A DFT analyses for molecular structure, electronic state and spectroscopic property of a dithiolene tungsten carbonyl complex

Article abstract of DOI:10.1016/j.saa.2013.12.107

Bis(dithiolene) tungsten carbonyl complex, W(S₂C ₂Ph₂)₂(CO)₂ was successfully synthesized and the structure, frontier molecular orbital and optical properties of the complex were investigated theoretically using density functional theory calculations. The investigation started with a molecular structure construction, followed by an optimization of the structural geometry using generalized-gradient approximation (GGA) in a double numeric plus polarization (DNP) basis set at three different functional calculation approaches. Vibrational frequency analysis was used to confirm the optimized geometry of two possible conformations of [W(S₂C₂Ph₂) ₂(CO)₂], which showed distorted octahedral geometry. Electronic structure and optical characterization were done on the ground states. Metal to ligand and ligand to metal charge transfer were dominant in this system.

Full text of DOI:10.1016/j.saa.2013.12.107

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 375–382
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A DFT analyses for molecular structure, electronic state
and spectroscopic property of a dithiolene tungsten carbonyl complex
Khuzaimah Arifin a,b, Wan Ramli Wan Daud a,b, Mohammad B. Kassim a,c,
⇑
a Fuel Cell Institute, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia
b Department of Chemical and Process Engineering, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia
c School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
ꢀ
Molecular structure of two tungsten
carbonyl complex isomers were
constructed.
Optimization geometry processes
were done on three different GGA
calculations.
The IR spectrum of the complex
matched the calculated vibrational
frequency spectra.
Orbital profiles for HOMO/LUMO of
the cis and trans [W(S2C2Ph2)2(CO)2]
are presented.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 June 2013
Received in revised form 7 November 2013
Accepted 23 December 2013
Available online 8 January 2014
Bis(dithiolene) tungsten carbonyl complex, W(S2C2Ph2)2(CO)2 was successfully synthesized and the
structure, frontier molecular orbital and optical properties of the complex were investigated theoretically
using density functional theory calculations. The investigation started with a molecular structure con-
struction, followed by an optimization of the structural geometry using generalized-gradient approxima-
tion (GGA) in a double numeric plus polarization (DNP) basis set at three different functional calculation
approaches. Vibrational frequency analysis was used to confirm the optimized geometry of two possible
conformations of [W(S2C2Ph2)2(CO)2], which showed distorted octahedral geometry. Electronic structure
and optical characterization were done on the ground states. Metal to ligand and ligand to metal charge
transfer were dominant in this system.
Keywords:
Metal carbonyl
Charge-transfer
DFT
HOMO–LUMO
Dithiolene
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
medical application as coenzyme, antioxidant and anticancer
[2–4]. Furthermore, metal carbonyl complexes are also frequently
Transition metal carbonyl complexes have been extensively
studied due to their attractiveness for luminescence and electron
transfer reactions. Several of these complexes have been shown
to be effective as catalysts in the catalytic process [1] and in
used as starting materials for other organometallic complexes
since the CO ligands can easily be replaced partially or completely
in chemical or photochemical reactions [5]. Carbonyl complexes
[M(CO)xL6Àx] bearing dithiolene ligands are among the most
widely investigated [6,7]. These complexes prepared from
M(CO)5(solvent) that react readily with any available donor atom
of dithiolene ligands [5,8,9]. Molybdenum, tungsten and ruthe-
nium are transition metals that are frequently used in dithiolene
carbonyl complexes.
⇑
Corresponding author at: School of Chemical Sciences and Food Technology,
Faculty of Science & Technology, Universiti Kebangsaan Malaysia, 43600 Bangi,
Selangor, Malaysia. Tel.: +60 3 89213980; fax: +60 3 89212410.
E-mail address: mbkassim@ukm.my (M.B. Kassim).
1386-1425/$ - see front matter Ó 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.12.107

376
K. Arifin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 375–382
Currently, computational explorations on carbonyl complexes
Preparation of [W(S2C2Ph2)2(CO)2] complex
have received much attention [2,10–13]. Although successful syn-
thesis of carbonyl complexes have been reported previously, some
of fundamental aspects such as molecular orbital configurations
remain unsolved. With the aid of modern computational simula-
tion method, the orbital, optical and structural properties can be
accurately obtained and in most cases the results were comparable
to the experimental values [14,15]. Therefore, the physical, chem-
ical and optical data of various materials in various forms such as
crystals, nano-materials and surface alloys can be predicted with-
out experimental work [16].
