Caspian J. Chem.
C
2(20133) 19-26
DFT Application to
t the Analy
ysis of Quad
drupole Cou
upling Consstant of Aluminum Metthyl
Chlo
oride Dimerrs
Fatemeh
F
elmi*
*a, Maryam M
Mitra Elmib
a
b
Department off Chemistry, University of M
Mazandaran, Bab
abolsar, Iran
Cellular and Mo
olecular Biolog
gy Research Ceenter, Babol Unniversity of Meedical Sciencess, Babol,Iran

Corresp
ponding author: Ph
hone and fax numb
mber +98 11253423388.
E-mail add
dress: [email protected]
Receiveed 18 June 2013|R
Received in revised
d form 15 Septembber 2013|Acceptedd 21September 20113
o the 27Al and
d 35Cl quadrup
pole coupling pparameters of aluminum meethyl chloride ddimers
Abstract: The analysis of
b
of the den
nsity functionall theory (DFT)). The availablee experimentall values of quaarupole
were carrieed out on the basis
coupling constants
c
weree compared wiith their calcu
ulated ones. Inn this investigaation, the corrrelations were made
between caalculated 27Al and
a 35Cl nucleaar quadrupole coupling
c
consttant, χ, and dihhedral angles , of dimers. Thhese s
were produ
uced through th
he ring puckerring motions ab
bout the hinge line which joiins the two briddge atoms. χs oof 27Al
and 35Cl were
w
used as prrobes for moniitoring the dep
parture of the ssymmetry of thhese dimers froom a high sym
mmetry
point grou
up to the lowerr one. It was also found thaat the commonn symmetry pooint group attrributed to alum
minum
methyl chlloride dimers iss valid only up
p to dihedral an
ngle, 20. Afteer this point, puuckering motioons can cause ffurther
break dow
wn of symmetrry. Moreover, the replacemeent of bridgedd chloride by m
methyl can appparently decreease 
values of 27Al atom. Thiss could be due to the alteration of the orbitall density in aluuminum atoms.
Key words: DFT; 27Al an
nd 35Cl NQR; aluminum metthyl chloride diimers.
®
2013 Pub
blished by Univ
versity of Mazaandaran. All rig
ghts reserved.
1. Introdu
uction
form
m. However, in Al2X6 (X=Cl,Br), dimers unndergo
The molecular structures of organo-aluminum halidess
ring puckering mootion through tthe hinge line which
R and Raman
n
were studied by experiimental Far-IR
joinss the bridge hallogens [5,6]. A consequence of the
hese studies suggest thatt
spectroscopy [1,2]. Th
ring puckering mootion is the coonversion of higher
uminum halidees preferably occur in thee
organo-alu
metry into loweer symmetry [55]. Among these, the
symm
form of dim
mers and the bridge
b
atom miight be formed
d
moree favorable strructure is the one which iss more
either by alkyl or by chloride (Fig..1) [3,4]. Thee
capabble to accom
mmodate large amplitude of ring
d model for theese compound
ds is their rigid
d
anticipated
puckkering motionss. These dim
mers are relevaant to
19 Elmi et al./ Caspian J. Chem. 2(2013) 19-26 Ziegler-Natta catalysis [7,8]. It is shown that
Quadrupolar nuclei (I >1/2) are associated with
spectroscopic methods especially when they coupled
nuclear quadrupole coupling constant, :
with theoretical calculations have the potential to

achieve a detailed understanding of the active sites at
e 2 Qq zz
h
(1)
the molecular level [7]. Theoretical calculations have
Where the unit of electrostatic charge is e, h is the
been used to investigate Ziegler-Natta catalysts [9-
plank constant and eQ is the nuclear electric
16]. Theoretical investigation of the role of AlR3
quadrupole moment.  values are proportional to
(R=CH3,Cl) as cocatalyst for the Ziegler-Natta
EFG tensor which originates from the internal
reaction reveals that AlR3 facilitates the reduction of
electrostatic charges at the site of the quadrupolar
the Ti atoms by means of an exchange between the R
nucleus [26,27]. Electric quadrupole moments of 27Al
and Cl ligands [17].
