FT-IR and Raman spectroscopic and quantum chemical investigations of some metal halide complexes of 1-phenylpiperazine

Article abstract of DOI:10.1016/j.saa.2011.12.020

New metal halide complexes in the form of M(pp)₂Cl₂ (where pp = 1-phenylpiperazine and M = Pd or Hg) have been prepared for the first time and their FT-IR and FT-Raman spectra are reported in the region of 4000-10 cm^-1 and 4000-50 cm^-1, respectively. The optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of the present compounds are theoretically examined by means of B3LYP hybrid density functional theory (DFT) method together with Lanl2dz basis set. Furthermore, reliable vibrational assignments made on the basis of potential energy distribution (PED) were calculated and the thermodynamics functions, the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) of these compounds have been predicted. According to the results, theoretical values have been successfully compared against experimental data.

Full text of DOI:10.1016/j.saa.2011.12.020

Spectrochimica Acta Part A 88 (2012) 144–155
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
FT-IR and Raman spectroscopic and quantum chemical investigations of some
metal halide complexes of 1-phenylpiperazine
Gürkan Ke s¸ an , Özge Ba g˘ layan , Cemal Parlak , Özgür Alver , Mustafa S¸ enyelb
a
b
c,∗
b
a
Institute of Physical Biology, University of South Bohemia, Zamek 136, 37333 Nove Hrady, Czech Republic
Department of Physics, Science Faculty, Anadolu University, Eski s¸ ehir 26470, Turkey
Department of Physics, Dumlupınar University, Kütahya 43100, Turkey
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 August 2011
Received in revised form
New metal halide complexes in the form of M(pp) Cl (where pp = 1-phenylpiperazine and M = Pd or
2
2
Hg) have been prepared for the first time and their FT-IR and FT-Raman spectra are reported in the
−1
−1
region of 4000–10 cm and 4000–50 cm , respectively. The optimized geometric parameters, normal
mode frequencies and corresponding vibrational assignments of the present compounds are theoreti-
cally examined by means of B3LYP hybrid density functional theory (DFT) method together with Lanl2dz
basis set. Furthermore, reliable vibrational assignments made on the basis of potential energy distri-
bution (PED) were calculated and the thermodynamics functions, the highest occupied and the lowest
unoccupied molecular orbitals (HOMO and LUMO) of these compounds have been predicted. According
to the results, theoretical values have been successfully compared against experimental data.
© 2011 Elsevier B.V. All rights reserved.
2
1 November 2011
Accepted 15 December 2011
Keywords:
Halide complexes
Vibrational spectra
DFT
1
-Phenylpiperazine
1
. Introduction
Metal halides are compounds between metals and halogens, and
chemistry, particularly in the study of compounds containing heavy
elements.
In our previous studies, we reported the vibrational spec-
probably the most widespread class of complexes involving ligands
is that of the complexes of the halide ions, i.e. the fluoride, chloride,
bromide, and iodide ions. The synthesis and study of metal halide
complexes for organometallic chemistry are currently active and
important areas [1–4].
troscopic study of pp [12], M(pp) Ni(CN)4 (M = Ni, Co, Cd, Pd
2
or Mn) Hofmann type complexes [5], Ni(pp) Ni(CN)4 (M = Cd or
2
Hg) Hofmann T -type complexes [6], M(pp) Ni(CN) ·2C H5NH
d
2
4
6
2
(M = Ni, Co and Cd) Hofmann type aniline clathrates [7] and
M(pp) Ni(CN) ·2C H O (M = Ni, Co and Cd) Hofmann type dioxane
2
4
4
8
2
The free pp ligand molecule consists of a bulky phenyl group
clathrates [8]. Studies of various complexes of pp exhibit its coor-
dination properties. As continuation of our studies on coordinated
pp, we wish to extend investigations using the theoretical model.
The essence of this study is briefly to report the experimental and
theoretical vibrational features of pp and some of its metal halide
(
C6H5), with high basic strength, attached to one of the nitrogens
of piperazine (C H10N ). This molecule has been used as a ligand in
4
2
various complexes [5–11]. The free pp exists in a chair conformation
because of the steric crowding present in the boat form [9,12]. This
molecule, however, can coordinate in the boat and chair forms as
a bidentate ligand [10,11] or as a unidentate ligand coordinating
only through the NH nitrogen [5–9].
The DFT/B3LYP method exhibits good performance on electron
affinities, excellent performance on bond energies and reasonably
good performance on vibrational frequencies and geometries of
inorganic or ionic compounds [13,14] as well as organic and neutral
compounds [12,15–21]. The Lanl (Los Alamos National Laboratory)
basis sets, also known as Lanl2dz (Lanl-2-double zeta) and devel-
oped by Hay and Wadt [22–24], have been widely used in quantum
complexes. For the above goals, two new M(pp) Cl2 (M = Pd or Hg)
2
complexes have been synthesized for the first time and their vibra-
−
1
tional spectra are reported in the region of 4000–10 cm together
with FT-Raman and FT-FIR spectra of pp. The structural parameters,
vibrational frequencies and corresponding assignments together
with the PED, thermodynamics, HOMO and LUMO data of the
present complexes are also calculated at DFT/B3LYP level of the-
ory using the Lanl2dz basis set. The results of the theoretical and
spectroscopic studies are reported here.
