CHINESE OF CHEMICAL PHYSICS
VOLUME 27, NUMBER 3
JUNE 27, 2014
ARTICLE
Triangular Halogen Bond and Hydrogen Bond Supramolecular Complex
Consisting of Carbon Tetrabromide, Halide, and Solvent Molecule: A
Theoretical and Spectroscopic Study
Yu-jie Wu † , Xiao-ran Zhao, Hai-yue Gao, Wei-jun Jin ∗
College of Chemistry, Beijing Normal University, Beijing 100875, China
(Dated: Received on July 11, 2013; Accepted on May 4, 2014)
The theoretical calculation and spectroscopic experiments indicate a kind of triangular three bonding supramolecular complexes CBr4 · · · X− · · · H−C, which consist of carbon
tetrabromide, halide, and protic solvent molecule (referring to dichloromethane, chloroform and acetonitrile), can be formed in solution. The strength of halogen and hydrogen bonds in the triangular complexes using halide as common acceptor obeys the order
of iodide>bromide>chloride. The halogen and hydrogen bonds work weak-cooperatively.
Charge transfer bands of halogen bonding complexes between CBr4 and halide are observed
in UV-Vis absorption spectroscopy in three solvents, and then the stoichiometry of 1:1, formation constants K and molar extinction coefficients ε of the halogen bonding complexes
are obtained by Benesi-Hildebrand method. The K and ε show a dependence on the solvent
dielectric constant and, on the whole, obey an order of iodide>bromide>chloride in the same
solvents. Furthermore, the C−H vibrational frequencies of solvent molecules vary obviously
with the addition of halide, which indicates the C−H· · · X− interaction. The experimental
data indicate that the halogen bond and hydrogen bond coexist by sharing a common halide
acceptor as predicted by calculation.
Key words: Halogen bond, Hydrogen bond, Halide, Carbon tetrabromide, Charge transfer
bond donor and acceptor has prove to be an important
way for monitoring halogen bond [12−15].
Resnati et al. confirm that halogen bond is more competitive with hydrogen bond by experiments in some
cases [16]. Meanwhile, sometimes the halogen and hydrogen bonds are collaborative, e.g., they can coexist
in cocrystals, biological systems [16]. Zhou et al. report by calculation and survey of crystal data base
that a halogen-water-hydrogen bridge might exist in
some biological systems and be contributive to stabilize biomacromolecules or to improve the interaction
between biomacromolecules [17]. Li et al. show by calculation the XB and HB exhibit positive cooperativity,
i.e., the binding strengths of the halogen and hydrogen
bond are enhanced by each other’s presence, XB at one
site of a molecule can significantly enhance HB at another site [18]. The orthogonality in both energy and
direction between XB and HB is possible in protein systems, too, by sharing common acceptor, carbonyl C=O,
in which HB and XB act on the lone pair electrons of
oxygen and π electrons of carbonyl, respectively [19].
These results show that the investigation on relationship of XB and HB has really practical significance.
It has been demonstrated by our calculation that a
novel triangular bonding interaction pattern consisting of carbon tetrabromide, halide and protic solvent
molecule, as shown in Fig.1, CBr4 · · · X− · · · H−C for
simplification hereafter exists in gas phase [20]. In this
I. INTRODUCTION
Noncovalent interactions play an important role in
the fields of chemistry, biology and physics [1]. Hydrogen bond as one of the noncovalent interactions has
been widely investigated by experimental and theoretical methods [2, 3]. Halogen bond similar to hydrogen bond, a highly-directional noncovalent interaction
between a covalently-bonded halogen and a negatively
charged group (Lewis base, e.g, the lone pair electrons,
π electrons and anion, etc), has drawn much attention
recently [4]. It is described as electrostatic interaction
between the positive region, σ-hole (σh ), of halogen
atoms and negative species [5]. The covalently-bonded
halogen atoms can interact with both nucleophile and
electrophile due to the anisotropy of electron density
distribution on them and it has been confirmed by experiments [6−8]. In fact, halogen bond is a comprehensive result from electrostatic attraction, exchange
repulsion, induction, dispersion, etc. [9−11]. The absorption band of charge transfer (CT) between halogen
† Current
address: Chengdu Yulin High School, Chengdu 610041,
Sichuan, China
∗ Author to whom correspondence should be addressed. E-mail:
[email protected], Tel./FAX: +86-10-58802146
DOI:10.1063/1674-0068/27/03/265-273
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FIG. 1 Triangular bonding interaction pattern consisting of
carbon tetrabromide, halide and protic solvent molecule.
work, further investigation on the properties of the interaction pattern in solution has been completed. The
geometries and bonding energies of the triangular bonding complexes in solution are obtained by calculation
and spectroscopy. The results indicate the triangular
bonding complexes can also exist in solution.
