Synthesis, mesomorphism and luminescence properties of palladium(II) and platinum(II) complexes with dimeric Schiff base liquid crystals

Article abstract of DOI:10.1016/j.ica.2009.11.028

A series of ortho-metallated Pd and Pt complexes containing dimeric liquid crystals Schiff base as cyclometallated ligands and N-benzoyl thiourea derivatives as co-ligands were prepared and investigated for their liquid crystalline properties. Their structures were assigned based on elemental analysis, IR and ¹H NMR spectroscopy while the mesogenic properties were investigated by DSC and polarising optical microscopy. The complexes show either monotropic or enantiotropic transitions with nematic and smectic A phases being displayed, with the mesomorphic behaviour strongly related to the type of N-benzoyl thiourea as well as the metal center used. The structure of a palladium(II) complex has been solved by X-ray diffraction. The platinum(II) complexes show photoluminescence properties both in solution and in solid state at room temperature, with the emission band centered around 600 nm. These are the first examples of metallomesogens based on Schiff base cyclometallated ligands that display luminescence properties.

Full text of DOI:10.1016/j.ica.2009.11.028

Inorganica Chimica Acta 363 (2010) 729–736
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, mesomorphism and luminescence properties of palladium(II)
and platinum(II) complexes with dimeric Schiff base liquid crystals
Ana S. Mocanu a, Monica Ilißs a, Florea Dumitraßscu b, Mihaela Ilie c, Viorel Cîrcu a,
*
a Department of Inorganic Chemistry, University of Bucharest, 23 Dumbrava Rosie St., Sector 2, Bucharest 020464, Romania
b Centre of Organic Chemistry ‘‘C.D. Nenitzescu”, Romanian Academy, Spl. Independentei 202B, Bucharest 060023, Romania
c Department of Toxicology, University ‘‘Carol Davila”, 6 Traian Vuia St., Bucharest, Romania
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2009
Received in revised form 12 November 2009
Accepted 19 November 2009
Available online 26 November 2009
A series of ortho-metallated Pd and Pt complexes containing dimeric liquid crystals Schiff base as cyclo-
metallated ligands and N-benzoyl thiourea derivatives as co-ligands were prepared and investigated for
their liquid crystalline properties. Their structures were assigned based on elemental analysis, IR and 1H
NMR spectroscopy while the mesogenic properties were investigated by DSC and polarising optical
microscopy. The complexes show either monotropic or enantiotropic transitions with nematic and smec-
tic A phases being displayed, with the mesomorphic behaviour strongly related to the type of N-benzoyl
thiourea as well as the metal center used. The structure of a palladium(II) complex has been solved by X-
ray diffraction.
Keywords:
Liquid crystals
Palladium
The platinum(II) complexes show photoluminescence properties both in solution and in solid state at
room temperature, with the emission band centered around 600 nm. These are the first examples of met-
allomesogens based on Schiff base cyclometallated ligands that display luminescence properties.
Ó 2009 Elsevier B.V. All rights reserved.
Platinum
Orthometallation
N-benzoyl thiourea
Imine
Luminescence
1. Introduction
tropic phases, with an intercalated arrangement within the SmA
phase [6,7] in which specific molecular interactions between the
The liquid crystal dimers (also known as dimesogens), com-
posed of either two identical (symmetric) or non-identical (non-
symmetric) mesogenic units connected via a flexible central
spacer, have been extensively studied for their ability to act as
model compounds for semi-flexible main-chain liquid crystalline
polymers and for their interesting physical properties [1].
Few studies have been reported so far concerning metallomes-
ogens containing dimeric liquid crystals as ligands [2,3]. The first
examples of metallomesogens derived from achiral non-symmetri-
cal bidentate dimeric ligands, Pd(II) and Cu(II) complexes with li-
gands based on salicylaldimine core, were reported recently [2].
The same authors reported the synthesis and mesomorphism of
the first examples of optically active (cholesterol-based) dimeric
bidentate ligands and their Cu(II) and Pd(II) complexes [3]. Metallo-
mesogens (liquid crystals containing metal ions) are intensively
studied due to their interesting properties which are influenced
by the presence of the metal ion, such as colour, polarisability,
electrical and magnetic properties [4,5].
two different mesogenic units account for this specific phase
behaviour.
In this work, these Schiff bases were used in the ortho-metalla-
tion reaction with palladium(II) and platinum(II) precursors to give
the nematogen dinuclear complexes which further leads to mono-
nuclear complexes by reacting them with sodium salts of simple
N,N-dialkyl-N0-benzoyl thiourea derivatives. Our previous results
have shown that mixed-ligands palladium(II) and platinum(II)
complexes with imine and N-benzoyl thioureas ligands show li-
quid crystals properties, with nematic and SmA phases being dis-
played, the mesomorphic behaviour of such complexes being
strongly dependent on the type of the imine ligand employed as
well as the type of co-ligand [8,9]. The liquid crystal properties of
mononuclear compounds were investigated by mean of DSC and
polarising light microscopy and they will be discussed in connec-
tion with the type of metal and the alkyl chain length of the N-ben-
zoyl thiourea derivative used as co-ligands.
The non-symmetric dimeric liquid crystal Schiff bases
a-(4-
cyanobiphenyl-40-yloxy)- -(4-n-alkyloxyanilinebenzylidene-40-
x
2. Results and discussion
oxy)hexane were reported previously to show SmA and N enantio-
The preparation of the palladium(II) and platinum(II) com-
plexes is depicted in Scheme 1. The dinuclear acetato-bridged
palladium complexes, intermediates in the preparation of the
* Corresponding author.