In this paper we describe the synthesis, molecular structure and
density functional study (DFT) analysis of a dithiolenes complex
[W(S2C2Ph2)2(CO)2]. The complex has been prepared from a reac-
tion of thioester and [W(CO)5] fragment, where [W(CO)5(solvent)]
was photogeneratively prepared from W(CO)6 in THF or CH3OH
solvents [17]. In this class of complexes, the tungsten metal centre
assumed an octahedral geometry and since W(L)4(CO)2 molecule
has two thio bidentat ligands, there are two isomers of the com-
plex namely, cis-[W(L)4(CO)2] and trans-[W(L)4(CO)2] as shown in
Fig. 1. The molecular structures reported in this paper were devel-
oped computationally based on the elemental and spectroscopy (IR
and UV–visible) results. The computational calculation began with
geometry optimization of the complex structure, which was con-
structed as described in the experimental section.
A solution of W(CO)6 (1 g) in tetrahydrofuran (THF) (40 ml) was
irradiated under UV light in N2 atmosphere at room temperature
for 2 h to generate the W(CO)5THF intermediate. Thioester (II)
(0.5 g) was added to this solution and the mixture was stirred for
about 1 h at room temperature. The solvent was then removed un-
der reduced pressure. An orange–red solid was isolated upon the
addition of 30 ml of Et2O/hexane mixture (1:2 v:v) at approxi-
mately À15 °C. Yield: 39%. IR-spectra (cmÀ1): 3026 (CAH); 2071
and 1980 (C@O); 1677 cmÀ1 (C@C); 1155 cmÀ1 (CAS) and 697
(W@S). Elemental CHNS Analysis (%): C 50.28 (49.73); H 3.01
(2.78), S 15.92 (17.70).
Computational details
The molecular geometry and density functional theory (DFT)
calculations were performed using the Dmol3 module in Materials
Studio 5.5, Accelrys Inc. DMol3 is a unique, accurate, and reliable
DFT quantum–mechanical code that can be used to predict the
properties of materials and can be applied to simulations of pro-
cesses in a gas phase, solvent, on a surface and solid state [18].
The molecular structure of the tungsten carbonyl complex was
constructed based on octahedral geometry system. Self-consistent
field (SCF) method was used for calculating the electronic structure
with the treatment to DFT Semi-core Pseudopots (DSPP)[19] for
being polarizable and spin-unrestricted. Generalized-gradient
approximation (GGA) in
a double numeric plus polarization
Experimental
(DNP) basis set was used in the simulation. The structure was opti-
mized via the use of the following functions: the Becke exchange
functional (B88) [20] in conjunction with the Perdew–Wang
correlation (BP)[21], Lee–Yang–Parr correlation (BLYP) and
Perdew–Burke–Enzerhof (PBE) functions [22]. Furthermore, TDDFT
calculation was conducted on ground state in restricted
Hatree-Folk (RHF) at vacuum and some of salvation schemes.
Materials and instrumentations
Benzoin, tungsten hexacarbonyl, phosphorus pentasulfide and
solvents were purchased from Sigma–Aldrich and were used as re-
ceived. IR spectra were determined using a Thermo Nicolet 6700
FTIR spectrometer, 1H and 13C NMR spectra were recorded using
an Avans Bruker 400 MHz spectrometer and the absorption spectra
were recorded using a Varian Cary 5000 UV–Vis spectrophotome-
ter. Elemental analyses were performed using an Elemental Micro
CHNS analyser.
Results and discussion
Synthesis and spectroscopic characterization
Bis(dithiolene) tungsten carbonyl complex, W(S2C2Ph2)2(CO)2,
originally was prepared via the reaction of photogenerated inter-
mediate of W(CO)5THF with a thioester that was prepared previ-
ously from the reaction of benzoin and P4S10 [23] (Fig. 2). The
complex was collected as a purple–red solid, soluble in CH3CN,
THF, and dichloromethane (DCM) but was insoluble in non-polar
solvents. The physical characteristics of the [W(S2C2Ph2)2(CO)2]
were similar to those previously reported in the literature [24].
The complex was stable as a solid under refrigeration but became
unstable in solution. The FTIR spectrum exhibited two CO bands at
2071 (w) and 1980 cmÀ1 (s) indicating the presence two of CO [25].