2. Experimental
All the chemicals used were reagent grade (Aldrich) and they
∗ Corresponding author. Tel.: +90 274 265 20 51x3116; fax: +90 274 265 20 56.
E-mail address: cparlak@dpu.edu.tr (C. Parlak).
were used without further purification. M(pp) Cl2 (M = Pd or Hg)
compounds were prepared by adding slightly more than 2 mmol
2
1
386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.12.020

G. Ke s¸ an et al. / Spectrochimica Acta Part A 88 (2012) 144–155
145
of the liquid pp to 1 mmol of MCl2 dissolved in the distilled water.
3. Calculations
The obtained products were filtered and washed successively with
distilled water, ethanol, ether and dried in a desiccator using P O5
as desiccant.
All the calculations were performed by using Gaussian 09.A.01
program [25] on a personal computer and GaussView 5.0.8 [26]
and Chemcraft 1.6 [27] programs were used for visualization of the
structure and simulated vibrational spectra. For the calculations,
the structures in Fig. 1 were first optimized in the gas phase at
B3LYP level of theory using Lanl2dz basis set. The optimized geo-
metric structures concerning to minimum on the potential energy
surface were provided by solving self-consistent field equation iter-
atively and optimizations were performed without any molecular
restrictions.
2
FT-MIR and FT-FIR spectra of the present compounds or pp
−
1
−1
were recorded in the region of 4000–400 cm and 400–10 cm
with Perkin-Elmer FT-IR 2000 and Bruker IFS 66v/S vacuum
−
1
−1
FT-IR spectrometers at
a
resolution of 4 cm
and 2 cm ,
respectively. In order to provide better identifications for the
vibrational bands of the complexes prepared in this study
two different mulls (nujol and hexachloro-1,3-butadiene) were
used. In the MIR region of spectra, bands of nujol were
−
1
−1
−1
−1
reported at 1377 cm , 1461 cm , 2858 cm , 2925 cm
and
After the optimization, in order to confirm the conver-
gence to minima on the potential surface and to evaluate the
zero-point vibrational energies, harmonic vibrational frequencies
and corresponding vibrational intensities of the title complexes
were determined using analytic second derivatives with the
B3LYP/Lanl2dz method under the keyword freq = Raman and
pop = full and then scaled to generate the corrected frequencies.
−1
−1
−1
of hexachloro-1,3-butadiene at 655 cm , 793 cm , 852 cm
41 cm , 981 cm , 1170 cm , 1564 cm , 1610 cm , respec-
,
−1
−1
−1
−1
−1
9
tively. FT-Raman spectra of the compounds and pp molecule were
−1
recorded in the region of 4000–50 cm with Bruker Senterra Dis-
persive Raman Microscope using the 532 nm excitation from a 3B
−1
diode laser having 3 cm resolution.
ꢀ
ꢀ
N
i
exp
i
N
i
2
The compounds were analyzed for Pd and Hg metals with a
Perkin Elmer 4300 ICP-OES and for C, H and N via a Fisons EA-
w it hw
(w it h
)
Scaling factors are calculated using the ꢀ =
/
[
13,14,16] where ꢀ is scaling factor, N is the total number of vibra-
1
3
108 elemental analyser. Pd and Hg metals were investigated at
40.458 nm and 253.652 nm, respectively. The results are as fol-
th
exp
tional modes, w and w
are the theoretical and experimental
−1
frequencies (cm ), respectively.
lowing; (found %/calculated %) Pd(C10H14N ) Cl (Mr = 501.79):
2
2
2
PED calculations, which show the relative contributions of the
redundant internal coordinates to each normal vibrational mode
of the molecule and thus make it possible to describe the char-
acter of each mode numerically, were carried out by the VEDA 4
C(47.52/47.87), H(5.55/5.62), N(11.02/11.17), Pd(21.00/21.21) and
Hg(C10H14N ) Cl (Mr = 595.96): C(40.13/40.31), H(4.68/4.74),
2
2
2
N(9.26/9.40), Hg(33.49/33.66).
Fig. 1. The optimized structures and atom numbering of palladium (a) and mercury (b) chloro complexes.

1
46
G. Ke s¸ an et al. / Spectrochimica Acta Part A 88 (2012) 144–155
(
Vibrational Energy Distribution Analysis) [28]. The VEDA does not
k, c and T are Planck and Boltzmann constants, speed of light and
scale the elements of force constant matrix as proposed by Pulay
et al. [29]. For details of the PED analysis for VEDA program, more
information was published in Ref. [30].
temperature in Kelvin, respectively [20,31].