E-mail address: viorel_carcu@yahoo.com (V. Cîrcu).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.11.028

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A.S. Mocanu et al. / Inorganica Chimica Acta 363 (2010) 729–736
NC
O
O
(CH2)6
N
O
CmH2m+1
LH-m
i) Pd(OAc)2/CH2Cl2
or
ii) BTUNa/CH2Cl2
[Pt(μ-Cl)(η3-C4H7)]2/CH3OH
NC
O
O
(CH2)6
N
O
CmH2m+1
M
S
O
NR2
N
R = -CnH2n+1
M = Pd, PdL-m,n
M = Pt, PtL-m,n
NC
O
O
(CH2)6
N
O
CmH2m+1
Pd
AcO
2
[PdL-mOAc]2
Scheme 1. The preparation of ortho-metallated palladium(II) and platinum(II) complexes (m = 1, 10; n = 2–4, 6, 8).
corresponding palladium(II) mononuclear species, were obtained
with good yield by ortho-palladation reaction between Pd(OAc)2
and the two Schiff bases LH-m in glacial acetic acid. These dinucle-
ar complexes were used in the next step for the preparation of the
mononuclear palladium(II) complexes by reacting them with a ser-
ies of sodium salts of N,N-dialkyl-N0-benzoyl thiourea derivatives.
All the mononuclear palladium(II) complexes are microcrystalline
yellow products, which are stable in normal conditions.
thiourea ligand in a trans or cis position to the nitrogen atom of
the imine group of the Schiff base ligand). This is the only case
when a mixture of isomers was found.
The formation of the mixed-ligands ortho-platinated complexes
can be confirmed readily by 1H NMR spectroscopy where the signal
corresponding to the imine proton of the Schiff base is accompa-
nied by 195Pt satellites with 3JPt–H coupling constants within the ex-
pected range for such complexes [11,12].
The dinuclear chloro-bridged ortho-platinated compound was
prepared by ortho-platination reaction of the Schiff base LH-1
using [Pt(l-Cl)(g
3-C4H7)]2 as starting material [10]. In this case,
3. Description of crystal structure of complex PdL-10,3
the crude products were used in the next step without further
characterisation and purification. Thus, the mononuclear plati-
num(II) complexe was prepared by a ligand exchange reaction of
the chloro-bridged dinuclear platinum(II) complexes using the cor-
responding sodium salts of the N,N-dialkyl-N0-benzoyl thiourea
derivatives. The new platinum(II) complexes were prepared in
moderate to low yields as orange microcrystalline solid products
which are stable under ambient conditions. Their structures were
confirmed by elemental analysis, IR spectroscopy as well as 1H
and, in one case, by X-ray diffraction.
Single crystals of complex PdL-10,3 suitable for X-ray diffrac-
tion were obtained by cooling a solution of this compound in a
mixture of dichloromethane and ethanol (ca. 1/1 v/v) at ꢀ25 °C.
The molecular structure of this compound is shown in Fig. 1, while
crystallographic data are collected in Table 1 and selected bond
and angles are presented in Table 2.
The crystal structure of this compound shows Pd(II) in a square-
planar environment bound to the imine ligand in an ortho-metal-
lated fashion and chelated to the N,N-dipropyl-N0-benzoyl thiourea
derivative with palladium surrounded by one aromatic carbon
atom (metallated phenyl ring), one nitrogen atom (imine group)
and one sulfur atom and one oxygen atom of the N-benzoyl thio-
urea derivative. The sulfur atom is situated trans to the nitrogen
atom from the imine group of the Schiff base as it is the case for
previously reported related palladium complexes bearing 4-hexyl-
oxybenzylidene-40-hexyloxyaniline as Schiff base [11]. The corre-
It was found that the 1H NMR spectra indicate the presence of
only one isomer in solution (one set of signals) for all prepared pal-
ladium(II) complexes, while in the case of their analogues with
platinum(II), the 1H NMR spectrum of complex PtL-1,4 reveals
two sets of signals corresponding to the imine proton and methyl
group of the Schiff base, their integration showing a 50:50 mixture
of the two possible isomers (the sulfur atom of the N-benzoyl

A.S. Mocanu et al. / Inorganica Chimica Acta 363 (2010) 729–736
731
Fig. 1. The molecular structure of compound PdL-10,3.
Table 1
Table 2
Crystallographic data for compound PdL-10,3.
Selected bond lengths (Å) and angles (°).
