Journal of Molecular Structure: THEOCHEM 761 (2006) 89–95
www.elsevier.com/locate/theochem
Intermolecular ligand exchange in alkyltin trihalides:
Semiempirical and density functional theory calculations
Bellie Sundaram Krishnamoorthy a, Ravichandran Lalitha a,
Krishnaswamy Panchanatheswaran a,*, Pratim Kumar Chattaraj b
a
b
Department of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, India
Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India
Received 26 August 2005; received in revised form 30 November 2005; accepted 1 December 2005
Available online 23 February 2006
Abstract
The mechanism of intermolecular exchange of methyl and ethyl groups for chlorine in CH3SnCl3 and C2H5SnCl3, respectively, has been probed
through semiempirical (PM3) and density functional theory (B3PW91 and B3LYP) calculations. The reaction is explained by a mechanism
involving the formation of the transition state comprising bridging alkyl and chloro groups. The PM3 calculated activation energies are 37.5 and
36.4 kcal molK1 while the B3LYP/LANL2DZ calculated activation energies are 50.4 and 41.3 kcal molK1 for the methyl and ethyl analogues,
respectively. The rate constants calculated at the DFT level are in close agreement with the corresponding experimental values.
q 2006 Elsevier B.V. All rights reserved.
Keywords: Ligand scrambling; Organotin; PM3; DFT
1. Introduction
Since, the discovery of diethyltin iodide [1] several useful
[2,3] organotin compounds have been synthesized. However, the
mechanistic aspects of only few reactions involving organotin
compounds such as insertion [4], cycloaddition [4] and
hydrostannylation [5], have been analyzed through semiempirical methods. To explain the stereospecificity in reactions of
allylstannanes with aldehydes [6] and the transmetallation of
2-trimethylstannylbuta-1,3-diene with SnCl4 [7] calculations
have been performed at the B3LYP/6-31G** level whereas
MP2/6-31CG* calculations have been carried out for the
reactions of allyltin complexes, with water and carbonyl
compounds in the gas phase. It was shown that the latter would
be less reactive toward hydrolysis than allylation [8]. Intermolecular ligand exchange (disproportionation) is a common
process in organotin chemistry although examples for such
reactions are known for the compounds of other elements like Mo
[9], Si [10], Al [11], Zr [11] and Au [12]. The fourth Sn–C bond in
tintetraalkyls is lower in energy [13] and may contribute for the
* Corresponding author. Tel.: C91 431 2407053; fax: C91 431 2407045.
E-mail address: [email protected] (
K. Panchanatheswaran).
0166-1280/$ - see front matter q 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.theochem.2005.12.011
dissociation. Thus, the tetraalkyltin compounds readily participate in ligand redistribution reactions as observed in the
Kocheshkov reaction [14] with R4Sn (RZalkyl or aryl) and
SnCl4 with or without solvent [15]. In the presence of catalytic
amount of phosphine complexes of palladium and platinum,
dialkyltin chlorides also undergo ligand exchange with SnCl4
[16]. The ligand exchange reaction, with trialkyltin halides is
catalyzed by nucleophiles. The exchange reaction in MeSnCl3, to
form SnCl4 and Me2SnCl2 [17] as well as halide-allyl exchange
have been observed between two molecules of Bu2(CH2aCH–
CH2)SnCl [18]; Bu2SnCl2 and Bu2Sn(CH2aCH–CH2)2 yield
Bu2(CH2aCH–CH2)SnCl upon reaction as neat reactants or in
the presence of water or organic solvents. Ligand exchange
process also decides the course of certain organotin reactions. For
example, reaction of tribenzyltin chloride with 1,10-phenanthroline yielded the complex, (C6H5CH2)2SnCl2.(o-phenanthroline)
[19] as one of the products. The reaction of (C6H5CH2)2SnCl2 and
o-phenanthroline yielded the complex of C6H5CH2SnCl3.(ophenanthroline) [20]. The results can be accounted for by a ligand
redistribution of (C6H5CH2)3SnCl and (C6H5CH2)2SnCl2 to form
other tin halides. Ligand redistribution occurs more readily
between R3SnMe and Me2SnCl2 with small alkyl groups [21].