The WAS vibration frequency is indicated by the peak at 670 cmÀ1
(vs) [23]. Other features of the IR-spectrum included various sig-
nals at 2953 cmÀ1 (CAH aromatic), 1677 cmÀ1 (C@C aromatic)
and 1155 cmÀ1 (CAS) as shown in Fig. 3A. The CHNS elemental
analysis confirmed the empirical formula of the product as
Preparation of [W(S2C2Ph2)2(CO)2] complex
Preparation of (S2C2Ph2) (II) ligand
Benzoin (30 g) and phosphorus pentasulfide P4S10 (45 g) were
dissolved in dry dioxane (250 ml). The mixture was refluxed for
3–4 h in inert atmosphere. Hydrogen sulfide produced from the
reaction was trapped using lead acetate. The mixture was then
cooled to room temperature, filtered and the filtrate was concen-
trated in vacuo to give dark-red oil with a 37.5% yield. IR-spectra
(cmÀ1):1254 (P@O); 1081 and 958 (PAO and PAOAP); 870 (P@S).
UV/Vis spectrum kmax/nm (
300 nm (35,000) and 400 nm (23,000).
e
 104 MÀ1 cmÀ1) in acetone solution:
C30H20O2S4W that corresponded to the desired bis(dithiolene)
tungsten carbonyl complex (III) in Fig. 2.
Molecular structure and geometry optimization
The molecular structure of W(S2C2Ph2)2(CO)2 complex was con-
structed by computations based on the results from the elemental
and spectral analyses. The bond lengths and angles were adjusted
according to references [26,27]. Construction of the complex
started with fixing an octahedral geometries of tungsten metal
Fig. 1. Molecular conformations for octahedral of W(L)4(CO)2 complexes.

K. Arifin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 375–382
377
Fig. 2. The reaction scheme for preparation of W(S2C2Ph2)2(CO)2 complex.
values from the infrared spectra was used as an additional measure
to confirm the molecular structure of [W(S2C2Ph2)2(CO)2.
The optimized structure and energy of the cis and trans
[W(S2C2Ph2)2(CO)2] calculated using BLYP, BP and PBE functions
are shown in Table 1. The optimized functional energies in
ascending order were BLYP, BP, and PBE, respectively. In the func-
tional calculation, energy of optimized cis was larger than that of
transgeometry with only slight differences in bond length and
angle of similar moeities. The bond lengths (Å) and angles (°) were
collected in Table 2 and a comparison to similar structure reported
in the literature was also presented. All calculated bond lengths
were found to be longer than the experimental data. However,
the magnitudes of bond length and angle of PBE were the closest
to the standard values reported by Allen et al. and Chandrasekaran
et al. [24,29]. PBE functional results also depicted the greatest
kinetic energy which, resulted in the shortest bond length that
was in agreement with experimental data. Since geometry optimi-
zation process of W(S2C2Ph2)2(CO)2 using PBE functional was more
accurate compared to BLYP and BP calculations, the structure was
applied in DFT investigations and calculations.
In the optimized geometry, cis [W(S2C2Ph2)2(CO)2] has four
S-atom from the chelating dithiolene bonded to tungsten metal
centre and two C-atom of the CO ligands, in a distorted octahedral
geometry. PBE calculations showed that SAWAS angles in two
five-member (WS2C2) rings denoted by \S1WS2 and \S3WS4 were
78.847° and 78.602°, respectively. Whereas the angles of the
SAWAS between two five-member (WS2C2) rings denoted by
\S1WS3 and \S2WS4 were 77.070° and 138.613°, respectively,
while the angle of the CAWAC was 97.797°. The calculated angles
were smaller than that was reported for the X-ray single crystal
structure of [W(S2C2Me2)2(CO)2] complex denoted by \S1WS2,
\S3WS4, \S1WS3, and \S2WS4 with values of 81.05°, 80.96°,
88.80° and 148.03°, respectively [24]. The differences indicated
that the octahedral distortion suggested by the theoretical model-
ing was greater than experimental values, in which the bidentate
dithiolene ligand was supposed to affect the geometry. In addition,
the calculated WAS bond lengths were between 2.456 Å and
2.471 Å, which were longer by between 0.04 and 0.09 Å, respec-
tively, compared to the X-ray structural data reported for sulfido-
bridged dinuclear tungsten (V) complex of dithiolene reported by
Umakoshi et al. [30]. However, the calculated results were
Fig. 3. Comparison of FTIR experiment (A) and harmonic vibrational frequencies
spectrum of: cis [W(S2C2Ph2)2(CO)2] (B) and trans-[W(S2C2Ph2)2(CO)2](C).
centre before adding the ligand at the appropriate positions using
the Materials Studio suite of programmes. The calculation began
with a geometry optimization of the complex structure using the
Dmol3 module. The geometrical optimization was an iterative pro-
cedure in which the coordinates of the atoms were adjusted until
the energy of the structure was brought to a stationary value.
