Synthesis and ferroelectric properties of platinum(II) complexes with chiral isoxazoline ligand

Article abstract of DOI:10.1016/j.poly.2013.05.024

Four chiral square-planar (SP-4) alkynylplatinum(II) complexes Pt(L)(C≡C-Ph) (1), Pt(L)(C≡C-Ph-Br) (2), Pt(L)(C≡C-Ph-CH ₃) (3) and Pt(L)(C≡C-Ph-OCH₃) (4) (L = (1S,5S)-6,6-dimethyl-3′-(pyridin-2-yl)-4′H-spiro[bicyclo[3.1.1] heptane-2,

Full text of DOI:10.1016/j.poly.2013.05.024

Polyhedron 60 (2013) 85–92
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and ferroelectric properties of platinum(II) complexes
with chiral isoxazoline ligand
⇑
Xiao-Peng Zhang, Jian Liu, Jing-Xuan Zhang, Jia-Hao Huang, Cheng-Zhang Wan, Cheng-Hui Li ,
Xiao-Zeng You
⇑
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures, Nanjing University,
Nanjing 210093, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Four chiral square-planar (SP-4) alkynylplatinum(II) complexes Pt(L)(C„C–Ph) (1), Pt(L)(C„C–Ph–Br)
(2), Pt(L)(C„C–Ph–CH3) (3) and Pt(L)(C„C–Ph–OCH3) (4) (L = (1S,5S)-6,6-dimethyl-30-(pyridin-2-yl)-
40H-spiro[bicyclo[3.1.1]heptane-2,50-isoxazole]) were prepared by the complexation of ligand L with
K2PtCl4 and subsequent treatment with corresponding alkynes. Their structures were characterized by
single crystal X-ray diffraction and electronic circular dichroism (CD) spectra. Although there are little
differences in the molecular structures, these complexes exhibit significantly different molecular packing
modes in their crystal structures. Moreover, complexes 1 and 4 crystallize in the polar space group P21,
while complexes 2 and 3 crystallize in the nonpolar space groups (I222 for 2 and P212121 for 3, respec-
tively). Consequently, complexes 1 and 4 show distinct ferroelectric behaviors and nonlinear optical
properties. To the best of our knowledge, our study represents the first example of chiral platinum(II)
complexes demonstrating ferroelectric properties.
Received 25 February 2013
Accepted 14 May 2013
Available online 23 May 2013
Keywords:
Platinum(II) complexes
Chiral
Luminescence
Ferroelectric
Circular dichroism
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Moreover, the ferroelectric properties of molecular crystals can
be easily tailored by chemical modification. A large number of fer-
Ferroelectric materials, which possess a spontaneous electric
polarization that can be reversed by the application of an external
electric field, are of great interest due to their versatile applications
in the field of electronics and optics, such as ferroelectric random
access memory (FeRAM) [1,2], ferroelectric field-effect transistor
(FeFET) [3,4] and anomalous ferroelectric photovoltaics [5–7].
According to the definition, the ferroelectric materials must pos-
sess a permanent dipole moment and this moment must be revers-
ible in the presence of an applied voltage. A prerequisite for
ferroelectric materials is that they crystallize in a space group
belonging to one of the ten polar point groups (C1, Cs, C2, C2v, C3,
C3v, C4, C4v, C6, C6v). The origins of ferroelectricity include displacive
motion, order–disorder transformation and indirect type [8].
Molecular-based ferroelectric materials bear some advantages
as compared to the typical inorganic ABO3-type ferroelectrics. For
example, molecule-based complexes have larger spontaneous
polarization because of polar groups in the organic ligands. Neutral
mononuclear molecule-based ferroelectric materials can be evapo-
rated at lower temperature than ionic inorganic compounds by
chemical vapor deposition (CVD) methods, making the fabrication
of ferroelectric devices more convenient and controllable.
roelectric molecular crystals have been reported in recent years
[9–13]. Particularly, introduction of chiral groups has shown to
be effective to create molecular polar crystal with ferroelectric
properties [14–17].
Platinum(II) complexes are always inclined to adopt square-
planar geometry, many of which show prominent conductivity
and intriguing spectroscopic properties as a result of Pt–Pt and
p–p stacking interaction [18–24]. By incorporation of specifically
tailored ligands (such as bulky or chiral ligands), the planarity of
platinum(II) complexes could be reasonably distorted, which pro-
duces the corresponding molecular chirality [25–29]. In the litera-
ture, numerous of chiral platinum(II) complexes have been
reported and their application in asymmetric catalysis and medic-
inal chemistry have been described [30–33]. However, no reports
have been devoted to their ferroelectric properties. In this work,
we obtained four square-planar platinum(II) complexes containing
chiral bidentate isoxazoline ligand: Pt(L)(C„C–Ph) (1), Pt(L)(C„C–
Ph–Br) (2), Pt(L)(C„C–Ph–CH3) (3) and Pt(L)(C„C–Ph–OCH3) (4)
(L = (1S,5S)-6,6-dimethyl-30-(pyridin-2-yl)-40H-spiro[bicyclo[3.1.1]
heptane-2,50-isoxazole]) (Scheme 1). Their structures were deter-
mined via X-ray crystallgraphy data. The chirality of these com-
plexes was determined by CD spectroscopy. Moreover, the
ferroelectric and dielectric properties of complexes 1 and 4 also
have been studied.
