Neutral mononuclear luminescent Pd(II) complexes with heterocyclic thiolate ligands and chelating phosphines. Structural and photophysical assignments

Article abstract of DOI:10.1016/j.poly.2015.04.007

Two heterocyclic thiolate ligands, namely pymt and py2S (pymt = pyrimidine2-thiolate and py2S = pyridine-2-thiolate) and the diphosphines bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dpp

Full text of DOI:10.1016/j.poly.2015.04.007

Accepted Manuscript
Neutral mononuclear luminescent Pd(II) complexes with heterocyclic thiolate
ligands and chelating phosphines. Structural and photophysical assignments
P.A. Apanikolaou, A.G. Papadopoulos, A. Hatzidimitriou, P. Aslanidis
PII:
S0277-5387(15)00194-1
DOI:
http://dx.doi.org/10.1016/j.poly.2015.04.007
POLY 11269
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
20 January 2015
8 April 2015
Please cite this article as: P.A. Apanikolaou, A.G. Papadopoulos, A. Hatzidimitriou, P. Aslanidis, Neutral
mononuclear luminescent Pd(II) complexes with heterocyclic thiolate ligands and chelating phosphines. Structural
and photophysical assignments, Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.04.007
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Neutral mononuclear luminescent Pd(II) complexes with
heterocyclic thiolate ligands and chelating phosphines.
Structural and photophysical assignments.
P. A. Papanikolaou,*a A. G. Papadopoulos,*b A. Hatzidimitriou,a P. Aslanidisa
[a] Aristotle University of Thessaloniki, Department of Chemistry, Laboratory of Inorganic
Chemistry, P.O.B. 135, GR-541 24 Thessaloniki, Greece. Fax: +30 2310 997738; E-mail:
panpapan@chem.auth.gr, hatzidim@chem.auth.gr, aslanidi@chem.auth.gr
[b] Aristotle University of Thessaloniki, Department of Chemistry, Laboratory of Applied
Quantum Chemistry, P.O.B. 135, GR-541 24 Thessaloniki, Greece. Fax: +30 2310 997738;
E-mail: anastp@chem.auth.gr
____________________________________________________________________
1

Abstract
Two heterocyclic thiolate ligands, namely pymt and py2S (pymt = pyrimidine2-
thiolate
and
py2S
=
pyridine-2-thiolate)
and
the
diphosphines
bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe),
1,3-bis(diphenylphosphino)propane (dppp), were used in the synthesis of three neutral
Pd(II) complexes (cis-[Pd(dppm)(pymt)2] (1), cis-[Pd(dppe)(pymt)2] (2) and cis-
[Pd(dppp)(pyrt)2] (3)). Crystallographic analysis of the isolated complexes reveals
their square planar arrangement and the coordination of the thiolate moieties through
their exocyclic sulphur atom. The complexes absorb in the visible part of the spectrum
through charge transfer transitions while after photoexcitation at 385 nm they appear
to emit with a broad band located at 465 nm.
Keywords: Palladium, Thiolate ligands, Luminescence, DFT calculations.
___________________________________________________________
2

1. Introduction
Heterocyclic thiones constitute an extended and very interesting class of
multifunctional donor ligands [1] that combine soft and hard coordination sites thus
being able to selectively bind various metal centers [2]. Further the ability of these
ligands to coordinate in a monodentate or a bridging mode results in a high structural
diversity of their complexes [1, 3-6]. As has been seen, extended structures also can
be supported by the incorporation of bidentate P-donor molecules with small saturated
carbon chains [7].
Due to the presence of the thioamide group in their skeleton, pyrimidine-type
thiones and thiolates and their complexes with a variety of metals have been the
subject of many studies related to model systems of sulphur-analogues of DNA-bases
[4]. Based on this characteristic, research interest largely focused on the possibility of
developing novel complexes with targeted properties, mainly anticarcinogenic [8-10].
As far it concerns the Pd(II) metal core, its d8-outershell electronic configuration
imposes a square planar coordination environment and in conjunction to the
implementation of the aforementioned ligands could lead to the development of new
DNA intercalating metallodrugs [11]. It should be noted that the combination of
heavy metals with S,N-donor atoms has already been recognized to result in
interesting anticarcinogenic properties [4].
Besides the biological importance of sulphur-containing complexes, much
research effort has been devoted to the exploitation of their redox and photophysical
properties. In this respect, a large class of dithiolene complexes of group 10 metals
(Ni, Pd, Pt) has been studied extensively owing to their intriguing spectroscopic
behaviour [12-15]. Recently also, a series of coinage metal complexes incorporating
heterocyclic thiones or thiolates in combination with aryl-phosphines or
3

