Helical structures of tribenzylamine supramolecular complexes with [CoCl4]2-/[CuCl4]2-, and conformational comparisons of tribenzylamine in different supramolecular complexes

Article abstract of DOI:10.1007/s10870-013-0445-7

The compound tribenzylamine (TBA) and its derivatives are a type of classical tripodal ligands in building up diversity of supramolecular arrays or networks. In the present contribution, we described two new supramolecular complexes 2[C₂₁H₂₂N⁺]·[CoCl ₄]^2-·(1) and 2[C₂₁H₂₂N ⁺]·[CuCl₄]^2- (2) by reacting protonated TBA with CoCl₂·6H₂O/CuCl₂·2H ₂O. Different from previous TBA supramolecular complexes, these two supramolecular complexes were easier to obtain by grinding protonated TBA and CoCl₂·6H₂O/CuCl₂·2H₂O in an agate mortar than using conventional solution method. The two supramolecular complexes form fascinating 3D helical architectures, with two types of interwoven helical chains involved inside the structures. A comparison of the geometries of TBA in these two supramolecular complexes with the previously reported TBA supramolecular complexes shows that the significant differences are due to the conformation of the three arms of phenyl rings around the N center.

Full text of DOI:10.1007/s10870-013-0445-7

J Chem Crystallogr (2013) 43:471–477
DOI 10.1007/s10870-013-0445-7
ORIGINAL PAPER
Helical Structures of Tribenzylamine Supramolecular Complexes
with [CoCl4]22/[CuCl4]22, and Conformational Comparisons
of Tribenzylamine in Different Supramolecular Complexes
•
Hong-yu Guan Hui-de Shao Lei Li
•
•
•
Jian-ming Jia Fang Guo
Received: 6 December 2012 / Accepted: 10 July 2013 / Published online: 26 July 2013
Ó Springer Science+Business Media New York 2013
Abstract The compound tribenzylamine (TBA) and its
derivatives are a type of classical tripodal ligands in
building up diversity of supramolecular arrays or networks.
In the present contribution, we described two new supra-
molecular complexes 2[C21H22N?]Á[CoCl4]2-Á(1) and
2[C21H22N?]Á[CuCl4]2- (2) by reacting protonated TBA
with CoCl2Á6H2O/CuCl2Á2H2O. Different from previous
TBA supramolecular complexes, these two supramolecular
complexes were easier to obtain by grinding protonated
TBA and CoCl2Á6H2O/CuCl2Á2H2O in an agate mortar than
using conventional solution method. The two supramo-
lecular complexes form fascinating 3D helical architec-
tures, with two types of interwoven helical chains involved
inside the structures. A comparison of the geometries of
TBA in these two supramolecular complexes with the
previously reported TBA supramolecular complexes shows
that the significant differences are due to the conformation
of the three arms of phenyl rings around the N center.
tribenzylamine [8] (TBA) and its derivatives, [9–15] have
attracted much attention in building up diversity of supra-
molecular arrays or networks. The compound TBA,
N(CH2C6H5)3, is an aliphatic tertiary amine with bulky
substituents, which may exhibit various kinds of confor-
mations, since the molecule has six intramolecular rotation
axes. Therefore, taking into account such conformational
flexibility, the supramolecular diversity and complexity of
H-bonding networks can be further developed by changing
the length and flexibility of the three arms of TBA, which
could influence the structural and functional properties.
By searching CSD [16], a series of supramolecular com-
plexes of TBA have been reported, including TBA supra-
molecular complex with carbon tetrabromide solvate
C21H21NÁCBr4 [17], TBA supramolecular complex by react-
ing melted TBA with cluster molybdenum dichloride
3(C21H22N?)ÁCl13Mo6O3 [18] and TBA supramolecular
-
complex with (l3-oxo)-heptakis(l3-chloro)-hexachloro-
hexa-molybdenum C21H22N?ÁC10HO12Os3S- [19]. In addi-
tion, TBA supramolecular complexes with tetrachlorometal-
lates or hexachlorometallates have also been reported, such as
Keywords Tripodal ligand Á Tribenzylamine Á
[CoCl4]2-/[CuCl4]2- Á Helices Á Conformation
2(C21H22N?)Á[AuCl4]2-ÁCl-, [20] 3 (C21H22N?) [PtCl6]2-
.
