Synthesis, experimental and theoretical characterization of palladium(II) and platinum(II) saccharinate complexes with 2-(2-pyridyl)benzimidazole

Article abstract of DOI:10.1016/j.saa.2011.04.038

New palladium(II) and platinum(II) complexes of saccharinate (sac) with 2-(2-pyridyl)benzimidazole (pybim) have been synthesized and characterized by elemental analysis and spectroscopic techniques. From the experimental studies, these complexes were formulated as [Pd(pybim)(sac)₂] (1), and [Pt(pybim)(sac)₂]·4H₂O (2). The ground-state geometries of both complexes were optimized using density functional theory (DFT) methods at the B3LYP level. A bidentate pybim ligand together with two N-coordinated sac ligands form the square-planar MN₄ coordination geometry around the palladium(II) and platinum(II) ions. The calculated IR and UV-vis spectral data have been correlated to the experimental results. Thermal analysis data support the molecular structures of both complexes.

Full text of DOI:10.1016/j.saa.2011.04.038

Spectrochimica Acta Part A 79 (2011) 1171–1178
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, experimental and theoretical characterization of palladium(II) and
platinum(II) saccharinate complexes with 2-(2-pyridyl)benzimidazole
Emel Guney , Yunus Kaya , Veysel T. Yilmaz , Sedat Gumusb
a
a
a,∗
a
Department of Chemistry, Faculty of Arts and Sciences, Uludag University, 16059 Bursa, Turkey
Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayis University, 55139 Samsun, Turkey
b
a r t i c l e i n f o
a b s t r a c t
Article history:
New palladium(II) and platinum(II) complexes of saccharinate (sac) with 2-(2-pyridyl)benzimidazole
Received 1 March 2011
Received in revised form 13 April 2011
Accepted 15 April 2011
(pybim) have been synthesized and characterized by elemental analysis and spectroscopic tech-
niques. From the experimental studies, these complexes were formulated as [Pd(pybim)(sac)2] (1), and
[
Pt(pybim)(sac)2]·4H2O (2). The ground-state geometries of both complexes were optimized using den-
sity functional theory (DFT) methods at the B3LYP level. A bidentate pybim ligand together with two
N-coordinated sac ligands form the square-planar MN4 coordination geometry around the palladium(II)
and platinum(II) ions. The calculated IR and UV–vis spectral data have been correlated to the experimental
results. Thermal analysis data support the molecular structures of both complexes.
Keywords:
Saccharinate
2
-(2-Pyridyl)benzimidazole
Palladium(II)
Platinum(II)
DFT
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
dazole ligands and their complexes are good candidates for optical
materials. By contrast, the reported palladium and platinum com-
plexes of pyridyl benzimidazoles are relatively insufficient and only
a few palladium(II) and platinum(II) complexes appeared in this
field [9,11,16–19]. It has been reported that some of these com-
plexes exhibited significant cytotoxic activity [17,18].
Saccharin (also named as 1,1-dioxo-1,2-benzothiazol-3-one or
o-benzosulfimide) is a well-known commercial sweetener. In addi-
tion to its use in the preparation of sugar-free products, the
coordination chemistry of saccharin has been extensively interest-
ing in the last decades because of its coordination ability forming
complexes from mononuclear species to coordination polymers [1].
Saccharin readily loses the imine hydrogen in solutions to form
the respective anion, saccharinate (sac). The sac anion has several
potential donor atoms such as an imino nitrogen, a carbonyl and
two sulfonyl oxygen atoms, which enable the monoanion to behave
as a polyfunctional ligand in coordination chemistry.
As a result of our current research on metal complexes
of saccharin, we recently reported several palladium(II) and
platinum(II) complexes of saccharinate with some py deriva-
ꢀ
ꢀ
ꢀꢀ
ꢀ
tives such as with 2,2 :6 ,2 -terpyridine [20], 2,2 -bipyridine
ꢀ
[21], 2,2 -dipyridylamine [22], 2-aminomethylpyridine [23], 2-
aminoethylpyridine [23] and bis(2-pyridylmethyl)amine [24].
In this study, we synthesized and characterized new palla-
dium(II) and platinum(II) complexes of sac containing 2-(2-
Platinum(II) compounds have received great attention
because cisplatin cis-[PtCl (NH ) ], carboplatin [Pt(cbdca)(NH ) ]
pyridyl)benzimidazole (pybim), namely [Pd(pybim)(sac) ] (1) and
2
3
2
3
2
2
(
cbdca = 1,1-dicarboxylato-cyclobutane) and oxaliplatin [Pt(1,2-
[Pt(pybim)(sac) ]·4H O (2). The characterizations and spectro-
2
2
2−
dach)(ox)] (dach = 1,2-diaminocyclohexane and ox = oxalate ) are
the clinically applied and effective anticancer platinum(II) agents
in treatment of a variety of tumors [2–5]. Owing to the significant
similarity between the coordination chemistry of palladium(II)
and platinum(II), in recent years, palladium(II) complexes have
also received increasing interest as potential antitumor agents [6].