phenanthroline revealed interesting photophysics [16-20]. The emission energy of
these systems can be tuned through a thione-modification while their emitting state is
readily assigned as MLCT or LMCT on the basis of both experimental and theoretical
data. As far as it concerns the Pd(II) center, its coexistence with ligands of low energy
π-acceptor orbitals can give rise to charge transfer bands resulting to luminescence in
the visible part of the spectrum [21]. In the same framework, the spin-orbit coupling
induced by the “heavy-atom” nature of this nucleus can promote an efficient
intersystem crossing towards triplet states and which results to long-lived
phosphorescence with possible applications in lighting technologies [22-24].
In the framework of our ongoing investigations on the molecular and
photophysical properties of heteroleptic S,N,P-containing metal complexes, we herein
explore the structural, electronic and spectroscopic characteristics of a series of
neutral Pd(II) compounds bearing a diphosphine ligand combined with an
heterocyclic S,N-thiolate moiety.
2. Results and Discussion
2.1. Synthesis and Spectroscopic Details
All of the presented complexes were synthesized under atmospheric
conditions by reacting a methanolic solution of PdCl2 with the respective diphosphine,
followed by the addition of two equivalents of the deprotonated (with KOH in
MeOH) thiol. The products were isolated as air stable orange to red microcrystalline
solids, soluble in common organic solvents such as methanol, dichloromethane and
chloroform, resulting in yellow to deep orange colored solutions.
For both sulfur containing ligands and with reference to their protonated
neutral forms, a prototropic thiol-thione tautomerism occurs including a proton-
4

migration between the sulfur and an endocyclic nitrogen atom. As has been suggested,
this atom transfer is incomplete [25] while in solution, the thione form of the neutral
ligands is reported to prevail over the respective thiole form [26]. On the other hand
no reports seem to exist on the charge localization and the relative stability of the
deprotonated ligands. Scheme I comprises the structures of the anions of the two
tautomers of each sulfur-ligand used and should not be merged with resonance
structures as the negative charge refers to the σ-system of the molecular skeleton [27].
Scheme I
In both anionic forms of each S-ligand, coordination may occur either through
the sulfur or/and the pyridine nitrogen atom(s) of the heterocyclic ring [28]. In the
present case, X-ray crystallography reveals their monodentate interaction with the
5

metal center through the sulfur atom. This is somewhat expected as the pre-
coordinated phosphines increase the soft character of the metal predisposing the
binding of pymt and py2S through their soft-base site. Additionally and because of the
stereochemical demands imposed by the bulky phosphines, the coordination of both
anions through their sulfur atom should also be favored due to a longer metal-ligand
bond which contributes to reduce steric repulsions within the coordination sphere. The
complexes (1), (2) and (3) were all isolated as mononuclear species containing a
chelating phosphine and two thiolate ligands coordinated on the metal core in a cis-
square planar arrangement (Scheme II).
Scheme II
The infrared spectra of the prepared complexes show the expected distinct and
strong vibrational features attributed to the phosphine moieties. These bands appear as
a set of sharp peaks located around 690 and 510 cm-1 and reveal small shifts upon
coordination to the metal center [29, 30]. In all cases, a strong band located in the
region 1559-1565 cm-1 for both pymt and py2S systems can be assigned to the
stretching vibrations of the –C=N– and –C=C– bonds of the heterocyclic rings.
Moreover, the spectra of the studied compounds lack both the characteristic stretching
frequency of the –NH group in the 3150 cm-1 region [31, 32] and the ν(SH) bands at
ca. 2500-2600 cm-1 which verifies the presence of the sulfur-ligand in its deprotonated
anionic form.
6

2.2. X-ray Structures
The molecular structures of the complexes (1), (2) and (3), (details of crystal and
structure refinement are given bellow in Table 3) have been established by single-
crystal X-ray diffraction. Plots for the structures are presented in Figs. 1–3 and
selected bond lengths and angles are given in the legends to the respective plots.
Fig. 1. A view of 1 with the atomic numbering schemes. Displacement ellipsoids are
shown in the 50% probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) Pd1–S1 2.3267(9); Pd1–S2 2.3613(9); Pd1–P1 2.2895(8); Pd1–P2
2.2937(8); S1–C1 1.757(3); S2–C5 1.722(4) and bond angles (o) S1–Pd1–S2
80.56(3); S1–Pd1–P1 103.62(3); S2–Pd1–P1 174.55(3); S1–Pd1–P2 176.67(3); S2–
Pd1–P2 102.73(3); P1–Pd1–P2 73.07(3); Pd1–S1–C1 113.80(11); Pd1–S2–C5
110.79(12).
7