II. COMPUTATIONAL AND EXPERIMENTS DETAILS
The full geometrical optimizations of the complexes and monomers in solution were performed at
MP2(full) [21] level with the basis set aug-cc-pVDZPP for iodine atom and aug-cc-pVDZ for all the
other atoms [22]. Calculations were performed via
the standard polarizable continuum model (PCM)
[23]. The total interaction energy was estimated as
the difference between the energy of the trimer and
the sum of total energies of the three monomers
∆Etotal =EABC −(EA +EB +EC ). The individual halogen bond or hydrogen bond interaction energy was approximately estimated as the difference between the
energy of the interactive pair with coordinates frozen
in the trimers and the sum of the energies of the two
monomers. The cooperative effects of the halogen bond
and hydrogen bond of these trimers complexes were assessed by computing a three-body non-additive energy
∆Ecoop =∆Etotal −(∆EXB +∆EHB +∆EHB0 ). The basis
set superposition error (BSSE) was eliminated by the
standard counterpoise method of Boys and Bernardi
[24]. All calculations were performed using Gaussian
03 program packages [25].
Dichloromethane (CH2 Cl2 ), chloroform (CHCl3 ),
and acetonitrile (CH3 CN) were purchased from Beijing
Chemical Reagent Co. with a purity of 99.5%. Carbon tetrabromide (CBr4 ), and tetra-n-butylammonium
chloride were obtained from TOKYO Chemical Industry Co., Ltd. with a purity of 98%. Tetra-nbutylammonium bromide and tetra-n-butylammonium
iodide were obtained from Alfa Aesar with a purity of
98%, all solvents were dried by calcined 3 Å molecular
sieve.
The absorption spectra of CBr4 · · · X− complexes
were measured by an UV-Vis spectrophotometer (GBC
Corporation of Australia), in 2 mm×10 mm quartz cells.
The background line was recorded over the desired spectral region by filling both reference and sample cells
with selected solvent. Then the absorption spectra of
CBr4 or the halide solution were recorded. Sequentially,
DOI:10.1063/1674-0068/27/03/265-273
Yu-jie Wu et al.
charge transfer spectra were recorded by gradual titration of halide anion into CBr4 solution.
Infrared spectra were recorded on a Nicolet 380 FTIR spectrophotometer (Nicolet, USA) using NaCl windows and precision of wavenumber ≤0.5 cm−1 , the resolution was less than 0.5 cm−1 . The concentration of
carbon tetrabromide and tetrabutylammonium halide
in stock solution was 0.5 and 1.0 mol/L, respectively.
The liquid film was prepared by dropping the stock solution on a NaCl window.
Cyclic voltammetry (CV) was performed on a
CHI660 electrochemical workstation (CH Instrument
Inc, USA) with iR compensation at the rate of 0.1 V/s
under nitrogen atmosphere. A platinum disk, platinum gauze and a saturated calomel electrode were used
as working electrode, counter electrode and reference
electrode, respectively. Working solutions consisted of
4 mmol/L alkylammonium halide and 0.1 mol/L supporting electrolyte (NBu4 + PF6 − ).
All experiments were carried out under dark conditions at room temperature. Carbon tetrabromide and
halide solutions must be freshly prepared before the experiment.
III. RESULTS AND DISCUSSION
A. Geometries parameters
The structures of the triangular bonding complexes
CBr4 · · · X− · · · H−C in solution are got through the
full optimization at MP2(full)/aug-cc-pVDZ(-PP) level
with the standard polarizable continuum model (PCM).
The structures of the complexes and key geometries parameters are shown in Fig.2. All optimum Br· · · X− ,
H· · · X− , H· · · Br distances are within the sum of van
der Waals radii of corresponding atoms, which reveals
the existence of the halogen bond and hydrogen bond.
The hydrogen atom of solvent molecule interacts with
both bromine atom of CBr4 and halide anion. The two
hydrogen bonds combine with the halogen bond to form
the triangular bonding systems (Fig.1).