The reaction depends upon the nature of tin substrates and
halogens and also the temperature. At high temperature multistep exchange occurs. Again exchange is more favourable for
organotin chlorides than for organotin bromides.
90
B.S. Krishnamoorthy et al. / Journal of Molecular Structure: THEOCHEM 761 (2006) 89–95
Scheme 1.
As part of our investigation into the mechanistic aspects of
reactions involving some organotin compounds by semiempirical and DFT methods, we have probed the mechanism of
disproportionation of CH3SnCl3 and C2H5SnCl3.
2. Computational details
The semiempirical molecular orbital calculations are carried
out using standard PM3 [22] method available in MOPAC 6.0
program package [23]. Structures of molecules are drawn on
the PCMODEL package of Serena software [24] and then
optimized, which are used as inputs for MOPAC. Transition
states are located by the reaction coordinate method [25],
refined by gradiant norm minimization and the stationary
points are characterized by calculating force constants [26].
Intrinsic reaction coordinate calculations using internal
coordinates are performed to verify that computed transition
states are saddle points between reactants and products. The
PM3 optimized geometries are given as inputs for DFT
calculations. The DFT calculations are performed using the
GAUSSIAN 03 program [27]. Both B3LYP [28,29] and B3PW91
[30] functionals are used for this purpose. In order to check the
usefulness of PM3 results, which is often important for large
molecules for which more sophisticated methods take large cpu
time we compare the PM3 results with two standard DFT level
results in the present work. The standard LANL2DZ [31] basis
set is used throughout the study since it is known to provide
reliable results. It was successfully employed for assessing
relative stability of SnaSb and SnbSb systems [32], geometry
optimization of ReSnCl2 structures [33] and orbital interactions
in the hypothetical MbSn bonds (MaCr, Mo, W) [34]. All the
structures obtained in the present computations are confirmed
to be real minima or transition states via frequency analysis.
Solvent effects are studied by performing self consistent
reaction field (SCRF) single point energy calculations using the
static isodensity surface polarized continuum model (IPCM)
[35] for all the B3PW91/LANL2DZ and B3LYP/LANL2DZ
optimized structures. Since, conceptual DFT has been quite
successful in providing theoretical foundations of popular
qualitative chemical concepts [36], we have calculated global
hardness, an index of reactivity [hZ(IKA)/2], chemical
potential, which gives the escaping tendency of electron
cloud [mZK(ICA)/2], global softness [37] [SZ1/2h] and
electrophilicity [38] [uZm2/2h] values for all the molecules to
study the reaction course, where I and A are ionization potential
and the electron affinity of the molecular system. From
Koopmans’ theorem they are related to HOMO and LUMO
energies as IZKEHOMO and AZKELUMO. A finite difference
approximation together with Koopmans’ approximation provide [39], mZ(EHOMOCELUMO)/2; hZ(ELUMOKEHOMO)/2.
3. Results and discussion
The reaction mechanism proposed for the intermolecular
ligand exchange in alkyltin trihalides is given in Scheme 1
Trichloromethyltin undergoes ligand exchange reaction
[17] (at 50 8C, 98 h) to give SnCl4 and Me2SnCl2 in presence
of solvents. Similarly, the exchange of methyl group in the
R3SnMe and Me2SnCl2 is also assisted by solvents [21].
However, ligand exchange can occur even in the absence of
solvent [15]. In the present theoretical computations at DFT
and semiempirical level (PM3), reaction is modeled through
the formation of the chloro and methyl bridged transition
states. The activation energies for this reaction are 50.4 and
37.5 kcal molK1 at DFT and PM3 levels, respectively. The
PM3 computed thermodynamic properties are given in Table 1.
