Palladium(II) and platinum(II) complexes of a new imineoxime ligand - Structural, spectroscopic and DFT/time-dependent (TD) DFT studies

Article abstract of DOI:10.1016/j.jorganchem.2013.12.011

A new imineoxime compound, (1E,2E)-[(2-hydroxyethyl)imino]-2-phenyl-ethanal oxime (heipeoH) and its palladium(II) and platinum(II) complexes ([M(heipeo)₂]) have been synthesized and characterized by elemental analysis, IR, NMR, UV-vis, mass spectra and X-ray diffraction. The geometry of heipeoH was optimized by both B3LYP with 6-311++G(d,p) and LANL2DZ basis sets, while the molecular structures of both complexes obtained from X-ray diffraction were compared with the optimized geometries using the B3LYP with the LANL2DZ basis set. In addition, the quantum chemical studies of title compounds have been carried out to correlate geometry and spectroscopic properties such as electronic, vibrational and NMR chemical shifts. The atomic charges of the title compounds were calculated by natural bond orbital (NBO) analysis.

Full text of DOI:10.1016/j.jorganchem.2013.12.011

Journal of Organometallic Chemistry 752 (2014) 83e90
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Palladium(II) and platinum(II) complexes of a new imineoxime
ligand e Structural, spectroscopic and DFT/time-dependent
(TD) DFT studies
,
a
a
b
Yunus Kaya a , Ceyda Icsel , Veysel T. Yilmaz , Orhan Buyukgungor
*
a Department of Chemistry, Faculty of Arts and Sciences, Uludag University, 16059 Bursa, Turkey
b Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayis University, 55139 Samsun, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A new imineoxime compound, (1E,2E)-[(2-hydroxyethyl)imino]-2-phenyl-ethanal oxime (heipeoH) and
its palladium(II) and platinum(II) complexes ([M(heipeo)2]) have been synthesized and characterized by
elemental analysis, IR, NMR, UVevis, mass spectra and X-ray diffraction. The geometry of heipeoH was
optimized by both B3LYP with 6-311þþG(d,p) and LANL2DZ basis sets, while the molecular structures of
both complexes obtained from X-ray diffraction were compared with the optimized geometries using the
B3LYP with the LANL2DZ basis set. In addition, the quantum chemical studies of title compounds have
been carried out to correlate geometry and spectroscopic properties such as electronic, vibrational and
NMR chemical shifts. The atomic charges of the title compounds were calculated by natural bond orbital
(NBO) analysis.
Received 17 September 2013
Received in revised form
18 November 2013
Accepted 5 December 2013
Keywords:
Imineoxime
Coordination compound
Crystal structure
DFT calculation
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
hydrolysis mechanism of ppeieoH in solution has been clarified [43].
In addition, the electronic, vibrational and NMR spectra of ppeieoH
Imineoximes include both oxime and imine groups in their
structure. They have been extensively used in analytical chemistry
for detection and separation of metal ions [1e5], due to the fact that
imineoximes act as chelating ligands via the imine and oxime
groups [6e8]. Moreover, some oximes and their complexes have
been reported to have significant biochemical activities [9e17].
Specifically palladium(II) and platinum(II) complexes of oximes
received considerable attention due to their DNA binding affinities
[9,18e20].
In the last decade, density functional theory (DFT) was used
extensively in the modeling of oximes and their metal complexes
[21e28]. Literature surveys have revealed the high degree of accu-
racy of DFT methods in reproducing the experimental values in
terms of geometry, dipole moment, electronic transitions, vibra-
tional frequency and NMR chemical shifts [21,29e40]. Recently, we
reported a combined experimental and theoretical study of an imi-
neoxime, namely (1E,2E)-phenyl-[(1-phenylethyl)imino]-ethanal
oxime (ppeieoH) [41] and its palladium(II) [42] and platinum(II) [43]
complexes. The cisoid and transoid conformations of E- and Z-iso-
mers of ppeieoH have been identified [41]. At the same time, the
and its palladium(II) complex have been characterized using DFT.
As a part of our work, in this paper, we report the synthesis of a
new imineoxime, (1E,2E)-[(2-hydroxyethyl)imino]-2-phenyl-etha-
nal oxime (heipeoH) and its palladium(II) and platinum(II) com-
plexes, namely [Pd(heipeo)2] and [Pt(heipeo)2]. Both metal
complexes were obtained as single crystals, while all attempts for
the crystallization of the heipeoH ligand failed. The theoretical
studies including electronic, vibrational and NMR spectra and NBO
charges have been performed by DFT, and the calculations were
correlated with the experimental values. The results show that
these calculations are valuable for providing insight into molecular
properties of the imineoxime compound and its complexes.
2. Experimental and calculations
2.1. Instrumentation
The elemental analyses (C, H and N) were performed using a
EuroEA 3000 CHNS elemental analyser. Mass spectrum of heipeoH
was obtained using an Agilent-LCMS spectrometer. UVevis spectra
were measured on a PerkineElmer Lambda 35 UV/vis spectro-
photometer using 1 ꢀ 10ꢁ4 M EtOH solution in the 200e800 nm
range. IR spectra were recorded on a Thermo Nicolet 6700 FT-IR
spectrophotometer as KBr (in the frequency range 4000e
* Corresponding author. Tel.: þ90 224 2941738; fax: þ90 224 2941898.