The stationary value of the minimum energy was determined by
analysis of the vibrational frequencies at the ground state geome-
try of the complex. The absence of imaginary eigenvalues con-
firmed the geometry’s validity, from which further properties can
be calculated [28]. Fig. 3 was shown a comparison of FTIR experi-
ment and harmonic vibrational frequencies spectra of cis and trans
[W(S2C2Ph2)2(CO)2]. Although the spectra are not exactly the same,
however, the important peaks appear in both spectra. A compari-
son between the calculated frequencies and the experimental

378
K. Arifin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 375–382
Table 1
Energy calculation for structural optimization of two isomers of W(S2C2Ph2)2(CO)2 at three different DFT functional calculations.
W(S2C2Ph2)2(CO)2
Energy optimization
PBE method:
Kinetic = À7.8076 Ha
Electrostatic = À10.6172 Ha
Exchange–correlation = 4.3706 Ha
Spin polarization = 2.5425 Ha
BLYP method:
Kinetic = À6.6301 Ha
Electrostatic = À10.9469 Ha
Exchange–correlation = 4.2750 Ha
Spin polarization = 2.2988 Ha
BP method:
Kinetic = À7.3574 Ha
cis-
Electrostatic = À10.9701 Ha
Exchange–correlation = 4.4917 Ha
Spin polarization = 2.5742 Ha
PBE method:
Kinetic = À6.6823 Ha
Electrostatic = À11.7075 Ha
Exchange–correlation = 4.3619 Ha
Spin polarization = 2.5425 Ha
BLYP method:
Kinetic = À5.8251 Ha
Electrostatic = À11.7120 Ha
Exchange–correlation = 4.2638 Ha
Spin polarization = 2.2988 Ha
BP method:
Kinetic = À6.2779 Ha
trans-
Electrostatic = À12.0158 Ha
Exchange–correlation = 4.4841 Ha
Spin polarization = 2.5742 Ha
considered to be in the normal range [26]. The two five-member
(WS2C2) rings in the model were neither symmetrical nor planar.
In addition, the two dithiolenes bidentat ligands were twisted
relative to each other and the phenyl rings attached to each CAC
olefin were position away from each other. The average calculated
values of CAS and CAC bond lengths in the dithiolene moieties
were 1.734 Å and 1.385 Å, respectively. The considerably shorter
and longer values for both CAS and CAC olefin bond lengths,
respectively, are significant in the determination of the oxidation
state of the complex (Fig. 4). Dithiolene ligands are known poten-
tially to be redox active non-innocent ligands, meaning that they
can exhibit a variety of redox states and that frequently show
interesting optical properties [31,32]. Similarly, the calculated
bond length for CAS and CAC could also be influenced by the
involvement of a thienyl radical monoanion from both dithiolene
ligands resulting in the tungsten centre to exhibit a W(II) oxidation
state in the cis-[W(S2C2Ph2)2(CO)2] molecule.
conformations are different. The band gap is an important measure
of stability [16,33] which influences the light absorption ability of a
molecule. The HOMO and LUMO band gap of cis [W(S2C2Ph2)2
(CO)2] is 0.05906 Ha (1.607 eV), while that of trans [W(S2C2Ph2)2
(CO)2] is 0.03563 Ha (0.970 eV). These energy gaps were reflected
in the light absorption characteristics of the molecules which
showed the trans molecule absorbs light radiation in a wider range
compared to the cis molecule (Fig. 7).
The HOMO of cis [W(S2C2Ph2)2(CO)2] is located on the tungsten
and sulfur atoms with some electron density in the aromatic ring,
and surprisingly, no involvement was found from the CO ligands.
While the LUMO was concentrated on the W, S and CAC olefin of
the W(S2C2) ring and the carboxyl ligands. On the other hand,
the trans [W(S2C2Ph2)2(CO)2] molecular orbital configuration was
slightly different to the cis [W(S2C2Ph2)2(CO)2] isomer. The HOMO
of trans [W(S2C2Ph2)2(CO)2] is located along the W(S2C2) rings and
WACO bonds. The LUMO configuration of trans was similar to the
HOMO, the electron density populates the same atoms and bonds,
but the electron density population in both HOMO and LUMO were
slightly different.
The molecular orbital of the HOMO À 1 in the cis [W(S2C2Ph2)2
(CO)2] complex was found to be concentrated on the WAS bonds
and the CO ligands with some density in the CAC olefin and aro-
matic rings. In the HOMO À 2, the distribution of molecular orbital
was similar to HOMO À 1, however the electron density was found
to be more concentrated on WACO bonding. In the LUMO + 1 and
LUMO + 2, the electronic distributions were similar to the LUMO,
which were concentrated on the W and CAO ligands with some
electron density found at the S and C-olefin atoms. The HOMO À 1
and HOMO À 2 energies were À5.606 and À5.940 eV, respectively.