The PM3 bonding parameters for the MeSnCl3, SnCl4 and
Me2SnCl2 are given in Fig. 1. The transition state geometry and
selected metrical parameters are presented in Fig. 2. The
normal mode associated with the imaginary frequency at
Table 1
Thermodynamic properties at 298 K, and dipole moment values of MeSnCl3, TS1, SnCl4, Me2SnCl2, C2H5SnCl3, TS2 and (C2H5)2SnCl2 obtained from PM3
calculations
Molecules
Heat of formation
(kcal molK1)
Enthalpy
(kcal molK1)
Entropy
(kcal K molK1)
Free energy
(kcal molK1)
Ionization potential
(eV)
Dipole moment
(debye)
MeSnCl3
TS1
SnCl4
Me2SnCl2
C2H5SnCl3
TS2
(C2H5)2SnCl2
K83.62
K129.72
K101.21
K63.47
K87.62
K138.87
K70.98
6.26
12.44
5.79
6.75
7.18
14.42
8.46
0.10
0.16
0.09
0.10
0.11
0.17
0.12
K22.88
K33.93
K21.69
K23.74
K25.96
K36.30
K27.06
11.38
10.88
11.72
10.98
11.07
10.35
10.59
3.76
3.13
0.00
4.53
4.23
3.81
4.89
B.S. Krishnamoorthy et al. / Journal of Molecular Structure: THEOCHEM 761 (2006) 89–95
91
Fig. 1. B3LYP/LANL2DZ optimized geometries of MeSnCl3, SnCl4, Me2SnCl2, C2H5SnCl3 and (C2H5)2SnCl2 along with bonding parameters.
B3PW91[B3LYP](PM3) (Å, 8).
591.7 cmK1 describes mainly the C6–Sn2 bond stretching of
the TS1.
Intermolecular ligand exchange reaction of EtSnCl3 can
also proceed by the same mechanism through the chloro and
ethyl bridged transition state (TS2). DFT and PM3 calculated
activation energies for this reaction are 41.3 and
36.4 kcal molK1, respectively. The PM3 calculated thermodynamic parameters are included in Table 1. The normal mode
associated with the imaginary frequency at 375.7 cmK1
describes mainly the Sn4–Cl3 stretching of TS2. In the
transition states, tin acts as an electrophilic centre and chlorine
and alkyl groups as nucleophiles. This is revealed by the charge
distribution among the atoms in the TS1 and TS2. Further, the
charge on tin in both the transition states are significantly
higher than the charges on tin in CH3SnCl3 and C2H5SnCl3.
Therefore, the feasibility of the reaction of nucleophiles with
tin is enhanced. This, coupled with the fact that tin can assume
six coordinated geometry readily indicates nucleophiles will
have a significant role in stabilizing the transition states. The
enhancement of the rate of the reaction in presence of
nucleophiles as observed is thus indicated.
The heats of formation values indicate that the transition states
are less stable than the reactants or the products taken together
(Table 1). The enthalpy change of the reaction and free energy
change of the reaction are very low indicating that there is no new
bond formation and only redistribution of bonds (Table 2) takes
place. Kinetic parameters (rate constants) of both the reactions
reveal that the reaction involving methyl group undergoes ligand
exchange faster than involving ethyl group. The dipole moments
of TS1 and TS2 indicate that they are considerably polar. The
ligand exchange reactions of n-propyl, iso-propyl and n-butyltin
trihalides were also probed through PM3 calculations. The PM3
calculated activation energies for the reactions involving
n-propyl and n-butyltin trihalides (37.0 and 38.4 kcal molK1)
are close to the activation energy values of methyl and ethyl
species. However, the activation energy of the ligand exchange
92
B.S. Krishnamoorthy et al. / Journal of Molecular Structure: THEOCHEM 761 (2006) 89–95
Fig. 2. B3LYP/LANL2DZ optimized geometries for TS1 and TS2 with selected bond parameters.
reaction involving iso-propyl group is considerably higher
(44.5 kcal molK1) than those of the methyl, ethyl, n-propyl and
n-butyl groups. Location of similar bridged transition state is not
successful in case of ligand exchange reaction involving terbutyltin trichloride. We conclude that ligand exchange in the case
of latter would not occur readily.
with SnCl4 [7], and also in the stereospecific reactions of
1-alkoxy and 1-alkyl-alk-2-enylstannanes with aldehydes [6].