4. Results and discussion
Calculated Raman activities are converted to relative Raman
intensities using the following relationship derived from the inten-
sity theory of Raman scattering:
The results of the calculations on the geometrical parameters for
the present compounds are discussed first. A brief discussion of the
experimental and theoretical vibrational frequencies and intensi-
ties together with PED, HOMO and LUMO data is then presented.
4
f (ꢁ − ꢁ ) S
0
i
i
Ii = ꢁi
[1 − exp(−hcꢁ /kT)]
i
4.1. Geometrical structures
where ꢁ0 is the laser exciting wavenumbers in cm 1, ꢁi is the
−
To clarify the vibrational frequencies, it is essential to examine
vibrational wavenumbers of the ith normal mode, S is the Raman
the geometry of any compound as small changes in geometry can
potentially cause substantial changes in frequencies. The optimized
structures for square planar palladium and tetrahedral mercury
i
scattering activity of the normal mode ꢁ and f is a suitably cho-
i
−
14
sen common normalization factor for all peak intensities, 10
. h,
Fig. 2. MIR spectra of M(pp)2Cl2 (M = Pd (a and b) and Hg (c and d)) in nujol (a and c) and hexachloro-1,3-butadiene (b and d). N and H: bands of nujol and hexachloro-1,3-
butadiene.

G. Ke s¸ an et al. / Spectrochimica Acta Part A 88 (2012) 144–155
147
Table 1
Some optimized geometric parameters of M(pp)2Cl2 (M = Pd and Hg) complexes.
Parameters
B3LYP/Lanl2dz
Pd
M(pp)2Cl2
Hg
Bond lenghts ( A˚ )
a
M
M
C
C
C
N
2.088
2.421
1.540
1.489
1.089
2.515
a
Cl
2.555
1.540
1.488
1.099
a
C
a
a
N
H
◦
Bond angles ( )
a
C
C
H
C
N
C
N
C
111.3
111.7
108.1
111.4
112.1
107.8
a
Ha
Cl
M
N
2
1
1
2
–55–28
–55–28
–55–3
87.7
92.3
92.3
87.7
98.5
95.7
95.7
98.5
–55–3
M
N C
2
3
5
4
9–28–55
0–28–55
–3–55
113.5
113.0
113.5
113.0
113.1
114.0
113.1
114.0
–3–55
◦
Dihedral angles ( )
C
5
5
4
4
3
3
2
2
N M Cl
–3–55–1
–3–55–2
–3–55–2
–3–55–1
0–28–55–1
0–28–55–2
9–28–55–1
9–28–55–2
62.9
−116.9
116.6
−63.6
63.5
−116.6
−63.0
116.9
−45.4
159.1
31.2
−173.3
173.2
−31.2
45.3
−159.2
a
Average value of the related bond lenghts or angles.
Pd N and Hg N bond distances are ranging from 1.998 A˚ to 2.033 A˚
[
4] and from 2.190 A˚ to 2.565 A˚ [33,34], respectively, while the cal-
culated distances of these bonds are about 2.088 A˚ and 2.515 A˚ .
Overall, the calculated bond lengths are in good agreement with
experimental results.
The calculated bond lengths for piperazine of pp ligand in the
present complexes are also similar to previously reported exper-
imental data. The average C C, C N and C H bond distances of
piperazine are experimentally 1.540 A˚ , 1.467 A˚ and 1.110 A˚ [35],
respectively, whereas the calculated distances of these bonds are
1
.540 A˚ , 1.489 A˚ and 1.089 A˚ for Pd and 1.540 A˚ , 1.488 A˚ and 1.099 A˚
for Hg. Similarly, the average C
angles of piperazine are experimentally 110.4 , 109.0 and 109.1
C
N, C
N
C and H
C
H bond
◦
◦
◦
◦
◦
[
35], respectively, while the calculated angles are 111.3 , 111.7
◦
◦
◦
◦
and 108.1 for Pd and 111.4 , 112.1 and 107.8 for Hg (Table 1).
Table 2
Some thermodynamic parameters of M(pp)2Cl2 (M = Pd and Hg) complexes.
Fig. 3. FIR spectra of pp (a) and M(pp)2Cl2 (M = Pd (b) or Hg (c)).