Compound
PdL-10,3
C56H68N4O4PdS
PdL-10,3
Empirical formula
Formula weight (g molꢀ1
T (K)
Wavelength (Å)
Crystal system
Space group
Pd–C
Pd–N
Pd–S
Pd–O
N(Pr2)–C
N–C(S)
N–C(O)
C–O
1.983(3)
2.096(2)
)
999.60
293(2)
0.71073
triclinic
2.2324(9)
2.085(2)
1.332(4)
1.341(4)
1.323(4)
1.262(4)
1.720(3)
1.505(4)
1.282(4)
1.140(5)
80.70(11)
96.58(9)
92.25(6)
90.31(9)
ꢀ
P1
Unit cell dimensions
a (Å)
b (Å)
c (Å)
12.4533(9)
14.7928(9)
15.7227(10)
C–S
C(O)–C(Ph)
C–N(imine)
C–N (cyano group)
C–Pd–N
N–Pd–O
O–Pd–S
S–Pd–C
Unit cell angles
a
(°)
85.368(5)
77.773(5)
69.040(5)
2643.4(3)
b (°)
c
(°)
Volume (Å3)
Z
2
Density (calculated) (Mg mꢀ3
)
)
1.256
0.438
1052
Absorption coefficient (mmꢀ1
F(0 0 0)
4. Thermal behaviour
Crystal
yellow
Crystal size (mm3)
0.50 ꢃ 0.35 ꢃ 0.20
2.50–33.24
ꢀ16 6 h 6 19, ꢀ22 6 k 6 22,
ꢀ24 6 l 6 24
50 224
All palladium and platinum complexes were investigated for
their potential liquid crystal properties by hot stage polarising
optical microscopy and differential scanning calorimetry. The ther-
mal data are summarized in Table 3. Mesophases were assigned
based on their optical texture and two examples are presented in
Figs. 3 and 4. The mesogenic behaviour of these complexes is
strongly influenced by the nature of the ortho-metallated imine
fragment. All palladium(II) and platinum(II), except complexes
PdL-1,6, PdL-1,8 and PtL-1,6, exhibit an enantiotropic or a mono-
tropic nematic phase, which was identified on the basis of the
characteristic Schlieren optical texture that show two- and four-
point singularities observed when viewed under the polarised light
microscope; this texture also flashed when subjected to mechani-
cal stress. The influence of the N-benzoyl thiourea fragment on the
mesogenic behaviour of the metal complexes is much more pro-
nounced in the case of complexes bearing the LH-1 Schiff base.
On cooling the nematic phases exhibited by PdL-1,4 and PtL-1,4
under the polarised light microscope a well defined focal conic
fan texture is developed, as it can be seen in Fig. 3. For this series,
either an enantiotropic (PdL-1,2) or a monotropic nematic phase
(PdL-1,3) was observed for the short-chain length N,N-dialkyl-N0-
benzoyl thioureas, both monotropic SmA and N phases at interme-
diate-chain length (complexes PdL-1,4 and PtL-1,4), and only the
SmA phase for the derivatives with two hexyl and octyl chains
(complexes PdL-1,6, PdL-1,8 and PtL-1,6). The SmA phase of these
late complexes could be assigned by the typical fan-shaped texture
which can be aligned homeotropically. A similar influence of the
co-ligands on the mesomorphic behaviour of palladium(II) com-
plexes bearing imine ligands was found for ortho-metallated palla-
dium(II) complexes with aliphatic b-diketonate derivatives [14].
h Range for data collection (°)
Index ranges
Reflections collected
Independent reflections
Maximum and minimum
transmission
19 514 [Rint = 0.0485]
0.8758 and 0.8317
Data/restraints/parameters
19 514/4/613
1.020
R1 = 0.0669, wR2 = 0.1362
R1 = 0.1313, wR2 = 0.1500
0.679 and ꢀ0.685
Goodness-of-fit (GOF) on F2
Final R indices [F2 > 2
R indices (all data)
r
(F2)]
Largest difference in peak and hole
(e Åꢀ3
)
sponding chelate ring around the Pd center is essentially planar
with a maximum deviation from the mean plane of 0.054 Å.
However, while the metallated phenyl ring is almost coplanar with
respect to the mean plane, the unmetallated ring of the Schiff base
is twisted by 39.7° with respect to the core plane. Also, the two
rings of the biphenyl group are rotated by ꢁ31°.
An important factor that contributes to the crystal packing of
this compound is intermolecular C–NꢂꢂꢂH1 hydrogen bonds which
leads to the formation of dimers (Fig. 2). These type of interactions
are usually found in the 4-n-alkyloxy-40-cyanobiphenyls liquid
crystals family of compounds [13].
1
Hydrogen bonds for PdL-10,3: C(21)–H(21)ꢂꢂꢂN(4) 3.49 Å, H(21)ꢂꢂꢂN(4) 2.60 Å.
Symmetry transformation used to generate equivalent atoms: x, y, z; ꢀx. ꢀy, ꢀz.

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Fig. 2. Hydrogen bonds CNꢂꢂꢂH in dimers.
Table 3
Thermal data for palladium(II) and platinum(II) complexes.
Compound
M
Transition
T (°C)
D )
H (kJ molꢀ1
[PdL-1OAc]2
[PdL-10OAc]2
Cr–I (dec)
Cr–N
227
145
186
70
145
150
(148)
133
141
82
143
167
(149)
135
139
144
158
(144)
(114)
104
118
138
61
145
151
113
130
111
138
96
80.0
89.6
13.4
4.1
N–I
PdL-1,2
Cr–Cr0
Cr0–N
N–I
4.4*
(I–N)
Cr–N
N–I
Cr–Cr0
Cr0–Cr00
Cr00–I
(I–N)
Cr–Cr0
Cr0–N
N–I
2.3
61.1
1.8
12.9
10.4
23.2
1.9
47.9
10.4
1.19
42.6
(2.5)
(0.3)
12.9
33.6
1.6
4.1
24.7
9.8
41.8
1.4
33.8
9.5
PdL-10,2
PdL-1,3
Pd
PdL-10,3
PdL-1,4
PdL-10,4
PdL-1,6
Cr–I
(I–N)
(N–SmA)
Cr–Cr0
Cr0–N
N–I
Cr–Cr0
Cr0–SmA
SmA–I
Cr–N
PdL-10,6
PdL-1,8
PdL-10,8
PtL-1,3
N–I
Cr–SmA
SmA–I
Cr–N
32.2
1.3
11.5
46.4
2.5
N–I
118
91
Pt
Cr–Cr0
Cr0–N
N–I
127
180
137
176
(140)
(126)
98
Fig. 3. Polarised optical pictures of the nematic phase of compound PdL-1,4 at
120 °C (a) and of the SmA phase at 90 °C, (b) (same region on cooling).