5. DFT calculations
The same mechanism has been probed through DFT
calculations using B3PW91 and B3LYP functionals with
LANL2DZ basis set, to get the better insight into the
reaction mechanism. The B3LYP/LANL2DZ optimized
structures of MeSnCl3, SnCl4, Me2SnCl2, EtSnCl3 and
Et2SnCl2 are given in Fig. 1. The bond parameters of all
the species obtained from the DFT and PM3 calculations
are quite similar.
B3LYP/LANL2DZ optimized transition state geometries
along with selected metrical parameters are given in Fig. 2. The
DFT optimized transition state geometries are quite similar to
the TS geometries obtained from PM3 calculations. The
charges of the tin atoms are computed to be 1.066 and 1.082 in
TS1 and 1.079 and 1.064 in TS2.
The energetics of the molecules calculated at the
B3PW91/LANL2DZ, B3LYP/LANL2DZ, B3LYP//MP2/LANL2DZ, and with solvent effects of water and toluene at
B3LYP/LANL2DZ levels are given in Table 3. The total
electronic energies of TS1 and TS2 at B3LYP/LANL2DZ level
are K176.36664 and K254.93407 hartrees while the single point
4. Structure of the transition state
The geometry around both the tin atoms is distorted trigonal
bipyramidal. In both TS1 and TS2 the two alkyl groups occupy
equatorial positions and the chlorine atoms Cl1, Cl3 and Cl3,
Cl12 are disposed axially around Sn2 and Sn4, respectively. In
TS2 the two ethyl groups occupy the equatorial positions. Bond
order analyses of TS1 and TS2 indicate the three center
bonding nature of the SnCSn bridge, the contribution of tin
being 19.6 and 19.1% in TS1 and 22.3 and 21.4% in TS2.
Similar type of transition state structures with the trigonalbipyramidal geometry around both the tin atoms, are also
obtained for the ligand exchange reactions involving n-propyl,
iso-propyl and n-butyltin trichlorides at PM3 level of
calculation. Such a transition state with five coordinated tin
has been already identified in all the six steps of the
transmetallation reaction of 2-trimethylstannylbuta-1-3-diene
Table 2
PM3 Computed thermodynamic parameters at 298 K, for the reactions studied (kcal molK1)
2MeSnCl3/Me2SnCl2CSnCl4
2EtSnCl3/Et2SnCl2CSnCl4
DH
DS
DG
Ea
DH#
DS#
DG#
0.017
K0.11
K0.00
K0.01
0.34
3.17
37.5
36.4
K0.08
0.05
K0.04
K0.05
11.84
15.61
B.S. Krishnamoorthy et al. / Journal of Molecular Structure: THEOCHEM 761 (2006) 89–95
93
Table 3
Calculated energies (without zero-point energy correction) and activation energies obtained from B3PW91/LANL2DZ, B3LYP/LANL2DZ, MP2/LANL2DZ//
B3LYP/LANL2DZ levels and with solvent effect of H2O and toluene at B3PW91/LANL2DZ and B3LYP/LANL2DZ levels obtained from SCRF calculations
(IPCM method)
Molecules
B3PW91/
LANL2DZ
energy
(Hartrees)
B3PW91/
LANL2DZ
energy with
solvent effect
of H2O (IPCM
method)
(hartrees)
3Z78.39
B3PW91/
LANL2DZ
energy with
solvent effect
of toluene (IPCM
method)
(hartrees)
3Z2.37
B3LYP/
LANL2DZ
energy
(Hartrees)
B3LYP/
LANL2DZ
energy with
solvent effect
of H2O(IPCM
method)
(hartrees)
3Z78.39
B3LYP/
LANL2DZ
energy with
solvent effect
of toluene(IPCM
method)
(hartrees)
3Z2.37
MP2/
LANL2DZ//
B3LYP/
LANL2DZ
energy
(hartrees)
MeSnCl3
TS1
Me2SnCl2
SnCl4
Eab (kcal/mol)
EtSnCl3
TS2
Et2SnCl2
Eac (kcal/mol)
K88.28661
K176.49822
K113.15125
K63.40855
47.1
K127.55075
K255.04081
K191.67507
38.1
K84.16412
K168.28513
K111.78500
K57.94194
27.1
K123.45671
K246.89332
K188.95683
12.6
K84.16412
K168.27320
K110.94757
K57.94194
34.5
K123.45671
K246.87737
K188.95683
22.6
K88.22345
K176.36664
K113.12329
K63.31049
50.4
K127.49992
K254.93407
K191.67190
41.3
K84.09863
K168.14798
ta
K57.84012
30.9
K123.40329
K246.78069
K188.95223
16.3
K84.098633
K168.136638
K110.915787
K57.840122
38.0
K123.403293
K246.765039
K188.952229
26.1
K87.335135
K174.585061
K112.261571
K62.395623
53.5
K126.442515
K252.815504
K190.473239
43.6
a
b
c
t, not converged.