Pyridyl benzimidazoles are an important class of ligands in
coordination chemistry [7–15]. The crystal structures and optical
properties of metal complexes of the pyridyl benzimidazole have
been well studied. The results indicate that the pyridyl benzimi-
scopic properties of these complexes have been reported. In
addition, the paper also describes the use of DFT and TD-DFT
calculations to provide molecular structures, IR and UV–vis spec-
tra of both complexes, since combining computational studies
with experimental results facilitates a deeper understanding of the
structures and spectroscopic properties of transition metal com-
plexes.
2. Experimental
2.1. Materials and measurements
∗ Corresponding author. Tel.: +90 2242941749; fax: +90 2242941899.
E-mail address: vtyilmaz@uludag.edu.tr (V.T. Yilmaz).
All reagents and chemicals were purchased and unless other-
wise stated, were used as received. Elemental analyses for C, H,
1
386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.04.038

1
172
E. Guney et al. / Spectrochimica Acta Part A 79 (2011) 1171–1178
and N were performed using a Costech elemental analyser. UV–vis
spectra were measured on a Shimadzu UV-1700 spectrophotome-
−5
ter using 1 × 10 M DMSO solutions in the 200–800 nm range. IR
spectra were recorded on a Thermo Nicolet 6700 FT-IR spectropho-
−
1
tometer as KBr pellets in the frequency range 4000–400 cm
.
2.2. Synthesis of the metal complexes
II
II
[
M(pybim)Cl ] (M = Pd and Pt ) were prepared according to the
2
reported method [17]. A 5 ml aqueous solution of Na(sac)·2H O
2
(
1 mmol, 0.24 g) was added to a solution of [M(pybim)Cl ]
2
(
9
0.5 mmol) in DMSO (50 ml) and then, this solution was stirred at
0 C for 3 h. The volume of the solutions was reduced to 15 ml
◦
under vacuum. The resulting solutions were allowed to stand
at room temperature, but no crystallization occurred. Eventually,
complexes 1 and 2 were obtained as microcrystalline yellow pow-
ders.
◦
[Pd(pybim)(sac) ] (1): Yield 85%. M.p. 353–357 C (decomposi-
2
tion). Anal. Calc. for C26H17N5O S Pd: C, 46.9; H, 2.6; N, 10.5. Found:
6
2
−
1
C, 46.7; H, 2.8; N, 10.7%. IR (Solid KBr pellet): ꢀ (cm ) 3252sh,
3
1
6
092vw, 3060vw, 2917vw, 1648vs, 1588m, 1461m, 1385w, 1335m,
289m, 1258vs, 1151vs, 1120m, 1052w, 969s, 749s, 678m,
3
−1
−1
09w, 543w. UV–vis in DMSO, ꢁmax/nm (ε/dm mol cm ): 339
(
18,000).
Pt(pybim)(sac) ]·4H O (2): Yield 85%. M.p. 220–224 C (decom-
◦
[
Fig. 1. A view of the optimized molecular structure of 1 and 2 (M = PdII or PtII).
2
2
position). Anal. Calc. for C26
Found: C, 38.0; H, 2.9; N, 8.3%. IR (Solid KBr pellet): ꢀ (cm ) 3446sb,
H N5O S Pd: C, 37.8; H, 3.0; N, 8.5.
25 10 2
−
1
only in DMF and DMSO. All attempts to obtain single crystals of both
complexes failed.
3
1
5
256sh, 3089vw, 3060vw, 2921vw, 1648vs, 1588m, 1467s, 1336m,
290s, 1257vs, 1152vs, 1121s, 1053m, 969s, 750s, 677m, 596w,
3
−1
−1
65w, 541w. UV–vis in DMSO, ꢁmax/nm (ε/dm mol cm ): 338
(
19,200).