Parameters
B3LYP/Lanl2dz
Pd(pp)2Cl2
Hg(pp)2Cl2
halide complexes are shown in Fig. 1. The optimized geometric
parameters such as bond lengths, bond and dihedral angles cal-
culated by B3LYP/Lanl2dz are also listed in Table 1. Generally, it
is expected that the bond distances calculated by electron cor-
related methods are longer than the experimental distance. This
situation is clearly observed as expected. According to the experi-
Thermal total energy (kcal/mol)
Heat capacity (kcal/(mol K))
Entropy (kcal/(mol K))
Vibrational energy (kcal/mol)
Zero point vibrational energy (kcal/mol)
Rotational constants (GHz)
A
B
310.495
0.101
0.187
308.718
293.767
309.197
0.010
0.021
307.419
291.425
0.4676
0.0435
0.0420
1.3905
0.11368
0.06396
0.04687
5.1402
mental geometric parameters, Pd Cl and Hg Cl bond distances are
ranging from 2.294 A˚ to 2.316 A˚ [4,32] and from 2.475 A˚ to 2.514 A˚
C
Dipole moment (Debye)
[
2], respectively, whereas the calculated distances of these bonds
for Lanl2dz basis set are about 2.421 A˚ and 2.555 A˚ . Experimental
The vibrational energies are at room temperature.

1
48
G. Ke s¸ an et al. / Spectrochimica Acta Part A 88 (2012) 144–155
Fig. 4. Raman spectra of pp (a) and M(pp)2Cl2 (M = Pd (b) or Hg (c)).
The optimized and important Cl
bond or dihedral angles for the present metal halide complexes
calculated by B3LYP/Lanl2dz are shown in Table 1.
M
N, M
N
C and C
N
M
Cl
moment for Hg halide complex is considerably larger than Pd due
to the electronegativity.
Several thermodynamics parameters, capacity, zero point
energy, entropy, etc. calculated by B3LYP/Lanl2dz level are pre-
sented in Table 2. The variation in the zero point vibrational
energy of the both compounds seems to be insignificant. The dipole
4.2. Vibrational studies
The measured and calculated vibrational frequencies for
the present compounds along with corresponding vibrational

Table 3
Experimental and calculated vibrational frequencies (cm−1) of M(pp)2Cl2 (M = Pd and Hg) complexes.
Mode
Experimental
B3LYP/Lanl2dz
Pd(pp)2Cl2
PED (≥10%)
pp
Pd(pp)2Cl2
IR
Hg(pp)2Cl2
IR
Hg(pp)2Cl2
Scaled
Ass.a
IRa
R
R
R
Scaled
IIR
IR
IIR
IR
b
b
freq .
freq .
ꢁ
ꢁ
1
2
ꢁ(NH)
3278 sb
3091 m
3059 m
3036 m
3023 m
2944 s
2910 m
2881 w
2824 vs
1670 w
1600 vs
1579 m
1498 vs
1452 s
–
3325 vw
3215 m
3228 m
3212 vs
3089 vw
3060 sh
–
3210 vw
3330
3328
25.26
5.46
11.21
0.91
3372
3372
1.82
1.89
7.05
5.10
ꢁ(NH) 100/97
ꢁ(NH) 99/97
ꢁ
ꢁ
9
ꢁ(CH)
–
–
3080 m
–
3099
3099
9.99
7.99
8.80
8.11
3080
3080
14.64
0.74
10.03
8.17
ꢁ(CH) 77/81
ꢁ(CH) 78/81
10
ꢁ
ꢁ
15
16
ꢁ(CH)
3067 m
–
–
3067 m
3096
3096
4.28
0.01
2.01
3.51
3077
3077
19.61
13.52
6.77
5.12
ꢁ(CH) 66/83
ꢁ(CH) 67/84
ꢁ
ꢁ
17
18
ꢁ(CH)
–
3038c vw
3006c vw
3037 vw
–
3082
3081
18.57
7.69
2.45
2.02
3072
3071
18.57
8.84
2.17
1.33
ꢁ(CH) 89/97
ꢁ(CH) 89/98
ꢁ
ꢁ
19
20
ꢁ(CH)
–
–
3021c vw
–
3049
3049
37.85
0.96
4.10
0.09
3047
3046
41.13
2.89
2.11
0.01
ꢁ(CH) 93/94
ꢁ(CH) 93/95
ꢁ
ꢁ
21
22
CH2 str.
CH2 str.
CH2 str.
CH2 str.
(NH)def.
2950 w
2982c
2931c
w
w
2991 m
2975c
w
2976 m
3025
3025
4.38
2.96
6.20
0.04
3010
3010
17.29
21.12
8.27
2.17
ꢁ(CH) 76/96
ꢁ(CH) 76/97
ꢁ
ꢁ
23
24
–
–
2953c vw
2930c vw
2954 w
2927 w
3023
3023
37.24
0.39
3.09
0.10
3002
3002
14.67
20.62
5.90
3.08
ꢁ(CH) 86/94
ꢁ(CH) 86/95
ꢁ
ꢁ
25
26
–
2978c vw
2829c
2961 w
2900c vw
2900 w
2874
2874
225.07
7.97
16.71
1.05
2878
2878
195.89
41.31
15.80
3.19
ꢁ(CH) 85/84
ꢁ(CH) 85/84
ꢁ
ꢁ
27
28
2825 w
w
–
2869c vw
2805c vw
2870 w
2836 w
2865
2865
87.14
1.60
7.02
1.01
2869
2869
81.52
4.67
5.00
1.06
ꢁ(CH) 93/84
ꢁ(CH) 94/83
ꢁ
ꢁ
29
30
–
1632c vw
1595 s
–
1627 w
1654c vw
1600 vs
1576 w
1493 s
–
1583
1583
15.65
6.99
2.03
3.01
1583
1583
15.63
6.85
2.14
2.03
ꢁ(CC) 55/45
ꢁ(CC) 47/34
ꢁ
ꢁ
33
34
C
C str.