Ea, energy of activation calculated for the reaction 2MeSnCl3/Me2SnCl2CSnCl4.
Ea, energy of activation calculated for the reaction 2EtSnCl3/Et2SnCl2CSnCl4.
calculations at MP2 level with the same basis set give
K174.58506 and K252.81550 hartrees for the TS1 and TS2,
respectively. Free energy of the reaction, free energy of
activation and rate constants calculated at B3LYP/LANL2DZ
level are given in Table 4. There is not much difference in the free
energy of activation for the reactions involving methyl and ethyl
species (26.9, 27.2 kcal/mol), calculated at B3LYP/LANL2DZ
level. The rate constant values for the reactions involving methyl
and ethyl species (1.1!10K7 and 6.7!10K8 l molK1 sK1)
are in close agreement with the experimental value
(2!10K7 l molK1 sK1 for the methyl tintrichloride) [14].
6. Solvent effects
Self consistent reaction field (SCRF) single point calculations (IPCM method) on the B3LYP/LANL2DZ optimized
structures show that the solvents have considerable effect on
the reaction. The energy of activation for the reactions
involving methyl and ethyl species in water are 30.9 and
16.3 kcal/mol (Table 3). These are quite lower than the values
of the gas phase energy of activations, i.e. 50.4 and
41.3 kcal molK1, respectively, and imply that the reaction is
faster in solvent like water. On comparing the energy of
Table 4
Free energy of the reactions, free energy of activation and the rate constants at 298 K, for the reactions calculated at B3LYP/LANL2DZ level
Reactions
Free energy of the reaction
DG (kcal molK1)
Free energy of activation DG#
(kcal molK1)
Rate constant
(l molK1 sK1)
2MeSnCl3/Me2SnCl2CSnCl4
2EtSnCl3/Et2SnCl2CSnCl4
K0.4
1.1
26.9
27.2
1.1!10K7
6.7!10K8
Table 5
DFT calculated global hardness, chemical potential, electrophilicity, global softness and dipole moment values of the molecules at B3LYP/LANL2DZ level
Compounds
Hardness (h)
(IKA)/2 (eV)
Chemical potential
(m)Z[K(ICA)/2]
Electro-philicity
uZm2/2h
Softness SZ1/2h
(eV)K1
Dipole moment
(debye)
MeSnCl3
TS1
Me2SnCl2
SnCl4
EtSnCl3
TS2
Et2SnCl2
0.106
0.075
0.123
0.091
0.104
0.073
0.118
K0.227
K0.250
K0.182
K0.269
K0.221
K0.246
K0.171
0.242
0.417
0.134
0.397
0.233
0.416
0.124
4.701
6.651
4.077
5.501
4.791
6.859
4.239
4.420
5.347
4.764
0.001
4.938
4.784
5.377
94
B.S. Krishnamoorthy et al. / Journal of Molecular Structure: THEOCHEM 761 (2006) 89–95
Table 6
Global hardness, chemical potential, electrophilicity, global softness and Dipole moments of the molecules obtained from B3PW91/LANL2DZ level
Molecules
Hardness
(h)Z(IKA)/2 (eV)
Chemical potential
(m)Z[K(ICA)/2]
Electro-philicity
uZm2/2h
Softness SZ1/2h
(eV)K1
Dipole moment
(debye)
MeSnCl3
TS1
SnCl4
Me2SnCl2
EtSnCl3
TS2
Et2SnCl2
0.107
0.076
0.092
0.123
0.105
0.075
0.118
K0.23
K0.253
K0.272
K0.184
K0.223
K0.25
K0.173
0.246
0.42
0.404
0.137
0.237
0.417
0.126
4.66
6.563
5.453
4.062
4.772
6.688
4.232
4.499
6.993
0.001
5.039
5.136
5.557
5.523
activation in the solvents, water and toluene (Table 3), the
reaction is shown to be more feasible in the more polar solvent.