PtL-1,4
Cr–Cr0
2.2
Cr0–I
42.6
(2.2)
(0.4)
10.2
30.6
(4.0)
(I–N)
(N–SmA)
Cr–Cr0
Cr0–I
PtL-1,6
154
(142)
(I–SmA)
*
Combined enthalpies.
On the other hand, the Pd(II) complexes bearing the Schiff base
with decyloxy group (LH-10) show only an enantiotropic nematic
phase with melting and clearing points that are influenced by the
chain length of the N,N-dialkyl-N0-benzoyl thiourea derivative.
There is a very small increase of thermal stability of the nematic
phase on going from ethyl to propyl (ca. 3 °C) followed by a clear
tendency of decrease of the stability of the nematic phase with
the increasing the chain length from propyl to octyl (Fig. 5). Such
a behaviour could be explained by considering the molecular
anisotropy of these complexes [15]. Increasing the length of the al-
kyl chain of the N-benzoyl thiourea derivatives leads to the in-
crease of the molecular breadth with consequences on the
mesogenic behaviour as it is the case for the previous reported
complexes bearing such co-ligands [8].
Fig. 4. Polarised optical picture of the Schlieren texture of the nematic phase of
compound PtL-1,4 at 137 °C (200ꢃ).

A.S. Mocanu et al. / Inorganica Chimica Acta 363 (2010) 729–736
733
Fig. 6. The UV–Vis spectrum of Pt(II) complex PtL-1,3 recorded in CH2Cl2 solution
(c = 1.01 ꢃ 10ꢀ4 M).
Fig. 5. Dependence of the melting points and clearing temperatures on the chain
lengths of the N,N-dialkyl-N0-benzoyl thiourea derivative for Pd(II) complexes with
Schiff base bearing decyloxy group (LH-10).
If the mesomorphic behaviour of the palladium complexes is
compared to that of the platinum complexes which posses the
same structure, then the same type of mesophases is seen but with
higher transition temperatures in the later case, as a result of sub-
stitution of palladium with much heavier platinum atom which
brings an enhancement of the polarisation. A similar change in
mesomorphic properties when the palladium is replaced with plat-
inum was reported for other ortho-metallated complexes [16,17]. It
is worth to note here that complex PtL-1,6 shows an monotropic
smectic phase while its analogue with palladium PdL-1,6 shows
an enantiotropic smectic A phase.
5. Absorption and luminescence properties
Metallomesogens with luminescent properties are of great
interest for their promising application in electrooptical devices.
Emissive properties were reported for a series of metallomesogens
and these were recently reviewed by Binnemans [18]. There are
several studies dealing with light-emitting metallomesogens
incorporating palladium(II) and platinum(II) ions, all of them in
cyclometallated environment [19–21]. The explanation is that
one of the best strategies used to promote luminescence in plati-
num(II) complexes is to employ ligands with a very strong ligand
field in order to raise the d–d state, as it is the case for cyclometa-
lating ligands, mostly with 2-arylpyridine or 2-thienylpyridine
derivatives, resulting both homoleptic or heteroleptic complexes
[22–24].
The absorption data for platinum(II) complexes are summarized
in Table 4 while the absorption spectrum of complex PtL-1,3 is
shown in Fig. 6. The absorption spectra of the platinum(II) com-
plexes show intense bands in the ultraviolet region between 250
and 350 nm. These high energy bands can be assigned primarily
to the allowed intraligand transitions (one around 290 nm and a
shoulder around 345 nm). At lower energies two less intense bands
in the range 380–500 nm, with low extinction coefficients,
e, rang-
ing between 200 and 1500 Mꢀ1 cmꢀ1 were also observed.
Table 4
Absorption and emission properties of the Pt(II) complexes at room temperature.
Complex
kmax(abs.) (nm) (
e
/Mꢀ1 cmꢀ1
)
kmax(em.) (nm)
Solution
Solid
608
PtL-1,3
PtL-1,4
PtL-1,6
290(6120), 343sh(2260),
385(810), 440sh(220)
283(6040), 343sh(2030),
387(1480), 440(410)
187(6080), 344sh(2150),
385(960), 441(370)
371, 485, 604
365, 493, 602
368, 502, 604
590
602
Fig. 7. Normalised luminescence and excitation spectra of PtL-1,3 dissolved in
CH2Cl2 (concentration 1 ꢃ 10ꢀ4 M) in the UV region (kexc = 295 nm) (a) and in Vis
range (kexc = 385 nm) (b).

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A.S. Mocanu et al. / Inorganica Chimica Acta 363 (2010) 729–736
Proton and carbon NMR spectra were recorded on a Varian
Gemini 300 BB spectrometer operating at 300 MHz, using CDCl3
as solvent. 1H chemical shifts were referenced to the solvent peak
position, d 7.26 ppm. X-ray data for crystal PdL-10,3 were collected
at room temperature on a STOE IPDS II diffractometer. The struc-
ture was solved by direct methods and refined by full-matrix least
squares techniques based on F2. The non-H atoms were refined
with anisotropic displacement parameters. Calculations were per-
formed using SHELX-97 crystallographic software package.
The UV–Vis absorption spectra of Pt(II) complexes were re-
corded in dichloromethane using a Cary 100 Bio (Varian Inc.)
spectrophotometer.