Fig. 2. A view of 2 with the atomic numbering schemes. Displacement ellipsoids are
shown in the 50% probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) Pd1–S1 2.3754(6); Pd1–S2 2.3773(6); Pd1–P1 2.2744(6); Pd1–P2
2.2724(6); S1–C1 1.734(3); S2–C5 1.739(2) and bond angles (o) S1–Pd1–S2
89.05(2); S1–Pd1–P1 90.85(2); S2–Pd1–P1 175.06(2); S1–Pd1–P2 172.92(2); S2–
Pd1–P2 95.72(2); P1–Pd1–P2 84.85(2); Pd1–S1–C1 101.89(9); Pd1–S2–C5 97.62(8).
Fig. 3. A view of 3 with the atomic numbering schemes. Displacement ellipsoids are
shown in the 50% probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) Pd1–S1 2.3835(5); Pd1–S2 2.3606(6); Pd1–P1 2.2598(5); Pd1–P2
8

2.2759(5); S1–C1 1.745(2); S2–C6 1.735(3) and bond angles (o) S1–Pd1–S2
91.13(2); S1–Pd1–P1 85.15(2); S2–Pd1–P1 176.27(2); S1–Pd1–P2 175.23(2); S2–
Pd1–P2 91.63(2); P1–Pd1–P2 92.102(19); Pd1–S1–C1 100.63(8); Pd1–S2–C6
99.81(9).
All three complexes are four-coordinate monomers comprising the palladium(II)
cation in a distorted square planar coordination environment generated by the S atoms
of two thiolate moieties and two P atoms of the respective diphosphine. Within the
central core of each complex, angular distortions from the ideal geometry can be
certainly attributed to the bite angle of the chelating diphosphine. Thus, while the
three complexes do not differ significantly from each other with regard to their S–Pd–
P trans angles (ranging between 172.92o and 176.67o), there is a direct relation
between each P–Pd–P bite angle and its respective opposite S–Pd–S angle. In fact, a
small P–Pd–P bite angle of 73.03o in compound 1 is responsible for the narrowing of
the S–Pd–S angle at a value of 80.56o, while a more wide P–Pd–P bite angle (84.85o
and 92.102o in 2 and 3 respectively) is associated with the correspondingly widened
S–Pd–S angle of 89.05o in 2 and 91.13o in 3. Considering interbond distances
involving the central metal ion, which are very close to those found in other related
complexes [4, 28], there are no significant differences between the three complexes.
It is to note that a crystal structure of compound 2 has been already described by
others [4]. Comparing the two structures together, one can notice a marked
conformational difference that concerns the orientation of the two pyrimidine rings.
Thus, in the earlier described structure the two pyrimidine rings are nearly
perpendicular to each other, each of them directed parallel to a phenyl ring of the
phosphine ligand with a distance of 3.907 Å between their respective centroids. In the
9

actual structure of 2, however, the dihedral angle between the planes of the two
pyrimidine rings is only 72.45o, consequently only one of these rings is allowed to
participate in such a π-stacking interaction, however at the clearly shorter distance of
3.618 Å. Finally, in addition to this π-stacking interaction, intramolecular hydrogen
…
…
…
bonding C24–H N2 (C N = 3.518 Å, H N = 2.586 Å, < C–H–N = 165.49o)
appears to contribute both to the orientation of the pyrimidine rings and to the overall
stabilization of the molecule in the solid state.
2.3. Photophysical Studies
The electronic spectra of the three complexes in dichloromethane display a
strong absorption in the ultraviolet region (290-315 nm) with ε values ranging from
ca. 17000 to 35000 M-1cm-1 (Figure 4). This band is assigned to intraligand π-π*
transitions of the aromatic rings of the phosphines with contributions from high
energy electronic excitations located in the heterocyclic rings of the thiolate ligands.
In the case of (1) and (3), a low intensity shoulder (ε ~ 4000 M-1cm-1) appears at ca
350 nm followed by an absorption tail extending up to 430 nm (Table 1). For (2) a
clear absorption band appears at 410 nm (ε ~ 3000 M-1cm-1) extending up to 460 nm.
According to literature data [23, 33] and the results of theoretical calculations (vide
infra) the latter absorptions are assigned as a mixture of charge transfer transitions
comprising the metal core and both type of ligands (MLCT/LLCT). Additionally and
because of the spin-orbit coupling induced by the presence of the Pd-heavy nucleus, a
participation of excitations from the ground state towards low lying triplets (S0 → Tn)
of the complexes could also be expected. Such transitions would be of a very low
intensity and potently contribute in the tails of the lowest energy absorptions
appearing in the electronic spectra of the compounds.
10

