of the molecular structures of 3 (a) and 4 (b). Thermal ellipsoids are drawn at 50% probability level. The oxygens/nitrogens are
displayed as light grey, the bromine atoms as dark grey ellipsoids.
desired crystal structure including examples of these com-
pound classes is not without its problems. Nevertheless,
deduced from the given discussion certain trends in forming
cluster aggregates via strong hydrogen bonding or non-
cluster type structures being founded on weak hydrogen
bond type and related interactions can be read from the com-
ments of this paper that could be supportive for purposes of
crystal engineering in the field.
mm, Merck). For analytical thin layer chromatography silica
gel 60 F254 (Merck) was used.
Materials
Organic solvents were purified by standard procedures.
Starting
compounds
bromobenzene
and
4-bromo-
benzophenone were purchased from Acros Organics.
4-Biphenylyl phenyl ketone was synthesized as described.3
Preparation of the trityl compounds 1–4
Experimental
IJ4-Bromophenyl)diphenylmethanol (1). To a solution of
phenyl magnesium bromide (8.8 g, 48.6 mmol) in dry diethyl
ether (50 ml), prepared from bromobenzene (7.6 g, 48.6
mmol), a solution of 4-bromobenzophenone (10.83 g, 44.2
mmol) in dry diethyl ether (100 ml) was added dropwise
under an atmosphere of argon. The mixture was refluxed for
1 h and then stirred at room temperature for 2 h. After that,
the mixture was cooled in ice and quenched with a saturated
aqueous solution of NH4Cl. The organic layer was separated
and the aqueous layer extracted with diethyl ether. The com-
bined organic phases were washed with water, dried IJNa2SO4)
General
Melting points (uncorrected) were determined using a micro-
scope heating stage PHMK Rapido (VEB Wägetechnik). IR
spectra were measured on a FT-IR 510 Nicolet as KBr pellets.
1H and 13C NMR spectra were recorded in chloroform solu-
tion at room temperature on a Bruker Avance DPX 400 at 400
MHz, respectively. Elemental analyses were performed on a
Hereus CHN rapid analyzer. Mass spectra were obtained
using a Hewlett-Packard GC-MS 5890. Column chromatogra-
phy was performed on a silica gel (particle size 0.063–0.1
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Fig. 7 Packing illustration of 3 viewed down the crystallographic c-axis. The oxygen atoms are displayed as dotted, the bromine atoms as cross-
hatched circles. Dotted double lines represent C–H⋯π interactions.
and evaporated. The crude product (yellow-orange oil) was
crystallized from diethyl ether-n-hexane (1 : 9, ν/ν) to yield 7.5
g (50%) colorless crystals. M.p. 75 °C (lit.21 74 °C, lit.22 99–
100 °C). Found: C, 67.48; H, 4.53; C19H15OBr requires C,
67.27; H, 4.46%; νmax (KBr cm−1) 3566 (OH), 3079, 3056, 3022
(CAr–H), 1597, 1489, 1448 (CC, Ar), 1394, 1154, 1033, 1008,
821 (disubst. Ar), 764, 698 (monosubst. Ar); δH (400 MHz;
3
CDCl3; Me4Si) 2.77 (s, 1H, OH), 7.16 (d, JHH = 8.0 Hz, 2H,
3
Ar–H), 7.22–7.30 (m, 10H, Ar–H), 7.47 (d, JHH = 8.8 Hz, 2H,
Ar–H); δC (100 MHz; CDCl3; Me4Si) 81.7 (C–OH), 121.4 (C–Br),
127.5–129.7, 131.0, 145.9, 146.4 (Ar–C); m/z: 338 [M–H]+, 261,
183, 155, 105 (100%), 77, 51.
4-Biphenylyldiphenylmethanol (2). Solutions of phenyl
magnesium bromide (8.8 g, 48.6 mmol) and of 4-biphenylyl
phenyl ketone (12.50 g, 44.2 mmol) in dry diethyl ether were
reacted and worked up following the above procedure. Crys-
tallization of the crude product from chloroform yielded 73%
colorless crystals. M.p. 104–105 °C. νmax (KBr cm−1) 3441
(OH), 3027 (CAr–H), 1598, 1486, 1445 (CC, Ar), 1401, 1157,
1005, 898 (disubst. Ar), 762, 695 (monosubst. Ar); δC (500.1
MHz; CDCl3; Me4Si) 81.9 (C–OH), 126.6, 127.1, 127.3, 127.9,
128.0, 128.3, 128.8, 140.0, 140.6, 145.9, 146.8 (Ar–C); δH (400
MHz; CDCl3; Me4Si) 2.83 (s, 1H, OH), 7.25–7.37 (m, 13H, Ar–
3
H), 7.43 (t, 2 H, Ar–H), 7.54 (d, JHH = 8.8 Hz, 2H, Ar–H), 7.59
3
(d, JHH = 8.8 Hz, 2H, Ar–H); m/z: 336 [M–H]+, 259, 181, 152,
105, 77, 51.
ij(4-Bromophenyl)diphenylmethyl] methyl ether (3). To a
mixture of sodium hydride (1.2 g, 50 mmol, suspension in
Fig. 8 Structure of the supramolecular strand of 4 with labelling of
relevant atoms. The nitrogens are displayed as hatched, the bromine
paraffin oil) in dry THF was added 1 (1.6 g, 5 mmol) under
an atmosphere of argon. After having stirred for 30 min,
atoms as cross-hatched circles. Broken double lines represent N–H⋯π
interactions.