⇑
Corresponding authors. Tel.: +86 25 83592969; fax: +86 25 83314502.
E-mail addresses: chli@nju.edu.cn (C.-H. Li), youxz@nju.edu.cn (X.-Z. You).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.05.024

86
X.-P. Zhang et al. / Polyhedron 60 (2013) 85–92
beta-Pinene
N
NH2-OH.HCl
O
N
N
OH
N
N
O
(oxime)
(L)
K2PtCl4
alkynes
O
N
N
O
N
Pt
N
Pt
Cl
Cl
R
R
(R = Br, H, CH3, OCH3)
Scheme 1. Synthesis of the L and complexes 1–4 (1, R = H; 2, R = Br; 3, R = CH3; 4, R = OCH3).
and pyridine (0.5 ml) was stirred at 60 °C for 30 min under argon
2. Experimental
atmosphere. After the completion of the chlorination reaction, a
CHCl3 solution of beta-pinene (5 mmol) and Et3N (1 mL) was added
slowly and stirred at 50 °C for 2 h. The solvent was evaporated in
vacuo and the residue was extracted with CH2Cl2. The organic
phase was separated and dried (Na2SO4), and the solvent was re-
moved. At last the product was purified by chromatography on a
silica gel column using PE:EA = 10:1. Yield: 80%. 1H NMR
2.1. Materials and methods
All reagents were purchased from commercial suppliers and
used as received. Mass spectra were acquired on LCQ Fleet ESI
Mass Spectrometer. 1H NMR spectra were obtained using a DRX
500 NMR spectrometer. Chemical shifts are referenced to TMS.
Coupling constants are given in hertzs. UV–Vis spectra were mea-
sured by UV-3600 spectrophotometer using a quartz cell of 1 cm
length in dichloromethane solution. ECD spectra were recorded
by a Jasco J-810 spectropolarimeter. Emission spectra were re-
corded by a Hitachi F-4600 luminescence spectrometer. The Elec-
tric hysteresis loops were recorded by a Ferroelectric Tester
Precision Premier II by using powdered samples in pellets at room
temperature. The temperature dependence of the dielectric con-
stant and dielectric loss at 102–106 Hz frequencies were measured
by using a dielectric impedance analyzer, Concept 80 system
(Novocontrol, Germany).
(500 MHz, CDCl3):
d 8.61 [d, 1H, J = 5 Hz], d 8.03 [d, 1H,
J = 7.5 Hz], d 7.72 [td, 1H, J = 7.5 Hz, 2 Hz], d 7.29 [t, 1H, J = 5 Hz],
d 3.35 [d, 2H, J = 3 Hz], d 2.41–2.46 [m, 1H], d 2.28–2.31 [m, 1H],
d 2.16 [t, 1H, J = 5 Hz], d 2.06–2.10 [m, 1H], d 1.97–2.04 [m, 2H],
d 1.87–1.90 [m, 1H], d 1.66 [d, 1H, J = 10.5 Hz], d 1.28 [s, 3H], d
1.02 [s, 3H]. MS (ESI) (m/z): [M]+ Anal. Calc. for C16H20N2O: 256.2.
Found: 256.5.
2.2.3. Synthesis of Pt(L)Cl2
A HCl (0.2 M) solution of L (1 mmol) and K2PtCl4 (1 mmol) was
stirred for 5 h at reflux under argon atmosphere. Yellow precipi-
tates were obtained, which were filtrated and washed with water
and n-hexane. Yield: 85%. 1H NMR (500 MHz, DMSO): d 9.26 [d,
1H, J = 5.5 Hz], d 8.36 [t, 1H, J = 8 Hz], d 7.97 [d, 1H, J = 8 Hz], d
7.83 [t, 1H, J = 7.5 Hz], d 3.40–3.43 [m, 2H], d 2.30–3.33 [m, 2H],
d 2.27–2.29 [m, 2H], d 1.95–2.00 [m, 2H], d 1.80–1.83 [m, 1H], d
1.42 [d, 1H, J = 9.5 Hz], d 1.27 [s, 3H], d 0.97 [s, 3H]. MS (ESI)
(m/z): [M]+ Anal. Calc. for C16H20Cl2N2OPt: 521.1. Found: 521.3.