3.2. Geometry optimization
2
.3. Computational details
Since complexes 1 and 2 do not crystallize, in an accompany-
ing theoretical study, DFT calculations have been performed to
obtain the respective geometry-optimized structures of 1 and 2,
excluding the water of crystallization (Fig. 1). Table 1 gives an
overview of the main geometric parameters of these optimized
structures. The palladium(II) ion in 1 has a square-planar geom-
etry with a bidentate pybim ligand and two monodentate sac
ligands and the platinum(II) complex resembles that of 1 with a
fully square-planar geometry (Fig. 1) and indistinguishable bond
distances and angles around the metal center (Table 1). In fact,
the coordination environment around the metal(II) ions is a dis-
torted square-planar geometry, due to the bite angle of the pybim
ligand, which gives rise to a narrowing of N3–M–N4 angles to
The molecular geometry predicted from the elemental analy-
sis was used as a starting point for the calculations. The molecular
structures of 1 and 2 were optimized at a B3LYP/mixed base set
of DFT, which includes the base set LanL2DZ for the Pd and Pt
atoms, and the base set 6-31G* for the C, H, N, O and S atoms of
the molecules. No symmetry constrains were applied during the
geometric optimizations. The calculations were carried out in the
GAUSSIAN 03W version of GAUSSIAN software [25]. The vibrational
frequencies of the molecules were carried out for the complete
equilibrium geometry obtained by the same quantum chemical
model in the gas phase. The calculated IR frequencies are scaled
by 0.9614 [26]. The assignments of the IR bands were performed
by the aid of the GAUSSVIEW 3.09 animation software [27], while
molecular views were obtained by Mercury CSD software [28].
The absorption spectra of the complexes in DMSO were cal-
culated based on the optimized singlet-states using restricted
time-dependent DFT (TD-DFT) with the Polarizable Continuum
Model (PCM) using the integral equation formalism variant (IEF-
PCM) at the B3LYP/LanL2DZ mixed level. GaussSum was used to
calculate group contributions to the molecular orbitals and to sim-
ulate the UV–vis absorption spectra [29].
◦
around 79.2 (Table 1). These distortions agree well with the
geometries observed in the corresponding palladium(II) and plat-
◦
inum(II) complexes of pybim such as [Pd(pybim)Cl ] 80.22(11)
2
◦
◦
[17], [Pt(pybim)Cl ] 79.7(3) [18] and [Pt(pybim)I ] 79.5(2) [18].
2
2
On the other hand, the calculated M–N(pybim) bond distances
in Table 1 are in the range of 2.060–2.104 A˚ , being in good
agreement with the experimental data ranging from 1.978(8) to
2.090(6) A˚ observed in [Pd(pybim)Cl ] [17], [Pt(pybim)Cl ] [18] and
2
2
[Pt(pybim)I ] [18]. The geometric parameters of the pybim ligand
2
are also consistent with those reported for the corresponding pal-
ladim(II) and platinum(II) complexes [17,18].
3
. Results and discussion
Two sac ligands in both structures tend to be oriented per-
pendicularly to the palladium or platinum coordination plane in
order to reduce steric hindrance. This behavior was observed in
the palladium(II) and platinum(II) complexes containing bidentate
3.1. Synthesis
ꢀ
ꢀ
Addition of Na(sac) to the starting complexes, [M(pybim)Cl ]
ligands such as 2,2 -bipyridine [21], 2,2 -dipyridylamine [22] and
bis(2-pyridylmethyl)amine [24]. Moreover, the pybim molecule is
2
II
II
(
M = Pd and Pt ), resulted in complexes 1 and 2 in high yields (85%).
◦
As shown in Scheme 1, two chloro ligands bonded to palladium(II)
and platinum(II) are replaced by two anionic sac ligands, leading to
new complexes [Pd(pybim)(sac) ] (1) and [Pt(pybim)(sac) ]·4H O
practically planar, but the py ring tilts by ca. 3.5 from the ben-
zimidazole ring. In addition, pybim is almost coplanar with the
coordination plane. The calculated dihedral angles between the
mean planes of the sac (N1, N2) and pybim rings range from
2
2
2
(
2). Both complexes are not soluble in common solvents, but soluble

E. Guney et al. / Spectrochimica Acta Part A 79 (2011) 1171–1178
1173
Scheme 1. Synthesis of complexes 1 and 2.
◦
◦
◦
7
5.19 to 88.72 . In addition, the dihedral angles between two sac
the range of 2.01–2.03 A˚ . These observations clearly indicate that
the calculated M–N(sac) bond distances of 1 and 2 are typical to
◦
rings are 65.82 for 1, and 68.85 for 2. The calculated M–N(sac)
bond lengths in both complexes are similar, ranging from 2.032
to 2.037 A˚ and compare well with those found in the palladium(II)
those documented previously.
and platinum(II) complexes with sac [19–23,30,31]. Although the
3.3. Atomic charges
shortest and longest M–N(sac) bond distances were found in the
platinum(II) complexes of sac, {K[Pt(sac) (H O)]·H O} 1.983(5) A˚
3
2
2
2
Both Mulliken’s atomic net charges [32] and the NBO/NPA
atomic charges [33,34] were calculated using the B3LYP/mixed base
set. The results are listed in Table 2. The remarkable differences
[
31] and cis-[PtCl(sac)(PPh ) ]·4CHCl 2.064(6) A˚ [30], respectively,
3
2
3
the Pd–N(sac) and Pt–N(sac) bond distances are usually observed in
Table 1
Calculated structural parameters of [Pd(pybim)(sac)2] (1) and [Pt(pybim)(sac)2] (2).