Transition temperatures were measured using
a Linkam
THMS600 hot stage and a TMS94 temperature controller attached
to a Nikon 50i Pol polarising microscope. These temperatures were
confirmed by differential scanning calorimetry (Perkin–Elmer Dia-
mond instrument using 10 °C/min heating rate). Two or more heat-
ing/cooling cycles were performed on each sample. Mesophases
were assigned by their optical texture [25]. Solid state fluorescence
spectra were recorded using a JASCO FP6500 spectrofluorimeter
while fluorescence spectra in solution were recorded using a Per-
kin–Elmer LS 50 B spectrofluorimeter.
The synthesis of the two Schiff bases (LH-1 and LH-10) was car-
ried out as described elsewhere [6,7]. The N-benzoyl thiourea
derivatives as well as their sodium salts used in this work were
prepared according to the methods published in literature [26,27].
Fig. 8. Solid state luminescence spectrum of complex PtL-1,4 (kexc = 380 nm).
The luminescence and excitation spectra of the platinum(II)
complexes dissolved in CH2Cl2 and in solid state were measured
at room temperature and the data are included in Table 4.
It was found that the excitation with the wavelength k = 295 nm
produced the emission around 370 nm while the excitation with
k = 385 nm produced two emission bands located at 470 and
600 nm (Fig. 7a and b). The solid state luminescence spectra of
all three platinum(II) complexes recorded at room temperature
using kexc = 380 nm exhibit an emission band around 600 nm
(Fig. 8).
Unfortunately, the mesophase stability at high temperatures
makes no possible the recording of luminescence properties in
the mesophase.
8. Synthesis of dinuclear palladium(II) and platinum(II)
complexes
In the heteroleptic ortho-metallated platinum(II) complexes the
strong field associated with the ortho-metallated carbon should fa-
vour luminescence but it is not always necessarily sufficient to in-
duce room temperature emission – in this case a strong influence
has the ancillary ligands. It is obvious that for platinum(II) com-
plexes the position of the emission bands both in the solution
and solid state luminescence spectra is very little affected by the
alkyl chain length of the N,N-dialkyl-N0-benzoyl thiourea used as
ancillary ligands, but it proved that together with the ortho-metal-
lated Schiff base fragment could constitute good candidates for
luminescent metallomesogens and further investigations are cur-
rently underway.
A mixture of Schiff base (compound LH-1 or LH-10, 0.55 mmol)
and palladium acetate (0.55 mmol) in glacial acetic acid (10 ml)
was heated under reflux for 7 h. The resulting green-yellow precip-
itate was filtered hot and washed several times with acetic acid.
The crude product was recrystallised from a mixture of CH2Cl2/
C2H5OH (1/1) at ꢀ25 °C to afford a green-yellow microcrystalline
solid.
In the case of chloro-bridged dinuclear platinum(II) complex,
the starting material was [Pt(
pared according to literature data [10]. The mixture of the Schiff
base ligand and [Pt( -Cl)(
3-C4H7)]2 in methanol, in molar ratio
l-Cl)(g
3-C4H7)]2, which was pre-
l
g
2:1, was stirred for 1 day at room temperature. The resulting
green-brown precipitate was filtered and washed several times
with cold methanol. The preparation of the dinuclear platinum(II)
complex followed the one described in literature [28]. The crude
product was used in the next step, for the preparation of mononu-
clear species, without further purification.
6. Conclusions
A
series of organometallic palladium(II) and platinum(II)
complexes bearing dimeric liquid crystals Schiff bases and N,N-
dialkyl-N0-benzoyl thiourea as co-ligands were prepared and inves-
tigated for their liquid crystal and photoluminescence properties.
These complexes show either monotropic or enantiotropic transi-
tions with nematic and smectic A phases being displayed, with
the mesomorphic behaviour strongly related to the type of N-ben-
zoyl thiourea as well as the metal center used. The structure of a
palladium(II) complex has been solved by X-ray diffraction.
The platinum(II) complexes show photoluminescence proper-
ties both in solution and in solid state at room temperature, with
the emission band centered around 600 nm. These are the first
examples of metallomesogens based on Schiff base cyclometallat-
ed ligands that display luminescence properties.
9. Synthesis of mononuclear palladium(II) and platinum(II)
complexes
The solid sodium salt of N,N-dialkyl-N0-benzoyl thiourea deriv-
ative (0.30 mmol) was added to a solution of the corresponding
binuclear complex (0.10 mmol) in CH2Cl2 (15 ml) and the resulting
mixture was stirred at room temperature for 1 day. The solvent
was removed and the solid was purified on silica using CH2Cl2 as
eluant. The crude yellow solid was recrystallised from a mixture
of CH2Cl2/C2H5OH (1/1) at ꢀ25 °C in the case of palladium(II) com-
plexes. The platinum(II) complexes were recrystallized from a mix-
ture of acetone/methanol (1/1) at ꢀ25 °C.
7. Experimental
The yields, elemental analysis results as well as 1H NMR and IR
data are presented below:
Dichloromethane was distilled from phosphorus pentaoxide;
other chemicals were used as supplied.
LH-1. Yield 68%, off-white solid. Anal. Calc. for C33H32N2O3: C,
78.6; H, 6.4; N, 5.6. Found: C, 78.3; H, 6.7; N, 5.3%.

A.S. Mocanu et al. / Inorganica Chimica Acta 363 (2010) 729–736
735
1H NMR (300 MHz, CDCl3): 8.40 (s, 1H), 7.83 (AA0BB0 system,
3J = 8.8 Hz, 2H), 7.67 (m, 4H), 7.53 (AA0BB0 system, 3J = 9 Hz, 2H),
7.22 (AA0BB0 system, 3J = 9.1 Hz, 2H), 7.01–6.91 (m, 6H), 4.04 (m,
4H), 3.84 (s, 3H), 1.87 (m, 4H), 1.59 (m, 4H).