As shown in Fig.2, the halogen bond lengths
Br· · · Cl− of CBr4 · · · Cl− · · · H−C, vary from 3.019 Å
to 3.106 Å (less than 3.600 Å, the sum of the
vdW radii of chlorine and bromine). The ranges
of Cl− · · · H and Br· · · H distances are 2.291−2.775
and 2.860−2.969 Å, respectively. The changes of
hydrogen bond length depend on the proton acidity of the solvent molecule in addition to the general
solvent effects. From the data in Fig.2, the halogen bond length decreases with the decrease of the
hydrogen bond in the trimers. The Br· · · Cl− distances change from 3.106 Å in CBr4 · · · Cl− · · · CH3 CN
to 3.066 Å in CBr4 · · · Cl− · · · CH2 Cl2 and 3.019 Å
in CBr4 · · · Cl− · · · CHCl3 , while the Cl− · · · H distances
change parallelly from 2.775 Å to 2.497 and 2.291 Å.
Generally speaking, the shorter the bond length is, the
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Triangular Halogen and Hydrogen Bond Supramolecular Complex
C-Br-Cl=170.5
C-Br-Cl=167.6
C-H-Cl=171.1
6
C-H'-Br'=142.7
2.497
.0
2.775
C-H-Br=118.1
3
3
.1
0
6
C-H-Br=102.5
6
C-H-Br=99.8
267
C-Br-Cl=175.1
C-H-Cl=169.6
C-H-Cl=165.1
3
.0
1
9
Chin. J. Chem. Phys., Vol. 27, No. 3
2.918
2.969
2.291
2.860
1
91
2.
...
4
-
Cl
...
CHCl
3
C-Br-Br=173.3
C-H-Br=163.0
9
4
C-H-Br=170.4
2.614
.1
C-H-Br=101.1
C-H'-Br'=144.8
C-H-Br=121.1
2.453
3
3
3
.2
3
9
C-H-Br=97.4
2.833
CBr
4
C-Br-Br=170.8
C-Br-Br=167.3
C-H-Br=164.6
-
CBr ...Cl ...CH2Cl 2
7
...CH CN
3
2
-
.1
...
CBr4 Cl
3.017
2.804
2.954
2.879
...
CBr4 Br ...CH CN
-
CBr ...Br ... CH2Cl2
C-Br-I=168.3
C-Br-I=171.5
...
4
Br
-
...
CHCl
3
C-Br-I=173.8
C-H-Br=101.3
2
2.649
2
C-H-I=158.5
2.784
.3
C-H-I=172.0
C-H-Br=121.8
3
6
1
3.030
3
.3
39
6
C-H-Br=98.4
3.
C-H-I=166.7
CBr
4
3
C-H'-Br'=146.3
2.809
2.968
3.018
2.855
... CBr4 I ...CH3CN
-
CBr ...I ... CH2Cl 2
4
CBr
...
4
I
-
...
CHCl
3
FIG. 2 Structures and key geometrical parameters of triangular bonding complexes optimized by MP2(full)/aug-cc-pVDZPP (bond length in Å and bond angle in (◦ )).
higher the bond strength is. That is, the halogen bond
in CBr4 · · · Cl− · · · H−C is reinforced by the enhanced
hydrogen bond strength. It indicates the cooperative
effects are present between halogen bond and hydrogen bond in the trimers CBr4 · · · Cl− · · · H−C in solution
based on the change of bond length.
The same trends are observed in CBr4 · · · Br− · · · H−C
and CBr4 · · · I− · · · H−C complexes. The Br· · · Br− distances vary from 3.127 Å to 3.239 Å (less than 3.700 Å,
the sum of the vdW radii of two bromine atoms).
The Br· · · I− distances vary from 3.322 Å to 3.396 Å
(less than 3.960 Å, the sum of the vdW of bromine
and iodine). All Br− · · · H, I− · · · H and Br· · · H distances in CBr4 · · · Br− · · · H−C and CBr4 · · · I− · · · H−C
complexes are also less than the sum of the vdW
radii of the corresponding atoms. The halogen bond
length of Br· · · Br− in CBr4 · · · Br− · · · H−C and Br· · · I−
in CBr4 · · · I− · · · H−C becomes parallelly shorter as
the decrease of the hydrogen bond lengths.
So,
the halogen bond and hydrogen bond in the trimers
CBr4 · · · Br− · · · H−C and CBr4 · · · I− · · · H−C also show
cooperativity.