Fig. 4. Absorption spectra of [Pd(dppm)(pymt)2] (1) (red curve), [Pd(dppe)(pymt)2]
(2) (blue curve) and [Pd(dppp)(py2S)2] (3) (green curve) in dichloromethane.
Table 1. Photophysical data of the synthesized Pd(II) complexes in fluid solution.
λabs, nma
Compound
λem, nmb,c
(εabs, M-1cm-1)
[Pd(dppm)(pymt)2] (1) 359 (sh, 3754)
458
472
471
[Pd(dppe)(pymt)2] (2)
[Pd(dppp)(py2S)2] (3)
408 (3015)
356 (sh, 3902)
arefers to the longest wavelength absorption in dichloromethane
bλexc = 385 nm, cdichloromethane solution
All of the prepared complexes were tested for their ability to emit in fluid
solution. After excitation at 385 nm of an optically diluted sample of each complex in
dichloromethane, a broad peak maximizing around 465 nm is detected (Figure 5). The
selected photoexcitation cannot directly populate any pure phosphine-residing
(intraligand, IL) π-π* singlet excited state because of their expected higher lying
energies, thus the observed luminescence can be readily assigned to the lowest lying
3
state being a LLCT/3MLCT/3IL [24]. The triplet character of the emitting state is
supported by a heavy atom effect [22-24, 33-35] induced by the Pd-nucleus while the
participation of the metal center orbitals is indicated by the unstructured profile of the
emission band [36a]. The relatively large Stokes shift of the emission (ca. 80 nm) also
11

agrees with its triplet nature. At this point it should be mentioned that mixed-ligand
complexes of Pd(II) bearing dithiolate moieties appear to be in general non
luminescent due to strong interactions with the solvent and/or non-totally symmetric
distortions [36b].
Fig. 5. Normalized emission spectra of [Pd(dppm)(pymt)2] (1) (red curve),
[Pd(dppe)(pymt)2] (2) (blue curve) and [Pd(dppp)(py2S)2] (3) (green curve) in
dichloromethane after photoexcitation at 385 nm.
2.4. Theoretical Results
In order to unravel some marked structural and electronic features of the
synthesized compounds we performed DFT and TD-DFT calculations on (2) as
representative case. The PBE1PBE [37] functional along with the LANL2DZ [38]
basis set for the metal core and the 6-31G(d,p) [39] basis sets for the light atoms were
selected for the calculations. The structure of the neutral complex was optimized in a
dichloromethane environment. The obtained geometrical parameters are presented in
Table S1. In the optimized structure (Figure S1), the complex retains its square planar
configuration with two slightly unequivalent Pd-P and two also slightly varying Pd-S
bond lengths. The metal-sulfur bonds appear to be somewhat longer than the two Pd-P
bonds (ca. 2.40 and 2.31 Å, respectively) while the bond angles within the
12

chromophoric PdP2S2 unit deviate from the ideal value of 90o with the P-Pd-S bond
angles been larger than the P-Pd-P and S-Pd-S angles. All of the theoretically
resulting geometrical features are in good agreement with the crystallographically
determined values for the complex.
Fig. 6. Frontier MOs of [Pd(dppe)(pymt)2] (2) as they resulted from geometry
optimization in dichloromethane.
The electronic structure of (2) was further probed by inspecting the symmetry
and localization of the frontier MOs of the system obtained from DFT calculations.
As can be seen in Figure 6, the highest occupied orbital (HOMO) mainly locates in
13

the π-system of the heterocyclic thiolate ligands with a partial d-σ antibonding
character between the metal core and the phosphorus atoms. The same holds for
HOMO-1 with the difference of a bonding character for the Pd-P interactions.
HOMO-2 bears large contributions from the d AOs of the metal center along with a
smaller participation of the thiolates’ ring system and the exocyclic sulfur atoms. On
the other hand, the lowest unoccupied orbital (LUMO) is of a d-σ antibonding nature
extending in the region of the PdP2S2 chromophore with a negligible contribution
from the π-system of the phosphine phenyl rings. The sulfur atoms of the thiolates do
not participate in LUMO+1 which mainly localizes on the Pd-phosphine region while
LUMO+2 mainly locates in the phosphine moiety with a small participation of the
thiolates’ heterocyclic π-system. In Figure 7, a simulation of the experimentally
obtained light absorption of the complex under study through TD-DFT calculations is
presented. The computed eigenvectors offer a very good representation of the
recorded spectrum. According to the shape of the involved MOs, the nature of the
electronic transitions (Figure 8 and Table 2) contributing to the visible-part
absorption band of the complex is assigned as thiolate to phoshine charge transfer
with large contributions from the metal core in the donor orbitals (LLCT/MLCT).
Higher energy excitations bear either an IL or MLCT character. The results are in
agreement with the nature of the emissive state of the complex, as discussed above.
14