(I=5/2)
The study of molecular structures of non-transition
Q  81.65 1027 cm2 and
metal halogenides with the help of nuclear magnetic
and
35
Cl
(I=3/2)
are
taken
Q  146  10 27
as
cm2,
respectively [28]. Equation 1 was used to direct the
resonance (NMR) spectra can be complicated by the
relation of the calculated EFG tensors changes with
possibility of rapid interchange of terminal and
the ring puckering motion and available experimental
bridging groups. However, these complexes are
nuclear quadrupole coupling constant. The
particularly interesting from the point of view of
 values
of 27Al and 35Cl were calculated by equations 2 and 3,
nuclear quadrupole resonance spectroscopy (NQR)
respectively:
[18-24]. Our pervious study shows that NQR is an
efficient method for the recognition of dimers with
different conformers [25]. The important physical
 ( 27 Al)  34.454  q zz (MHz)
(2)
properties
 ( 35 Cl) 19.189  q zz (MHz)
(3)
that
can
be
determined
both
experimentally and theoretically are the nuclear
quadrupole coupling constant,  and the asymmetry
2.1. Computational Methods
parameter, .  is sensitive to the shape of electronic
The EFG at a nucleus, q zz , produced by electron
charge distribution in molecules and  measures the
distribution in the molecule, can be obtained with a
departure of the electric field gradient (EFG) from
reasonable effort from DFT calculations. Since it
axial symmetry. Density functional theory (DFT) was
involves only the ground state wave function, it is
employed to calculate 27Al and 35Cl EFG tensors for
calculated more readily than, for instance, the
six aluminum methyl chloride dimers. The EFG
chemical shift in NMR. The DFT molecular orbital
tensors were converted into the . The results are
calculations were carried out with the Gaussian 98
summarized in Tables 1-6.
program [29]. Six conformers of aluminum methyl
chloride were selected (Fig.1).
2. Theory
20 Elm
mi et al./ Caspiian J. Chem. 2 (2013) 19-26
Fig.1. Moleccular structure of a-f
a aluminum methhyl chloride comp ounds.
a: AlCl3,A
AlCl1met2(t)
b:AlCl1mett2(t),AlCl1met2(t)
d: AlCll3,AlCl2met1(b)
e:AlCl2met
m 1(t),AlCl1met2(tt)
c:AlC
Cl2met1(t),AlCl2m
met1(t)
f: :AlCl3,AlCl2met1((t)
y optimization
n at constantt
The partiaally geometry
varyiing the ring puuckering anglee, . The anglle was
dihedral an
ngles, s <dih
h (Xb1Al1-Al2Xb2) (Xb=Cl orr
varieed from 0 up to 40, using 10 incrementts. Our
CH3) and the
t computatio
on of the components of EFG
G
perviious study sshows that nnuclear quaddrupole
tensors, eq
q xx , eq yy and eq
e zz in principaal axis system
m
couppling constantt is a betteer alternative than
(PAS) werre done at B3L
LYP/6-311G* level
l
of theory.
metrical param
meters for disttinguishing beetween
geom
The relevaant study also applied
a
B3LYP
P method with
h
differrent conformerrs of Al2Cl6 as well as Al2Br6 [25].
the 3-21G
G and 6-311
1G* basis sets
s
of NQR
R
parameterss for the dim
mers of transittion and non--
I: AllCl3,AlCl1met2(t)
transition metal
m
halogeniides [30]. Theiir research hass
At eequilibrium, Fiig.1a, the poinnt group sym
mmetry,
proved th
he reliability of DFT meethod for thee
minum and chhloride
C2v shows two kkinds of alum
description
n of the geomeetry and NQR frequencies off
(Tablle 1). Changinng the dihedraal angle from 0 to
these dim
mers. Further investigation established a
20, apparently cauuse no significcant variations in the
correlation
n coefficient between expeerimental and
d
 vaalues of this dimer. Afterr 20, there is no
theoretical 27Al s of alu
uminum chloride compoundss
symm
metry element((s) to convert the bridge chllorides
[31]. The results
r
of the calculations arre summarized
d
into eeach other. Hoowever, for terrminal chlorides this
in Tables 1-6.