1600 s
1609 vs
1600 s
1577 vw
–
1615
1615
27.53
271.62
12.63
4.41
1615
1614
146.85
113.39
7.70
7.13
ꢁ(CC) 42/42
ꢁ(CC) 42/42
ꢁ
ꢁ
37
38
Ring str.
Ring str.
CH2 sci.
–
–
1498
1497
26.86
169.68
0.01
0.00
1497
1496
120.01
71.49
0.00
0.02
ı(HCC) 44/47
ı(HCC) 44/47
ꢁ
ꢁ
41
42
–
1452 w
–
1496 w
1452 m
–
1489
1488
2.14
80.67
1.11
3.15
1487
1487
21.67
57.01
1.54
2.42
ı(HNC) 38/23
ı(HNC) 30/22
ꢁ
ꢁ
43
44
1457 w
–
1453 s
1453 vw
1443 m
1450
1450
7.42
0.00
1.64
4.04
1448
1448
1.66
0.26
1.12
0.01
ı(HCH) 76/76
ı(HCH) 74/75
ꢁ
ꢁ
45
46
Ring
str. + CH2
sci.
1427c
w
1431c vw
–
1448
1448
10.39
0.67
0.01
4.42
1441
1441
23.04
0.03
0.10
1.67
ꢁ(CC)
20/– + ı(HNC)
18/50
ı(HNC) 30/50
ꢁ
ꢁ
47
48
CH2 wag.
1407
–
–
–
1401 sb
–
1391
1391
15.89
121.73
0.09
0.03
1389
1389
45.43
21.62
0.10
0.02
ı(HCH) 26/35
ı(HCH) 29/34
ꢁ
ꢁ
51
52
NC6H5
str.
1380 s
1378 w
1380c
s
1378 m
1380c
m
1377 m
1376
1375
7.54
8.10
8.03
3.86
1378
1376
2.24
1.88
4.75
1.01
ꢁ(NC)
22/11 + ı(HCH)
1
ꢁ
2
1
0/–
(NC)
2/10 + ı(HCH)
2/–
ꢁ
ꢁ
57
58
Ring
str. + CH2
twi.
1325 s
1324 w
1341 w
–
1317 s
–
1345
1345
0.80
0.07
1.08
3.04
1344
1344
9.93
3.52
5.77
2.69
ı(HCC) 28/11
ı(HCC) 28/10

Table 3 (Continued)
Mode Experimental
B3LYP/Lanl2dz
Pd(pp)2Cl2
PED (≥10%)
pp
Pd(pp)2Cl2
IR
Hg(pp)2Cl2
IR
Hg(pp)2Cl2
Scaled
Ass.a
IRa
R
R
R
Scaled
IIR
IR
IIR
IR
b
b
freq .
freq .
ꢁ
ꢁ
59
60
ꢁring + ı(CH)
ı(CH)
1285 m
1190 m
1146
1285 w
–
1248 vs
1175 w
1158 vw
1099 w
1067 m
1019 s
998 w
1260 s
1241 vs
1240 m
1168 m
–
1245
1244
36.04
440.89
15.59
0.13
1238
1237
198.97
194.92
8.76
2.02
ꢁ(CC) 33/33
ꢁ(CC) 35/35
ꢁ
ꢁ
65
66
1173 m
1188 m
1168 vw
1179
1178
17.55
3.54
1.17
3.84
1177
1177
2.32
0.81
3.05
0.44
ı(HCC) 28/60
ı(HCC) 31/60
ꢁ
ꢁ
71
72
ı(CH)
1156 m
1104 m
1058 m
1032 s
991 vs
937 m
–
–
1158 vw
1144 w
1164
1160
3.09
4.24
7.03
0.71
1144
1144
1.74
20.74
2.79
0.07
ı(HCC) 13/22
ı(HCC) 15/22
ꢁ
ꢁ
75
76
ı(CH) + CH2
rock.
1081 m
1059 s
1032 s
992 s
–
1086 w
–
1095
1093
26.76
0.03
2.43
0.08
1102
1102
36.95
0.32
0.10
0.01
␶(HNCC) 29/11
␶(HNCC) 10/11
ꢁ
ꢁ
77
78
Ring str.