Cl- [21]. We also reacted TBA with hexachlorotellurate/
hexachlorostannate/hexachlororhennate to successfully pro-
duce supramolecular complexes, [2(C21H22N?)Á[TeCl6]2-
and [SnCl6]2-/[ReCl6]2-] [22]. TBA can also form supra-
molecular complex with tetrachloro-cooper (II)(C21H22N?Á
C14H16N?Á[CuCl4]2-), however the dibenzylammonium was
also included in the supramolecular complex [23]. In this
article, we have successfully obtained two novel supramo-
lecular complexes with [CoCl4]2- and [CuCl4]2-, producing
2[C21H22N?]Á[CoCl4]2- and 2[C21H22N?]Á[CuCl4]2- (1 and
2). These two complexes are isostructural and crystallized in
orthorhombic system, which are different from the previous
reported TBA supramolecular complexes. It is worth
Introduction
Tripodal ligands are of particular research interest owing to
their assembling capacity into the construction of well-
defined metal coordination complexes and the potential
properties in photoluminescence, magnetism, electronics
and catalysis etc [1–7]. Thus, tripodal ligands such as
H. Guan Á H. Shao Á L. Li Á J. Jia Á F. Guo (&)
College of Chemistry, Liaoning University,
Shenyang 110036, China
e-mail: fguo@lnu.edu.cn
123

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J Chem Crystallogr (2013) 43:471–477
addressing that the two supramolecular complexes were ren-
dered difficult using conventional solution method, instead,
they can be easily obtained by grinding protonated TBA and
CoCl2Á6H2O/CuCl2Á2H2O in an agate mortar with a very
small amount of ethanol to aid the process. A comparison of
the geometries of TBA in these two supramolecular com-
plexes with the previously reported TBA supramolecular
complexes [17–23] shows that the significant differences are
due to the conformation of the three arms of phenyl rings
around the N center.
After the crystals were separated out by filtration, recrys-
tallization with anhydrous ethanol gave rise to blue and
transparent block crystals 1. mp 157–159 °C. IR (KBr),
k
max/cm-1 3,010 (w, ArH), 2,955 (s, CH2), 1,637, 1,498,
1,457 (s, Ar), 2,780, 2,725, 2,609 (w, N?H). 1H NMR
(DMSO, 300 MHz) d 4.17(12H, s, CH2), 7.41–7.48 (30H,
m, ArH), 10.80 (2H, s, N?H).
Preparation of Supramolecular Complex
of [2HÁ2TBA]2?Á[CuCl4]2- (Crystal 2)
0.56 g TBA, 25 mL ethanol and 0.51 g CuCl2Á2H2O were
placed in a 50 mL Erlenmeyer flask, then 1 mL concen-
trated hydrochloric acid was added and the mixture was
shaken until the contents were dissolved. The flask was
allowed to stand for about 6–7 days at room temperature.
After the crystals were separated out by filtration, recrys-
tallization with anhydrous ethanol gave yellow and trans-
parent block crystals 2. mp 134.3–136.5 °C. IR (KBr),
Experimental
Materials
All starting materials were commercially available, reagent
grade, and used without further purification. IR spectra
were obtained with a PerkinElmer 100 FT-IR spectrometer
1
using KBr pellets. H-NMR spectra were recorded on a
k
max/cm-1 3,003 (w, ArH), 2,947 (s, CH2), 1,629, 1,495,
Mercury-Plus 300 spectrometer (VARIAN, 300 MHz) at
1,454(s, Ar), 2,782, 2,721, 2,604 (w, N?H). 1H NMR
(DMSO, 300 MHz) d 4.27(12H, s, CH2), 7.45–7.21 (30H,
m, ArH), 11.24 (2H, s, N?H).
25 °C with TMS as internal reference.
Preparation of Ligand TBA and its Hydrochloride
Crystal [TBAÁH]?Cl-
Crystallography
19 mL dibenzylamine was slowly added to a solution of
17.32 g NaHCO3 and 20 mL distilled water. 16.5 ml
benzyl chloride then continuously added into the above
mixture solution. After the reaction was heated to 90 °C
and stirred for 8 h, the mixture was cooled to room tem-
perature. The reaction product was filtered out, and then
washed with distilled water for three times. Recrystalliza-
tion using anhydrous ethanol and drying in vacuo produced
white crystals of TBA 30.74 g, yield 53.55 %. mp
92–93 °C. IR (KBr), kmax/cm-1 3,083, 3,062, 3,026 (w,
ArH), 1,602, 1,584, 1,493, 1,452 (s, Ar), 2,923, 2,880 (s,
Single-crystal X-ray diffraction measurements of com-
plexes were carried out on a Bruker Smart CCD diffrac-
tometer equipped with a graphite monochromator. The
determination of unit cell parameters and data collection
˚
were performed with Mo Ka radiation (k = 0.71073 A).