E-mail address: ykaya@uludag.edu.tr (Y. Kaya).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.12.011

84
Y. Kaya et al. / Journal of Organometallic Chemistry 752 (2014) 83e90
400 cmꢁ1) and CsI (in the frequency range 400e250 cmꢁ1) pellets.
1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were recorded
on a Varian Mercury plus spectrometer in DMSO-d6 and CDCl3. TMS
was used as an internal standard.
B3LYP/6-311þþG(d,p) basis set, while those of the complexes were
calculated at B3LYP/LANL2DZ basis set.
The computed frequency values contain systematic errors [47]
and therefore, we have used scaling factors: In the calculations
made by the B3LYP/6-311þþG(d,p) basis set, scaling factors 0.958
[48] and 0.978 [49] were used for 4000e1700 cmꢁ1 and 1700e
400 cmꢁ1 ranges, respectively. In the calculations by the B3LYP/
LANL2DZ basis set, a modified wavenumber-linear-scaling (WLS)
approach [50,51] was employed after completing the vibrational
mode assignments for palladium(II) and platinum(II) complexes.
This method was derived by determining the best-fit linear func-
tion between the experimental and theoretical data. The resulting
functions are shown in Eqs. (1)e(4).
2.2. Synthesis of ligand and its complexes
(1E,2E)-[(2-hydroxyethyl)imino]-2-phenyl-ethanal oxime (hei-
peoH) was prepared by refluxing a mixture of a solution containing
isonitrosoacetophenone (inapH) (0.750 g, 5 mmol) in 10 mL EtOH
and a solution containing monoethanolamine (0.310 g, 5 mmol) in
5 mL EtOH. The reaction mixture was refluxed for 3 h. The reaction
mixture yields a polycrystalline white powder. Yield 87%. M.p.
134.1 ꢂC; Anal. Calc. for C10H12N2O2 (192.2 g molꢁ1): C, 62.49; H,
6.29; N, 14.57. Found: C, 61.80; H, 6.16; N, 14.36%, ESI-MS, (m/
z) ¼ 192.6 [Mþ].
For the palladium(II) complex:
ꢀ
ꢁ
y ¼ 1:0165x ꢁ 240:91
y ¼ 1:0203x ꢁ 39:465
R2 ¼ 0:99 for 4000 ꢁ 1700 cmꢁ1
In synthesis of [Pd(heipeo)2] and [Pt(heipeo)2] complexes, a
solution of a heipeoH (0.192 g, 1 mmol) in EtOH (30 mL) was added
drop wise to a solution of Na2[PdCl4] (0.147 g, 0.5 mmol) and
K2[PtCl4] (0.208 g, 0.5 mmol) in water (10 mL). After the addition of
NaOH (0.040 g,1 mmol) in 2 mL water, the mixtures were stirred for
4 h at ambient temperature. The volumes of the solutions were
reduced to 10e15 mL under vacuum and then the resulting pre-
cipitate was filtered, and dried in air. X-ray quality orange and
yellow crystals of the palladium(II) and orange crystals of the
platinum(II) complexes were obtained by the slow evaporation of
the EtOH solutions at ambient temperature within two days. For
[Pd(heipeo)2] complex; Yield 76%. M.p. 202e212 ꢂC (decomp.);
Anal. Calc. for C20H22N4O4Pd (488.8 g molꢁ1): C, 49.14; H, 4.54; N,
11.46. Found: C, 48.96; H, 4.32; N, 11.43%. For [Pt(heipeo)2] com-
plex; Yield 73%. M.p. 259e264 ꢂC (decomp.); Anal. Calc. for
(1)
ꢀ
ꢁ
R2 ¼ 0:99 for 1700 ꢁ 250 cmꢁ1
(2)
For the platinum(II) complex:
ꢀ
ꢁ
y ¼ 1:0109x ꢁ 228:040
R2 ¼ 0:99 for 4000 ꢁ 1700 cmꢁ1
(3)
ꢀ
ꢁ
y ¼ 1:0287x ꢁ 50:142
R2 ¼ 0:99 for 1700 ꢁ 250 cmꢁ1
(4)
C
20H22N4O4Pt (577.5 g molꢁ1): C, 41.60; H, 3.84; N, 9.70. Found: C,
The assignment of the calculated frequencies is aided by the
animation option of GaussView 3.0 graphical interface for Gaussian
programs, which gives a visual presentation of the shape of the
vibrational modes [52]. Furthermore, theoretical vibrational
spectra of the title compounds were interpreted by means of PEDs
using VEDA 4 program [53].
41.52; H, 3.69; N, 9.66%.
2.3. Crystal structure determination
The intensity data of the palladium(II) and platinum(II) com-
plexes were collected using a STOE IPDS 2 diffractometer with
1H and 13C NMR chemical shifts (dH and dC) of heipeoH and its
complexes were calculated using the GIAO method [54] in DMSO
and chloroform at the B3LYP/LANL2DZ level and using the TMS
shielding calculated as a reference.