1067 s
1004 m
–
1076 vw
1045 vw
1058 m
1031 m
993 vs
930 w
1076
1066
0.12
152.31
11.95
4.10
1049
1047
2.56
0.47
7.38
4.71
ꢁ(CC) 32/20
ꢁ(CC) 31/20
ꢁ
ꢁ
81
82
ꢁring
1016 vw
1020
1016
23.92
177.60
5.90
6.48
1002
1002
0.55
0.50
1.39
1.15
ꢁ(CC) 42/42
ꢁ(CC) 48/47
ꢁ
ꢁ
85
86
Ring
breath.
993 w
985
985
1.57
19.31
8.28
2.90
980
980
3.47
3.67
6.08
2.21
ı(CCC) 47/53
ı(CCC) 47/54
ꢁ
ꢁ
91
92
CH2 wag.
937 s
920 s
936 w
888 vw
–
921 m
932
927
1.47
13.07
2.01
0.01
926
926
3.16
5.90
1.85
0.01
ı(HCC) 22/22
ı(HCC) 21/21
ꢁ
ꢁ
101
102
ꢂ(CH) + Ring
str.
881 s
880 vw
760 s
883 m
860 w
886 vw
856 w
899
898
3.20
11.66
0.12
0.02
897
898
27.21
5.95
0.09
0.01
␶(HCCC) 67/53
␶(HCCC) 45/43
ꢁ
ꢁ
109
110
(CH)def.
758 vs
735 sh
–
761 vs
761 w
770
770
138.23
19.14
1.03
0.01
770
770
63.77
92.28
0.03
0.01
␶(HCCC) 42/31
␶(HCCC) 31/31
ꢁ
ꢁ
111
112
ꢂ(CH)
732 m
732 vw
–
735 w
723 vw
735 m
715
715
1.33
23.30
4.07
0.11
710
710
0.26
9.88
5.01
1.07
ꢁ(NC)
23/33 + ı(CCC)
1
ꢁ
2
2
8/21
(NC)
3/34 + ı(CCC)
0/22
ꢁ
ꢁ
115
116
ꢂring
693 vs
–
693 s
686 m
693 s
–
701
701
73.35
3.35
0.47
0.01
701
701
42.47
33.23
0.09
0.01
ꢁ(MN)
15/22 + ␶(MCCN)
1
ꢁ
1
1
8/49
(MN)
5/21 + ␶(MCCN)
4/48
ꢁ
ꢁ
117
118
ıring + Ring
band
625 s
517 vs
485 w
617 m
564 m
–
630 sh
520 w
481 vw
–
666 vw
650 vw
653 m
–
620
620
0.71
0.07
0.88
3.90
619
619
0.37
1.06
2.17
1.55
ı(CCC) 71/71
ı(CCC) 71/71
ꢁ
ꢁ
121
122
ıring
527 vw
456 vw
525 w
498 vw
524
524
28.85
0.08
2.30
0.02
523
523
22.01
3.95
1.98
0.76
␶(NCCC) 34/30
␶(NCCC) 34/30
ꢁ
ꢁ
125
126
(NH)rock.
480 vw
455 vw
482 vw
457 m
471
471
2.18
1.43
0.01
0.14
467
465
3.98
0.67
0.03
1.02
ı(CNC)
41/– + ␶(CCCC)
–
/60
ı(CNC)
4
–
1/– + ␶(CCCC)
/51
ꢁ
ꢁ
129
130
ıring
437 m
435 m
430 vw
421 vw
417 vw
430 vw
426
424
0.49
3.65
1.24
0.97
414
414
1.71
1.10
0.45
0.05
ı(CNC) 29/23
ı(CNC) 17/24

ꢁ
ꢁ
131
132
378 w
–
–
–
362
356
13.83
0.41
0.04
0.81
317
317
4.47
0.33
1.05
1.37
ꢁ(MN) 27/10
ꢁ(MN) 20/20
ꢁ
ꢁ
133
134
348 s
322 m
344 m
293 vs
331 vs
324 sh
315 m
–
316
336
35.34
27.32
0.56
3.97
302
304
5.31
0.77
1.02
0.06
ꢁ(MCl) 54/58
ꢁ(MCl) 59/53
ꢁ
ꢁ
136
137
276 sh
–
285 vw
274
261
3.04
0.06
0.19
4.01
247
245
0.15
10.67
0.14
0.03
ı(MNC) 10/11
ꢁ(MCl)
9
7/– + ı(MNC)
–
/11
ꢁ
138
–
–
–
269 s
229 s
267 s
259
6.09
0.01
243
15.68
5.61
ꢁ(MCl)
–
2
/96 + ı(CNC)
0/–
ꢁ
ꢁ
141
142
211 s
210 m
224
205
5.92
16.95
0.99
0.02
162
158
0.00
1.61
0.56
0.12
ꢁ(MN)
24/– + ı(MNC)
1
ꢁ
2
1
3/13
(MN)
4/10 + ı(MNC)
0/–
ꢁ
ꢁ
143
144
182 s
185 m
–
–
178
176
0.06
21.06
0.45
0.02
117
112
1.48
1.35
0.01
1.90
ꢁ(MN)
–/31 + ı(CNM)
1
7/–
ı(NMN)
27/– + ␶(CCCN)
10/– + ␶(MCCN)
–/17
ꢁ
ꢁ
145
146
144 m
–
132 w
93 vs
–
146
122
4.19
1.24
3.76
0.32
85
83
0.73
0.79
1.03
0.02
ı(ClMCl)
12/32 + ı(ClMN)
2
3/24
ı(CNC) 11/11
ꢁ
ꢁ
147
148
116
112
6.91
0.50
0.14
2.25
82
77
3.77
0.06
0.24
0.04
ı(ClMCl)
44/52 + ␶(ClNClM)
1
–
14 s
127 s
118 vs
1
5/12
ꢁ
