Formation of novel Olefin-Copper(I) coordination compound dependent on conformation of Olefin ligand

Article abstract of DOI:10.1016/j.inoche.2011.01.033

Solvothermal treatments of (E)-1,3-diallyl-2-styryl-3 H -benzo[d]imidazol-1-ium bromide olefin ligand 1 and CuX (Br, 2 and XCl, 3) in the presence of methanol as solvent at 75 °C for 1 week offer organic-inorganic hybrid compound 2 and olefin-copper(I) co

Full text of DOI:10.1016/j.inoche.2011.01.033

Inorganic Chemistry Communications 14 (2011) 626–631
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Formation of novel Olefin–Copper(I) coordination compound dependent on
conformation of Olefin ligand
⁎
Wei Wang, Li Zhang, Xiong-Bin Xu, Qiong Ye
Ordered Matter Science Research Center, Southeast University, Nanjing 211189, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Solvothermal treatments of (E)-1,3-diallyl-2-styryl-3 H -benzo[d]imidazol-1-ium bromide olefin ligand 1 and
CuX (X Br, 2 and X Cl, 3) in the presence of methanol as solvent at 75 °C for 1 week offer organic–inorganic
hybrid compound 2 and olefin–copper(I) compound 3. The conformation of olefin cation ligand affects the
coordination of allyl group. Two allyl groups existing at different sides of benzoimidazole plane successfully
coordinate to copper(I) centers to form olefin–copper(I) coordination compound 3, which shows two-
dimensional structure of (4,4) network with [Cu6Cl4Br4]2− cluster nods. The dielectric measurement results
show there is no dielectric anomaly observed within the temperature range of 120 K to 300 K for compound 3.
© 2011 Elsevier B.V. All rights reserved.
Received 22 October 2010
Accepted 25 January 2011
Available online 21 March 2011
Keywords:
Solvothermal
Olefin–copper(I)
Cluster
Dielectric
Ligand conformation
It has been one century since the discovery of the first unstable
olefin–copper(I) coordination compound [1], while it is just several
decades after Thompson reported the first stable olefin–copper(I)
coordination compound [2]. However, in recent decades, much
attention has been attracted to molecular architecture and self-
assembly of coordination polymers in coordination and organome-
tallics chemistry. Copper(I) as the transition metal has played a
central role in the construction of supramolecular arrays supporting
by a variety of organic ligands. Also some interesting physical
properties such as fluorescence, ferroelectric, dielectric, second
harmonic generation of these copper(I) coordination compounds
have been investigated [3,4]. As a part of these works, olefin–copper
(I) coordination compounds are known to play an important role in
biochemistry and modern organic chemistry, where they are
employed as active species in copper catalysis [5]. Generally,
significant progress has been made over the past years in the area
of highly stable Cu(I)–olefin coordination oligomers and polymers [6].
Simple copper(I) ions and olefin ligands have been demonstrated to
be useful in the construction of intriguing coordination polymeric
architectures, which is dependent on Cu/X ratios, counterions,
additional organic ligands, as well as other reaction and crystallization
conditions. It may be expected that novel organometallic materials
and interesting molecular architectures with new topologies can be
achieved through a controllable solid-state design using the olefin–Cu
(I) or other metal–ligand systems. As a continuing work of physical
property investigations and syntheses of olefin–copper(I) coordina-
tion compounds under solvothermal conditions, herein we report the
formation and dielectric property of novel olefin–copper(I) organo-
metallic compound with flexible olefin ligand, where the conforma-
tion of flexible ligand is the key point for the formation of olefin–
copper(I) organometallic compound.
Olefin ligand, (E)-1,3-diallyl-2-styryl-3 H-benzo[d]imidazol-1-ium
bromide, can be obtained in high yield by three-steps of organic
reactions (Scheme 1 and Supporting information). Single crystal X-ray
diffraction is used to check the conformation of novel olefin ligand
product. (E)-1,3-diallyl-2-styryl-3 H-benzo[d]imidazol-1-ium bromide
crystallized in a chiral space group P212121 with cell data a=7.6019(8)Å,
b=11.7832(13)Å, c=20.594(2)Å and α=β=γ=90° owing to the
twisty structure of cation (E)-1,3-diallyl-2-styryl-3 H-benzo[d]imidazol-
1-ium. The details of X-ray data collection and refinement as well as
selected bond distance, angles and torsion angles have been listed in
Tables S1 and S2. As shown in Fig. 1, one (E)-1,3-diallyl-2-styryl-
3 H-benzo[d]imidazol-1-ium cation and one bromide anion are the
crystallographically independent units of compound 1. The atoms of
benzoimidazole ring (C17, C18, C12, C14, C16, C13, N2, C11, and N1) are
almost in one plane with a little deviation, while atoms of styryl group
(C3, C4, C6, C8, C20, C21, C19 and C45) are deposited on the same plane.
It needs to be noted that the olefin conformation is E or that the
benzoimidazole and benzene rings exist at different sides of the olefin
bond. The dihedral angle between the benzoimidazole and benzene
rings is 5.2°. That is, the two rings are almost sharing one plane. Two allyl
groups of one cation exist at the same side of benzoimidazole ring plane
and look like arms to hug the neighboring cation molecule.
Fig. 2 shows the packing structure of compound 1. The left part of
Fig. 2 shows the cation arrangement of olefin ligand 1 on ac plane.
Strong π–π interactions with a Cg(benzoimidazole)―Cg(benzene)
⁎
Corresponding author. Fax: +86 25 52090626.
E-mail address: yeqiong@seu.edu.cn (Q. Ye).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.01.033