The unit cell parameters were obtained with least-squares
refinements and the structures were determined using direct
methods and refined (based on F2 using all independent
data) by full-matrix least-square methods (SHELXTL 97)
[24, 25]. The details of data collection, data reduction, and
crystallographic data are summarized in Table 1, and
CCDC 913624–913625 contain the supplementary crys-
tallographic data for crystal 1 and 2 in this paper. CCDC
720917 contains the supplementary crystallographic data
for the crystal of TBA hydrochloride [TBAÁH]?Cl-.
Powder X-ray diffraction data were recorded at ambient
temperature in transmission mode on a Siemens D5000
diffractometer, using Ge monochromated CuKa radiation
1
CH2). H NMR (CDCl3, 300 MHz): d 3.55 (6H, s, CH2),
2.46 (4H, s, CH2), 7.22–7.42 (15H, m, ArH). 0.001 mol
TBA product, 1 mL concentrated hydrochloric acid and
25 mL ethanol were mixed and dissolved in 50 mL
Erlenmeyer flask. The flask was allowed to stand for
overnight, giving rise to white and transparent hydrochlo-
ride crystals [TBAÁH]?Cl-.
˚
(k = 1.5406 A).
Preparation of Supramolecular Complex
of [2HÁ2TBA]2?Á[CoCl4]2- (Crystal 1)
Results and Discussion
0.72 g TBA, 25 mL ethanol and 0.81 g CoCl2Á6H2O were
placed in a 50 mL Erlenmeyer flask, then 1 mL concen-
trated hydrochloric acid was added and the mixture was
shaken until the contents were dissolved. The flask was
allowed to stand for about 10 days at room temperature.
Synthesis
The formation of two supramolecular complexes of
[2HÁ2TBA]2?Á[XCl4]2- (X = Co, Cu) was rendered
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J Chem Crystallogr (2013) 43:471–477
473
Table 1 Crystal data and refinement summary for crystal 1 and 2
Empirical formula
1
C42H44Cl4CoN2
2
C42H44Cl4Cu N2
Formula weight
777.52
782.13
Crystal dimensions
(mm)
0.26 9 0.20 9 0.12 0.26 9 0.20 9 0.12
Crystal temperature (K) 113(2)
113(2)
Orthorhombic
P212121
4
Crystal system
Space group
Z
Orthorhombic
P212121
4
˚
a (A)
10.403(2)
13.393(3)
28.013(6)
90
10.228(2)
13.275(3)
28.485(6)
90
˚
b (A)
˚
c (A)
Fig. 1 Comparison of PXRD patterns of supramolecular complex 1
from solution synthesis (1) and solid-state synthesis (2)
a (°)
b (°)
c (°)
90
90
90
90
3
˚
V (A )
3,902.8(14)
1.323
3,867.7(13)
1.343
two components of [C21H22N]ÁHCl and CuCl2Á2H2O in 2:1
Dx (Mg cm-3
)
molar ratio were ground in an agate mortar.
l (mm-1
F (000)
Rint
)
0.745
0.873
1,620
1,628
Crystal Structures of 1 and 2
0.0387
26,665
6,871
0.0352
28,575
6,813
No. of total reflns
X-ray crystallography reveals that both structures 1 and 2
are orthorhombic P212121, with a similar crystal lattice.
One asymmetric unit contains one dianion [CoCl4]2- (in 1)
or [CuCl4]2- (in 2) and two protonated independent mol-
ecules of TBA (Fig. 2). A detailed description will be
presented only for 1, as 2 is similar to 1 except for slight
variations in structural and thermal parameters which may
be ascertained from the Supplementary material.