The halogen bond angles in the trimers range from
167.3◦ to 175.1◦ . The ranges of the hydrogen bond anDOI:10.1063/1674-0068/27/03/265-273
gles of H−C· · · X− and H−C· · · Br are 158.5◦ −172.0◦
and 97.4◦ −121.8◦ . It can be seen that the angles of
hydrogen bond deviate more remarkably from 180◦ because of semi-global positive electrostatic potential of
hydrogen atom. Additionally, the mutual effect of halogen bond and hydrogen bond in the triangular bonding
complexes is another factor making the corresponding
angles deviated from linearity.
The halogen bond length and hydrogen bond length
in solution are longer than those in gas phase [20].
The Br· · · Cl− bond elongates by 0.367 Å in CH3 CN,
0.302 Å in CH2 Cl2 and 0.208 Å in CHCl3 , respectively. The elongating amplitudes of the Br· · · Br− and
Br· · · I− bonds are 0.177−0.356 Å and 0.195−0.345 Å.
The hydrogen bond lengths are also elongated in solution though the variations are not so notable. The
general solvent effects should result in the relaxation of
the molecular structures. So the polarity of the solvents
has a pronounced effect on the halogen bond distances.
The varying amplitude of the distances is smaller in the
solvents with lower polarity. The same conclusion was
drawn in C2 F3 I· · · X− and C6 F5 I· · · X− reported by Lu
et al. [26].
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Yu-jie Wu et al.
TABLE I Corrected total interaction energies, halogen bonding and hydrogen bonding energies, and cooperative energies
of the trimers in solution (in kcal/mol)a .
CBr4 · · · Cl− · · · H−C
CBr4 · · · Br− · · · H−C
CBr4 · · · I− · · · H−C
CH3 CN
CH2 Cl2
CHCl3
CH3 CN
CH2 Cl2
CHCl3
CH3 CN
CH2 Cl2
CHCl3
∆Etotal
−7.14
−11.24
−14.59
−8.91
−12.24
−15.17
−9.61
−13.98
−14.65
∆E XB
−3.08
−3.75
−4.83
−3.74
−4.30
−5.27
−4.86
−5.05
−5.77
∆EHB
−2.11
−3.54
−5.65
−2.04
−4.09
−5.83
−2.38
−4.21
−4.22
∆EHB0
−1.39
−3.23
−3.47
−2.52
−3.14
−3.38
−1.86
−3.84
−3.87
∆Ecoop
−0.56
−0.72
−0.64
−0.61
−0.71
−0.69
−0.51
−0.88
−0.79
a
The BSSE-corrected interaction energies in solution are obtained in vacuum with the structural coordinates frozen in
solution.
B. Interaction energies
The total interaction energies, halogen bond and hydrogen bond energies of the trimers in solution were calculated at MP2(full)/aug-cc-pVDZ-PP level and results
are listed in Table I. The BSSE is eliminated through
the single point energy correction in vacuum with the
structural coordinates frozen in solution by the standard counterpoise method. The uncorrected interaction energies are also collected in the Table S1 (supplementary material). The BSSE should be considered
for the halogen and hydrogen bond interaction energies
herein due to the large BSSE-percentage of the total
interaction energy (e.g. the BSSE is 6.01 kcal/mol for
CBr4 · · · Br− · · · H−C, 40.3% of the uncorrected total interaction energy).
As discussed above in term of the bond lengths,
the cooperative effects occur between halogen bond
and hydrogen bond in all the trimers. Here the
cooperativity is further confirmed from the interaction energies.
The XB/HB (Cl− · · · H−C) interaction energies are −3.08/−2.11 kcal/mol for
trimer CBr4 · · · Cl− · · · CH3 CN, −3.75/3.54 kcal/mol for
CBr4 · · · Cl− · · · CH2 Cl2 and −4.83/5.65 kcal/mol for
CBr4 · · · Cl− · · · CHCl3 . The halogen bond interaction
energies increase as the hydrogen bond interaction energies, which is consistent with the changing trend of
bond lengths, vide ante. Meanwhile the secondary hydrogen bonds formed by CBr4 and solvent molecules
also obey the same trend. The cooperative effects
are also proven by all the negative cooperative energy
∆Ecoop . It can be concluded that the cooperative effects really occur in the trimers CBr4 · · · Br− · · · H−C
and CBr4 · · · I− · · · H−C from the ∆Ecoop .