◦
Bond distances (Å)
(1)
1.384
(2)
1.385
Bond angles ( )
(1)
(2)
C1–N1
C1–O1
N1–S1
S1–O2
S1–O3
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C6–C7
C7–S1
N1–C1–O1
O1–C1–C2
C2–C3–C4
C4–C5–C6
C6–C7–S1
C7–S1–N1
O2–S1–O3
124.71
124.78
126.63
120.93
128.46
93.23
125.08
124.58
118.33
120.91
128.39
93.19
1.223
1.689
1.474
1.465
1.499
1.392
1.397
1.401
1.399
1.388
1.793
1.360
1.394
1.395
1.392
1.396
1.338
1.457
1.328
1.364
1.384
1.402
1.388
1.413
1.390
1.397
1.416
1.388
2.032
2.036
2.104
2.082
1.222
1.693
1.475
1.465
1.499
1.392
1.397
1.401
1.399
1.388
1.791
1.365
1.393
1.394
1.393
1.394
1.341
1.452
1.330
1.363
1.386
1.401
1.388
1.413
1.390
1.396
1.416
1.388
2.035
2.037
2.074
2.060
117.96
119.22
125.43
107.36
131.08
108.16
121.94
121.76
116.33
132.09
107.70
128.38
111.16
125.41
118.79
119.08
119.80
114.49
125.33
140.11
112.52
92.27
118.06
122.65
122.99
139.38
131.29
107.97
121.92
121.72
116.38
131.93
107.72
129.31
111.10
125.78
118.94
119.32
119.39
115.10
125.22
139.38
113.19
90.83
C1–N1–M1
S1–N1–M1
C15–N4–C21
N4–C15–C16
N4–C15–C20
C16–C17–C18
C17–C18–C19
C18–C19–C20
C19–C20–N5
C20–N5–C21
N5–C21–C22
N4–C21–N5
C21–C22–C23
C22–C23–C24
C24–C25–C26
C22–N3–C26
C22–N3–M1
C26–N3–M1
C15–N4–M1
C21–N4–M1
N1–M1–N2
N1–M1–N3
N1–M1–N4
N2–M1–N3
N2–M1–N4
N3–M1–N4
N3–C22
C22–C23
C23–C24
C24–C25
C25–C26
C26–N3
C22–C21
C21–N4
C21–N5
N4–C15
C15–C16
C16–C17
C17–C18
C18–C19
C19–C20
C20–C15
C20–N5
M1–N1
M1–N2
M1–N3
M1–N4
93.41
93.80
170.17
168.92
96.17
171.70
171.04
96.69
79.13
79.24
◦
Dihedral angles ( )
sac–sac
65.82
85.88
79.92
2.58
68.85
88.72
75.19
3.49
sac(N1)–pybim
sac(N2)–pybim
py–bim

1
174
E. Guney et al. / Spectrochimica Acta Part A 79 (2011) 1171–1178
Table 2
Atomic charges of [Pd(pybim)(sac)2] (1) and [Pt(pybim)(sac)2] (2) calculated using the B3LYP/mixed base set.
a
Atoms
1
2
Mulliken
NBO
0.876
Mulliken
NBO
0.894
M1
N1
N2
N3
N4
N5
O1
O2
O3
O4
O5
O6
S1
0.601
−0.701
−0.694
−0.265
−0.285
−0.426
−0.283
−0.557
−0.565
−0.285
−0.555
−0.571
0.967
0.977
−0.815
−0.813
−0.372
−0.421
−0.430
−0.277
−0.557
−0.564
−0.278
−0.555
−0.569
0.970
−0.870
−0.856
−0.498
−0.519
−0.583
−0.621
−0.839
−0.846
−0.618
−0.839
−0.853
1.928
−0.884
−0.872
−0.503
−0.525
−0.582
−0.622
−0.836
−0.845
−0.616
−0.835
−0.850
1.928
S2
0.965
1.929
0.968
1.929
C1
0.309
0.686
0.314
0.689
C2
C3
C4
C5
C6
C7
C8
0.325
−0.121
−0.159
−0.195
−0.190
−0.198
−0.178
0.688
0.324
−0.120
−0.159
−0.195
−0.190
−0.198
−0.179
0.691
−0.336
−0.199
−0.208
−0.261
−0.071
0.329
−0.335
−0.199
−0.208
−0.262
−0.067
0.334
C9
0.329
−0.117
−0.159
−0.196
−0.191
−0.199
−0.178
0.163
−0.178
−0.206
−0.190
−0.252
0.166
0.446
0.183
−0.224
−0.155
−0.222
0.133
0.328
−0.117
−0.159
−0.195
−0.191
−0.198
−0.179
0.166
−0.177
−0.205
−0.189
−0.251
−0.168
0.446
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
C24
C25
C26
Dipole moment
−0.338
−0.198
−0.209
−0.263
−0.069
0.164
−0.281
−0.231
−0.183
−0.360
0.253
−0.337
−0.199
−0.209
−0.263
−0.066
0.173
−0.270
−0.233
−0.183
−0.359
0.252
0.271
0.279
0.289
0.307
0.180
−0.261
−0.175
−0.165
−0.155
9.652
−0.273
−0.177
−0.170
−0.126
9.487
−0.221
−0.158
−0.220
0.134
a
Atomic charge units.