No. of unique reflns
No. of data with I [ 2r 6,579
(I)
6,499
No. of parameters
varied
450
460
s
1.062
1.049
Rf/wRf
0.0284/0.0635
0.0300/0.0644
0.0271/0.0594
0.0292/0.0607
All data Rf/wRf
The Co atom in 1 has a highly distorted tetrahedral
coordination environment from Cl atoms, with the Co–Cl
˚
bond lengths in the range of 2.2611(8)–2.2947(7) A,
difficult using solution method. We have tried using dif-
ferent solvents (e.g. MeOH, EtOH, DMSO, THF, Acetone
et al.) to grow the crystals of supramolecular complexes,
thus far, the only one successful crystallization is obtained
by slow evaporation from the ethanol, but the outcome is
not readily reproducible. Instead, the mechanochemical
synthesis [26], where two or more solids react induced by
mechanical energy (i.e., external stimuli) such as manual
grinding or ball milling, can be readily applied into the
preparation of two supramolecular complexes of TBA
using liquid assisted grinding [27]. During the preparation
of supramolecular complex 1, two components of
[C21H22N]ÁHCl and CoCl2Á6H2O in 2:1 molar ratio were
ground in an agate mortar for 20 min with 10 lL anhy-
drous ethanol to aid the process. The comparison between
the X-ray powder diffraction measured on the ground
polycrystalline product and that calculated on the basis of
the structure determined by single crystal X-ray diffraction
is shown in Fig. 1. The same experimental operation was
carried out for the preparation of complexes 2, in which the
and Cl–Co–Cl bond angles in the range of
107.01(3)–114.48(3)°. The two independent TBA ligands
(labelled La and Lb) in one asymmetric unit arrange in a
different structural feature. The three benzyl groups are
more symmetric in one ligand (labelled La) than the other
ligand (labelled Lb) (Fig. 3), which can be identified by the
distances of centroids of three phenyl rings. In one ligand,
the distances are nearly equal with 6.139, 6.312 and
˚
6.397 A, respectively; while for the other ligand, one
benzyl ring is significantly tilted with respect to the other
benzyl group, with the distance between the centroid of
˚
two benzyl rings is shortened to 4.417 A, and the other two
distances between the centroids of benzyl rings are 5.336
˚
and 7.474 A, respectively.
The structure of 1 contains a fascinating 3D helical
architecture, consisting of two similar types of interwoven
helical chains illustrated in Fig. 4. In type I, one period of
the helix comprises four ligands and two [CoCl4]2- anions.
˚
The helix is ca. 28.0 A in pitch. The two independent
ligands are assembled into a dimer through C–HÁÁÁp
123

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J Chem Crystallogr (2013) 43:471–477
Fig. 2 Crystal structures of
supramolecular complex 1
(a) and 2 (b)
(a)
(b)
Fig. 3 The conformation
comparison of two TBA
molecules in one asymmetric
unit
interactions (C13phenyl–H13ÁÁÁCg (centroid of phenyl
in which two chloride atoms of [CoCl4]2- anions
acting as acceptors are hydrogen bonded to the
adjacent ligand dimers through N–HÁÁÁCl interactions
˚
ring [C30–C35] in the other ligand): 3.298 A, 129.2°).
The dimers are further connected with [CoCl4]2- anions,
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J Chem Crystallogr (2013) 43:471–477
475
˚
[N2–H2ÁÁÁCl2 3.244 A, 162.4°] and C–HÁÁÁCl interactions
nitrogen atoms in TBA. When the nitrogen atom is not
protonated, the distances between centroid of the three
˚
benzene rings are nearly equilateral, for example, 6.280 A/
˚
[C11–H11ÁÁÁCl1 3.620 A, 147.0°], as seen in Fig. 4a.
The grooves of the helices are mutually occupied by
type II of helices. The ligand dimer formed by above C–
HÁÁÁp interactions is also connected with [CoCl4]2- anions
through the other N–HÁÁÁCl hydrogen bonding [N1–
˚
6.334 A/6.377 A in TBA (Fig. 5I); 6.143 A/6.296 A/
˚
˚
˚
˚
6.302 A in the supramolecular complex of TBAÁCBr4
˚
˚
˚
(Fig. 5II), and 6.140 A/6.234 A/6.634 A in the supramo-
lecular complex with (l3-oxo)-heptakis(l3-chloro)-hexa-
chloro-hexa-molybdenum (Fig. 5III). After the nitrogen
atom is protonated and form supramolecular complex
TBAH?Cl- (IV), the three distances between the centroid
of the benzene rings become completely equilateral with
˚
H1ÁÁÁCl1 3.241(1) A, 166.3(1)°] and C–HÁÁÁCl interaction
˚
[C36–H36ÁÁÁCl2 3.669 A, 145.9°], constructing one period
of the helix. The periods are further linked into the helical
chain along c axis through C–HÁÁÁp interactions between
C20 of phenyl ring [C16–C21] and centroid (Cg) of phenyl
˚
˚
6.587 A. This change can be ascribed to the protonated N
ring [C23–C28] (C20–H20ÁÁÁCg 3.370 A, 135.3°), as seen
in Fig. 4b.
atoms and its hydrogen bonding with chloride anions, in
which the chloride anions as acceptor, are hydrogen
Two types of infinite double helices as well as their
interlocking are shown in Fig. 4c.