From the interaction energies listed in Table I,
the strength of halogen bond in solution obeys
the
order
CBr4 · · · Cl− <CBr4 · · · Br− <CBr4 · · · I− ,
which is contrary to that in gas phase [20]. For
example, the interaction energies of CBr4 · · · X−
are
−3.08 kcal/mol
in
CBr4 · · · Cl− · · · CH3 CN,
−3.74 kcal/mol
in
CBr4 · · · Br− · · · CH3 CN
and
−4.86 kcal/mol in CBr4 · · · I− · · · CH3 CN. For the
same solvent molecule, the order of hydrogen bond
DOI:10.1063/1674-0068/27/03/265-273
strength in solution is also contrary to that in gas phase
and obeys Cl− · · · H−C<Br− · · · H−C<I− · · · H−C. The
halogen bond and hydrogen bond interaction energies
in solution are obviously smaller than that in gas phase.
The general solvent effects should be the main reason
of change of the bond strength. A solvent cage around
the complex molecule must be created in the solution.
The ion-dipole, dipole-dipole and dipole-induced dipole
forces will occur between the complex and solvent
molecules. The molecule structures should be relaxed
and the energies go down because of these interactions.
If the nature of the halogen bonding is only
charge transfer (CT), the interaction energy should
obey the order of iodide>bromide>chloride [27],
while for electrostatic interaction dependent on surface charge density the energy order should be
chloride>bromide>iodide [28−30]. Therefore, in order
to insight into the nature of the triangular bonding complexes further, the UV-Vis absorption and FT-IR spectroscopy are measured.
C. UV-Vis absorption spectra of CBr4 · · · X− complexes
and halide
The absorption spectra of halogen bond complex are
examined in three representative solvents with different
the dielectric constants, 37.5 (CH3 CN), 10.4 (CH2 Cl2 ),
and 4.9 (CHCl3 ), respectively. The absorption spectra
of carbon tetrabromide are characterized by the absorption peak λmax at 225 nm in CH3 CN, 230 nm in CH2 Cl2
and 236 nm in CHCl3 . The tetrabutylammonium halide
also shows different absorption bands dependent on solvents. The absorption spectra of CBr4 · · · X− complexes
in different solvents are shown in Fig.3, with increasing halide concentration gradually. Specifically, when
tetrabutylammonium iodide is added into the CBr4 solution, a new absorption band emerged at 344 nm in
acetonitrile, 345 nm in dichloromethane and 357 nm
in chloroform (Fig.3, upper panels) and the absorption spectra grow with the increase of the tetrabutylammonium iodide concentration. Similar spectral behavior is observed as concentration of bromide or chloc
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Triangular Halogen and Hydrogen Bond Supramolecular Complex
269
FIG. 3 Absorption spectra of CBr4 · · · X− complexes as functions of halide concentration and solvents (a) CH3 CN,
(b) CH2 Cl2 , (c) CHCl3 . Upper panels for iodide, middle panels for bromide, and bottom panels for chloride. [CBr4 ] is
fixed at 4 mmol/L in all cases except No.0 at 0 mmol/L, which is the absorption curve of halide in selected solvent. The
highest concentration used for different halide is labeled in the panels, over which the spectra produce little distortion.
ride changes. The maximum absorption wavelengths
of the complexes dependent on solvents are 294 nm in
acetonitrile, 292 nm in dichloromethane, and 288 nm
in chloroform for Br− complex; 269 nm in acetonitrile,
268 nm in dichloromethane, and 264 nm in chloroform
for Cl− complex. The results are consistent with those
reported previously as 265 nm for Cl− , 292 nm for Br− ,
and 345 nm for I− all in dichloromethane in Ref.[31].
In brief, the absorption spectra of CBr4 · · · X− complexes show the following tendencies: the maximum
absorption of the complex undergoes a blue-shift with
the decreasing dielectric constant of the solvent. The
DOI:10.1063/1674-0068/27/03/265-273
distance between the absorption peaks of the CBr4 itself and CBr4 · · · X− complex are significantly decreased
upon declining the dielectric constant of the solvent.
However, it appears that the tetrabutylammonium iodide does not obey this tendency in chloroform, presumably because the CBr4 · · · I− complex is more easily
oxidized in it. The maximum absorption of the complex varies with different halides in the same solvent,
and displays a little difference for the same halide in
different solvents and the absorption is linearly dependent on concentration of halide in a wide range in all
cases.
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Yu-jie Wu et al.