between these two methods are due to the different theoretical
background. The natural population analysis (NPA) satisfies Pauli’s
exclusion principle and is regarded as more important compared
to the Mulliken population analysis, which shows great variations
depending on the type of base sets. The discussion here is based on
the natural bond orbital (NBO) charges.
shows similar tendencies, they are usually lower than the NBO
charges. The calculated dipole moments obtained by two meth-
ods are almost the same, being 9.652 and 9.487 D for complexes 1
and 2, respectively.
3.4. IR spectra
As seen from Table 2, the NBO charges on the palladyum and
platinum atoms are equal to 0.876 and 0.894, respectively, being
lower than the formal charge +2. It is a consequence of charge dona-
tion from the donor atoms of both sac and pybim. All donor N atoms
of the ligands have negative charges, but the N atoms (N1 and N2) of
the sac ligand are more negative, being about twice of those on the
N atoms (N3 and N4) of the pybim ligand. This is due to the fact that
the N atoms of sac are originally negatively charged by the lost of
the imino hydrogen atom, but they are reduced to ca. −0.86 atomic
charge unit (a.ch.u.) upon coordination to palladium(II) and plat-
inum(II). The carbonyl and sulfonyl O atoms of sac contain negative
charges, but the C (C1 and C8) and S (S1 and S2) atoms bonded to
these O atoms have positive charges. All carbon atoms of the ben-
zene rings of both sac anions have negative charges, however, C6
and C13 are the most negative atoms. In the pybim ligand, the C
atoms adjacent to the N atoms have positive charges, while all the
other C atoms are negative. The most positively charged C atom
is the imidazole C atom (C21, 0.446 a.ch.u) nearest to the py ring.
Although the character of the Mulliken net charge distributions
The simulated and experimental IR spectra of complexes 1 and
2 are illustrated in Fig. 2, while the experimental and calculated IR
absorption bands are given in Table 3 together with their assign-
ments. In the IR spectrum of 2, the strong and broad absorption
−
1
band centered at around 3446 cm
are attributed to the ꢀ(OH)
vibrations of the lattice water molecules involved in hydrogen
bonding. The calculated spectra do not present any band in this
region, because the water molecules were not taken into consid-
eration in the computational calculations. The ꢀ(NH) vibration of
−1
the pybim moiety appears at ca. 3250 cm , but the calculated
−
1
value at ca. 3520 cm clearly indicates that the hydrogen bond-
ing in the solid state is responsible for the lower frequency of
the ꢀ(NH) bands. Similarly, in the spectra of the palladium(II) and
platinum(II) complexes of two benzimidazoles derivatives, the the-
oretically stretching band of the NH group of the benzimidazoles is
−
1
found at higher frequency near 3570 cm [35]. In the CH stretching
region, a number of weak bands were observed between ca. 2920
−
1
and 3090 cm , which are comparable with the calculated values. In

E. Guney et al. / Spectrochimica Acta Part A 79 (2011) 1171–1178
1175
Table 3
Selected IR spectral data for complexes 1 and 2.