2.2. Synthesis of the ligand L and complexes 1–4
2.2.1. Synthesis of (E)-picolinaldehyde oxime
This compound was prepared following the literature method
[34]. Hydroxylamine hydrochloride (11 mmol) were added in a
solution of 2-pyridinecarboxaldehyde (1 mmol) in EtOH/H2O
(40 mL, 9:1) mixture under argon atmosphere. NaOH (1.1 mmol)
in H2O (2 mL) was then added slowly. The mixture was heated at
80 °C for overnight. The solvents were removed in vacuo and the
residue was extracted with CH2Cl2. The organic phase was sepa-
rated and dried (Na2SO4), and the solvent was evaporated. At last
the product was purified by chromatography on a silica gel column
using PE:EA = 1:1. Yield: 95%. 1H NMR (500 MHz, CDCl3): d 10.96 [s,
1H], d 8.65 [d, 1H, J = 5 Hz], d 8.41 [s, 1H], d 7.89 [d, 1H, J = 8 Hz],
7.74 [td, 1H, J = 8 Hz, 1.5 Hz], 7.30 [t, 1H, J = 6 Hz]. MS (ESI) (m/z):
[M]+ Anal. Calc. for C6H6N2O: 122.1. Found: 122.2.
2.2.4. Synthesis of Pt(L)(C„C–Ph) (1)
Complex 1 was synthesized as describe of the Sonogashira
method [37]. In the absence of light, phenylacetylene (1.2 mmol)
were added in a anhydrous dichloromethane solution of Pt(L)Cl2
(1 mmol), Et3N and CuI (10 mg) under argon atmosphere. After
stirring at room temperature for 24 h, the solvent was evaporated
in vacuo, and the product was purified by chromatography on a sil-
ica gel column using PE:EA = 1:1. Yield: 85%. 1H NMR (500 MHz,
CDCl3): d 9.26 [d, 1H, J = 5.5 Hz], d 8.00 [t, 1H, J = 7.5 Hz], d 7.65
[d, 1H, J = 7 Hz], d 7.46 [d, 4H, J = 7.5 Hz], 7.42 [t, 1H, J = 6.5 Hz],
7.28 [t, 2H, J = 7.5 Hz], 7.23 [t, 2H, J = 7.5 Hz], 7.18 [t, 1H,
J = 7.5 Hz], 7.12 [t, 1H, J = 7.5 Hz], d 3.56 [d, 1H, J = 17 Hz], d 3.19
[d, 1H, J = 17 Hz], d 2.62–2.69 [m, 1H], d 2.30–2.38 [m, 3H], d
1.96–2.01 [m, 2H], d 1.72–1.77 [m, 1H], d 1.68 [d, 1H, J = 11 Hz],
2.2.2. Synthesis of the ligand L
This compound was prepared following the literature method
[35,36]. A mixture of (E)-picolinaldehyde oxime (5 mmol) and
N-chlorosuccinimide (NCS, 5 mmol) in anhydrous CHCl3 (15 mL)

X.-P. Zhang et al. / Polyhedron 60 (2013) 85–92
87
d 1.60 [s, 1H], d 1.25 [s, 3H], d 0.86 [s, 3H]. MS (ESI) (m/z): [M]+ Anal.
2.3. X-ray structure determination
Calc. for C32H30N2OPt: 653.2. Found: 653.4.
Single-crystal X-ray diffraction measurements were carried out
with a Bruker SMART APEX CCD diffractometer operating at room
temperature. Intensities were collected with graphite monochro-
2.2.5. Synthesis of Pt(L)(C„C–Ph–Br) (2)
Compound 2 was obtained with the same procedure for 1.
Yield: 75%. 1H NMR (500 MHz, CDCl3): d 9.40 [d, 1H, 5 Hz], d 8.06
[t, 1H, J = 7.5 Hz], d 7.58 [d, 1H, J = 7.5 Hz], d 7.54 [t, 1H, J = 7 Hz],
7.40 [d, 2H, J = 8 Hz], 7.34 [q, 6H, J = 8.5 Hz], d 3.35 [d, 1H,
J = 17.5 Hz], d 3.17 [d, 1H, J = 17.5 Hz], d 2.65–2.72 [m, 1H], d
2.34–2.41 [m, 2H], d 2.17–2.22 [m, 1H], d 2.05–2.08 [m, 2H], d
1.84–1.86 [m, 1H], d 1.68 [d, 1H, J = 10.5 Hz], d 1.30 [s, 3H], d
0.95 [s, 3H]. MS (ESI) (m/z): [M]+ Anal. Calc. for C32H28Br2N2OPt:
812.0. Found: 812.4.
matized Mo K
30 mA, using
a
radiation (k = 0.71073 Å) operating at 50 kV and
x
/2h scan mode. The data reduction was performed
with the Bruker SAINT package [38]. Absorption corrections were
performed using the SADABS program [39]. The structures were
solved by direct methods and refined on F2 by full-matrix least-
squares using SHELXL-97 with anisotropic displacement parameters
for all non-hydrogen atoms in all two structures. Hydrogen atoms
bonded to the carbon atoms were placed in calculated positions
and refined as riding mode, with C–H = 0.93 Å (methane) or
0.96 Å (methyl) and Uiso(H) = 1.2 Ueq (Cmethane) or Uiso(H) = 1.5 Ueq
(Cmethyl). The water hydrogen atoms were located in the difference
Fourier maps and refined with an O–H distance restraint
[0.85(1) Å] and Uiso(H) = 1.5 Ueq(O). All computations were carried
out using the SHELXTL-97 program package [40].
2.2.6. Synthesis of Pt(L)(C„C–Ph–CH3) (3)
Compound 3 was obtained with the same procedure for 1.
Yield: 79%. 1H NMR (500 MHz, CDCl3): d 9.22 [s, 1H], d 8.00 [t,
1H, J = 7.5 Hz], d 7.68 [d, 1H, J = 8 Hz], d 7.40 [t, 1H, J = 7.5 Hz],
7.36 [d, 4H, J = 7.5 Hz], 7.10 [d, 2H, J = 8 Hz], 7.05 [d, 2H,
J = 7.5 Hz], d 3.60 [d, 1H, J = 18 Hz], d 3.19 [d, 1H, J = 17.5 Hz], d
2.61–2.69 [m, 1H], d 2.37 [s, 3H], d 2.34 [s, 3H], d 2.28–2.33 [m,
3H], d 1.97–2.01 [m, 2H], d 1.72–1.76 [m, 1H], d 1.67 [d, 1H,
J = 11 Hz], d 1.63 [s, 1H], d 1.25 [s, 3H], d 0.86 [s, 3H]. MS (ESI)
(m/z): [M]+ Anal. Calc. for C34H34N2OPt: 681.2. Found: 681.4.
3. Results and discussion
3.1. Crystal structures description
Complexes 1–4 were firstly obtained as orange powders from
reactions between Pt(L)Cl2 and corresponding alkynes. All single
crystals suitable for X-ray diffraction analysis were obtained by
recrystallization in CH2Cl2/acetone. Complexes 1 and 4 crystallize
in the polar space group (P21) of a monoclinic system, while com-
plexes 2 and 3 crystallize in I222 and P212121 of orthorhombic sys-
tem, respectively (Table 1). As shown in the Fig. 1, the
2.2.7. Synthesis of Pt(L)(C„C–Ph–OCH3) (4)
Compound 4 was obtained with the same procedure for 1.
Yield: 66%. 1H NMR (500 MHz, CDCl3): d 9.28 [d, 1H, J = 5 Hz], d
8.01 [t, 1H, J = 7.5 Hz], d 7.64 [d, 1H, J = 8 Hz], d 7.41–7.42 [m,
1H], 7.39 [d, 4H, J = 7.5 Hz], 6.83[d, 2H, J = 9.5 Hz], 6.78 [d, 2H,
J = 9.5 Hz], d 3.82 [s, 3H], d 3.80 [s, 3H], d 3.54 [d, 1H, J = 18 Hz], d
3.18 [d, 1H, J = 17 Hz], d 2.62–2.69 [m, 1H], d 2.28–2.37 [m, 3H],
asymmetrical unit of complex
1 contains one molecule of
Pt(L)(C„C–Ph). The Pt–C bond lengths vary from 1.906(14) to
1.963(10) Å, whereas the Pt–N distances lie between 2.032(7)
and 2.107(11) Å. All these bond lengths are in the typical range
[41,42]. Both of the phenylacetylene rings are displaced towards
d
1.97–2.02 [m, 2H], d 1.74–1.78 [m, 1H], d 1.67 [d, 1H,
J = 11 Hz], d 1.61 [s, 1H], d 1.24 [s, 3H], d 0.87 [s, 3H]. MS (ESI)
(m/z): [M]+ Anal. Calc. for C34H34N2O3Pt: 713.2. Found: 713.3.
Table 1
Crystallographic data of complexes 1–4.