W. Wang et al. / Inorganic Chemistry Communications 14 (2011) 626–631
627
H
N
H
N
NH2
NH2
CH3COOH
Benzaldehyde
N
N
N
Br
1
NaH, THF, 60oC
N+
Br-
Scheme 1. The synthesis of olefin ligand 1.
distance of 3.504 Å can be easily found between neighboring benzene
and benzoimidazole rings separately from different cation molecules,
which lead to the formation of cation columns along a axis. While
neighboring cation columns show contrary orientations (left part of
Fig. 2). As shown in the right part of Fig. 2, bromide anion and (E)-1,3-
diallyl-2-styryl-3 H-benzo[d]imidazol-1-ium cation columns extend
along a direction to stack in a three-dimensional place. One bromide
anion column is surrounded by four cation columns to balance the
charge in the whole system. There is almost no classic hydrogen
bonding interaction found in compound 1. Intermolecular non-classic
H-bonds are formed between allyl groups and N atoms from the
benzoimidazole ring to fix the conformation of allyl groups. Also the
Br atom has H-bond contact with neighboring carbon atoms from
cation to result in the 3D structure formation.
The novel olefin ligand 1 is used as a building block to construct
olefin–copper(I) organometallic compounds by solvothermal treat-
ment of (E)-1,3-diallyl-2-styryl-3 H -benzo[d]imidazol-1-ium bro-
mide and CuX (X Br, 2 and X Cl, 3) in the presence of methanol as a
solvent at 75 °C for 1 week (Scheme 2). The organic–inorganic hybrid
compounds 2 and 3, which are stable at ambient environment, have
been certified or characterized by element analysis, IR and X-ray
diffractions. The X-ray crystal structure analysis revealed that 2
belongs to the monoclinic space group P21/n and is a novel organic–
inorganic hybrid compound with complicated one-dimensional
[Cu2Br3]− anion polymer chain. Unfortunately, three double bonds
of cation failed to coordinate to the copper(I) center. The crystallo-
graphically independent structure of compound 2 involves three
copper(I) atoms, two bridging bromide atoms and one olefin cation
ligand. Fig. 3 shows the asymmetric structure of compound 2, where
the coordination geometries of two crystallographically independent
copper(I) centers can be described as a distorted tetrahedron.
Although the coordination geometry of copper(I) center is fulfilled
by the same bromide anion, the ideal tetrahedral coordination
geometry fail to form owing to the copper(I)―copper(I) contact
between neighboring copper(I) centers as shown in Fig. 3 and Table
S2 (Cu1―Cu2, 2.473 Å; Cu1―Cu1, 2.635 Å; Cu2―Cu2, 2.794 Å). Fig. 4
shows the one-dimensional chain structure of [Cu2Br3]− anion
polymer in the organic–inorganic hybrid compound 2, where three
crystallographically independent bridging bromide anions coexist.
Br1 as a μ2 bridging ligand that links Cu1 and Cu2; Br2 coordinates to
two Cu1 and one Cu2 metal centers; while Br3 also acts as a μ3
bridging ligand to connect two neighboring Cu2 and one Cu1 atoms.
That is, the coordination geometry of Cu1 is fulfilled by two Br2, one
Br1 and one Br3; Cu2 coordinates to two Br3, one Br1 and one Br3;
tetrahedral polyhedrons of neighboring copper(I) centers connect
together by sharing one edge to result in the formation of a [Cu2Br3]−
anion polymer chain. For the olefin cation ligand part, benzoimidazole
and benzene rings exist at different sides of the olefin bond and form
the dihedral angle of 6.5°. While two allyl groups of one cation orient
at the same side of benzoimidazole ring plane owing to H-bond
interactions among carbon atoms of double bonds and nitrogen atoms
of benzoimidazole ring(C2―H2A―N2 and C1―H1B―N1). Similar
packing structure as that of compound 1 has been found in compound
2, where the [Cu2Br3]− anion polymer chain extends along a direction
and is surrounded by four olefin cation columns as shown in Fig. 5. The
formation of an olefin cation column can be attributed to π–π stack
(3.589 Å) between benzoimidazole and phenyl rings from neighbor-
ing olefin ligands.
Different from organic–inorganic hybrid compound 2, the solvother-
mal reaction between olefin ligand 1 and CuCl offers an olefin–copper(I)
organometallic compound 3. The X-ray single crystal diffraction
discloses that double bonds of two allyl groups from the same olefin
ligand participate in the coordination to copper(I) centers as shown in
Fig. 6, although double bond connecting benzoimidazole and phenyl
rings fails to coordinate to metal center owing to steric hindrances from
neighboring moieties. The allyl groups of cation and bromide anions
from olefin ligand as well as chloride anions of copper(I) salt act as
bridging ligands to coordinate to copper(I) centers. The crystallograph-
ically independent units involve two chloride, two bromide, three
copper(I) atoms and one olefin cation ligand. [Cu6Cl4Br4]2− copper(I)
cluster is formed owing to the bridging coordination of Cl and Br atoms,
where all Br atoms coordinate to two metal centers (Cu1 and Cu2). Two
Cl atoms act as bidentate ligands to connect Cu1 and Cu3, while others
are tridentate ligands to coordinate to one Cu1 and two Cu3 atoms. As
shown in Fig. 6, the coordination geometry of the Cu1 center can be
described as a slightly distorted tetrahedron, which is fulfilled by two Cl,
one Br atom and one double bond of an allyl group from olefin cation
ligand. Cu2 coordinates to two Br atoms and one double bond of an allyl
group from an olefin cation ligand to form trigonal coordination
environment, while Cu3 is surrounded by one Br and three Cl atoms. On
the other hand, each olefin cation ligand connects neighboring [Cu6Cl4-
Br4]2− copper(I) clusters by two double bonds of allyl groups to result in
the formation of a two-dimensional structure. The conjunctional
systems involving benzoimidazole and phenyl rings just surround
Fig. 1. The molecular structure of olefin ligand 1, (E)-1,3-diallyl-2-styryl-3 H- benzo[d]
imidazol-1-ium bromide, where two allyl groups deposit at the same side of
benzoimidazole ring plane.