Assignmentb,d
[Pd(pybim)(sac)2] (1)
[Pt(pybim)(sac)2]·4H2O (2)
Experimentala
Calculatedc
Experimentala
Calculatedc
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(OH)
(NH)
(CH)py
(CH)bim
(CH)sac
(CH)bim
(CH)py
(CH)bim
(CH)sac
(CH)py
(CO)
(CO)
(C C)py, ꢀ(C C)bim
(C C)sac
(C C)bim
(C C)py, ꢀ(C N)py
(C N)py, ꢀ(C C)py, ı(NH)
–
–
3446sb
3256sh
–
3252sh
3521(85)
3137(24)
3126(21)
3103(11)
3099(13)
3099(8)
3098(18)
3083(17)
3084(6)
1700(200)
1695(215)
1595(51)
1584(14)
1577(26)
1566(6)
1521(25)
1466(55)
1449(6)
1442(10)
1439(77)
1360(8)
1327(17)
1291(21)
1278(5)
1263(120)
1261(151)
1250(142)
1244(233)
1225(28)
1222(155)
1219(276)
1123(90)
1111(157)
1087(194)
1023(19)
950(5)
3522(94)
3152(20)
3140(15)
3103(11)
3099(19)
3098(11)
3090(11)
3085(18)
3084(5)
1704(195)
1699(210)
1598(37)
1584(13)
1579(23)
1561(5)
1522(23)
1468(65)
1450(6)
1442(11)
1441(73)
1360(7)
1327(20)
1291(15)
1275(10)
1262(129)
1262(152)
1251(157)
1245(212)
1225(20)
1226(164)
1222(258)
1125(63)
1112(170)
1088(183)
1024(22)
942(6)
3092vw
3077vw
3031vw
2925vw
2917vw
1651vs
1648vs
3089vw
3084vw
3052vw
3032vw
2921vw
1648vs
1588m
1520w
1461m
1588s
1523w
1467m
ı(CH)bim, ı(CH)py
ı(CH)sac
ı(CH)sac
ı(CH)py, ı(CH)bim
1401w
1404w
ꢀ
ꢀ
ꢀ
(C C)bim
(C C)sac
(CH)bim, ꢀ(C C)bim, ꢀ(CN)bim
ı(CH)bim
ı(CH)sac, ꢀ(CH)bim, ꢀ(CC)sac, ꢀs(CNS)
ı(CH)sac, ꢀ(CH)bim, ꢀ(CC)sac, ꢀs(CNS)
ꢀ
1335m
1336m
as(SO2)
as(SO2)
1288vs
1258vs
1290vs
1257vs
ꢀ
ı(CH)bim, ı(NH)
ı(CH)sac, ı(CH)bim
ı(CH)sac, ꢀ(CH)bim, ꢀ(CC)sac, ꢀ(CN)sac
ı(CH)sac, ꢀ(CH)bim, ꢀ(CC)sac, ꢀ(CN)sac
ı(CH)sac, ꢀs(SO2)
ı(CH)sac, ı(CH)bim, ꢀs(SO2)
ı(C C)sac, ꢀs(SO2)
1151vs
1053m
1152vs
1054m
ꢂ(CH)py
ꢀ
ꢀ
as(CNS)
as(CNS), ꢂ(CH)bim
969s
919(139)
914(71)
916(35)
773(24)
771(17)
763(20)
758(5)
743(23)
732(47)
727(23)
726(22)
654(24)
638(8)
557(93)
555(29)
535(26)
533(21)
518(14)
512(24)
494(28)
492(25)
441(65)
421(10)
408(9)
969s
917(95)
915(83)
913(12)
778(19)
777(15)
760(16)
759(9)
743(25)
733(20)
728(26)
726(23)
654 (21)
641(5)
557(85)
555(34)
535(34)
534(29)
519(14)
513(24)
494(23)
492(26)
438(50)
423(11)
407(17)
360(19)
256(9)
ꢂ(CH)bim
ı(C C)sac
ı(C C)sac
ꢂ(CH)sac, ꢂ(CH)py, ꢂ(CH)bim.
ꢂ(CH)sac., ꢂ(C C)sac.
ꢂ(CH)bim., ꢂ(C C)bim., ꢂ(CN)bim
ꢂ(CH)bim, ꢂ(C C)py, ꢂ(C N)py
ꢂ(CH)sac, ꢂ(CS)sac, ꢂ(C O)
ꢂ(CH)sac, ꢂ(CS)sac, ꢂ(C O)
ꢂ(CH)sac, ꢂ(CH)bim
776w
773w
749m
750m
707w
677m
637w
599m
562w
536w
524w
707w
677m
612w
595m
564w
540w
532w
ꢀ
(N–M)py, ꢂ(C C)py
ꢂ(SO2)
ꢂ(SO2)
ꢀ
s(N–M–N)sac
as(N–M–N)sac
ꢀ
ꢂ(N–M–N)sac, ꢂ(C C)sac
ꢂ(N–M–N)sac, ꢂ(C C)sac
ı(C C)sac, ı(CC)sac, ı(CNS)sac
ı(C C)sac, ı(CC)sac, ı(CNS)sac
ꢂ(NH)
ꢂ(N–M–N)sac., ꢂ(C C)sac
ꢂ(CH)sac, ꢂ(CH)py, ꢂ(CH)bim, ꢂ(NH)
ꢂ(SO2)
436vw
392w
251w
402w
356vw
258vw
358(6)
264(24)
ꢀ
(N–M)py, ꢀ(N–M)bim
a
b
c
−1
Frequencies in cm . b, broad; m, medium; vw, very weak; w, weak; vs, very strong; s, strong.
= stretching, ı = in-plane bending, and ꢂ = out-of- plane bending.