1
2 0.5C3H6O
3 C3H6O
4 0.5CH2Cl2
Formula
Mr
Crystal system
Space group
a (Å)
C32H30N2OPt
653.67
monoclinic
P21
6.1674(4)
13.0314(8)
16.6433(11)
90.00
C67H62Br4N4O3Pt2
1681.03
orthorhombic
I222
11.6252(17)
16.326(3)
35.041(5)
90.00
C37H40N2O2Pt
739.80
C69H70Cl2N4O6Pt2
1512.37
monoclinic
P21
11.209(2)
16.942(4)
16.362(4)
90.00
orthorhombic
P212121
6.977(2)
13.006(4)
35.853(11)
90.00
b (Å)
c (Å)
a
(°)
b (°)
91.2790(10)
90.00
1337.29(15)
2
90.00
90.00
6650.7(17)
4
90.00
90.00
3253.2(17)
4
92.010(3)
90.00
3105.3(11)
2
c
(°)
V (Å3)
Z
T (K)
296(2)
296(2)
296(2)
296(2)
k (Å)
0.71073
1.623
5.273
0.71073
1.679
6.651
0.71073
1.510
4.347
0.71073
1.617
4.642
Dcalc (g/cmꢀ3
)
l
(mmꢀ1
)
F(000)
644
3248
1480
1500
h (°)
1.98–25.00
6809
4462
0.0389
3796
1.38 –25.00
13343
5836
0.0662
4844
1.93 –25.00
15665
5716
0.0505
5531
2.17–26.00
17029
10983
0.0411
9165
Reflections measured
Unique reflections
Rint
Reflections with F2 > 2
r
(F2)
Number of parameters
325
1.024
0.0403, 0.0865
0.0469, 0.0881
2.560, ꢀ1.013
365
1.076
0.0637, 0.1675
0.0760, 0.1735
2.956, ꢀ2.855
385
1.083
0.0448, 0.1074
0.0464, 0.1080
2.598, ꢀ2.359
756
1.079
0.0415, 0.0679
0.0495, 0.0694
2.595, ꢀ1.135
Goodness-of-fit (GOF) on F2
b
R1a, wR2 [I > 2
r(I)]
R1,wR2 (all data)
D
q
max, Dqmin (e Åꢀ3
)
a
R1
wR2 = [
=
R
(|Fo| ꢀ |Fc|)/
R|Fo|.
b
2
R
w(Fo ꢀ Fc2)2/
R .
w(Fo2)2]1/2

88
X.-P. Zhang et al. / Polyhedron 60 (2013) 85–92
and/or p–p interactions are observed within the one-dimensional
chain. The shortest intermolecular Pt–Pt distances in complexes
1 and 3 are 7.797 and 8.054 Å, indicating the absence of metal–me-
tal interaction, which is due to the large steric hindrance of chiral
pinene groups when packing in the head-to-head mode. However,
the molecules of 2 and 4 form dimers in a staggered fashion
through Pt–Pt and
p
–
p
interactions. The dimers are then con-
inter-
nected by solvent molecules in the crystal lattice via C–Hꢁ ꢁ ꢁ
p
action to form one-dimensional chains (Figs. 3 and S5). The Pt–Pt
interactions are quite weak in 2 and 4 with the Pt–Pt distances
being 3.473 and 3.491 Å, respectively.
The one-dimensional chains are then aligned parallel to each
other to form the three dimensional structure. There is also signif-
icant difference in the arrangement of molecules in bc plane. For 1
and 4, the molecules are aligned in a zigzag fashion along b axis.
The adjacent zigzag chains point to the same direction (Figs. 4
and S6). However, the direction of adjacent zigzag chains in com-
plexes 2 and 3 are opposite to each other (Figs. 5 and S7). As each
molecule has an intrinsic dipole moment, while the dipole mo-
ments are cumulative along the zigzag chain, the crystals of 1
and 4 are expected to derive a net dipole moment along the b axis.
However, for complexes 2 and 3, the net dipole moments within
the zigzag chains will be cancelled by those of the adjacent zigzag
chains, leading to the loss of polarity in the crystals. These struc-
tural features are consistent with the measurement of ferroelectric
and non-linear properties (see below).
Fig. 1. The ORTEP view of complex 1 with 30% probability level ellipsoids. H atoms
are omitted for clarity.
3.2. UV–Vis absorption and circular dichroism (CD) spectra
the same side of the coordination plane which is similar to the
observation by Zelewsky and co-workers [43]. The molecule of 1
deviates from planar configuration slightly (the torsion angle be-
tween isoxazoline plane and phenylacetylene rings is 164.09°
and 158.14°). The molecular structures of 2–4 are very similar to
that of 1 (Figs. S1–S3). As shown in Table 2, the variance in bond
distances and bond angles in 1–4 are insignificant, indicating that
the electron donating/withdrawing effect of the substituents in the
phenylacetylene ligands are not strong enough to alter the struc-
tural parameters.