Fig. 7. Experimental absorption spectrum of [Pd(dppe)(pymt)2] (2) along with the
calculated excitation energies appearing as vertical lines.
Table 2. Selected principal singlet–singlet electronic transitions of the complex
[Pd(dppe)(pymt)2] (2) calculated at the PBE1PBE/6-31G(d,p),LANL2DZ level of
theory.
Excitation
E/eV
2.833
2.853
3.205
3.980
4.096
4.144
4.168
λ/nm Orbital Nature
Character
MLCT/LLCT
MLCT/LLCT
MLCT/LLCT
MLCT/LLCT
MLCT/LLCT
LLCT/IL
OS, f
→ LUMO
HOMO
437.7 d-σ*/πpymt → d-σ*/πPPh3
434.6 d-σ/πpymt → d-σ*/πPPh3
386.8 4dPd/πpymt → d-σ*/πPPh3
311.5 d-σ*/πpymt → d-σ*/πPPh3
302.7 d-σ*/πpymt → πPPh3
0.0194
0.0236
0.0186
0.0144
0.0591
0.1679
→ LUMO
HOMO-1
HOMO-2 → LUMO
HOMO → LUMO+1
HOMO-1 → LUMO+1
HOMO-3 → LUMO
299.2 πPPh3/σpymt→ d-σ*/πPPh3
297.5 d-σ*/πpymt → πPPh3/πpymt
→ LUMO+2
HOMO
MLCT/LLCT/IL 0.1205
→ LUMO
HOMO-4
4.196
4.336
295.5 4dPd/πPPh3 → d-σ/πPPh3
MLCT/IL
0.1354
HOMO-14 → LUMO
→ LUMO
HOMO-4
285.9 4dPd/πPPh3/πpymt → d-σ*/πPPh3/πpymt
MLCT/LLCT/IL 0.1949
HOMO-2 → LUMO+4
15

Fig. 8. Predicted electronic transitions and participating MOs with the higher CI
coefficients for the [Pd(dppe)(pymt)2] (2).
3. Conclusions
Three Pd(II) neutral complexes bearing two heterocyclic thiolate units and a
chelating diphosphine moiety were synthesized and characterized. As revealed by
crystallographic data, the complexes adopt in all cases a square planar arrangement in
accordance to the d8-character of the metal core. Further, coordination of the
deprotonated thiolates to the Pd(II) ion takes place through their exocyclic sulphur
atom while no interaction with the heterocyclic nitrogen atoms is detected. In
16

solution, the complexes absorb in the visible part of the spectrum with the lowest
energy transitions described as MLCT/LLCT according to DFT results. Further the
complexes are emissive in a dichloromethane solution after photoexcitation in their
CT-bands.
4. Experimental
4.1. Materials and Measurements
The starting materials PdCl2, bis(diphenylphosphino)methane, 1,2-
bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane), pyrimidine-2-
thione and pyridine-2-thione were used as received. Solvents of reagent grade were
also used without any prior purification or drying process. Elemental analyses for C,
H and N were performed with a Perkin-Elmer 240B elemental analyzer. Infrared
spectra were recorded in KBr pellets on a Nicolet FT-IR 6700 spectrophotometer.
Electronic absorption spectra were recorded in 1 cm cuvettes on a Shimadzu 160A
spectrophotometer. Emission studies in dichloromethane were performed on a Hitachi
F-7000 Fluorometer.
4.2. Computational Details
The geometry of (2) was optimized with DFT theory assuming a
dichloromethane medium and without symmetry constraints with the PBE1PBE [37]
functional. The obtained crystallographic data were used for the description of the
initial geometry. The 6-31G(d,p) [39] and LanL2DZ [38] basis sets were selected
respectively for the light elements and the metal core. TD-DFT calculations in the
aforementioned solvent system were performed on the same level of theory and with
the same basis sets. In all cases computations were executed with the Gaussian 03W
17

[40] package using the PCM [41] algorithm implemented in it. Vibrational
frequencies calculations ensured that the obtained geometry is real minimum in the
potential energy hypersurface. Visualization of the obtained structure and MOs was
performed with GaussView 5.0.
4.3. Crystal Structure Determination
Single crystals of cis-[Pd(ddpm)(pymt)2] (1), cis-[Pd(ddpe)(pymt)2] (2) and
cis-[Pd(ddpp)(py2S)2] (3), suitable for crystal structure analysis were obtained by
slow evaporation of their mother liquids at room temperature. For the structure
determination single crystals of the compounds were mounted on a Bruker Kappa
APEX II diffractometer equipped with a triumph monochromator. The collected
frames were integrated with the Bruker SAINT software package [42] using a
narrow-frame algorithm. Data were corrected for absorption effects using the
numerical method from crystal dimensions (SADABS) [43]. The structures were
solved using SUPERFLIP package [44] and refined by full–matrix least-squares
method on F2 using the CRYSTALS package version 14.48 [45]. All non hydrogen
atoms have been refined anisotropically. All hydrogen atoms were found at expected
positions and refined using soft constraints. By the end of the refinement they were
positioned using riding constraints. The crystal data and some details of the data
collection and structure refinement for all compounds are given in Table 3.
Illustrations were generated with CAMERON [46].
18