D. Mulliken correlations
According to Mulliken [32, 33], the optical (chargetransfer) transition is related to electron promotion
from the ground state to the excited state:
hνCT = EES − EGS
q
2
= (ED+ A− − ED,A )2 + 4HDA
q
0.0206
HDA =
νCT ∆ν1/2 εCT
RDA
(1)
(2)
Br· · · X− separation RDA taken from calculation (see
Fig.S1 in supplementary material) which are longer apparently than 3.09 Å (Br· · · Cl− ), 3.15 Å (Br· · · Br− )
and 3.30 Å (Br· · · I− ) reported in crystals [31].
The changes of the absorption energy in a series
of structurally related donors with the same acceptor, or the same donor with various acceptors are
determined mainly by differences in the energy gap
(ED+ A− −ED,A ) related to the donor/acceptor properties such as HOMO/LUMO energies. HDA represents
the electronic coupling matrix element. In solution,
these donor/acceptor interactions are evaluated via redox potentials [34]. According to Eq.(1), the absorption energy of a complex of a series of electron donors
(halides) with the same electron acceptor (CBr4 ) must
be linear with the oxidation potential of the donor, and
vice versa. The oxidation waves of chloride, bromide
and iodide were 1.05, 0.710, 0.378 eV in CH3 CN, 1.35,
0.896, 0.441 eV in CH2 Cl2 and 1.52, 1.12, 0.663 eV in
CHCl3 . As illustrated in Fig.4, the absorption energy of
CBr4 · · · X− complexes (hνCT ) and various donors with
0
vs. SCE) are linear cortheir oxidation potentials (Epa
relative.
E. Stoichiometry, formation constants and molar
extinction coefficients of CBr4 · · · X− complexes
The stoichiometry of halogen bonding complex can be
confirmed according to the Benesi-Hildebrand methodology [35].
The complexation between CBr4 and halide can be
expressed as follows:
CBr4 + X− ­ CBr4 · X−
(3)
The formation constant K and the molar extinction
coefficient ε of the complex can be obtained by Eq.(4).
1
c(CBr4 )l
1
+
=
A
ε
c(X− )εK
(4)
where A is the absorbance of the solution, l is the optic pathway length in cm. c(CBr4 ) and c(X− ) are the
concentrations of CBr4 and X− in mol/L, respectively.
The plot of c(CBr4 )l/A vs. 1/c(X− ) is linear according to Eq.(4) if the 1:1 complex forms. The experiment
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FIG. 4 Mulliken correlation between the energy of the CT
band and the oxidation potential of CBr4 · · · I− complexes
in different solvents. (a) CH3 CN, (b) CH2 Cl2 , (c) CHCl3 .
data obey Eq.(4) and the correlation coefficients are all
greater than 0.997, indicating the 1:1 stoichiometry of
CBr4 and the halide complex. The values of ε and K
are calculated from the intercepts and the slopes of the
fitted line, respectively, as listed in Table II.
Two conclusions could be drawn from the results in
Table II, first, the molar extinction coefficients and the
formation constant K values of the complexes increase
with dielectric constants. The formation constant of
the [CBr4 , Cl− ] complex changes in similar tendency
reported in Ref.[27], where the values 2.03 L/mol in
dichloromethane and 4.78 L/mol in acetonitrile were determined by vibrational spectra. A similar result from
the complexes between CBr4 and compounds nitrogencontaining has been reported by Kochi’s group [12]. For
iodide in CHCl3 , the K value is an exception to the rule.
Second, on the whole, extinction coefficients are apt to
be greater and the complexes tend to be more stable
going from iodide, bromide to chloride in the same solvent.
The electronic coupling element (HDA ) increases
with the dielectric constants of solvents. For example, the HDA of [CBr4 , Br− ] complex are 7075 cm−1
in CH3 CN, 6114 cm−1 in CH2 Cl2 and 4723 cm−1 in
CHCl3 . It indicates CBr4 · · · X− complexes have a
strong charge-transfer character with strongly coupled
potential-energy surface (PES) [13].
F. FT-IR spectra of CBr4 , CBr4 · · · X− , and H−C· · · X−
complexes
Carbon tetrabromide has a C−Br stretching vibration frequency at 676.7 cm−1 in CH3 CN. With addition of halide into the CBr4 solution, an apparent
shift could be observed from 676.7 cm−1 to 674.7,
669.6, and 665.1 cm−1 , respectively, in the CBr4 · · · Cl− ,
CBr4 · · · Br− , and CBr4 · · · I− complexes in CH3 CN.
This behavior also exists when CH3 CN is changed to
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Triangular Halogen and Hydrogen Bond Supramolecular Complex
271
TABLE II Spectroscopic and energetic characteristics of the charge-transfer complexes between CBr4 and halide anions in
different solventsa .