Distortion of tungsten octahedral geometry in the trans [W(S2-
C2Ph2)2(CO)2] was smaller than that of the cisgeometry. Angles of
\SWS bonds were between 92.058° and 97.056°, while the WAS
bond lengths were between 2.481 and 2.524 Å. The two five-mem-
bered (WS2C2) rings conformation was planar and the two dithio-
lenes bidentat ligands were twisted relative to each other.
Molecular orbital configuration
The orbital profiles for the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) of
cisand trans [W(S2C2Ph2)2(CO)2] complexes are presented in Figs. 5
and 6, respectively. The HOMO–LUMO band gaps in both

K. Arifin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 375–382
379
Table 2
Comparison of selected bond lengths (Å) and angles (°) of optimized W(S2C2Ph2)2(CO)2 geometries using three DFT functional calculations.
Parameter
cis-[W(S2C2Ph2)2(CO)2]
BLYP BP
X-ray (a)
trans-[W(S2C2Ph2)2(CO)2]
BLYP BP
PBE
PBE
Bond length (Å)
W(1)AS(1)
W(1)AS(2)
W(1)AS(3)
W(1)AS(4)
W(1)AC(5)
W(1)AC(6)
S(1)AC(1)
S(2)AC(2)
S(3)AC(3)
S(4)AC(4)
C(1)AC(2)
C(3)AC(4)
C(5)AO(1)
C(6)AO(2)
2.504
2.469
2.465
2.471
2.465
2.054
2.052
1.737
1.737
1.737
1.737
1.385
1.385
1.160
1.166
2.471
2.372
2.371
2.369
2.365
2.019
2.020
1.722
1.720
1.726
1.721
1.365
1.361
1.141
1.142
2.512
2.450
2.491
2.452
2.475
2.131
2.099
1.731
1.735
1.734
1.731
1.404
1.402
1.157
1.156
2.449
2.497
2.508
2.495
2.077
2.075
1.753
1.754
1.753
1.756
1.386
1.385
1.160
1.161
2.463
2.469
2.456
2.048
2.052
1.735
1.734
1.740
1.736
1.385
1.386
1.160
1.159
2.481
2.524
2.482
2.146
2.126
1.744
1.748
1.751
1.744
1.409
1.408
1.158
1.155
2.487
2.445
2.474
2.128
2.095
1.731
1.734
1.733
1.731
1.402
1.400
1.156
1.155
Angles (°)
S(1)AW(1)AS(2)
S(1)AW(1)AS(3)
S(1)AW(1)AS(4)
S(1)AW(1)AC(5)
S(1)AW(1)AC(6)
S(2)AW(1)AS(3)
S(2)AW(1)AS(4)
S(2)AW(1)AC(5)
S(2)AW(1)AC(6)
S(3)AW(1)AS(4)
S(3)AW(1)AC(5)
S(3)AW(1)AC(6)
S(4)AW(1)AC(5)
S(4)AW(1)AC(6)
C(6)AW(1)AC(5)
78.19
139.34
137.94
77.92
78.61
138.79
138.79
78.06
75.34
138.51
77.79
104.16
141.11
78.62
75.57
77.71
78.85
138.61
138.73
77.87
75.32
138.16
77.07
104.04
141.58
78.60
75.30
77.77
81.05
88.34
148.03
129.44
76.77
141.56
88.80
133.22
79.01
80.96
133.05
78.49
129.32
77.15
84.20
79.59
87.26
166.11
92.06
88.67
161.28
112.80
97.06
82.78
79.17
96.67
83.66
92.54
86.82
179.25
78.62
124.14
154.78
93.14
85.24
153.32
76.50
95.78
85.91
79.211
96.46
82.80
93.31
89.01
177.40
78.70
126.66
152.07
94.29
84.76
151.49
73.97
94.77
86.29
78.98
95.77
83.80
93.61
87.81
178.42
75.44
138.56
77.631
103.77
140.72
78.18
75.44
77.92
140.72
103.77
98.49
141.81
103.33
98.14
140.57
104.96
97.78
X-ray single crystal structure data of complex dithiolene-carbonyl [W(S2C2Me2)2(CO)2].
a
Ref. [23].
Fig. 4. Various oxidation states of a dithiolene ligand [23].