Fig. S8 shows the UV–Vis spectra of ligand L and complexes 1–4
in dichloromethane solution. The spectroscopic features are quite
similar to their analogous complexes. The intense bands of com-
plexes 1–4 at about 240–320 nm with
cmꢀ1 are originated from intraligand 1
ing ligand L and arylacetylide. In addition, the broad and weak low-
er energy bands (
> 103 L molꢀ1 cmꢀ1) near 400 nm are assigned
e
exceeding 104 L molꢀ1
–
p⁄ (1IL) transitions involv-
p
e
as a 1MLCT [5d(Pt)?p⁄(diimine)] transition. A correlation between
absorption energy and arylacetylide substitutents is observed and
tabulated in the Table 3. It is evident that the 1MLCT absorption
shifts to lower energy (from 405 nm for 2 to 416 nm for 4) as the
donicity of arylacetylide increase (Br < H < CH3 < OCH3), which is
consistent with the feature of MLCT transition.
The molecules of 1–4 are arranged into one-dimensional chains
along a axis via two different modes (head-to-head mode or
staggered fashion). In complexes 1 and 3, the molecules adopt a
head-to-head packing mode (Figs. 2 and S4). Distinct C–Hꢁ ꢁ ꢁ
p
The chirality of complexes 1–4 was confirmed by circular
dichroism (CD) spectra (Fig. S8). The CD spectrum of the ligand L
only shows positive Cotton effect at 262 nm. The dissymmetry of
complexes 1–4 mainly comes from the intrinsic chirality of the li-
gand L, and all of them show positive Cotton effect at ca. 300 nm,
with one extremely weak positive Cotton effects band at 410 nm.
Table 2
Structural parameters determined by X-ray single crystal diffraction.
1
2
3
4
Bond length
Pt1–C1
Pt1–C2
Pt1–N1
Pt1–N2
Pt2–C3
Pt2–C4
Pt2–N3
Pt2–N4
1.918(10)
1.954(11)
2.076(8)
2.032(7)
1.906(14)
1.953(14)
2.107(11)
2.041(11)
1.944(9)
1.947(9)
2.088(7)
2.040(8)
1.912(10)
1.963(10)
2.063(8)
2.062(8)
1.908(10)
1.927(10)
2.032(8)
2.055(8)
3.3. Luminescent properties
As presented in the Fig. S9, all complexes are emissive in fluid
solution at room temperature. The origin of emission band is con-
tributed from triplet MLCT [5d(Pt)?p⁄(diimine)] excited state
[44,45]. The emission band shifts to lower energy as the elec-
tron-donating ability of the arylacetylide ligands increases
(Table 3). The emission spectra of 1 and 2 exhibit vibrational pro-
gressional spacings (ca. 1300 cmꢀ1) which is the skeletal vibra-
tional frequency of the ligand L. The profile of excitation spectra
is similar to absorption spectra, which demonstrate efficient inter-
system crossing of electronic excited state. The large stocks shifts
also confirm that the emission originate from triplet excited states.
The solid-state emission spectra of all platinum(II) complexes
are highly resolved (Fig. 6), and the emission energies in solid state
are identical to that recorded in dichloromethane solution. There-
fore, the emission in solid-state can be similarly identified as MLCT
Bond angles
C1–Pt1–N1
C1–Pt1–N2
C1–Pt1–C2
N1–Pt1–N2
N1–Pt1–C2
N2–Pt1–C2
C3–Pt2–N3
C3–Pt2–N4
C3–Pt2–C4
N3–Pt2–N4
N3–Pt2–C4
N4–Pt2–C4
96.0(3)
173.4(3)
87.7(4)
77.3(3)
176.0(4)
98.9(4)
98.3(5)
175.6(5)
88.7(6)
77.4(5)
172.8(5)
95.6(5)
94.1(3)
171.5(3)
92.1(3)
77.7(3)
171.9(4)
96.3(3)
94.3(4)
171.8(4)
86.5(4)
77.5(3)
178.9(4)
101.7(4)
171.0(4)
93.2(3)
88.0(4)
78.1(3)
100.7(4)
177.9(4)

X.-P. Zhang et al. / Polyhedron 60 (2013) 85–92
89
Fig. 2. The one-dimensional chain structure of 1 along a axis, with dashed lines indicating the C–Hꢁ ꢁ ꢁ
p and p–p interactions. The H-atoms not involved in C–Hꢁ ꢁ ꢁp
interactions are omitted for charity.
Fig. 3. The one-dimensional chain structure of 2 along a axis, with dashed lines indicating the Pt–Pt, C–Hꢁ ꢁ ꢁ
p and p–p interactions. The H-atoms not involved in C–Hꢁ ꢁ ꢁp
interactions are omitted for charity.
Fig. 4. The molecular packing diagram of complex 1 in bc plane.