Halide
Solvent
λmax /nm
ε/10−4 (L/(mol·cm))
K/(L/mol)
HDA /cm−1
Cl−
CH3 CN
269
0.54±0.13
6.07±1.51
6726
CH2 Cl2
268
0.43±0.11
3.25±1.08
6056
CHCl3
264
0.18±0.02
2.49±0.94
4349
Br−
CH3 CN
294
0.66±0.12
6.09±0.97
7104
CH2 Cl2
292
0.48±0.06
4.68±0.87
6133
CHCl3
288
0.27±0.05
4.11±0.89
4649
I−
CH3 CN
344
0.78±0.03
7.26±1.52
6528
CH2 Cl2
345
0.72±0.41
3.24±0.44
6279
CHCl3
357
0.41±0.12
8.97±2.93
4423
a
In all cases, absorption of CBr4 at interested wavelength has been deducted from total absorption of complex+CBr4 .
TABLE III Carbon-bromide stretching vibration frequency of CBr4 and CBr4 · · · X− complexes in different solvents (in
cm−1 ).
σCBr4
σCBr4 ·Cl−
∆σ c
σCBr4 ·Br−
Expt.
676.7
674.7
−2.0
669.6
b
Calc.
691.4
689.9
−1.5
685.3
CH2 Cl2
Expt.
672.1
671.7
−0.4
665.9
Calc.
690.0
689.4
−0.6
685.3
CHCl3
Expt.
669.6
668.8
−0.8
668.7
Calc.
688.1
686.3
−1.8
684.1
a
Expt. means experimental data and each datum is the average of duplicate.
b
Calc. means computational data which are got at MP2(full) level.
c
∆σ= σCBr4 ·Cl− −σCBr4 .
d
∆σ= σCBr4 ·Br− −σCBr4 .
e
∆σ= σCBr4 ·I− −σCBr4 .
Solvent
CH3 CN
a
CH2 Cl2 and CHCl3 , as listed in Table III. The magnitudes of the red-shifts, ∆σ, of C−Br stretching vibration frequency are dependent on both halide and
solvent. Halide affects the C−Br stretching vibration
of CBr4 , on which I− has the greatest influence, followed by Br− and Cl− in turn. This influence weakens with the decrease of the dielectric constant of solvents. The order is consistent with formation constants
got from the UV-Vis absorption spectra. The computational results at MP2(full) level in Table III are in agreement with the experimental data well which indicates
that the computations at MP2(full)/aug-cc-pVDZ(-PP)
level are credible.
Furthermore it is noticed that C−Cl and C−H
stretching vibration frequencies of solvent molecules
shift when Cl− , Br− and I− is added into CHCl3 , as
shown in Table IV. So it is possible that halide can
bond weakly not only with CBr4 but also with the solvent molecules. The stretching vibration frequencies of
solvent molecules are also computed and listed in Table
S2 (supplementary material).
As shown in Table IV, the C−H bond of CH3 CN
and CH2 Cl2 has lower stretching vibration frequencies
(equivalent to a longer bond) when adding halide into
them. For example, adding I− makes the C−H vibraDOI:10.1063/1674-0068/27/03/265-273
∆σ d
−7.1
−6.1
−6.2
−4.7
−0.9
−4.0
σCBr4 ·I−
665.1
677.6
664.6
676.3
669.0
673.4
∆σ e
−11.6
−13.8
−7.5
−13.7
−0.6
−13.8
tion frequency shift from 2944.1 cm−1 to 2941.8 cm−1
in CH3 CN, and from 3054.3 cm−1 to 3052.8 cm−1 in
CH2 Cl2 . Adding both halide and CBr4 , the frequency
is almost the same as adding only halide. This indicates
that hydrogen bond is formed between halide and protic
solvents CH3 CN, CH2 Cl2 . Based on the magnitude of
frequency-shifts of C−H and C−Cl of CH2 Cl2 , halogen
bond between solvent molecule and halide may occur
in C−Cl· · · X− pattern, but the hydrogen bond pattern C−H · · · X− should be overwhelming. According
to reports in Ref.[36], the hydrogen in CHCl3 should be
acidic with the ability to accept charge from oxygen of
triethylphosphine oxide. Durov et al. reported that the
dimer O· · · H−CCl3 or trimer Cl3 C−H· · · O· · · H−CCl3
patterns between chloroform and acetone might occur
[37]. These previous findings indicate that the photon
in chlorinated solvent can indeed act as hydrogen bond
donor [37−39].