Transition energies and oscillator strengths for the electronic
excitation of the first 12 singlet-to-singlet excited states of heipeoH
and 48 singlet-to-singlet excited states of the metal complexes
were calculated using time-dependent (TD) DFT at the B3LYP/
LANL2DZ level. Each excited state was interpolated by a Gaussian
convolution with the full width at half-maximum (fwhm) of
3000 cmꢁ1. In addition, the electronic absorption spectra were
calculated in EtOH using the IEFPCM method. Orbital contribution
was analyzed using GaussSum software [55].
ꢀ
graphite-monochromated MoKa radiation (
l
¼ 0.71073 A). The
structures were solved by direct methods and refined on F2 with
the SHELX-97 program [44]. All non-hydrogen atoms were found
from the difference Fourier map and refined anisotropically. All
hydrogen atoms were positioned geometrically and refined by a
riding model. The details of data collection, refinement and crys-
tallographic data are summarized in Table S1.
2.4. Computational details
All calculations were conducted using DFT with the BeckeeLeee
YangeParr functional (B3LYP) method [45] as implemented in the
GAUSSIAN 03 program package [46]. In the first step of the calcu-
lation, to elucidate conformational features of the heipeoH, the
selected degrees of torsional freedom, T(N2eC7eC8eN1) and
T(C7eN2eC9eC10), were varied from ꢁ180ꢂ to þ180ꢂ in every 10ꢂ
and the potential energy curve (PES) was obtained with the B3LYP/
6-31G(d) level of theory. In potential energy curve, the stationary
points were confirmed by the frequency analysis as minima with all
real frequency and with no imaginary frequency implying no
transition state. For the lowest energy conformer, the geometric
structure was reoptimized in ground state at the DFT level of theory
by using 6-311þþG(d,p) and LANL2DZ basis sets. Ground state
geometry optimization of the palladium(II) and platinum(II) com-
plexes were started from the X-ray experimental atomic positions
and fully optimized at B3LYP and LANL2DZ level. The harmonic
vibrational frequencies of the heipeoH were calculated using the
Natural bond orbital (NBO) analysis for the title compounds
have been obtained using the B3LYP/LANL2DZ basis set.
3. Results and discussion
3.1. Conformational analysis of heipeoH
The N2eC7eC8eN1 and C7eN2eC9eC10 dihedral angles are
the most relevant for conformational flexibility for the heipeoH
molecule (Fig. S1). Conformations of this molecule are also feasible
depending on the orientation around C7eC8 and N2eC9 bonds.
Conformational analysis was carried by the potential energy sur-
face scan to find all possible conformers with B3LYP method using
6-31G(d) basis set. The potential energy surface of heipeoH is

Y. Kaya et al. / Journal of Organometallic Chemistry 752 (2014) 83e90
85
shown in Fig. S2. All of the possible geometries of the conformers
were optimized to find out the most stable configuration. The most
stable conformer of heipeoH was then subjected to the geometrical
optimization by B3LYP method using 6-311þþG(d,p) and LANL2DZ
basis sets to obtained geometrical parameters, vibrational fre-
quencies, NMR, the atomic charges, electronic and thermodynamic
properties. In the most stable conformer, the N2eC7eC8eN1 and
C7eN2eC9eC10 dihedral angles were computed as ꢁ176.5
and ꢁ147.5ꢂ. An intramolecular hydrogen bond was formed be-
tween the hydrogen of the hydroxyethyl group and the nitrogen
atom of the imine group. This hydrogen bonding further contrib-
utes to the stability of the conformer.
hydroxyl hydrogen atom and the oxime O atom (Table 1). The
hydrogen bonds result in a one-dimensional chain running along
the b axis and these chains are held together by weak CeH/O
hydrogen bonds involving the phenyl and aldehyde hydrogens, and
the hydroxyl O atoms leading to a three-dimensional network. The
polymorphism affects the packing of the molecules in [Pd(heipeo)2]
(C1) and contrary to the Ci polymorph, this complex is stabilized by
two OeH/O hydrogen bonds involving hydroxyl hydrogen atom
and the oxime O atom and hydroxyl hydrogen atom and the hy-
droxyl O atom (Table 1).