While the LUMO + 1 and LUMO + 2 energies were À2.917 and
À2.466 eV, respectively. The HOMO À 1 to HOMO energy gap is
about 0.201 eV, which is smaller than the energy gap between
LUMO to LUMO + 1 (0.881 eV). This indicates that the cis
[W(S2C2Ph2)2(CO)2] geometry is much easier to be oxidized rather
than reduced.
ergy gap was about 0.405 eV while the energy gap of LUMO to
LUMO + 1 was much lower, 0.055 eV. The energy separation between
HOMO – 1 to HOMO of transgeometry were larger compared that
of LUMO to LUMO + 1. A comparison between the energy of the cis
and the transgeometry suggested that the trans [W(S2C2Ph2)2(CO)2]
molecule will be easier to be reduced than oxidized.
The HOMO À 1 of trans [W(S2C2Ph2)2(CO)2] was distributed on
the WAS bond, CAC olefin and aromatic rings but there was no
contribution from the CO ligand. While The HOMO À 2 was distrib-
uted evenly throughout the molecule except for sulfur atoms.
HOMO À 1 and HOMO À 2 energies were À5.004 and À5.409 eV,
respectively. While the energy of LUMO + 1 and LUMO + 2 were
À3.980 and À2.393 eV, respectively. The HOMO À 1 to HOMO en-
Electronic spectra
TDDFT excitation energies
Dithiolene carbonyl complexes of d6 metals are known as highly
photoactive material [34]. By using the TD-DFT approach, the
electronic transitions of these complexes can be evaluated. Table 3

380
K. Arifin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 375–382
Fig. 5. Energies and orbital structures of cis-[W(S2C2Ph2)2(CO)2].
Fig. 6. Energies and orbital structures of trans-[W(S2C2Ph2)2(CO)2].

K. Arifin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 375–382
381
Fig. 7. Calculated absorption spectra of cis-[W(S2C2Ph2)2(CO)2] (A) and trans-[W(S2C2Ph2)2(CO)2] (B) in vacuum.
Table 3
Summary of 12 lowest singlet TDDFT excitations energies for optical transitions of cis- and trans- [W(S2C2Ph2)2(CO)2] in vacuum.
cis
Overlap Excitation
eV nm
Oscilator
strength
Charge
transfer
trans-
Overlap Excitation
eV nm
Oscilator
strength
Charge
transfer
From To
Ha
From To
Ha
147 ? 148 0.75
146 ? 148 0.68
145 ? 148 0.58
147 ? 149 0.59
144 ? 148 0.43
143 ? 149 0.54
142 ? 148 0.37
141 ? 148 0.34
146 ? 148 0.70
140 ? 148 0.43
139 ? 148 0.38
138 ? 148 0.48
1.97 631 0.07226 0.00773
2.03 610 0.07472 0.25851
2.26 548 0.08317 0.01031
2.59 478 0.09532 0.00115
2.63 472 0.09661 0.01239
2.66 466 0.09771 0.00119
2.70 458 0.09939 0.00265
2.74 453 0.10054 0.00304
2.82 440 0.10347 0.07225
2.88 431 0.10581 0.09563
2.89 430 0.10602 0.00415
3.01 412 0.11072 0.02195
LMCT
147 ? 148 0.66
147 ? 149 0.70
146 ? 148 0.70
146 ? 149 0.74
145 ? 148 0.58
145 ? 149 0.64
144 ? 148 0.58
144 ? 149 0.65
143 ? 148 0.53
143 ? 149 0.46
142 ? 148 0.41
142 ? 149 0.40
1.06 1165 0.03912 0.00166
1.16 1071 0.04252 0.00018
MMCT, MLCT
MMCT, MLCT
LMCT, MLCT
LMCT, MLCT
LMCT, MLCT
LMCT, MLCT
LMCT, MLCT
LMCT, MLCT
LMCT, MLCT
LMCT
LMCT, MLCT
LMCT, MLCT
LMCT
LMCT
LMCT
LMCT
LMCT
LMCT
LMCT
1.57
1.62
1.88
1.99
2.26
2.35
2.38
2.41
2.43
2.48
790 0.05765 0.00599
763 0.05971 0.00846
659 0.06915 0.10799
622 0.07331 0.14867
549 0.08303 0.00384
527 0.08644 0.00145
520 0.08758 0.00345
515 0.08848 0.00055
510 0.08932 0.00520
499 0.09127 0.00208
LMCT
LMCT
LMCT
LMCT
Fig. 8. TDDFT excitations energies for optical transitions spectra of cis- [W(S2C2Ph2)2(CO)2] in benzene (A), ethanol (B), dimethylsulfoxide (C) and water (D).