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W. Wang et al. / Inorganic Chemistry Communications 14 (2011) 626–631
Fig. 2. The cation arrangement of olefin ligand 1 on ac plane (left). The packing view of olefin ligand 1 along a axis (right).
N
CuBr, MeOH
75oC
N
Cu2Br3
2
N+
Br-
Br-
N+
n
N
CuCl, MeOH
75oC
N
Cu3Br2Cl2
3
N+
N+
n
Scheme 2. The syntheses of compounds 2 and 3.
[Cu6Cl4Br4]2− copper(I) cluster with non-classical hydrogen bonding
interactions between Cl atoms and carbon atoms from phenyl rings as
shown in Fig. 6. Owing to the coordination of two allyl groups and a
steric hindrance in the three-dimensional space, benzoimidazole and
phenyl rings from one olefin cation ligand are not deposited on the same
plane and show a dihedral angle of 36°, which is different from those
found in free olefin ligand 1 and organic–inorganic hybrid compound 2.
Also it needs to be noted that two allyl groups distribute at the different
sides of the benzoimidazole ring plane. That is, the conformation of the
olefin cation ligand in compound 3 is absolutely distinguished from
those found in compound 2, where double bonds of allyl groups fail to
coordinate to the copper(I) metal center. The conformation of the olefin
cation ligand maybe the key point of the olefin–copper(I) coordination
compound formation. Fig. 7 shows the two-dimensional structure of
olefin–copper(I) compound 3 on bc plane after olefin ligands have been
simplified as lines. In compound 3, olefin cation ligands act as didentate
bridging ligands to form a two-dimensional plane structure with (4, 4)
net, where [Cu6Cl4Br4]2− copper(I) clusters can be looked as nods. If we
simplify [Cu6Cl4Br4]2− nod as one ball as shown in Fig. 8, the two-
dimensional planes constructed by the olefin cation ligand and copper
(I) cluster arrange in a three-dimensional place with A–A–A sequence.
There are almost noH-bonds and π–π interactions between neighboring
two-dimensional planes found in olefin–copper compound 3.
Generally, the nature of the σ- and π-bonding components between
a olefin moiety and copper(I) atom has been reported to result in their
coordination not being very stable or labile, which has lead to the
resultant copper–π-complex being easily molecule-polarized by an
external electric field. One possible outcome of this is that a copper–π-
complex may display a larger molecular polarizability and thus also a
larger dielectric response than that of normal coordination compounds.
On the other hand, judging from the crystal structure of compound 1, it
is a condensed insulated compound involving a metal cluster and can be
Fig. 3. The asymmetric molecular structure of organic–inorganic hybrid compound 2,
where two allyl groups of cation orient on the same side of benzoimidazole ring plane
and fail to coordinate to copper(I) center.
Fig. 4. The one-dimensional [Cu2Br3]− polymer chain structure, where Br as bridging
ligand connects neighboring copper(I) centers to form a 1D chain.