3.3. Optimized geometry
3.2. Description of the crystal structures of [Pd(heipeo)2] and
[Pt(heipeo)2]
The optimized parameters (bond lengths and bond angles) of
heipeoH, obtained using the B3LYP/6-311þþG(d,p) and LANL2DZ
basis sets are listed in Table 2. The optimized structure of heipeoH
together with the atomic numbering is shown in Fig. S1. For the
complexes, the selected structural parameters obtained experi-
mentally and calculated theoretically using the B3LYP/LANL2DZ
method are tabulated in Table 1. The most important bonds of
imineoxime compounds are C]N(imine) and C]N(oxime). These
The molecular structures of [Pd(heipeo)2] and [Pt(heipeo)2]
complexes are shown in Figs. 1 and 2, and the selected bond lengths
and angles are listed in Table 1. The title complexes are isomor-
phous and crystallize in a triclinic space group P1. Cocrystallization
of two polymorphs of [Pd(heipeo)2] was observed by the different
colors and shapes of the crystals and were identified by X-ray
measurements with C1 and Ci point groups. The polymorphism in
the palladium(II) complex seems to be due to the orientation of the
hydroxyethyl groups (Fig. 1). The Ci polymorph of [Pd(heipeo)2] and
[Pt(heipeo)2] are centrosymmetric and the metal ions lie on the
inversion center. In addition, the two phenyl rings are coplanar in
these complexes, while these aromatic rings form a dihedral angle
of 66.66ꢂ in the palladium(II) complex with the C1 point group. The
ꢀ
bond lengths of heipeoH were calculated 1.305 and 1.302 A,
respectively. On the other hand, the C]N bond lengths were ob-
ꢀ
tained between 1.325 and 1.331 A in the palladium(II) and plati-
num(II) complexes. These results show that both C]N bonds of the
ligand weaken upon complexation. The optimized parameters by
DFT show a small difference from those obtained by X-ray diffrac-
tion. The largest differences between the experimental observa-
tions and those obtained from the theoretical calculations are
ꢂ
ꢀ
ꢀ
PdeN and PteN bond distances range from 2.025(3) to 2.059(3) A
0.166 A in the OeH bond length and 2.8 in the C7eN2eC9 bond
angle. When the X-ray structures of the complexes are compared to
its optimized counterparts (see Fig. S3), slight conformational dis-
crepancies are observed between them. The most remarkable
discrepancy exists in the orientation of the hydroxyethyl group in
[Pt(heipeo)2] and the Ci polymorph of [Pd(heipeo)2] with the C9e
and are typical for previously reported palladium(II) and plati-
num(II) complexes containing imineoximes or oximes
[13,15,42,43,56e63].
The [Pd(heipeo)2] (Ci) and [Pt(heipeo)2] complexes are linked by
strong intermolecular OeH/O hydrogen bonds involving the
Fig. 1. X-ray and optimized structures of [Pd(heipeo)2], (a) Ci point group, (b) C1 point group.

86
Y. Kaya et al. / Journal of Organometallic Chemistry 752 (2014) 83e90
Table 2
Selected geometric parameters of heipeoH.
6-311þþG(d,p)
LANL2DZ
ꢀ
Bond length (A)
C1eC2
C2eC3
C3eC4
C4eC5
C5eC6
C1eC6
C6eC7
C7eC8
C9eC10
C8eN1
C7eN2
C9eN2
N1eO1
O1eH
C10eO2
O2eH
1.393
1.394
1.394
1.393
1.399
1.399
1.499
1.475
1.530
1.276
1.281
1.455
1.394
0.964
1.419
0.966
1.406
1.409
1.408
1.406
1.414
1.413
1.503
1.482
1.541
1.302
1.305
1.474
1.447
0.982
1.455
0.984
Bond angle (ꢂ)
C1eC2eC3
C2eC3eC4
C3eC4eC5
C4eC5eC6
C1eC6eC7
C2eC1eC6
C7eC8eN1
C8eN1eO1
C6eC7eN2
C6eC7eC8
N2eC9eC10
C7eN2eC9
C9eC10eO2
120.2
119.8
120.1
120.4
120.6
120.3
120.9
111.3
125.9
119.0
108.3
122.2
111.7
120.3
119.7
120.1
120.6
120.8
120.4
121.8
110.0
126.2
119.9
107.2
123.8
110.6
Fig. 2. X-ray and optimized structures of [Pt(heipeo)2].
C10eO2eH torsion angles of ꢁ60.1 and ꢁ96.7ꢂ, respectively. The
corresponding torsion angles were calculated as ca. ꢁ66.5ꢂ.
using DFT at LANL2DZ basis set. The corresponding frequencies
along with the assignments and intensities are given in Tables S2
and S3, while the observed and calculated vibrational spectra are
given in Fig. S4. The calculated frequencies with the intensity less
than 5 were not taken into consideration. It can be seen that, the
experiment has a better correlation with the calculations. In the IR
spectra of heipeoH, the OeH stretching vibrations of the oxime and
3.4. IR Spectra
The harmonic vibrational frequencies for heipeoH were calcu-
lated by using DFT method at 6-311þþG(d,p) basis set, while those
of [Pd(heipeo)2] and [Pt(heipeo)2] complexes were calculated by
hydroxyethyl groups were calculated at 3661 and 3618 cmꢁ1
,
Table 1
respectively, while observed at 3218 and 3429 cmꢁ1, respectively
[41,64,65]. The deviation between the experimental and calculated
values seems to be significant for the hydroxyl groups frequencies
with a difference of 443 and 189 cmꢁ1. Due to the nature of this
vibration mode, its frequency is very sensitive to the crystalline
state, in which the hydrogen bonding interactions involving this
group are present as discussed above, and thus exhibits much
larger deviation from the calculated values. At the same time, in the
high wavenumber region of the spectra, the anharmonicity can
explain substantial differences between the experimental and
calculated values [66]. The experimental C]N bands were
observed as sharp bands at 1624 cmꢁ1, which was computed at
ꢂ
ꢀ
Selected bond lengths (A) and angles ( ) for [Pd(heipeo)2] and [Pt(heipeo)2].