collects the electronic transitions of TDDFT for 12 lowest singlet
state excitation energies of the cis and trans [W(S2C2Ph2)2(CO)2]
complexes in vacuum, while the spectra are shown in Fig. 7. The
calculated optical transitions for the cis isomer showed the lowest
absorption band at 631 nm was attributed to the d–d transition
from HOMO to LUMO which was allowed due to the distorted
nature of the structure. Since it is symmetrically forbidden for
octahedral complexes, the corresponding extinction coefficient

382
K. Arifin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 375–382
was small. The highest oscillator strength at 610 nm corresponded
to the transition of the HOMO À 1 to LUMO. There are some possi-
bilities that other electronic transitions can occur such as a
metal-to-ligand-charge transfer (MLCT) from the W to dithiol
and ligand-to-metal charge transfer (LMCT). MLCT and LMCT also
possible occurred at 548 nm, which is transition of HOMO À 2 to
LUMO. In addition there were other intense transitions in the
region of 412–478 nm, which were attributed to LMCT form the
lower HOMO orbitals.
The electronic transitions of the trans [W(S2C2Ph2)2(CO)2]
showed HOMO to LUMO transition at 1165 nm, which is most
likely due to d–d transition or MLCT. The highest oscillator strength
at 622 nm was most likely originated from the HOMO À 2 to
LUMO + 1 transition for the LMCT and MLCT. The lowest absorption
band at 499 nm was contributed by LMCT transition from the
HOMO À 4 to LUMO + 1 orbitals.
showed that the trans molecule absorbs light radiation in a wider
range compared to the cis molecule. In addition the electronic
absorption spectra of the complexes were affected the choice of
the solvents.
Acknowledgments
The authors would like to acknowledge the Universiti Kebang-
saan Malaysia for sponsoring this project under the UKM-GUP-
07-30-190, UKM-AP-TK-08-2010 and UKM-OUP-TK-16-73/2010
and UKM-OUP-TK-16-73/2011 research grants.
References
[1] B.F.M. Kimmich, P.J. Fagan, E. Hauptman, W.J. Marshall, R.M. Bullock,
Organometallics 24 (2005) 6220–6229.
[2] P. Datta, A.P. Mukhopadhyay, P. Manna, E.R.T. Tiekink, P.C. Sil, C. Sinha, J. Inorg.
Biochem. 105 (2011) 577–588.
[3] D. Bandarra, M. Lopes, T. Lopes, J. Almeida, M.S. Saraiva, M. Vasconcellos-Dias,
C.D. Nunes, V. Felix, P. Brandao, P.D. Vaz, M. Meireles, M.J. Calhorda, J. Inorg.
Biochem. 104 (2010) 1171–1177.
[4] L. Glans, D. Taylor, C. de Kock, P.J. Smith, M. Haukka, J.R. Moss, E. Nordlander, J.
Inorg. Biochem. 105 (2011) 985–990.
[5] K. Arifin, W.R.W. Daud, M.B. Kassim, Ceramics Int. 39 (2013) 2699–2707.
[6] K.-B. Shiu, J.-Y. Chen, G.-H. Lee, F.-L. Liao, B.-T. Ko, Y. Wang, S.-L. Wang, C.-C.
Lin, J. Organomet. Chem. 658 (2002) 117–125.
[7] K.-B. Shiu, S.-J. Yu, Y. Wang, G.-H. Lee, J. Organomet. Chem. 650 (2002) 37–42.
[8] C.R. Lucas, Can. J. Chem. 61 (1983) 1096–1099.
[9] S.M. El-Medani, O.A.M. Ali, R.M. Ramadan, J. Mol. Struct. 738 (2005) 171–177.
[10] K. Seufert, M.-L. Bocquet, W. Auwarter, A. Weber-Bargioni, J. Reichert, N.
Lorente, J.V. Barth, Nat. Chem. 3 (2011) 114–119.
[11] A.J. Blake, N.R. Champness, T.L. Easun, D.R. Allan, H. Nowell, M.W. George, J. Jia,
X.-Z. Sun, Nat. Chem. 2 (2010) 688–694.
[12] C. Makedonas, C.A. Mitsopoulou, Spectrochim. Acta A 64 (2006) 918–930.
[13] H. Zhou, Y. Zhang, D. Zhu, Spectrochim. Acta A 86 (2012) 20–26.
[14] X. Zhou, J. Cui, Z.H. Li, G. Wang, Z. Liu, M. Zhou, J. Phys. Chem. A 117 (2013)
1514–1521.
[15] S. Sebastian, S. Sylvestre, N. Sundaraganesan, M. Amalanathan, S. Ayyapan, K.