(MN) 41/67
ꢁ
ꢁ
149
150
96
93
1.33
4.04
0.02
0.26
61
60
25.60
10.19
0.07
1.03
ı(MNC) 28/34
␶(ClNClM)
–
–
68 m
–
73 m
–
4
4/81
ꢁ
ꢁ
154
155
42 w
58
37
2.48
0.61
0.94
3.39
31
30
1.24
0.05
1.16
0.67
␶(CNCC) 19/57
␶(CNCC)
11/10 + ␶(NMNC)
29/33 + ␶(ClNNM)
32/35
a
b
c
Taken from Ref. [5].
Scaled with 0.9923.
In hexacholoro-1,3-butadiene.
Ass., assignments; str., stretching; sci., scissoring; twi., twist; wag., wagging; breath., breathing; def., deformation; rock., rocking; IR and R, experimental infrared and Raman frequencies; IIR and IR, calculated infrared and Raman
intensities; Freq, frequency; vs, very strong; s, strong; m, medium; w, weak; vw, very weak; b, broad; sh, shoulder. PED ≥ 10%, M = Pd or Hg. In PED list, the former represents Pd while the latter stands for Hg chloro complexes.

1
52
G. Ke s¸ an et al. / Spectrochimica Acta Part A 88 (2012) 144–155
Fig. 5. Theoretical IR and Raman spectra of M(pp)2Cl2 (M = Pd (a and b) or Hg (c and d)).

G. Ke s¸ an et al. / Spectrochimica Acta Part A 88 (2012) 144–155
153
assignments and intensities are given in Table 3 and their theoreti-
cal and experimental vibrational spectra are shown in Figs. 2–5. All
calculated frequency values presented in this paper are obtained
within the harmonic approximation which allows us to describe
vibrational motion in terms of independent vibrational modes each
of which is governed by a simple one dimensional harmonic poten-
tial. These compounds consist of 55 atoms, so they have 159 normal
vibrational modes and they belong to the point group C1 with only
identity (E) symmetry element or operation. It is difficult to deter-
mine vibrational assignments of these complexes in the observed
spectrum due to its low symmetry. Therefore, the assignments of
vibrational modes for the present complexes of pp have been tabled
according to the vibrational assignments of the free pp [12] and PED
data provided by VEDA 4 [28] in Table 3. According to the calcula-
tions, about 130 modes are in the mid-IR range and the rest are in
the far-IR region of spectrum.
stretching band attributed to phenyl attached to one of the nitro-
gens of piperazine has no shift in the compounds. Regarding the
phenyl molecule within the pp, the vibrational bands possess small
shifts due to the environmental changes on the complexion.
From the comparison of the spectral data presented in Table 3, it
can be concluded that the pp molecules in the present compounds
are coordinated in the chair form as a unidentate ligand coordinat-
ing only through the NH nitrogen. Unidentate coordination of the
pp has been supported by the shifts in the position of the NH defor-
−
1
−1
mation mode from the free ligand value of 1670 cm to 1600 cm
and no shift in the position of the CN stretching [5–9].