ꢀ
Frequencies scaled by 0.9614. The relative intensity of the calculated IR bands is given in parenthesis.
sac: saccharinate; py: pyridyl; bim: benzimidazole.
d
at 1648 cm 1 is due to the vibration of the carbonyl group of the
sac ligand, being well consistent with those of N-coordinated sac
complexes. The carbonyl group was observed as two split bands
−
metal complexes of sac, the stretchings of the carbonyl and sulfonyl
groups are the most employed IR frequencies for structural studies,
since the band positions of these groups usually correspond to the
coordination mode of the sac ligand. The very strong band observed
−
1
in the calculated spectra at 1695 and 1700 cm for 1, and 1699

1
176
E. Guney et al. / Spectrochimica Acta Part A 79 (2011) 1171–1178
Fig. 2. Experimental and calculated IR spectra of 1 and 2.
−
1
and 1704 cm for 2. The calculated values are significantly higher
−1
than the experimental values (ca. 1650 cm ). The remarkably low
experimental frequencies are due to the usual behavior of the car-
bonyl group in participation to hydrogen bonding. A pair of strong
Fig. 3. The experimental and calculated UV–vis spectra of 1 and 2.
−1
bands in the 1255–1290 cm region is assigned to the antisymetric
stretching (ꢀas) of the SO2 group of sac, being in a good correla-
absorption bands were not observed experimentally. The assign-
ment of the calculated orbital excitations to the experimental
bands was based on an overview of the contour plots and rela-
tive energy of occupied (HOMO) and unoccupied (LUMO) molecular
orbitals involved in the electronic transitions (Fig. 4). The high-
est occupied ␲ orbitals of 1 and 2 are mainly located on the
benzimidazolyl side, while the lowest unoccupied ␲* orbitals are
located on the whole pybim ligand. The HOMO → LUMO transitions
in both complexes are intraligand ␲ → ␲* transitions involving
the pybim ligand. In addition, in 1, the HOMO–1 → LUMO and
in 2, HOMO–2 → LUMO transitions are both ␲(pybim)–␲*(pybim)
transitions in nature. In the UV–vis spectra of complex 1, the
experimental band at 339 nm can reasonably be ascribed to the
−
1
tion with the calculated frequencies between 1245 and 1250 cm
.
The ꢀs(SO ) mode of sac occurs as a strong band centered at ca.
2
1
−
1
150 cm , being in accord with the calculated value. The calcu-
lated ꢀs(CNS) and ꢀas(CNS) stretchings of sac were found to be much
smaller compared to the corresponding experimental data.
The low-frequency vibrational data (500–200 cm−1) of both
complexes are also presented in Table 3. Although it is not easy
to distinguish the M–N stretching bands from other ring skele-
ton vibrations present in the same region, the ꢀ(N–M)py bands
−
1
of 1 and 2 clearly appeared at 637 and 612 cm , respectively.
The asymmetric and symmetric stretching modes as well as the
bending modes of M–N bonds occurred in the frequency range
−
1
5
40–525 cm and their theoretical assignments were easily made
␲
(pybim) → ␲*(pybim) transition at 333 nm with an oscillator
by the help of the GAUSSVIEW program.
strength of 0.28 between HOMO–1 and LUMO orbitals, while the
same band at 338 nm in 2 arises from the ␲(pybim)–␲*(pybim)
transition (HOMO–2 → LUMO; 345 nm) with an oscillator strength
of 0.23. These results clearly show that the calculated transition
energies are consistent with experimental data with a ca. 7 nm
wavelength shift. Furthermore, a similar ␲(pybim)–␲*(pybim)
3.5. Electronic spectra
Electronic structures and optical properties of both complexes
were studied using the TD-DFT. Geometries optimized at the
B3LYP/mixed level were used in TD-DFT calculations of the elec-
tronic spectra in DMSO. To predict the transition energies and
properties, singlet excited states were calculated. The calculated
absorptions with oscillator strengths lower than 0.03 were not
taken into consideration.
electronic transition in [Cu(pybim) (NO )](NO ) was observed at
2
3
3
3
22 nm, which compares well with the calculated value of 330 nm
[
36].