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Fig. 9 2D-fingerprint plots for the molecules 1 and 2 in the asymmetric unit of compound 1. Spikes labelled as 1–3 correspond to H⋯H, C⋯H and
Br⋯H interactions, respectively.
Fig. 10 2D-fingerprint plots for the molecules 2 in the polymorphs 2A and 2C. Spikes labelled as 1 and 2 correspond to H⋯H and C⋯H
interactions, respectively.
methyl iodide (4.25 ml, 66 mmol) was added dropwise and
the mixture stirred for 16 h at 40 °C. The mixture was
quenched with water, the organic layer separated and the
aqueous layer extracted with diethyl ether. The combined
organic phases were washed with water, dried IJNa2SO4) and
evaporated. The crude product (colorless oil) was crystallized
from DMF to yield 1.7 g (96%) colorless crystals. M.p. 69 °C.
Found: C, 68.19; H, 5.00; C20H17OBr requires C, 68.00; H,
4.85%; νmax (KBr cm−1) 3085, 3024, (CAr–H), 2950, 2851
(CH3), 1583, 1491, 1451 (CC, Ar), 1075, 1014, 823 (1,4-
disubst. Ar), 773, 706 (monosubst. Ar); δH (400 MHz; CDCl3;
Me4Si) 3.04 (s, 3H, OCH3), 7.23–7.34 (m, 12H, Ar–H), 7.40 (d,
3JHH = 8.8 Hz, 2H, Ar–H); δC (100 MHz; CDCl3; Me4Si) 52.1
(OCH3), 86.7 (C–OCH3), 121.0 (C–Br), 127.2–130.2, 130.9,
143.2, 143.6 (Ar–C); m/z: 352 [M–H]+, 352, 321, 273, 239, 197,
165, 105 (100%), 77.
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Fig. 11 2D-fingerprint plots for the six molecules 2 in the asymmetric unit of 2B.
IJ4-Bromophenyl)diphenylmethanamine (4). To a solution
of 1 (3.6 g, 10 mmol) in dry dichloromethane (50 ml) was
added freshly destilled thionyl chloride (4 ml, 55 mmol). The
mixture was stirred for 8 h at room temperature. The excess
thionyl chloride and the solvent were removed under vac-
uum. The residue was dissolved in dichloromethane (50 ml)
and to the solution was added conc. aqueous ammonia (100
ml) at 0 °C. The mixture was stirred for 48 h at room
temperature and then extracted with dichloromethane. The
combined organic phases were washed with water, dried
IJNa2SO4) and evaporated. Purification of the crude product
by column chromatography on silica gel using
dichloromethane as eluent yielded 2.8 g (83%) colorless crys-
talline solid. M.p. 79 °C. Found: C, 67.37; H, 4.73; N, 4.10;
C20H17NBr requires C, 67.47; H, 4.77; N, 4.14%; νmax (KBr
cm−1) 3357, 3294 (NH2), 3088, 3050, 3018 (CAr–H), 1603
(NH2), 1581, 1492, 1445 (CC, Ar), 1074, 1030, 1008, 821
(1,4-disubst. Ar), 767, 704 (monosubst. Ar); δH (400 MHz;
CDCl3; Me4Si) 2.30 (s, br, 2H, NH2), 7.15–7.29 (m, 12H, Ar–
3
H), 7.40 (d, JHH = 8.8 Hz, 2H, Ar–H); δC (100 MHz; CDCl3;
Me4Si) 66.0 (C–NH2), 120.7 (C–Br), 126.8–130.0, 130.9, 147.6,
148.1 (Ar–C); m/z: 337 [M–H]+, 260, 182 (100%), 104, 77, 51.
X-ray structure determination
The intensity data of 1–4 were collected on a Kappa APEX II
diffractometer (Bruker AXS) with MoKα radiation (λ = 0.71073
Å). Reflections were corrected for background, Lorentz and
polarisation effects. Preliminary structure models were
derived by application of direct methods40 and were refined
by full-matrix least-squares calculation based on F2 for all
reflections.41 With the exception of the hydroxy hydrogens in
1 and 2C as well as the amino hydrogens in 4, all other
hydrogen atoms were included in the models in calculated
positions and were refined as constrained to bonding atoms.
Crystallographic data for the structures in this paper have
Fig. 12 2D-fingerprint plot for the molecule in the structure of 3.
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Fig. 13 2D-fingerprint plots for the molecules 1 and 2 in the asymmetric unit of compound 4.
been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication numbers CCDC
1062479 (1), 1062483 (2B), 1062482 (2C), 1062481 (3) and
1062480 (4).
13 G. A. Jeffrey, An Introduction to Hydrogen Bonding, Wiley,
Chichester, 1997.
14 M. Canle, L. W. Clegg, I. Demirtas, M. R. J. Elsegood and H.
Maskill, J. Chem. Soc., Perkin Trans. 2, 2000, 85.
15 C. Glidewell and G. Ferguson, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 1994, 50, 924.
16 F. H. Allen and O. Kennard, J. Mol. Graphics, 1993, 8, 31.
17 M. A. Spackman and J. J. McKinnon, CrystEngComm,
2002, 4, 378.
18 Organic Crystal Engineering, ed. R. T. Tiekink, J. J. Vittal and
M. Zaworotko, Wiley, Chichester, 2010.
Acknowledgements
We thank Prof. L. R. Nassimbeni and Dr. E. Batisai (University
of Cape Town) for performing the Hirshfeld surface analyses
and their help with discussion of the results.
19 C. B. Aakeröy, N. R. Champness and C. Janiak,
CrystEngComm, 2010, 12, 22.
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