4.09–4.00 (m, 6H), 3.91–3.86 (m, 2H), 3.80–3.75 (m, 2H), 1.95–
1.25 (m, 28H), 1.03 (t, 3J = 7.4 Hz, 3H), 0.95–0.87 (m, 6H).
IR (KBr pellet): mmax in cmꢀ1 2224w, 1604s, 1579s, 1416vs,
1247vs.
PdL-1,4. Yield 63%, yellow crystals. Anal. Calc. for C49H54N4O4-
PdS: C, 65.3; H, 6.0; N, 6.2. Found: C, 64.9; H, 6.4; N, 6.0%.
1H NMR (300 MHz, CDCl3): 8.12 (s, 1H), 7.74 (m, 2H), 7.65
(m, 4H), 7.53 (AA0BB0 system, 3J = 8.7 Hz, 2H), 7.42–7.32 (m, 4H),
7.22 (m, 2H), 7.03–6.96 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz,
1H), 4.09–4.00 (m, 4H), 3.89–3.85 (m, 5H), 3.82–3.77 (m, 2H),
1.90–1.30 (m, 16H), 1.04 (t, 3J = 7.4 Hz, 3H), 0.92 (t, 3J = 7.4 Hz, 3H).
IR (KBr pellet): mmax in cmꢀ1 2224w, 1603s, 1579s, 1415vs,
1249vs.
PdL-10,4. Yield 85%, yellow crystals. Anal. Calc. for C58H72N4-
O4PdS: C, 67.8; H, 7.1; N, 5.5. Found: C, 67.4; H, 7.5; N, 5.2%.
1H NMR (300 MHz, CDCl3): 8.12 (s, 1H), 7.74 (m, 2H), 7.65 (m,
4H), 7.53 (AA0BB0 system, 3J = 8.7 Hz, 2H), 7.42–7.33 (m, 4H), 7.22
(m, 2H), 7.01–6.97 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz, 1H),
4.09–4.00 (m, 6H), 3.91–3.86 (m, 2H), 3.80–3.75 (m, 2H), 1.95–
1.25 (m, 32H), 1.05 (t, 3J = 7.2 Hz, 3H), 0.94–0.87 (m, 6H).
IR (KBr pellet): mmax in cmꢀ1 2224w, 1604s, 1580s, 1415vs,
1249vs.
PdL-1,6. Yield 53%, yellow crystals. Anal. Calc. for C53H62N4-
O4PdS: C, 66.5; H, 6.5; N, 5.9. Found: C, 66.3; H, 6.8; N, 5.6%.
1H NMR (300 MHz, CDCl3): 8.13 (s, 1H), 7.74 (m, 2H), 7.65
(m, 4H), 7.53 (AA0BB0 system, 3J = 8.7 Hz, 2H), 7.42–7.33 (m, 4H),
7.22 (m, 2H), 7.01–6.97 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz,
1H), 4.09–4.00 (m, 4H), 3.91–3.86 (m, 5H), 3.82–3.77 (m, 2H),
1.90–1.30 (m, 24H), 0.92 (t, 3J = 7.0 Hz, 3H), 0.85 (t, 3J = 7.0 Hz, 3H).
IR (KBr pellet): mmax in cmꢀ1 2225w, 1604s, 1578s, 1416vs,
1248s.
IR (KBr pellet): mmax in cmꢀ1 2237w, 1605s, 1574s, 1246vs.
LH-10. Yield 74%, off-white solid. Anal. Calc. for C42H50N2O5: C,
80.0; H, 8.0; N, 4.4. Found: C, 79.7; H, 8.2; N, 4.1%.
1H NMR (300 MHz, CDCl3): 8.40 (s, 1H), 7.82 (AA0BB0 system,
3J = 8.5 Hz, 2H), 7.67 (m, 4H), 7.53 (AA0BB0 system, 3J = 8.5 Hz,
2H), 7.22 (AA0BB0 system, 3J = 8.8 Hz, 2H), 7.01–6.90 (m, 6H),
4.07–3.95 (m, 6H), 1.90–1.20 (m, 24H), 0.89 (m, 3H).
IR (KBr pellet): mmax in cmꢀ1 2237w, 1606s, 1574s, 1250vs.
[PdL-1OAc]2. Yield 21%, green-yellow crystals. Anal. Calc. for
C70H70N4O10Pd2: C, 62.7; H, 5.3; N, 4.2. Found: C, 62.4; H, 5.7; N,
4.0%.
1H NMR (300 MHz, CDCl3): 7.60 (m, 4H), 7.47 (AA0BB0 system,
3
3J = 8.8 Hz, 2H), 7.41 (s, 1H), 7.05 (d, J = 8.2 Hz, 1H), 6.93 (AA0BB0
system, 3J = 8.8 Hz, 2H), 6.60 (m, 4H), 6.48 (dd, 3J = 8.5 Hz,
4J = 2.5 Hz, 1H), 5.96 (d, 4J = 2.5 Hz, 1H), 3.97 (t, 3J = 6.3 Hz, 2H),
3.71 (m, 4H), 3.52 (m, 1H), 1.82–1.45 (m, 11H).
IR (KBr pellet): mmax in cmꢀ1 2223w, 1603s, 1571s, 1250vs.
[PdL-10OAc]2. Yield 32%, green-yellow crystals. Anal. Calc. for
C88H104N4O10Pd2: C, 66.5; H, 6.6; N, 3.5. Found: C, 66.1; H, 7.0; N,
3.2%.