[5d(Pt)?p⁄(diimine)] excited state [46]. Although two packing
modes are adopted and different Pt–Pt distances are exhibited,
the energy of emissive state remained unchanged, suggesting that
the Pt–Pt interactions (dPt–Pt > 3.4 Å) in 2 and 4 are not strong en-
ough to form MMLCT state upon excitation as in bis(
nylacetylide) platinum(II) complexes [47].
r-fluorophe-

90
X.-P. Zhang et al. / Polyhedron 60 (2013) 85–92
Fig. 5. The molecular packing diagram of complex 3 in bc plane.
Table 3
The ferroelectric measurements revealed that complex 1 indeed
displays an obvious ferroelectric behavior and almost reaches the
Photophysical data in solution at 298 K.
Complex
kabs (nm) (
e
[L molꢀ1 cmꢀ1])
kem (nm)
Uem
saturated polarization status with a remnant polarization (Pr) of
ca. 0.08
field of 7 kV cmꢀ1 at 10 Hz. The saturation spontaneous polariza-
tion (Ps) is about 0.15
C cmꢀ2, which is compared with the typical
ferroelectrics NaKC4H4O6ꢁ4H2O (Rosal salt; Ps = 0.25
C cmꢀ2).
l
C cmꢀ2 and Ec of ca. 4.7 kV cmꢀ1 by applying an electric
1
2
3
4
273 (29380), 408 (7920)
283 (30100), 405 (6920)
274 (28700), 411 (7000)
275 (32780), 416 (6940)
604
599
617
636
0.068
0.046
0.060
0.019
l
l
The ferroelectricity of complex 1 can be ascribed to the struc-
tural distortion like non-hydrogen ferroelectrics BaTiO3 and LiN-
bO3 [48–51]. The complex adopts four-coordinated mode and
deviates from planar configuration, resulting that the positive
and negative charge centers separation to create a local dipole
moment.
3.4. Ferroelectric and dielectric behaviors
The space group P21 of complexes 1 and 4 belong to point group
C2, which is one of ten polar point groups, meeting for the prere-
quisite of ferroelectricity. Therefore, the ferroelectric properties
of 1 and 4 were investigated at 298 K with compressed powder
samples as shown in Figs. 7 and 8.
Complex 4 also crystallizes in the space group P21 and poten-
tially has ferroelectric property. Ferroelectric study of powdered
pellet sample clearly exhibits that an electric hysteresis loop was
observed with a spontaneous polarization (Ps) of 0.12
l
C cmꢀ2
1
2
3
4
1.0
0.8
0.6
0.4
0.2
0.0
0.20
7 kV/cm
0.15
ν = 10 Hz
0.10
0.05
0.00
*
-0.05
-0.10
-0.15
-0.20
600
700
800
-10
-5
0
5
10
Wavelength(nm)
E(kV/cm)
Fig. 6. The solid emission spectra of complexes 1–4 at room temperature
(excitation wavelength = 500 nm and ꢂ indicates artifact).
Fig. 7. Ferroelectric hysteresis loop for complex 1 at 298 K.

X.-P. Zhang et al. / Polyhedron 60 (2013) 85–92
91
0.15
0.10
0.05
0.00
-0.05
-0.10
-0.15
10 kV/cm
ν = 10 Hz
3
2
1
0
1
420
2
390
3
360
4
330
5
300
T (K)
-15
-10
-5
0
5
10
15
270
6
E(kV/cm)
Fig. 10. Temperature dependence of the dielectric constant e00 (imaginary part) of 1
Fig. 8. Ferroelectric hysteresis loop for complex 4 at 298 K.
at various frequencies (1 106 Hz).
l
C cmꢀ2 when the electric
According to our former study, the polarity of the crystal plays a
key role in determining the physical properties [53]. As complex 3
crystallizes in the non-polar space group P212121, their net dipole
moments are cancelled by three perpendicular twofold screw axes,
which lead to a smaller NLO effect. Complex 2 is similar to complex
3, and its molecular polarity is neutralized by three perpendicular
twofold axes.
However, both complexes 1 and 4 crystallize in the polar space
group P21, and they have only one twofold screw axes along the b
direction, where the net dipole moments are expected. So it is rea-
sonable that the larger second harmonic generation (SHG) re-
sponses of them are observed.
and remnant polarization (Pr) of ca. 0.06
field of 10 kV cmꢀ1 was applied.
In contrast, complexes 2 and 3 did not show ferroelectric effect,
in accordance with their non-polar crystal structures.
The ferroelectricity is commonly confirmed by the existence of
Curie point or dielectric anomaly. Therefore, we measured the
temperature dependence of dielectric constants of 1 and 4. As the
melting point of complex 1 is about 438 K, the permittivity was re-
corded from 273 to 412 K. The e0 and e00 remains almost unchanged
in the range of 273–383 K for complex 1, but a significant increase is
observed at 398 K (Fig. 9 and Fig. 10). The e0 and e00 did not show
peak maximum up to 412 K. Therefore, the ferroelectric phase tran-
sition point, if it is in presence, would be higher than the melting
point. The peak maximum was also not found in the dielectric loss.