Experimental LANL2DZ Experimental LANL2DZ
[Pd(heipeo)2], Ci
Pd1eN1 2.039(3)
Pd1eN2 2.045(3)
2.088
2.084
N2ePd1eN1 100.9(11)
N1ePd1eN1 180.0(1)
N1ePd1eN2 79.1(11)
N2ePd1eN2 180.0(1)
101.1
180.0
78.9
180.0
[Pd(heipeo)2], C1
Pd1eN1 2.046(3)
Pd1eN2 2.043(3)
Pd1eN3 2.035(3)
Pd1eN4 2.059(3)
2.080
2.083
2.077
2.091
N1ePd1eN2
N2ePd1eN3
N3ePd1eN4
79.5(13)
99.9(14)
79.4(13)
79.1
100.7
79.1
101.1
178.8
179.2
N4ePd1eN1 101.2(13)
N1ePd1eN3 179.1(15)
N2ePd1eN4 178.1(11)
1647 cmꢁ1
lated as 1634 cmꢁ1
In addition, strong characteristic absorption due to NeO stretching
vibration is observed at 985 cmꢁ1, and calculated at 973 cmꢁ1
NO
(64) þ CN (11)] [27,29,39,41,64,65]. In the IR spectra of [Pd(hei-
peo)2] and [Pt(heipeo)2], the (OeH) of the oxime group was not
[
n
CNimine (63) þ
n
CNoxime (18)] and 1597 cmꢁ1, calcu-
CNimine (12)] cmꢁ1 [30,39,41].
[Pt(heipeo)2]
Pt1eN1 2.025(18)
Pt1eN2 2.028(18)
[
n
CNoxime (59) þ
n
2.071
2.071
N1ePt1eN2
78.8(7)
78.5
180.0
101.5
180.0
N1ePt1eN1 180.0(8)
N2ePt1eN1 101.2(7)
N2ePt1eN2 180.0(8)
[n
d
n
Hydrogen bondsa
observed, due to the fact that the imineoxime loses this hydroxyl
proton upon complexation. The frequency of the hydroxyethyl
group was observed at 3483 cmꢁ1 in [Pd(heipeo)2] and 3430 cmꢁ1
in [Pt(heipeo)2], while calculated at 3429 and 3420 cmꢁ1, respec-
tively. The imine group (C]N) of [Pd(heipeo)2] and [Pt(heipeo)2]
was calculated at 1583 (%57 CN) and 1580 (%51 CN) cmꢁ1, observed
at 1623 and 1624 cmꢁ1 [22]. The oxime group (C]N) of both
complexes was observed at 1597 cmꢁ1, while calculated at ca.
1505 cmꢁ1 [67,68]. It is interesting that the frequencies of the imine
DeH/A (ꢂ)
ꢀ
ꢀ
ꢀ
DeH/A
DeH (A)
H/A (A)
D/A (A)
[Pd(heipeo)2], C1
O2eH2/O4i
O4eH2/O3ii
[Pd(heipeo)2], Ci
O2eH2/O1iii
[Pt(heipeo)2]
0.82
0.82
2.03
1.90
2.831(4)
2.683(4)
165.5
160.8
0.82
0.82
1.98
2.20
2.763(4)
2.755(3)
159.3
124.8
O2eH2/O1iv
a
Symmetry codes: (i) x, y, ꢁ1 þ z; (ii) 1 ꢁ x, ꢁy, 1 ꢁ z; (iii) x, y þ 1, z; (iv) x, y ꢁ 1, z.

Y. Kaya et al. / Journal of Organometallic Chemistry 752 (2014) 83e90
87
and oxime groups did not change in the complexes compared to the
free ligand. A substantial change is also observed in the NeO
stretching, which appears at 985 cmꢁ1 in the free heipeoH. The Ne
O absorptions were occurred at 1217 cmꢁ1 (calcd. 1234 cmꢁ1) for
[Pd(heipeo)2] and 1214 cmꢁ1 (calcd. 1236 cmꢁ1) for [Pt(heipeo)2],
indicating an increase in the double bond character of the NO bond
upon complexation [69,70]. Vibrational modes in the low wave-
since imineoximes exhibit a number of conformers and calculations
are referred to the static molecule [71,72]. However, in the case 13
C
NMR spectra, the experimental chemical shifts are in accordance
with the calculated values. In the computed 13C spectrum of the
ligand, the signal at 166.26 ppm belongs to the imine C atom and
was calculated as 166.38 ppm, while the signal at 152.55 ppm is
assigned to the C]NeO group of heipeoH (calcd. 158.73 ppm). The
signals between 126.2 and 135.1 ppm are assigned to the phenyl
carbon atoms of heipeoH. These signals were calculated between
122.03 and 127.08 ppm. The chemical shifts of the C9 and C10
atoms of heipeoH are observed at 56.21 and 61.45 ppm, respec-
tively and were calculated at 55.68 and 60.48 ppm. In the case of
metal complexes, the carbon of the imine group experiences
deshielding, while that of the oxime group exhibits shielding
compared those of the ligand.
number region of the spectra contain
with contributions of other several modes. The [Pd(heipeo)2] and
[Pt(heipeo)2] show two bands at 531e255 and 534e251 cmꢁ1
n(MeN) stretching together
,
respectively, which can be attributed to
n(MeN) (calcd. 530e
215 cmꢁ1) [42,43].