1H NMR (300 MHz, CDCl3): 7.60 (m, 4H), 7.47 (AA0BB0 system,
3
3J = 8.8 Hz, 2H), 7.41 (s, 1H), 7.05 (d, J = 8.2 Hz, 1H), 6.93 (AA0BB0
system, 3J = 8.8 Hz, 2H), 6.60 (m, 4H), 6.48 (dd, 3J = 8.5 Hz,
4J = 2 Hz, 1H), 5.96 (d, 4J = 2.5 Hz, 1H), 4.09–3.87 (m, 4H), 3.80
(m, 1H), 3.59 (m, 1H), 1.89–1.20 (m, 27H), 0.88 (m, 3H).
IR (KBr pellet): mmax in cmꢀ1 2224w, 1604s, 1570s, 1249vs.
PdL-1,2. Yield 53%, yellow crystals. Anal. Calc. for C45H46
-
N4O4PdS: C, 63.9; H, 5.5; N, 6.6. Found: C, 63.8; H, 5.7; N, 6.3%.
PdL-10,6. Yield 44%, yellow crystals. Anal. Calc. for C62H80N4-
O4PdS: C, 68.7; H, 7.4; N, 5.2. Found: C, 68.5; H, 7.7; N, 5.0%.
1H NMR (300 MHz, CDCl3): 8.12 (s, 1H), 7.74 (m, 2H), 7.65 (m,
4H), 7.53 (AA0BB0 system, 3J = 8.7 Hz, 2H), 7.42–7.33 (m, 4H), 7.22
(m, 2H), 7.01–6.97 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz, 1H),
4.09–4.00 (m, 6H), 3.91–3.86 (m, 2H), 3.80–3.75 (m, 2H), 1.90–
1.25 (m, 40H), 0.96–0.82 (m, 9H).
1H NMR (300 MHz, CDCl3): 8.13 (s, 1H), 7.73 (m, 2H), 7.65 (m,
4H), 7.53 (AA0BB0 system, 3J = 8.7 Hz, 2H), 7.42–7.33 (m, 4H), 7.22
(m, 2H), 7.01–6.97 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz, 1H),
4.05 (m, 6H), 3.89–3.82 (m, 5H), 1.86 (m, 4H), 1.62–1.38 (m, 7H),
1.25 (t, 3J = 6.6 Hz, 3H).
IR (KBr pellet): mmax in cmꢀ1 2223w, 1604 s, 1580s, 1418vs,
1249vs.
IR (KBr pellet): m
max in cmꢀ1 2223w, 1604s, 1579s, 1414vs, 1248s.
PdL-10,2. Yield 79%, yellow crystals. Anal.
Calc. for
PdL-1,8. Yield 71%, yellow crystals. Anal. Calc. for C57H70N4-
O4PdS: C, 67.5; H, 7.0; N, 5.5. Found: C, 67.2; H, 7.4; N, 5.2%.
1H NMR (300 MHz, CDCl3): 8.13 (s, 1H), 7.74 (d br, 2H), 7.65 (m,
4H), 7.53 (AA0BB0 system, 3J = 8.7 Hz, 2H), 7.42–7.32 (m, 4H), 7.22
(m, 2H), 7.03–6.96 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz, 1H),
4.10–4.00 (m, 4H), 3.89 (m, 5H), 3.78 (m, 2H), 1.90–1.25 (m,
32H), 0.91–0.83 (m, 6H).
C54H64N4O4PdS: C, 66.8; H, 6.6; N, 5.8. Found: C, 66.5; H, 6.9; N,
5.6%.
1H NMR (300 MHz, CDCl3): 8.12 (s, 1H), 7.74 (m, 2H), 7.65 (m,
4H), 7.53 (AA0BB0 system, 3J = 8 Hz, 2H), 7.42–7.33 (m, 4H), 7.22
(m, 2H), 7.01–6.97 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz, 1H),
4.09–4.00 (m, 6H), 3.91–3.86 (m, 2H), 3.80–3.75 (m, 2H), 1.90–
1.20 (m, 30H), 0.88 (t, 3J = 7.4 Hz, 3H).
IR (KBr pellet): mmax in cmꢀ1 2222w, 1602s, 1579s, 1415vs,
1246vs.
IR (KBr pellet): mmax in cmꢀ1 2223w, 1602s, 1582s, 1416vs,
1249vs.
PdL-10,8. Yield 43%, yellow crystals. Anal. Calc. for C66H88N4-
O4PdS: C, 69.5; H, 7.8; N, 4.9. Found: C, 69.1; H, 8.2; N, 4.6%.
1H NMR (300 MHz, CDCl3): 8.12 (s, 1H), 7.74 (m, 2H), 7.65 (m,
4H), 7.53 (AA0BB0 system, 3J = 8.7 Hz, 2H), 7.42–7.33 (m, 4H), 7.22
(m, 2H), 7.01–6.97 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz, 1H),
4.09–4.00 (m, 6H), 3.91–3.86 (m, 2H), 3.80–3.75 (m, 2H), 1.90–
1.25 (m, 48H), 0.96–0.82 (m, 9H).
PdL-1,3. Yield 38%, yellow crystals. Anal.
C47H50N4O4PdS: C, 64.6; H, 5.8; N, 6.4. Found: C, 64.2; H, 6.2; N,
6.2%.