1
happpens after 30. As Table 1 shhows, the  vaalue of
27
Al((2) is about 330 MHz highher than the oone of
3. Results and Discussio
on
27
Al((1). One may conclude that replacement oof one
The nucleear quadrupolle coupling constants
c
wass
termiinal electroneggative group, chloride, by m
methyl
performed
groupp increases thhe electron deensity in a bridged
to
differeentiate
betweeen
differentt
27
a
meethyl chloridee
conformers of six aluminum
ormers were geenerated by
compounds. These confo
21 Al((2) atom.
Elmi et al./ Caspian J. Chem. 2(2013) 19-26 Table 1.Calculated s, MHz, (27Al,35Cl) of (AlCl3,AlCl1met2(t))
a
Al(1)
Al(2)
Cl(b1)
Cl(b2)
Cl(t1)
Cl(t2)
0
13.461
43.100
22.489
22.505
26.470
26.470
10
13.434
43.134
22.560
22.590
26.531
26.410
20
13.365
43.055
22.783
22.906
26.600
26.482
30
13.511
42.453
23.287
23.737
26.700
26.842
40
15.967
42.053
23.978
24.926
26.883
27.404
a
Dihedral angle (Clb1-Al1-Al2-Clb2)
Table 2.Calculated s, MHz, (27Al,35Cl) of (AlCl1met2(t),AlCl1met2(t))
a
a
Al(1)
Al(2)
Cl(b1)
Cl(b2)
Exp. 27Alb
0
39.062
39.033
20.765
20.763
36.4
10
38.996
39.014
20.785
20.789
20
38.369
38.873
20.877
20.911
30
38.315
39.169
21.249
21.323
40
37.348
40.174
21.764
21.579
Dihedral angle (Clb1-Al1-Al2-Clb2)
b
M. J. S. Dewar, D. B. Patterson, W. I. Simpson, J. Am. Chem. Soc., 93 (1971), 1030.
II: AlCl1met2(t),AlCl1met2(t)
agreement with experimental ones, 36.4 MHz [23].
(AlCl1met2(t),AlCl1met2(t)),Fig.1b, has D2h symmetry
III: AlCl2met1(t),AlCl2met1(t)
in its static form. This means that there is an identical
(AlCl2met1(t),AlCl2met1(t)), Fig.1c, is expected to
 for bridge chlorides. Also, it implies having the
have C2h symmetry at equilibrium. Therefore, it has
same  for aluminums. Changing the dihedral angle
identical  values for both aluminums and chlorides.
from 0 to 10 appears not to cause any significant
Table 3 shows that the two bridge chlorides have
deviation from the assigned D2h symmetry. Within
similar chemical environment up to 20. The
the range of 10-20, there is a correlation between the
calculated  of 27Al, 27.4 MHz, is in agreement with
s of bridge chlorides.
experimental ones, 25.6 MHz [23]. The  of bridged
In this range, the symmetry point group is reduced to
chloride is 90.5% of the  value of terminal chloride.
C2v. After 20, puckering motions lead to further
This is in agreement with studies of RAlCl2 dimer
reduction of the symmetry, Table 2. From this point
which indicate that the bridging halogens exhibit
on, the s of two chlorides change appreciably. At
NQR transitions which are at 91.5-92.5% of the
equilibrium, the calculated  of 27Al, 39.0 MHz, is in
values for the terminal ones [23,32].
22 Elmi et al./ Caspian J. Chem. 2(2013) 19-26 Table 3.Calculated s, MHz, (27Al,35Cl) of (AlCl2met1(t),AlCl2met1(t)).
a
Al(1)
Al(2)
Cl(b1)
Cl(b2)
Cl(t1)
Cl(t2)
Exp.