˚
bonding with the protonated N atom (N–HÁÁÁCl 3.012 A,
˚
180°) and three methylene groups (3.581 A, 144.9°)
simultaneously.
Comparison of Conformation of TBA
However, in the supramolecular complex of TBA with
chlorometallates, it is noticed that one benzene ring is
significantly tilted with respect to the other benzene ring,
thus leading to the shortening of the distance between two
We have concerned with the question about to what extent
the conformation of TBA in different compounds is
changed from that of pure phase of TBA obtained previ-
ously. Bearing this question in mind, we have searched the
crystal structures containing TBA component from CSD
database [28]. For the convenience of comparison, we have
labeled the crystal structures as I (RefCode: TBENZA),
II (RefCode: RERCIB), III (RefCode: GINFEO),
IV(CCDC number: 720917), V (Refcode: YURQAE), VI
(RefCode: YURQEI), VII (RefCode: HATROJ), VIII
(RefCode: RERCIB TIPBUQ), IX (RefCode: DUMGIC),
respectively.
˚
˚
˚
benzene rings, for example, 3.983 A/5.893 A/7.541 A in
the supramolecular complex of [TBA]H?Á0.5[SnCl6]2-
?
2-
˚
˚
˚
(V), 4.030 A/5.868 A/7.548 A in [TBA]H Á0.5[ReCl6]
(VI). A similar case occurs in the cocrystal of TBA.
DibenzylamineÁ[CuCl4]2- (VII), the distances are 3.851 A/
˚
˚
˚
5.964 A/7.537 A respectively. When two or more TBA
ligands are involved in one asymmetric unit, it is found
that the significant change only occurs in one ligand,
for example, in the supramolecular complex of
˚ ˚ ˚
We have noticed that the conformation of TBA has
exhibited great difference due to the protonation of
3[TBAH?][PtCl6]2-Cl-(VIII), 3.915 A/6.017 A/7.556 A
˚
for one ligand, 6.519 A/6.557 A/6.666 A and 6.350 A/
˚
˚
˚
Fig. 4 a Type I of helices,
b Type II of helices, c Two
types of infinite double helices
as well as their interlocking
along c axis
123

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J Chem Crystallogr (2013) 43:471–477
Fig. 5 Conformational comparison of TBA in the reported TBA supramolecular complexes
Table 2 The dihedral angles between benzene rings and the plane formed by three methylene carbon atoms in TBA supramolecular complexes
I
II
III
IV
V
VI
VII
VIII
IX
Benzene ring 1
Benzene ring 2
Benzene ring 3
72
87
90
79.6
81.1
79.5
83.4
85.4
72.1
71.9
71.9
71.9
79.1
82.1
71.0
73.1
82.8
79.4
73.2
79.3
81.3
89.4
71.3
85.6
70.4
61.3
80.5
62.2
87.7
89.1
49.3
63.9
75.0
68.7
60.0
81.1
˚
˚
6.466 A/6.734 A for the other two ligands, respectively. In
the supramolecular complex of 2[TBAH?][AuCl4]2-(IX),
Conclusions
˚
˚
˚
˚
5.182 A/6.656 A/7.049 A for one ligand, and 6.422 A/
In the present contribution, we described two new supra-
molecular complexes 2[C21H22N?]Á[CoCl4]2- (1) and
2[C21H22N?]Á[CuCl4]2- (2) by reacting protonated TBA
with CoCl2Á6H2O/CuCl2Á2H2O. Different from previous
TBA supramolecular complexes, these two supramolecular
complexes were easier to obtain by grinding protonated
TBA and CoCl2Á6H2O/CuCl2Á2H2O in an agate mortar than
using conventional solution method. The two supramolec-
ular complexes form fascinating 3D helical architectures,
˚
˚
6.483 A/6.731 A for the other ligand. The change of con-
formation of TBA are to a large extent attributed to the
direct hydrogen bonding N–HÁÁÁCl interactions between N
atoms of TBA and chlorometallates.
In addition, by projecting the molecule on the plane
formed by three methylene carbon atoms, the dihedral
angles between this plane and benzene rings also exhibit
great difference, as listed in Table 2.
123

J Chem Crystallogr (2013) 43:471–477
477
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Excellent Talents in University (No. LJQ 2011003) and Foundation of
211 Project for Innovative Talents Training, Liaoning University.
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