3.5. NMR Spectra
Experimental 1H and 13C NMR spectra of heipeoH were taken in
DMSO-d6 solvent, while those of [Pd(heipeo)2] and [Pt(heipeo)2]
were measured in CDCl3. The chemical shifts are given in Table 3,
while the NMR spectra obtained by the DFT method at the GIAO/
B3LYP/LANL2DZ level with TMS as a reference are illustrated in
Figs. S5eS7. The numbering of the atoms is the same as in Figs. 1
and 2 and S1. In 1H NMR spectra of heipeoH, the resonances
centered at ca. 7.82, 3.58 and 3.21 ppm are assigned to the aldehyde
proton of the oxime group and the methylene protons of the
hydroxyethyl group. These signals were calculated as 9.17, 3.02 and
2.85 ppm. The corresponding protons in the complexes were
observed at 7.90/7.67, 3.87/4.12 and 3.69/3.83 ppm (Pd complex/Pt
complex), which are calculated at 7.82/7.91, 3.41/4.12 and 2.49/
3.83 ppm, respectively. The deuterium exchangeable protons of the
hydroxyimino and hydroxyethyl groups of the ligand show char-
acteristic chemical shifts and appear at a singlet at 11.70 and
4.57 ppm, respectively. They are calculated as 9.17 and 2.89 ppm.
The hydroxyethyl proton of both complexes was observed at ca.
4.35 ppm, while calculated at ca. 2.95 ppm. The multiple signals
between 7.17 and 7.51 ppm represent the aromatic protons of the
phenyl groups of both ligands and its complexes, and they were
calculated at 7.05e8.48 ppm. The 1H NMR spectra of the ligand and
its complexes are not correlated well with the calculated spectrum,
3.6. Electronic absorption spectra
The UVevis absorption spectra of heipeoH and its complexes
were measured in EtOH. The absorption bands of the compounds
were assigned based on TDDFT. The calculated excited states, ab-
sorption bands, oscillator strengths (fos), transition configuration
and their assignments are given in Table 4 together with the
experimental bands. Several absorption bands were observed in
the spectra of heipeoH, and its complexes (Fig. S8). Relative per-
centages of atomic contributions to the lowest unoccupied and
highest occupied molecular orbitals were placed in Table S4. The
assignment of the calculated transitions to the experimental bands
is based on the criterion of the energy and oscillator strength of the
calculated transitions. The absorption bands of the heipeoH appear
at around 227 and 286 nm. The absorption band at 227 nm can be
mainly assigned to a superposition of three calculated bands be-
tween 218 and 249 nm. We ascribe the absorption band at 286 nm
to the calculated transition at 275 nm with oscillator strength of
0.0629. Both transitions can be ascribed to the
[41].
p / p* transition
In the [Pd(heipeo)2] complex, LUMO and LUMO þ 1 are con-
structed mainly from the * orbital of imineoxime (74 and 70%,
respectively) and LUMO þ 2 consists of %36 * orbital of imi-
neoxime and 45% the d-orbitals of metal, while LUMO þ 3 consists
of %79 * orbital of the phenyl ring. The higher occupied molecular
orbitals (HOMOs) can be described as orbitals of imineoxime
p
p
p
Table 3
Experimental and calculated 1H and 13C NMR chemical shifts of heipeoH, [Pd(hei-
peo)2] and [Pt(heipeo)2] (ppm).a
p
(from HOMO to HOMO ꢁ 2),
p
orbitals of phenyl (from HOMO ꢁ 4
to HOMO ꢁ 7) and the metal d-orbitals (from HOMO ꢁ 10 to
HOMO ꢁ 14). On the other hand, in the [Pt(heipeo)2] complex, the
HeipeoH
Exp.
[Pd(heipeo)2]
Exp.
[Pt(heipeo)2]
Exp.
Calcd.
Calcd.
Calcd.
LUMO and LUMO þ 1 orbitals consist of the
p* orbital of imi-
1H NMR
O1eH
C8eH
C1eH
C2eH
C3eH
C4eH
C5eH
O2eH
C9eH2
C10eH2
13C NMR
C7
C8
C6
C1
C2
C3
C4
C5
C9
neoxime (72 and 70%, respectively), while LUMO þ 2 is composed
mainly of the metal d-orbitals (41%) and * orbital of imineoxime
(30%). In addition, LUMO þ 3 to LUMO þ 5 can be described as
orbital of phenyl group. The HOMO orbitals consist mainly of the
11.70
7.82
7.43e7.17
9.17
8.48
7.22
7.47
7.52
7.45
7.13
2.89
3.02
2.85
e
e
e
e
p
7.90
7.45e7.22
7.82
7.12
7.50
7.56
7.50
7.12
2.91
3.41
2.49
7.67
7.51e7.35
7.91
7.05
7.50
7.57
7.50
7.15
2.99
3.55
2.60
p*
p
orbitals of imineoxime and the phenyl group (from HOMO to
HOMO ꢁ 16, except HOMO ꢁ 4, HOMO ꢁ 11 and HOMO ꢁ 12). The
HOMO ꢁ 4, HOMO ꢁ 11 and HOMO ꢁ 12 orbitals have 40, 68 and
61% of the metal d-orbital character (Table S4). Moreover, the iso-
density plots for the HOMOs and LUMOs orbitals of [Pd(heipeo)2]
and [Pt(heipeo)2] complexes are shown in Fig. 3.