The activation energies obtained from the SCRF calculations at
B3PW91/LANL2DZ level also reflect the same trend.
Tables 5 and 6 give the global hardness, chemical potential,
electrophilicity, global softness and the dipole moment values
obtained from B3LYP/LANL2DZ and B3PW91/LANL2DZ
levels for the molecules involved in the reactions taken in this
study. The transition states TS1 and TS2 are softer than the
reactants, MeSnCl3 and EtSnCl3, respectively. These transition
states are higher in energy with respect to the reactants and
products and possess lower hardness. This is in accordance
with the maximum hardness principle (MHP), which states that
the minimum energy structure has the maximum hardness
[40,41]. The global hardness values of individual reactants and
products reveal that the hardest species lie in the product side.
The average hardness of the products is greater than the
average hardness of the reactants, which indicate that the
ligand exchange is energetically favourable in the forward
direction. The dipole moments of the transition states indicate
that they are considerably polar. The calculated electrophilicity
of the transition states are higher than that of the reactants
indicating their possible stabilization by nucleophiles.
7. Conclusion
The major outcome of the present computational study for
the experimentally studied disproportionation reaction of
MeSnCl3 may be summarized as follows: For qualitative
analysis of disproportionation reactions of alkyltin compounds
the PM3 results are adequate in most cases. There is not much
difference in the geometrical parameters obtained from PM3
and DFT calculations. In the transition states, tin centers are
electrophilic, and nucleophiles will stabilize the same.
Reactions proceed via chloro and alkyl bridged transition
states. There is no new bond formation and the bonds only get
redistributed. The TS structure around the tin center is distorted
trigonal bipyramidal in all cases. Polar solvents make the
reaction faster and more feasible presumably due to the polar
nature of the TS, as authenticated by their dipole moments,
atomic charges and electrophilicity values. Disproportionation
reactions discussed above are energetically favourable as is
indicated by the associated hardness values vis-à-vis the
maximum hardness principle. The rate constants calculated
from the DFT method is in good agreement with the
corresponding experimental values.
References
[1] G.J.M. Van Der Kerk, J.G.A. Luijten, in: A.K. Sawyer (Ed.), Organotin
Compounds, 1, Marcel Dekker, New York, 1971, p. 1.
[2] C.J. Evans, S. Karpel, Organotin Compounds in Modern Technology,
Elsevier Science Publishers, The Netherlands, 1985, p. 1.
[3] P.G. Harrison, in: P.G. Harrison (Ed.), Chemistry of Tin, Chapman &
Hall, New York, 1989, p. 359.
[4] M.J.S. Dewar, J.E. Friedheim, G.L. Grady, Organometallics 4 (1985)
1784.
[5] M.J.S. Dewar, G.L. Grady, D.R. Kuhn, K.M. Merz Jr., J. Am. Chem. Soc.
106 (1984) 6773.
[6] M.A. Vincent, I.H. Hillier, R.J. Hall, E.J. Thomas, J. Org. Chem. 64
(1999) 4680.
[7] K. Xu, D. Xie, J. Org. Chem. 68 (2003) 2673.
[8] L.W. Chung, T.H. Chan, Y.-D. Wu, Organometallics 24 (2005) 1598.
[9] M.H. Chisholm, A.M. Macintosh, J. Chem. Soc., Dalton Trans. (1999)
1205.
[10] P. Boudjouk, S.D. Kloos, B.-K. Kim, M. Page, D. Thweatt, J. Chem. Soc.,
Dalton Trans. (1998) 877.
[11] T.J. Pinnavaia, M.T. Mocella, B.A. Averill, J.T. Woodard, Inorg. Chem.
12 (1973) 763.
[12] S. Ahmad, Coord. Chem. Rev. 248 (2004) 231.