27
27
6-311G*/3-21Gc
25.6
27.8
Alb
a
0
27.426
27.421
22.511
22.514
24.879
24.877
10
27.717
27.449
22.420
22.425
24.483
24.393
20
27.817
27.336
22.691
22.744
24.500
24.419
30
27.658
27.236
23.256
23.411
24.456
24.662
40
27.492
27.931
24.081
24.299
24.401
24.980
Al
Dihedral angle (Clb1-Al1-Al2-Clb2).
b
M. J. S. Dewar, D. B. Patterson, W. I. Simpson, J. Am. Chem. Soc., 93 (1971), 1030.
c
O. Kh. Poleshchuk, E.L. Kalinina, J.N. Latosin'ska, J. Koput, J. Mol. Struc. (Theochem), 574 (2001), 233.
Table 4.Calculated s, MHz, (27Al,35Cl) of (AlCl3,AlCl2met1(b)).
a
Al(1)
Al(2)
Cl(b)
Cl(t1)
Cl(t2)
Cl(t3)
Cl(t4)
0
11.390
11.480
22.937
25.718
25.719
25.729
25.727
10
11.449
11.490
22.974
25.814
25.640
25.664
25.810
20
11.562
12.237
23.063
26.020
25.590
25.635
26.027
30
11.651
14.208
23.369
26.413
25.523
25.622
26.422
40
12.299
19.536
23.603
26.947
25.501
25.639
26.877
a
Dihedral angle (Al1-Clb-(CH3)b-Al2).
meaningfully decrease of 27Al s in this dimer.
IV: AlCl3,AlCl2met1(b)
This is a dimer in which one of the bridge halogens is
replaced by a –CH3 group (Fig.1.d). The symmetry
V. AlCl2met1(t),AlCl1met2(t)& AlCl3,AlCl2met1(t)
point group of this molecule at equilibrium is C2v. So,
Both of these dimers possess Cs point group at
one expects that all terminal chlorides have identical
equilibrium. Tables 5 and 6 indicate that the bridge
chemical environment. According to Table 4, their 
chlorides in these molecules have identical  values
values are the same up to 10.
up to 30. After this point on, the s of bridge
After 10, the terminal chlorides are clearly divided
chlorides are disintegrated. Consequently, their plane
into two groups. The difference between their s
of symmetry disappears. According to NQR, the
gradually increases. The  values of two aluminums
spectra for a number of aluminum alkyl halides, each
are the same up to 10.From this point on, the s of
replacement of one terminal chloride in dimer by
two aluminums differ considerably. A closer look at
methyl, can increase  of Al by ca.12 MHz [23]. The
the  values of 27Al presented in Tables 1-4 shows a
results of Tables 1and 5 confirm this conclusion.
23 Elmi et al./ Caspian J. Chem. 2(2013) 19-26 Table 5. Calculated s, MHz,(27Al,35Cl) of (AlCl2met1(t),AlCl1met2(t))
a
a
Al(1)
Al(2)
Cl(b1)
Cl(b2)
Cl(t)
0
26.022
41.166
21.462
21.452
24.303
10
25.994
40.975
21.552
21.548
24.266
20
25.883
40.863
21.756
21.754
24.287
30
25.470
40.909
22.254
22.207
24.248
40
25.339
42.034
22.946
22.405
24.244
Dihedral angle (Al1-Clb1-Clb2-Al2)
Table 6.Calculated s, MHz,(27Al,35Cl) of (AlCl3,AlCl2met1(t))
a
a
Al(1)
Al(2)
Cl(b1)
Cl(b2)
Cl(t1)
Cl(t2)
Cl(t3)
0
15.043
28.880
23.358
23.382
24.805
26.714
26.861
10
14.887
29.002
23.502
23.495
26.657
26.882
24.830
20
14.651
29.208
23.810
23.811
26.618
26.910
24.865
30
14.237
29.517
24.381
24.392
26.781
26.966
24.869
40
14.647
30.585
25.330
24.731
26.932
26.914
24.920
Dihedral angle (Clb1-Al1-Al2-Clb2)
4. Conclusion
aluminum methy chloride dimers is valid only
Nuclear quadrupole coupling constants of
27
Al
up to dihedral angle, 20. After this point,
and Cl in different conformers of six aluminum
puckering motions can cause further break down
methyl chloride dimers were calculated using
of symmetry. Moreover, the replacement of
DFT method. These conformers were created
bridged chloride by methyl can apparently
through the hinge line which joins the two
decrease  values of
bridge atom.
due to the alteration of the orbital density in
According to the results, the calculated  values
aluminum atoms.
35
are
in
good
experimental
between
constants,s
agreement
ones.
nuclear
and
Also,
with
the
quadrupole
dihedral
Al atom. This could be
available
correlations
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angles,s
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