Based on TDDFT calculations of [Pd(heipeo)2] and [Pt(heipeo)2]
complexes, the intense high-energy absorptions were observed at
lmax of 262 and 295 nm, respectively. The experimental band of
[Pd(heipeo)2] complex at 262 nm can be mainly assigned to a su-
perposition of four calculated bands between 261 and 276 nm, and
can be assigned to ligand to ligand charge transfer (LLCT), ligand to
metal charge transfer (LMCT) and metal to ligand charge transfer
(MLCT) transitions. On the other hand, the experimental band of
[Pt(heipeo)2] complex at 295 nm can be assigned to a superposition
4.57
3.58
3.21
4.38
3.87
3.69
3.42
4.12
3.83
166.26
152.55
135.07e
128.22
166.38
158.73
127.08
124.85
122.03
123.34
122.03
124.10
55.68
175.91
145.69
131.70e
127.21
170.43
150.30
124.95
123.20
123.53
125.13
123.26
124.47
48.66
177.72
146.52
131.31e
127.46
168.28
149.72
124.46
123.41
123.66
125.17
123.27
124.52
50.09
56.21
61.45
50.87
63.35
52.32
63.38
C10
60.48
59.59
59.72
a
In CDCl3 with TMS as a reference.

88
Y. Kaya et al. / Journal of Organometallic Chemistry 752 (2014) 83e90
Table 4
Experimental and calculated electronic transitions, oscillator strengths and their assignments for heipeoH, [Pd(heipeo)2] and [Pt(heipeo)2].a
Exp. (nm)
ε
Calcd. (nm)
fos
Major contribution (CI coeff)
Character
HeipeoH
286
227
0.121
3.569
275
249
240
218
0.0629
0.1127
0.1514
0.0956
H ꢁ 3 / L (%46)
H ꢁ 4 / L (%83)
H ꢁ 5 / L (%53)
H / L þ 1 (%40)
H ꢁ 1 / L þ 1 (%31)
p
p
p
p
p
(phen./imineoxime) /
(hydroxyethyl) / *(imineoxime)
(oxime) / *(imineoxime)
(phen.)/ (imineoxime) /
(phen./hydroxyethyl) /
p*(imineoxime)
p
p
p
p*(phen.)
p*(phen.)
[Pd(heipeo)2]
397
306
0.883
3.182
446
366
0.0300
0.0602
H / L (%70)
d(Pd)/
p(imineoxime) /
p
p
*(imineoxime)
*(imineoxime)
H ꢁ 1 / L þ 2 (%52)
H ꢁ 2 / L þ 1 (%27)
H ꢁ 4 / L (%83)
p
p
p
p
(imineoxime) / d(Pd)/
(oxime) / *(imineoxime)
(phen.) / p*(imineoxime)
(oxime) / d(Pd)/
(oxime) /
(phen.) / d(Pd)/
p
347
343
318
276
266
0.3322
0.1018
0.0614
0.0620
0.2492
H ꢁ 2 / L þ 2 (%63)
H ꢁ 10 / L (%48)
H ꢁ 5 / Lþ2 (%36)
H ꢁ 7 / L þ 2 (%18)
H ꢁ 5 / L þ 2 (%15)
H ꢁ 7 / L þ 2 (%62)
H ꢁ 14 / L (%59)
H / L þ 3 (%74)
p
p
*(imineoxime)
*(imineoxime)
d(Pd)/
p
262
4.699
p
p
p
p
*(imineoxime)
*(imineoxime)
(phen.) / d(Pd)/
263
261
244
0.0935
0.0967
0.1141
p(phen.) / d(Pd)/
p*(imineoxime)
d(Pd) /
d(Pd)/ (imineoxime) / p*(phen.)
p*(imineoxime)
p
[Pt(heipeo)2]
479
410
0.540
0.626
503
396
0.0300
0.0300
H / L (%83)
d(Pt)/
d(Pt)/
p
p
(imineoxime) /
(phen.) / *(imineoxime)
*(imineoxime)
*(imineoxime)
p*(imineoxime)
H ꢁ 4 / L (%35)
H ꢁ 1 / L þ 1 (%17)
H ꢁ 2 / L þ 1 (%16)
H ꢁ 4 / L (%57)
H ꢁ 11 / L (%42)
H ꢁ 8 / L (%24)
H ꢁ 12 / L (%39)
H ꢁ 2 / L þ 1 (%11)
H ꢁ 12 / L (%46)
H ꢁ 11 / L (%18)
H ꢁ 5 / L þ 1 (%79)
H / L þ 3 (%86)
H / L þ 5 (%51)
H ꢁ 2 / L þ 2 (%17)
H / L þ 5 (%40)
H ꢁ 16 / L (%14)
p
p
p
p
(imineoxime) /
(oxime) /
p
362
331
1.388
2.268
368
333
0.6329
0.0676
d(Pt)/
d(Pt)/
p
p
(phen.) /
(oxime) /
p
p
*(imineoxime)
*(imineoxime)
*(imineoxime)
p
(hydroxyethyl/oxime) /
d(Pt) / *(imineoxime)
(oxime) / *(imineoxime)
*(imineoxime)
*(imineoxime)
(phen./hydroxyethyl) / *(imineoxime)
p
295
2.818
314
302
0.1442
0.1403
p
p
p
d(Pt) /
p
d(Pt)/p(oxime) / p
286
253
243
0.0770
0.1723
0.1211
p
d(Pt)/
d(Pt)/
p
p
p
(imineoxime) /
(imineoxime) /
p
p
*(phen.)