[13] J.A. Zubieta, J.J. Zuckerman, Structural tin chemistry in: S.J. Lippard
(Ed.), Prog. Inorg. Chem., 24, Wiley, New York, 1978.
[14] K.A. Kocheshkov, Chem. Ber. 62 (1929) 996; K.A. Kocheshkov, Chem.
Ber. 66 (1933) 1661; K.A. Kocheshkov, M.M. Nad, Chem. Ber. 67 (1934)
717; K.A. Kocheshkov, M.M. Nad, A.P. Alexandrov, Chem. Ber. 67
(1934) 1348.
[15] D. Grant, J.R. Van Wazer, J. Organomet. Chem. 4 (1965) 229.
[16] S. Thoonen, B.-J. Deelman, G. van Koten, Chem. Commun. (2001) 1840.
[17] C.A. Bertelo, C. Duriez, S. Girois, B. Jousseaume, T. Toupance, Appl.
Organomet. Chem. 17 (2003) 631.
[18] D. Marton, G. Tagliavini, Appl. Organomet. Chem. 9 (2004) 553.
[19] B.S.
Krishnamoorthy,
S.
Chandrasekar,
P.
Arukumar,
K. Panchanatheswaran, Appl. Organomet. Chem. 19 (2005) 186.
[20] V.J. Hall, E.R.T. Tiekink, Acta Crystallogr. C52 (1996) 2141.
[21] G. Plazzogna, S. Bresadola, G. Tagliavini, Inorg. Chim. Acta 2 (1968)
333.
[22] J.J.P. Stewart, J. Comput. Chem. 10 (1989) 221.
[23] J.J.P. Stewart, MOPAC 6.0, QCMP 137, QCPE, Bloomington, IN, USA
[24] N.L. Allinger, J. Am. Chem. Soc. 99 (1977) 8127.
[25] M.J.S. Dewar, S. Krischner, J. Am. Chem. Soc. 93 (1971) 4290.
[26] J.W. McIver Jr., J. Komornicki, J. Am. Chem. Soc. 94 (1972) 2625;
J.W. McIver Jr., J. Komornicki, Chem. Phys. Lett. 10 (1971) 303.
[27] M.J. Frisch et al., GAUSSIAN03, Revision B.03, Gaussian, Inc., Pittsburgh
PA, 2003
[28] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785; A.D. Becke,
J. Chem. Phys. 98 (1993) 5648.
[29] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
B.S. Krishnamoorthy et al. / Journal of Molecular Structure: THEOCHEM 761 (2006) 89–95
[30] J.P. Perdew, Y. Wang, Phys. Rev. B 45 (1992) 13244.
[31] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270; W.R. Wadt, P.J. Hay,
J. Chem. Phys. 82 (1985) 284; P.J. Hay, W.R. Wadt, J. Chem. Phys. 82
(1985) 299.
[32] Y.-H. Hu, M.-D. Su, Int. J. Quant. Chem. 102 (2005) 72.
[33] M.A. Buntine, F.J. Kosovel, E.R.T. Tiekink, Cryst. Eng. Commun. 00
(2003) 1.
[34] N. Takagi, K. Yamazaki, S. Nagase, Bull. Korean Chem. Soc. 24
(2003) 832.
95
[35] J.B. Foresman, T.A. Keith, K.B. Wiberg, J. Snoonian, M.J. Frisch,
J. Phys. Chem. 100 (1996) 16098.
[36] P. Geerlings, F. De Proft, W. Langenaeker, Chem. Rev. 103 (2003) 1793.
[37] R.G. Parr, W. Yang, Density Functional Theory of Atoms and Molecules,
Oxford University Press, Oxford, UK, 1989.
[38] R.G. Parr, L.V. Szentpaly, S. Liu, J. Am. Chem. Soc. 121 (1999) 1922.
[39] R.G. Pearson, Proc. Natl Acad. Sci. USA 83 (1986) 8440.
[40] R.G. Pearson, J. Chem. Educ. 64 (1987) 561.
[41] R.G. Parr, P.K. Chattaraj, J. Am. Chem. Soc. 113 (1991) 1854.