Table 3. Crystal data and structure refinement details for compounds 1, 2 and 3
Compound
Formula
1
2
3
C33H28N4P2Pd1S2
C34H30N4P2Pd1S2
C37H34N2P2Pd1S2
Formula weight
713.09
727.12
739.17
Crystal system
Temperature (K)
Space group
Monoclinic
295
C2/c
a = 22.9567(7) Å
b = 8.8667(3) Å
c = 30.5007(9) Å
α = 90°
Monoclinic
295
P21/c
a = 8.5459(3) Å
b = 10.5547(3) Å
c = 35.2540(11) Å
α = 90°
Monoclinic
295
P21/c
a = 17.6938(5) Å
b = 8.6339(2) Å
c = 21.7762(6) Å
α = 90°
Unit cell dimensions
β = 90.528(2)°
γ = 90°
β = 102.751(2)°
γ = 90°
β = 92.156(2)°
γ = 90°
Z
8
4
4
Absorption coefficient
0.888
0.847
0.810
(µ) (mm-1)
Density (calculated)
(Mg/m3)
1.629
1.52
1.48
Theta range for data
collection (o)
F(000)
1.819 to 27.449
1.155 to 27.205
1.152 to 35.538
2896
1480
1512
Reflections collected
77202
35711
112840
Independent reflections 6852
6960
15101
Completeness up to
theta
Data / restraints /
parameters
99.6% (theta =
98.1% (theta =
99.2% (theta =
27.4489o)
6052/0/379
1.000
27.205 o)
35.538 o)
6720/0/388
1.000
R1=0.033,
wR1=0.052
10512/0/397
1.000
R1=0.039,
wR1=0.067
2
Goodness-of-fit on F
Final R indices
[I>2σ(I)]
R1=0.044,
wR1=0.069
Largest diff. peak and
0.61, – 1.70
0.78, – 0.39
1.06, – 0.60
hole (e.Å-3)
4.4. Synthesis of the complexes
All the complexes were prepared according to the following general
procedure. In a solution of PdCl2 (0.5 mmol) in 20 mL of methanol, the appropriate
amount of the respective solid diphosphine is added (0.5 mmol). After stirring for 30
min, 1 mmol of the selected thiole, deprotonated with KOH in 20 mL of methanol, is
19

added and the reaction mixture is stirred for 48 h under moderate heating (60 oC). The
resulting solution is filtrated for the removal of any residual solids and the filtrate is
left to stand in air after the addition of a small amount of a 1:1 mixture of
CH2Cl2/CHCl3. Slow evaporation of the solvent gave the products in the form of
crystals which were filtered off and dried under vacuum.
[Pd(dppm)(pymt)2] (1)
Red solid. Yield 92 % (0.46 mmol, 0.33 g). Elemental Analysis: Calcd for
C33H28N4P2PdS2: C, 55.58; H, 3.96; N, 7.86. Found: C, 55.50; H, 4.01; N, 7.78. IR
(KBr, cm-1): 3054 (w, =C-H), 2953 (w, -C-H), 1560 (s, -C=N-), 1536 (s, -C=C-), 1434
(s), 1371 (s), 1175 (s), 1097 (m), 744 (s), 691 (s), 505 (s).
[Pd(dppe)(pymt)2] (2)
Orange solid. Yield 94 % (0.47 mmol, 0.34 g). Elemental Analysis: Calcd for
C34H30N4P2PdS2: C, 56.16; H, 4.16; N, 7.71. Found: C, 56.31; H, 4.12; N, 7.70. IR
(KBr, cm-1): 3048 (w, =C-H), 2970 (w, -C-H), 1561 (s, -C=N-), 1531 (s, -C=C-), 1434
(s), 1371 (s), 1174 (s), 1099 (m), 740 (s), 687 (s), 521 (s).
[Pd(dppp)(py2S)2] (3)
Orange solid. Yield 93 % (0.46 mmol, 0.34 g). Elemental Analysis: Calcd for
C37H34N2P2PdS2: C, 60.12; H, 4.64; N, 3.79. Found: C, 60.32; H, 4.72; N, 3.82. IR
(KBr, cm-1): 3051 (w, =C-H), 2912 (w, -C-H), 1569 (s, -C=N-), 1542 (s, -C=C-), 1442
(s), 1435 (s), 1403 (s), 1175 (s), 1121 (m), 748 (s), 691 (s), 512 (s).
5. Appendix. Crystallographic data
20