Oudayakumar, B. Karthikeyan, Spectrochim. Acta A107 (2013) 167–178.
[16] P. Guo, R. Ma, L. Guo, L. Yang, J. Liu, X. Zhang, X. Pan, S. Dai, J. Mol. Graph. Mod.
29 (2010) 498–505.
Solvatochromism
The calculated optical absorption spectra and solvatochromism
effects study of cis [W(S2C2Ph2)2(CO)2] are shown in Fig. 8. The
calculations were done in different dielectric solvents, namely:
benzene (A), ethanol (B), dimethysulfoxide (C) and water (D). All
optical calculations were carried out using an energy function on
an optimized geometry structure of PBE. The spectrum in benzene
with dielectric constant K = 2.284, was similar to the spectrum in
vacuum (Fig. 7A). There were two major absorption bands in the
visible region with the highest oscillator strength maximizes at
around 440 and 620 nm, which were more likely belong to charge
transfer bands. The spectrum in benzene was red-shifted about
10 nm compared the spectrum in vacuum. The similar spectrum
pattern was also observed in ethanol (K = 24.3) and other similar
solvents. The spectra for these solvents were slightly red-shifted
in solvents with increasing of dielectric constants. A slightly differ-
ent spectrum pattern was found for dimethysulfoxide (K = 46.7), in
which a new peak appeared at around 420 nm, while others peaks
will remain the same with a shift to a much lower energy (red-
shifted). The spectrum pattern in DMSO and water with dielectric
constant K = 78.54 were very similar and the whole spectra were
[17] C.A. Goddard, R.H. Holm, Inorg. Chem. 38 (1999) 5389–5398.
[18] B. Delley, J. Chem. Phys. 113 (2010) 7756–7764.
[19] B. Delley, Phys. Rev. B. 66 (2002) 155125–155133.
[20] A.D. Becke, Phys. Rev. 38 (1988) 3098–3100.
[21] J.P. Perdew, Y. Wang, Phys. Rev. B: Condens. Matter Mater. Phys. 45 (1992)
13244–13249.
[22] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865–3868.
slightly red-shifted (
D = 10 nm).
The pattern of the simulated spectra in all solvent calculation
were relative similar with some changes in the peaks position
and appearance of new peak for high dielectric constant solvents.
However, the oscillator strength of each peak in all solvents was
not much different. This study has shown that the solvent affects
the optical properties of the [W(S2C2Ph2)2(CO)2] complex.
[23] G.N. Schrauzer, V.P. Mayweg, W. Heinrich, Inorg. Chem.
1617.
4 (1965) 1615–
[24] P. Chandrasekaran, K. Arumugam, U. Jayarathne, L.M. Perez, J.T. Mague, J.P.
Donahue, Inorg. Chem. 48 (2009) 2103–2113.
[25] D.M. Adams, Metal-Ligand and Related Vibrations: A Critical Survey of The
Infrared and Raman Spectra of Metallic and Organometallic Compounds, 1st
ed., Edward Arnold, London, 1967.
[26] F.H. Allen, O. Kennard, D.G. Watson, L. Brammer, A.G. Orpen, R.J. Taylor, J.
Chem. Soc. Perkin Trans. 1 (2) (1987) S1–S19.
Conclusion
[27] T. Fujihara, A. Kobayashi, M. Iwai, A. Nagasawa, Acta Cryst. E 60 (2004) 1172–
1174.
[28] G.J. Wilson, G.D. Will, Inorg. Chim. Acta 363 (2010) 1627–1638.
[29] G.C. Allen, N.S. Hush, Prog. Inorg. Chem. 8 (1967) 357–389.
[30] K. Umakoshi, E. Nishimoto, M. Sokolov, H. Kawano, Y. Sasaki, M. Onishi, J.
Orgmett. Chem. 611 (2000) 370–375.
[31] P. Eranda, P. Basu, Dalton Trans. 25 (2009) 5023–5028.
[32] M.D. Ward, J.A. McCleverty, J. Chem. Soc. Dalton Trans. (2002) 275–288.
[33] J.I. Aihara, J. Phys. Chem. A 103 (1999) 7487–7495.
[34] A. Vlcek Jr., S. Zalis, Coord. Chem. Rev. 251 (2007) 258–287.
The investigation of dithiolene tungsten carbonyl complex by
density functional theory study has successfully developed the
molecular structure and probe the electronic energy states for both
cis and trans [W(S2C2Ph2)2(CO)2] complex isomers. The HOMO and
LUMO and the electronic transitions in both isomers have been
determined. The CO ligand contribute more to the electronic
properties of transisomer compared to the cisisomer. The study