W. Wang et al. / Inorganic Chemistry Communications 14 (2011) 626–631
629
Fig. 7. The two-dimensional structure of olefin–copper(I) compound 3 on bc plane,
where olefin ligands have been simplified as lines and act as didentate bridging ligand
to form a two-dimensional plane structure with (4, 4) net.
Where ε0 is the permittivity of a vacuum, ρ is the mass density
(kg·m−3), M is the molar mass (kg·mol−1), α is the polarizability of
the molecules, which is the proportionality constant between the
induced dipole moment and the field strength E, NA is the Avogadro
number, and εr is the dielectric permittivity. Seen from this equation,
larger mass density and polarizability of the compound correspond to
larger dielectric constant. Also, it makes us possible to calculate
polarizability of olefin–copper(I) compound 3, for ε0 and NA are
constant as well as ρ and M can be obtained from the crystal
structure. Fig. 10 shows the temperature dependence of polarization
of compound 1, which changes from 9.72E−40 to 1.01E−39 F·m−2
within the measurement temperature range.
In order to confirm the conformation of the olefin ligand in free
ligand 1, organic–inorganic hybrid compound 2 and olefin–copper(I)
organometallic compound 3, their UV–vis properties have been
investigated. As show in Fig. 11, strong absorptions have been found
in the range of 260 nm to 300 nm for compounds 1, 2 and 3, which
correspond to the absorption of large π conjunction system.
Moreover, the absorption peak wavelength of compound 3 is smaller
Fig. 5. The packing structure of organic–inorganic hybrid compound 2 along a direction.
used as dielectric materials. As a result, we investigate its dielectric
properties. Temperature-dependent dielectric measurement results are
shown in Fig. 9. The temperature-dependent dielectric was measured
from 120 K to 300 K. Seen from Fig.9, the temperature dependence of
the dielectric constant (real part, ε1) as estimated from the gradient at a
frequency of 1 M Hz indicates that dielectric constant ε1 are almost
temperature independent; it increases smoothly from 6.3 to 6.9 within
the measured temperature range, which could be attributed to the low
dielectric loss (ε2) behavior. The dielectric constant of compound 3
hasn't been observed in dielectric anomaly, suggesting that no sudden
polar change or phase transition occurs within the dielectric measure-
ment temperature range. Moreover, the Clausius–Mossotti equation
holds:
εr−1
εr + 2
ρNAα
3Mε0
=
:
Fig. 6. The asymmetric molecular structure of olefin–copper(I) compound 3, where two allyl groups of olefin ligand orient on the different sides of benzoimidazole ring plane.