The experimental and calculated electronic spectra of both
complexes are illustrated in Fig. 3. The electronic transitions, oscil-
lator strengths and their assignments are given in Table 4. The
free pybim displays a main absorption band centered at 312 nm
3.6. Thermal decomposition
The DTA and TG curves of 1 and 2 are illustrated in Fig. 5. The
TG curve of 1 shows that this compound is thermally stable up to
3
−1
−1
◦
(
2
(
ε 36,559 dm mol cm ), followed by a shoulder at 326 nm (ε
355 C and then, begins to decompose with a gradual mass loss. It is
3
−1
−1
8,327 dm mol cm ), while sac has an absorption at 275 nm
impossible to distinguish the thermal decomposition processes of
the pybim and sac ligands. However, a highly exothermic DTA peak
3
−1
−1
ε 1589 dm mol cm ). However, complexes 1 and 2 exhibit
3
−1
−1
◦
single absorptions at 339 (ε 18,000 dm mol cm ) and 338 nm
(
centered at 449 C is related to the decomposition of the sac moiety
3
−1
−1
◦
ε 19,200 dm mol cm ), respectively. No absorption band was
and overlaps that of pybim. The end product at 460 C is PdO and
◦
observed at the low energy region beyond 400 nm. The TD-DFT
spectra of both complexes display a number of absorption bands
in the range of ca. 312–375 nm (Fig. 3). Some of the calculated
the total mass loss at 460 C is 82.0%, which is well consistent with
the calculated value of 81.6%. PdO decomposes to metallic Pd over
◦
ca. 780 C.

E. Guney et al. / Spectrochimica Acta Part A 79 (2011) 1171–1178
1177
Table 4
Experimental and calculated electronic transitions, oscillator strengths and their assignments for [Pd(pybim)(sac)2] (1) and [Pt(pybim)(sac)2] (2).
a
Major contribution
Character
Calculated ꢁ (nm), ꢃE (eV), fos
Experimental ꢁ (nm), ꢃE (eV), ε
1
H → L (75%)
␲(pybim) → ␲*(pybim)
d/␴(sac) → ␲*(pybim)
d/␴(sac) → ␲*(pybim)
␲(pybim) → ␲*(pybim)
d/␴(sac) → ␲*(pybim)
351
348
333
333
3.53
3.56
3.72
3.73
0.09
0.03
0.12
0.28
H − 2 → L (55%)
H − 3 → L (63%)
H − 1 → L (51%)
H − 3 → L (17%)
2
339
338
3.66
3.67
18,000
H → L (84%)
␲(pybim) → ␲*(pybim)
376
345
341
328
3.30
3.59
3.63
3.78
0.10
0.23
0.04
0.19
H − 2 → L (64%)
H − 1 → L + 3 (35%)
H − 4 → L (70%)
H − 2 → L (17%)
H − 1 → L + 1 (47%)
H − 1 → L + 3 (28%)
␲(pybim) → ␲*(pybim)
19,200
d/␴(sac)/␲(pybim) → ␲*(pybim)
d/␴(sac)/␲(sac, pybim) → ␲*(pybim)
␲(pybim) → ␲*(pybim)
d/␴(sac)/␲(pybim) → d/␲*(sac)
d/␴(sac)/␲(pybim) → d/␲*(sac)
313
3.96
0.04
fos = oscillator strength. H = highest occupied molecular orbital. L = lowest unoccupied molecular orbital.
a
ε = molar absorption coefficient (dm3 mol cm ).
−1
−1
Contrary to 1, complex 2 displays three distinct decomposition
◦
stages. In the first stage between 35 and 130 C, complex 2 dehy-
drates. The decomposition of the anhydrous compound takes place
◦
in the temperature range 220–410 C with the removal of pybim
◦
(
calcd. 23.6%, found 22.0%). In the third stage (410–507 C), the
exothermic degradation of sac occurs with a mass loss of 44.1%
◦
(
calcd. 44.3%). The end product at 507 C is PtO, which yields metal-
◦
lic Pt over ca. 800 C.
Fig. 5. Thermal analysis curves of 1 and 2.
4. Conclusions
In summary, new palladium(II) and platinum(II) complexes of
sac containing pybim have been synthesized and characterized.
The single crystals of both complexes could not be obtained and
the molecular structures of these complexes are modeled by the
DFT method. The metal ions are coordinated by a bidendate pybim
molecule and two sac anions, in agreement with the experimen-
tal findings. In addition, the vibrational spectra of these complexes
were investigated by the DFT method, while the TD-DFT calcula-
tions were used to probe the nature of the transitions observed in
the electronic absorption spectra. The scaled vibrational frequen-
cies were found to be in good agreement with the experimental FTIR
data. The absorption spectra of both complexes have characteristic
ꢁmax values near 338 nm, which are consistent with the calculated
spectra within a ca. 7 nm wavelength shift. The absorption bands
are originated mainly from the ␲(pybim)–␲*(pybim) transitions
between the pybim rings. The thermal analysis data are consistent
with the molecular structures of both complexes and the thermal
decomposition of two complexes leads to an oxide phase (PdO or
◦
PtO) at around 500 C.
Fig. 4. The molecular orbitals of 1 (a) and 2 (b), involved in the electronic transitions.

1
178
E. Guney et al. / Spectrochimica Acta Part A 79 (2011) 1171–1178
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