Vibrational modes in the low wavenumber region of the spec-
trum contain contributions of several internal coordinates and
their assignment is a reduction approximation to one of two of
the internal coordinates. As it can be seen from Table 3 and
Figs. 3 and 4, vibrational spectra of Pd chloro complex show two
−
1
−1
−1
The spectral data for pp in the complexes exhibit characteristics
IR and two Raman bands at 348 cm (IR), 344 cm (R), 322 cm
−
1
−
1
of a coordinated ligand. On coordination, the NH and CH stretching
(IR), 293 cm (R) and two IR and one Raman bands at 211 cm (IR),
2
−
1
−1
frequencies attributed to piperazine molecule within the pp lig-
and should decrease and increase due to the consecutive inductive
effects, respectively [36]. It is clearly observed in Table 3 that these
requirements are fulfilled for pp in the present compounds. These
shifts in frequencies are explained in terms of coupling of the inter-
nal vibration of pp ligand with M N vibrations [5–8]. The coupling
is not the only factor for the frequency shifts with respect to those of
the ligand. Due to the change of the geometrical parameters, diag-
onal force constants have small changes as well. Another strong CN
127 cm (R), 114 cm (IR) which can be attributed to ꢁ(Pd Cl)
and ꢁ(Pd N) stretches, respectively. However, vibrational spec-
tra of Hg chloro complex show three IR and two Raman bands at
−
1
−1
−1
−1
−1
−1
331 cm (IR), 324 cm (IR), 315 cm (R), 269 cm (IR), 267 cm
−
1
(R) and two IR and two Raman bands at 229 cm (IR), 210 cm
−
1
−1
(R), 118 cm (R), 93 cm (IR) which can be attributed to ꢁ(Hg Cl)
and ꢁ(Hg N), respectively. The observed values for ꢁ(M N) and
ꢁ(M Cl) stretches are in compliance with the previously reported
data for palladium and mercury chloro complexes of various ligands
Fig. 6. Plot of the calculated vs. experimental frequencies of M(pp)2Cl2 (M = Pd (a and b) or Hg (c and d)).

1
54
G. Ke s¸ an et al. / Spectrochimica Acta Part A 88 (2012) 144–155
Fig. 7. The atomic orbital compositions of the frontier molecular orbital for M(pp)2Cl2 (M = Pd (a) or Hg (b)).
[
37,38]. This suggests that the palladium and mercury chloro com-
performed by using FT-IR, FT-Raman and quantum chemical calcu-
lations. In conclusion, following results can be summarized:
plexes have structure in which the palladium and mercury atoms
are in square planar and tetrahedral environments, respectively.
The differences between the calculated and experimental values
for the some vibrational modes are often attributed to the neglect of
anharmonicity and incomplete inclusion of electronic correlation
effects. Additional reasons of these differences are the truncated
basis sets and approximations used in the B3LYP computational
model. As it can be seen from Table 3 and Figs. 2–5, there is a good
agreement between the experimental and theoretical vibrational
frequencies. In order to compare the experimental frequencies, we
have found the correlation graphics based on the average theo-
retical and experimental data. The correlation values between the
experimental and calculated vibrational frequencies are found to
be 0.9990 (IR and R) for Pd and 0.9990 (IR) and 0.9989 (R) for Hg
halide complexes. It can be seen that the B3LYP/Lanl2dz calcula-
tion is reliable for vibrational spectra and the results for Hg and Pd
metals are consistent with together (Fig. 6).
As it can be seen from Table 3, if the vibrational assignments are
investigated one-by-one for both metals, the assignments are gen-
erally consistent with together. When it is paid a special attention
on PED data for these compounds, however, some values are some-
what different. Regarding the calculated fundamentals, in general,
the computed vibrational intensities in the gas phase are in reason-
able agreement with the experimental results in both high and low
frequency regions. It is also important to note that calculations have
been performed for a single structure in the gaseous state contrary
to the experimental values recorded in the presence of intra- and
intermolecular interactions.
(1) The pp molecules in the compounds presented which are fur-
ther examples of metal halide complexes are coordinated in the
chair form as a unidentate ligand coordinating only through the
NH nitrogen.
(2) Comparing the computed vibrational frequencies with the
infrared experimental data, a scaling factor such as 0.9923 is
derived for B3LYP/Lanl2dz level in the M(pp) Cl (M = Pd or Hg)
2
2
complexes.
(3) The energy of the Pd complex is lower than that of the Hg com-
plex is not characteristic on the chemical system. However, it
is the result of the Lanl2dz effective core potentials used for Pd
and Hg.
(4) Theoretical applications of B3LYP/Lanl2dz for M(pp) Cl2
2
(M = Pd or Hg) complexes are in agreement with the experimen-
tal values. Theoretical results for vibrational data of Hg and Pd
metals have similar trends with correlation coefficients values
of 0.9990.
(5) Results indicate that B3LYP method with Lanl2dz effective core
basis set also makes easier the understanding of vibrational
spectrum and structural parameters of the metal halide com-
plexes.
Acknowledgements
We are deeply grateful to Dr. Michal Jamróz and M. Fatih Kaya
for the VEDA 4 program.
The HOMO describes the ability to donate an electron and LUMO
as an electron acceptor. The absorption of electronic transition is
defined from the ground to the first excited state. In other words,
the transitions can be described from HOMO to LUMO. The HOMO
is located over all carbon atoms of pp whereas the LUMO dominate
for Pd or Hg metal atoms and N atoms of pp which are bounded to
metals. The atomic compositions of frontier molecular orbital and
their orbital energies for palladium and mercury halide complexes
are shown in Fig. 7.
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