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W. Wang et al. / Inorganic Chemistry Communications 14 (2011) 626–631
Fig. 8. The arrangement of two-dimensional olefin–copper(I) planes in a three-dimensional space for compound 3, where the ball represents the [Cu3Br2Cl2]− cluster and the line
represents the olefin ligand.
than those found in compounds 1 and 2, which means a worse
conjunction system exists in compound 3. Such UV–vis measurement
results just certified the ligand conformations in all three compounds.
As described in structure parts, although olefin ligands of all three
compounds show trans-conformation (benzoimidazole and phenyl rings
deposit at different side of olefin bond), the dihedral angles of
benzoimidazole and phenyl rings are distinguished from each other.
Benzoimidazole and phenyl rings are almost on the same plane for
compounds 1 and 2, while the dihedral angles of benzoimidazole and
phenyl rings in compound 3 are ~36°, which partly destroy the
conjunction system. Fig. 11 shows the luminescent spectra of compounds
1, 2 and 3 in the solid state at room temperature with a maximum
emission peak at ca. 470 (λex =363 nm), 570 nm (λex =363 nm) and
650 nm (λex =363 nm), respectively. The emission spectrum of com-
pounds 2 and 3 could be assigned to MLCT (metal-to-ligand charge
transfer) since the fluorescent emission of the free ligand 1 is observed at
about 470 nm. A clear bathochromic shift occurs in 3 relative to
compound 2, which is probably due to π-back-donation from the filled
metal dπ orbital to the vacant antibonding π* orbital of the coordinated
olefin [7].
10
9
8
7
6
5
permittivityε1
4
3
2
Loss
ε2/ε1
1
0
To sum up, we reported the syntheses and crystal structures of
olefin ligand (E)-1,3-diallyl-2-styryl-3 H-benzo[d]imidazol-1-ium 1,
its organic–inorganic hybrid compound 2 and olefin–copper(I)
organometallic compound 3. Interestingly, allyl groups of olefin
cation ligand easily coordinate to copper(I) centers when they orient
at different sides of the benzoimidazole ring plane. The conformation
-1
-2
120 140 160 180 200 220 240 260 280 300
Temperature (K)
Fig. 9. The temperature-dependent dielectric properties of compound 3 at 1 M Hz.
1.0
1
2
3
5
0.8
0.6
0.4
0.2
0.0
ligand
3
2
4
3
2
1
0
-1
450
500
550
600
650
700
750
250
300
350
400
Wavelength(nm)
wavelength(nm)
Fig. 10. The temperature dependence of polarization of compound 31 molecule, which
is calculated from the dielectric permittivity at 1 M Hz.
Fig. 11. The fluorescent emission spectra of compounds 1, 2 and 3 at the solid state.

W. Wang et al. / Inorganic Chemistry Communications 14 (2011) 626–631
631
of the olefin cation ligand affects the olefin–copper(I) organometallic
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no dielectric anomaly observed within the temperature range of 120 K
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