However, the C−H vibration frequencies of CHCl3 at
1215.6 and 3018.6 cm−1 do not clearly change under
experimental conditions whether adding halide or not.
In contrast, C−Cl vibration frequencies of CHCl3 at
769.0 and 669.4 cm−1 decrease evidently when adding
halide into the solvent. For example, the addition of
Cl− makes the frequency shift from 769.0 cm−1 to
c
°2014
Chinese Physical Society
272
Chin. J. Chem. Phys., Vol. 27, No. 3
Yu-jie Wu et al.
TABLE IV Changes of vibrational frequencies relevant bonds of solvents in the presence of halides or both halide and CBr4 a
(in cm−1 ).
+Cl−
νC−H
2944.1
2941.7
νC≡N
2253.2
2252.0
δC−H
1444.1
1444.1
CH2 Cl2
νC−H
3054.3
3053.2
νC−H
2987.0
3036.6
δC−H
896.1
894.5
νC−Cl
740.5
739.8
νC−Cl
705.4
703.4
CHCl3
νC−H
3018.6
3018.5
δC−H
1215.6
1216.0
νC−Cl
769.0
756.1
νC−Cl
669.4
658.3
δC−Cl
667.8
a
Each datum is the average of duplicate.
Solvent
CH3 CN
+CBr4 ·Cl−
2942.6
2252.6
1445.9
3052.8
3035.3
895.2
739.3
704.0
3018.5
1215.8
757.4
658.2
668.8
756.1 cm−1 in CHCl3 . As shown in Table S2 (supplementary material), the hydrogen bond CHCl3 · · · X−
causes both the C−H and C−Cl vibration frequencies
changes. But in fact no obvious changes for C−H vibration frequencies are observed by FTIR spectra.
The bond length of CBr4 and solvent molecules are
obtained in Table S3 (supplementary material), the
formation of halogen bond between carbon tetrabromide and halide makes the C−Br bond longer. The
C−Br bond length varies from 1.944 Å to 1.957 Å. The
stronger halogen bond leads to more obvious elongation. The bond lengths of solvent molecules change little. The changes of bond lengths are in agreement with
the changes of vibrational frequencies.
IV. CONCLUSION
The
new
triangular
bonding
complexes
CBr4 · · · X− · · · H−C in solution are simulated at
the MP2(full)/aug-cc-pVDZ-PP and further confirmed
by UV-Vis and FTIR spectrophotometer. The strength
of halogen bond and hydrogen bond involved in the
complexes obeys the order of iodide>bromide>chloride,
which is opposite to this sequence in gas phase. Moreover, the halogen bond and hydrogen bond in the
triangular bonding complexes show weak cooperative
effects.
The 1:1 stoichiometry, extinction coefficients and formation constants of CBr4 and halide
are confirmed according to the Benesi-Hildebrand
methodology. The halogen bond strength can be
estimated through the formation constants, which is
in agreement with the computational results. The
interaction between the halide and solvents can also be
detected by the change of C−H vibrational frequency
via FTIR spectroscopy. This investigation is expected
DOI:10.1063/1674-0068/27/03/265-273
+Br−
2941.7
2251.8
1445.0
3053.8
3036.0
894.3
739.3
700.4
3018.6
1216.1
757.7
659.8
668.2
+CBr4 ·Br−
2942.5
2252.5
1445.0
3052.4
3036.9
894.8
740.1
703.7
3018.8
1215.7
756.2
659.0
668.7
+I−
2941.8
2252.0
1445.1
3052.8
3036.5
894.0
736.6
700.0
3018.9
1216.7
770.1
661.7
668.6
+CBr4 ·I−
2942.4
2252.4
1444.5
3051.8
3037.4
895.3
738.9
702.4
3018.9
1216.3
770.0
669.0
to be significant in considering the solvation of reaction
process in chemistry or biology, or designing new
solvation model in theory chemistry involving reactants
containing halogen or halide.
Supplementary material: The materials on the interaction energies, computed changes of vibrational frequencies relevant to bonds of solvents in the presence
of halides, the covalent bond length R of carbon tetrabromide and solvents and their change with addition of
halide are available on the web.
V. ACKNOWLEDGMENTS
This work was supported by the National Natural
Science Foundation of China (No.20675009 and No.
90922023). The basis set aug-cc-pVDZ-PP for iodine
atom is downloaded at the website http://bse.pnl.gov/
bse/portal.
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