Crystallographic data (without structure factors) for the structures reported in
this paper have been deposited with the Cambridge Crystallographic Data Centre
(CCDC) as supplementary publication no. CCDC-1042948 (1), CCDC-1042949 (2)
and CCDC-1042950 (3). Copies of the data can be obtained free of charge from the
CCDC (12 Union Road, Cambridge CB2 1EZ, UK; Tel.: +44-1223-336408; Fax:
+44-1223-336033;
e-mail:
deposit@ccdc.cam.ac.uk;
Web
site:
http://www.ccdc.ca.ac.uk).
6. Supplementary Materials
Electronic Supplementary Information (ESI) available: Optimized geometry
of the [Pd(dppe)(pymt)2] (2) (Figure S1), structural data for the optimized geometry
of the complex in dichloromethane (Table S1).
7. References
1. P. J. Cox, P. Aslanidis, P. Karagiannidis, S. Hadjikakou, Inorg. Chim. Acta, 310
(2000) 268.
2. L. Dahlenburg and M. Kühnlein, Eur. J. Inorg. Chem., 2000 2117.
3. a) P. Aslanidis, S. K. Hadjikakou, P. Karagiannidis, M. Gdaniec and Z.
Kosturkiewicz, Polyhedron, 12 (1993) 2221; b) P. Aslanidis, P. J. Cox, S.
Divanidis, A. C. Tsipis, Inorg. Chem., 41 (2002) 6875.
4. T. S. Lobana, R.Verma, G. Hundal, A. Castineiras, Polyhedron 19 (2000) 899.
5. E. S. Raper, Coord. Chem. Rev. 165 (1997) 475.
6. S. Miranda, E. Cerrada, A. Luquin, A. Mendia, M. Laguna, Polyhedron 43 (2012)
15 and references cited therein.
7. P. J. Cox, P. Aslanidis, P. Karagiannidis, Polyhedron 19 (2000) 1615.
8. P. J. Sadler, Adv. Inorg. Chem. Radiochem. 36 (1991) 1.
21

9. S. Miranda, E. Vergara, F. Mohr, D. De Vos, E. Cerrada, A. Mendía, M. Laguna,
Inorg. Chem. 47 (2008) 5641.
10. E. Vergara, A. Casini, F. Sorrentino, O. Zava, E. Cerrada, M. P. Rigobello, A.
Bindoli, M. Laguna, P. J. Dyson, ChemMedChem 5 (2010) 96.
11. E. Ramachandran, P. Kalaivani, R. Prabhakaran, M. Zeller, J. H. Bartlett, P. O.
Adero, T. R. Wagner, K. Nataraja, Inorg. Chim. Acta 385 (2012) 94.
12. R. S. Pilato, K. A. Van Houten, Prog. Inorg. Chem. 52 (2004) 369.
13. S. D. Cummings, R. Eisenberg, Prog. Inorg. Chem. 52 (2004) 315.
14. A. Zarkadoulas, E. Koutsouri, C. A. Mitsopoulou, Coord. Chem. Rev. 256 (2012)
2424.
15. A. Davison, N. Edelstein, R. H. Holm, A. H. Maki, Inorg. Chem. 3 (1964) 814.
16. a) P. Aslanidis, P. J. Cox, K. Kapetangiannis, A. C. Tsipis, Eur. J. Inorg. Chem.
2008, 5029; b) M. G. Babashkina, D. A. Safin, A. Klein, and M. Bolte, Eur. J.
Inorg. Chem. 2010, 4018.
17. P. Aslanidis, P. J. Cox, A. C. Tsipis, Dalton Trans. 39 (2010) 10238.
18. I. Papazoglou, P. J. Cox, A. G. Papadopoulos, M. P. Sigalas, P. Aslanidis, Dalton
Trans. 42 (2013) 2755.
19. V. W. W. Yam, C. H. Lam, W. K. M. Fung, K. K. Cheung, Inorg. Chem. 40
(2001) 3435.
20. R. Langer, M. Yadav, B. Weinert, D. Fenske, O. Fuhr, Eur. J. Inorg. Chem. 2013
3623.
21. J. G. Małecki, P. Zwoliński, Polyhedron, 39 (2012) 85.
22. X. Zarate, E. Schott, R. Ramirez-Tagle, D. MacLeod-Carey, R. Arratia-Pérez,
Polyhedron 37 (2012) 54.
22