Calc. for
1H NMR (300 MHz, CDCl3): 8.13 (s, 1H), 7.74 (m, 2H), 7.65 (m,
4H), 7.53 (AA0BB0 system, 3J = 8.7 Hz, 2H), 7.42–7.33 (m, 4H), 7.25
(m, 2H), 7.01–6.97 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz, 1H),
4.08 (t, 3J = 6.5 Hz, 2H), 4.03 (t, 3J = 6.5 Hz, 2H), 3.89–3.85 (m,
5H), 3.79–3.73 (m, 2H), 1.95–1.55 (m, 12H), 1.03 (t, 3J = 7.4 Hz,
3H), 0.93 (t, 3J = 7.4 Hz, 3H).
IR (KBr pellet): mmax in cmꢀ1 2225w, 1606s, 1579s, 1416vs,
1247vs.
PtL-1,3. Yield 27%, orange crystals. Anal.
Calc. for
IR (KBr pellet): mmax in cmꢀ1 2223w, 1604s, 1580s, 1416vs,
1249vs.
C47H50N4O4PtS: C, 58.7; H, 5.2; N, 5.8. Found: C, 58.4; H, 5.6; N,
5.5%.
PdL-10,3. Yield 45%, yellow crystals. Anal.
Calc. for
1H NMR (300 MHz, CDCl3): 8.39 (s, 1H, 3JPt–H = 110 Hz), 8.26 (m,
2H), 7.69–7.62 (m, 5H), 7.55–7.48 (m, 3H), 7.44–7.35 (m, 4H), 7.19
C56H68N4O4PdS: C, 67.3; H, 6.9; N, 5.6. Found: C, 67.0; H, 7.3; N,
5.3%.
3
(m, 2H), 7.09 (d, J = 2.5 Hz, 1H), 7.00 (AA0BB0 system, 3J = 8.3 Hz,
1H NMR (300 MHz, CDCl3): 8.12 (s, 1H), 7.74 (m, 2H), 7.65 (m,
4H), 7.53 (AA0BB0 system, 3J = 8.7 Hz, 2H), 7.42–7.33 (m, 4H), 7.22
(m, 2H), 7.01–6.97 (m, 5H), 6.59 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz, 1H),
2H), 6.59 (dd, 3J = 8.5 Hz, 4J = 2.5 Hz, 1H), 4.10–4.01 (m, 4H), 3.90
(s, 3H), 3.83–3.65 (m, 4H), 1.90–0.85 (m, 12H), 1.03 (t, 3J = 7.4 Hz,
3H), 0.93 (t, 3J = 7.4 Hz, 3H).

736
A.S. Mocanu et al. / Inorganica Chimica Acta 363 (2010) 729–736
IR (KBr pellet): mmax in cmꢀ1 2223w, 1605s, 1579s, 1417vs,
References
1246vs.
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PtL-1,4. Yield 25%, orange crystals. Anal. Calc. for C49H54
-
N4O4PtS: C, 59.4; H, 5.5; N, 5.7. Found: C, 59.1; H, 5.9; N, 5.4%.
1H NMR (300 MHz, CDCl3): 8.39, 8.38 (2s (two isomers syn and
anti), 1H, JPt–H = 114 Hz), 7.82 (AA0BB0 system, 3J = 8.5 Hz, 2H),
3
7.70–7.62 (m, 4H), 7.53 (AA0BB0 system, 3J = 8.8 Hz, 2H), 7.43–
7.35 (m, 3H), 7.22–7.17 (m, 2H), 7.09 (d, 3J = 2.5 Hz, 1H), 6.99
(AA0BB0 system, 3J = 8.8 Hz, 2H), 6.95–6.91 (m, 3H), 6.59 (dd,
3J = 8.3 Hz, 4J = 2.4 Hz, 1H), 4.08–4.01 (m, 4H), 3.90, 3.83 (2s (sy-
n + anti), 3H), 3.87–3.75 (m, 4H), 1.95–1.30 (m, 16H), 1.04 (t,
3J = 7.4 Hz, 3H), 0.92 (t, 3J = 7.4 Hz, 3H).
IR (KBr pellet): mmax in cmꢀ1 2222w, 1602s, 1580s, 1415vs,
1245vs.
PtL-1,6. Yield 33%, orange crystals. Anal. Calc. for C53H62
-
N4O4PtS: C, 60.8; H, 6.0; N, 5.4. Found: C, 60.3; H, 6.4; N, 5.3%.
1H NMR (300 MHz, CDCl3): 8.39 (s, 1H, 3JPt–H = 108 Hz), 8.26 (m,
2H), 7.69–7.62 (m, 5H), 7.55–7.48 (m, 3H), 7.44–7.35 (m, 4H), 7.19
(m, 2H), 7.09 (d, J = 2.5 Hz, 1H), 7.00 (AA0BB0 system, 3J = 8.3 Hz,
3
2H), 6.59 (dd, 3J = 8.5 Hz, 4J = 2.5 Hz, 1H), 4.10–4.01 (m, 4H), 3.90
(s, 3H), 3.83–3.65 (m, 4H), 1.90–1.30 (m, 24H), 0.93–0.85 (m, 6H).
IR (KBr pellet): mmax in cmꢀ1 2225w, 1606s, 1578s, 1414vs,
1248s.
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Acknowledgements
The authors wish to thank MECI (Romanian Ministry of Educa-
tion and Inovation, Project CNCSIS A1640, project PNII 210/2009
Brâncusi and Project PNII ID_954) for funding this study and to
Dr. Augustin Madalan for his help with the X-ray diffraction study.
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Appendix A. Supplementary material
CCDC 736202 contains the supplementary crystallographic data
for compound 4b. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.ica.2009.11.028.
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