*(phen.)
p
(oxime) / d(Pt)/
d(Pt)/ (imineoxime) /
(hydroxyethyl/phen.) /
p
*(imineoxime)
*(phen.)
*(imineoxime)
242
0.1395
p
p
p
p
a
ε ¼ Molar absorption coefficient (ꢀ104, dm3 molꢁ1 cmꢁ1), fos ¼ oscillator strength, H ¼ highest occupied molecular orbital, L ¼ lowest unoccupied molecular orbital,
phen. ¼ phenyl.
of three calculated bands at 286 (f ¼ 0.077), 302 (f ¼ 0.140) and
314 nm (f ¼ 0.144), and can be attributed to the MLCT and LLCT
observed at 306 nm in the [Pd(heipeo)2] complex can be assigned
to a superposition of four calculated bands between 318 and
366 nm with LLCT, MLCT and LMCT. The last experimental band at
397 nm (calcd. 446 nm) in the [Pd(heipeo)2] complex resulted from
HOMO to LUMO (70%). Thus this band is assigned to mixed LLCTand
transitions of d(Pt)
hydroxyethyl) /
/
p
*(imineoxime) and
p(phen./
p*(imineoxime). The other absorption band
MLCT involving d(Pd)/p(imineoxime) / p*(imineoxime) transi-
tion [42]. In the [Pt(heipeo)2] complex, the absorption at 331 nm
(calcd. 333 nm) originates from the transition between HOMO ꢁ 11
and LUMO (42%), HOMO ꢁ 8 and LUMO (24%). The absorption at
362 nm (calcd. 368 nm) is contributed by excitation from
HOMO ꢁ 4 to LUMO. The lower energy transitions at 410 (calcd.
396 nm) and 479 nm (calcd. 503 nm) mainly originate from the
electronic transition HOMO ꢁ 4 to LUMO and HOMO to LUMO,
respectively. Finally, the absorptions of the platinum(II) complexes
may be assigned to MLCT and LLCT transitions.
3.7. NBO atomic charges
Effective atomic charge calculations have an important role in
the application of quantum chemical calculation to molecular sys-
tem because of atomic charge changes effect dipole moment, mo-
lecular polarizability, electronic structure, acidityebasicity
behavior and more a lot of properties of molecular systems. In
addition, NBO charge calculations provide information about the
electrons movement between ligand and metal atom. The NBO
atomic charges [73,74] were calculated using the B3LYP/LANL2DZ
basis set. The results are listed in Table 5. As can also be seen from
Fig. 3. Molecular orbital surfaces for the HOMOs and LUMOs orbitals of (a) Pd(hei-
peo)2] and (b) [Pt(heipeo)2].

Y. Kaya et al. / Journal of Organometallic Chemistry 752 (2014) 83e90
89
Table 5
Appendix B. Supplementary data
NBO charge distribution on main atoms of heipeoH and its complexes.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.12.011.
HeipeoH [Pd(heipeo)2], C1 [Pd(heipeo)2], Ci [Pt(heipeo)2]
Pd/Pt
e
0.716
0.733
ꢁ0.078
ꢁ0.539
ꢁ0.494
ꢁ0.794
0.776
ꢁ0.090
ꢁ0.547
ꢁ0.499
ꢁ0.791
Noxime
Nimine
Ooxime
ꢁ0.149
ꢁ0.627
ꢁ0.586
ꢁ0.082, ꢁ0.081
ꢁ0.560, ꢁ0.544
ꢁ0.460
References
Ohydroxyethyl ꢁ0.794
ꢁ0.805, ꢁ0.808
ꢁ
ꢁ
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4. Conclusions
In this study,
a new imineoxime compound (1E,2E)-[(2-
hydroxyethyl)imino]-2-phenyl-ethanal oxime (heipeoH) and its
palladium(II) and platinum(II) complexes, namely [Pd(heipeo)2]
and [Pt(heipeo)2], have been synthesized and characterized by
various techniques including elemental analysis, IR, NMR, UVevis,
mass spectra and X-ray diffraction. Conformational analysis was
carried for heipeoH with B3LYP/6-31G(d) level, then the most sta-
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and C7eN2eC9eC10 were computed as ꢁ176.5ꢂ and ꢁ147.5ꢂ. X-ray
crystallographic analysis of the [Pd(heipeo)2] complex shows two
polymorphs due to orientation of the hydroxyethyl groups. In both
complexes, the palladium and platinum atoms are coordinated by
two imineoxime ligands, behaving as a bidentate ligand. In order to
study electronic, vibrational and NMR properties of the heipeoH,
[Pd(heipeo)2] and [Pt(heipeo)2] complexes, the theoretical calcu-
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