23. G. S. M. Tong, P. K. Chow, W. P. To, W. M. Kwok and C. M. Che, Chem. Eur. J.
20 (2014) 6433.
24. B. Z. Yang, X. Zhou, T. Liu, F. Q. Bai, H. X. Zhang, Int. J. Quant. Chem. 111
(2011) 2258.
25. J. Guillermo Contreras and J. B. Alderete, J. Mol. Struct. (THEOCHEM) 231
(1991) 257 and refs cited therein.
26. a) M. C. P. Lima, K. Coutinho, S. Canuto and W. R. Rocha, J. Phys. Chem. A 110
(2006) 7253; b) D. W. Aksnes, H. Kryvi, Acta Chem. Scand. 26 (1972) 2255; c)
M. J. Nowak, H. Rotkowska, L. Lapinski, J. Leszczynski, J. S. Kwiatkowski,
Spectrochim. Acta 47A (1991) 339; d) D. Moran, K. Sukcharoenphon, R. Puchta,
H. F. Schaefer, P. V. Schleyer, and C. D. Hoff, J. Org. Chem 67 (2002) 9061.
27. D. Kovala-Demertzi, P. Kyrkou and I. Zakharoba, Polyhedron 10 (1991) 1507.
28. T. S. Lobana, P. Kaur, G. Hundal, R. J. Butcher, A. Castineiras, Z. Anotg. Allg.
Chem. 634 (2008) 747.
29. P. Aslanidis, P. J. Cox, S. Divanidis, P. Karagiannidis, Inorg. Chim. Acta 357
(2004) 4231.
30. P. Viswanathamurthi and M. Muthukumav, J. Chem. Sci. 123 (2011) 567.
31. P. A. Papanikolaou, P. C. Christidis, A. Th. Chaviara, C. A. Bolos, and A. C.
Tsipis, Eur. J. Inorg. Chem. 2006 2083.
32. R. Allman, M. Krestl, C. Bolos, G. Manoussakis, G. St. Nikolov, Inorg. Chim.
Acta 175 (1990) 255.
33. P. Pratihar, S. Jha, T. K. Mondal, G. Mostafa, C. Sinha, Polyhedron 26 (2007)
4328.
34. M. A. Omary, M. A. Rawashdeh-Omary, H. V. K. Diyabalanage and H. V. Rasika
Dias, Inorg. Chem. 42 (2003) 8612.
23

35. H. Kunkely and A. Vogler, Inorg. Chem. Commun. 9 (2006) 866.
36. a) J. Ruiz, J. Lorenzo, C. Vicente, G. López, J. M. López-de-Luzuriaga, M.
Monge, F. X. Avilés, D. Bautista, V. Morendo and A. Laguna, Inorg. Chem. 47,
(2008), 6990; b) C. A. Mitsopoulou, Coord. Chem. Rev. 254 (2010) 1448 and refs
cited therein.
37. a) J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865; b)
J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett. 78 (1997) 1396.
38. a) P. J. Hay, W. R. Wadt, J. Chem. Phys. 82 (1985) 270; b) W. R. Wadt, P. J. Hay,
J. Chem. Phys. 82 (1985) 284; c) P. J. Hay, W. R. Wadt, J. Chem. Phys. 82 (1985)
299.
39. a) P. C. Hariharan, J.A. Pople, Theor. Chim. Acta 28 (1973) 213; b) M. M. Francl,
W. J. Petro, W. J. Hehre, J. S. Binkley, M. S. Gordon, D. J. DeFrees, J. A. Pople,
J. Chem. Phys. 77 (1982) 3654.
40. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M.
Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M.
Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R.
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G.
Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y.
24

Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M.
W. Wong, C. Gonzalez and J. A. Pople, Gaussian 03, Revision E.01-SMP,
Gaussian, Inc., Pittsburgh PA (2003)
41. a) S. Miertus, E. Scrocco, J. Tomasi, Chem. Phys. 55 (1981) 117; b) J. Tomasi, M.
Persico, Chem. Rev. 94 (1994) 2027; c) C. Amovilla, V. Barone, R. Cammi, E.
Cances, M. Cossi, B. Mennucci, C. S. Pomelli, J. Tomasi, Adv. Quantum Chem.
32 (1998) 227.
42. Bruker Analytical X-ray Systems, Inc. Apex2, Version 2 User Manual, M86-
E01078, Madison, WI. 2006.
43. Siemens Industrial Automation, Inc. SADABS: Area-Detector Absorption
Correction; Madison, WI. 1996.
44. L. Palatinus, G. Chapuis, SUPERFLIP – a computer program for the solution of
crystal structures by charge flipping in arbitrary dimensions, Journal of Applied
Crystallography 40, (2007) 786.
45. P.W. Betteridge, J.R. Carruthers, R.I. Cooper, K. Prout, D.J. Watkin, CRYSTALS
Version 12: Software for Guided Crystal Structure Analysis, Journal of Applied
Crystallography 36 (2003) 1487.
46. D.J. Watkin, C.K. Prout, L.J. Pearce, (1996). CAMERON, Chemical
Crystallography Laboratory, Oxford, UK.
25

Graphical Abstract - Pictogram

Graphical Abstract - Synopsis
The present study comprises the synthesis and photophysical investigation of three
new square planar palladium (II) compounds, each bearing two thiolate units and a
chelating diphosphine. DFT calculations are performed in order to rationalize their
spectroscopic behavior in solution.