The similar phenomena were also exhibited for complex 4 that
the e0 and e00 just have a raise upon increasing temperature, and no
dielectric anomalies were observed (Figs. S10 and S11).
4. Conclusions
In this work, we report the synthesis and characterization of
four platinum(II) complexes with chiral isoxazoline ligand.
Although there are little differences in the auxiliary ligands, these
complexes display two different packing arrangements and crys-
tallize in three different space groups. The absorption and emission
properties are more susceptible to the substitution groups in the
auxiliary ligands rather than the molecular packing modes. How-
ever, the different crystal structures result in significant difference
in crystal polarity. Complexes 1 and 4 crystallize in the polar space
group P21, and consequently show distinct ferroelectric behaviors
and nonlinear optical properties. Complexes 2 and 3 crystallize in
the nonpolar space groups (I222 for 2 and P212121 for 3, respec-
tively) and therefore no ferroelectric effect was observed. To the
best of our knowledge, our study represents the first example of
chiral platinum(II) complexes demonstrating ferroelectric
properties.
3.5. Second-order NLO properties
Both complexes 1 and 4 show distinct second-order NLO prop-
erties, while complexes 2 and 3 only exhibit very small NLO effects
and can be neglected. By using the Kurtz powder method [52], the
second harmonic generation (SHG) responses of complexes 1 and 4
are estimated to be 0.6 and 0.3 times that of urea, respectively.
10
9
8
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (Grant Nos. 91022031, 21021062, and 21001063),
Major State Basic Research Development Program (Grant Nos.
2013CB922102 and 2011CB808704).
7
1
420
2
390
3
360
4
330
Appendix A. Supplementary data
5
300
T (K)
270
6
CCDC 921963–921966 contain the supplementary crystallo-
graphic data for complexes 1–4. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
Fig. 9. Temperature dependence of the dielectric constant e0(real part) of 1 at
various frequencies (1–106 Hz).

92
X.-P. Zhang et al. / Polyhedron 60 (2013) 85–92
[26] E. Anger, M. Rudolph, C. Shen, N. Vanthuyne, L. Toupet, C. Roussel, J.
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.poly.2013.05.024.
´
Autschbach, J. Crassous, R. Reau, J. Am. Chem. Soc. 133 (2011) 3800.
[27] R. Romeo, L. Fenech, L.M. Scolaro, A. Albinati, A. Macchioni, C. Zuccaccia, Inorg.
Chem. 40 (2001) 3293.
[28] M. Gianini, A. von Zelewsky, H. Stoeckli-Evans, Inorg. Chem. 36 (1997) 6094.
[29] R.S. Chauhan, G. Kedarnath, A. Wadawale, A. Mun~oz-Castro, R. Arratia-Perez,
V.K. Jain, W. Kaim, Inorg. Chem. 49 (2010) 4179.
[30] G. Natile, L.G. Marzilli, Coord. Chem. Rev. 250 (2006) 1315.
[31] S. Oi, E. Terada, K. Ohuchi, T. Kato, Y. Tachibana, Y. Inoue, J. Org. Chem. 64
(1999) 8660.
References
[32] D. Brissy, M. Skander, P. Retailleau, G. Frison, A. Marinetti, Organometallics 28
(2009) 140.
[33] H.-Y. Peng, C.-K. Lam, T.C.W. Mak, Z. Cai, W.-T. Ma, Y.-X. Li, H.N.C. Wong, J. Am.
Chem. Soc. 127 (2005) 9603.
[34] G.A. Lee, Synthesis (1982) 508.
[35] P.G. Baraldi, A. Bigoni, B. Cacciari, C. Caldari, S. Manfredini, G. Spalluto,
Synthesis (1994) 1158.
[36] B. Das, H. Holla, G. Mahender, K. Venkateswarlu, B.P. Bandgar, Synthesis (2005)
1572.
[37] K. Sonogashira, Y. Fujikura, T. Yatake, N. Toyoshima, S. Takahashi, N. Hagihara,
J. Organomet. Chem. 145 (1978) 101.
[38] SAINT-PLUS, version 6.02. Bruker Analytical X-ray Systems, Madison, WI, 1999.
[39] G.M. Sheldrick, SADABS, Bruker Analytical X-ray Systems, Madison, WI, 1996.
[40] G.M. Sheldrick, SHELXTL-97, University of Göttingen, Germany, 1997.
[41] M. Hissler, W.B. Connick, D.K. Geiger, J.E. McGarrah, D. Lipa, R.J. Lachicotte, R.
Eisenberg, Inorg. Chem. 39 (2000) 447.
[42] S.-C. Chan, M.C.W. Chan, Y. Wang, C.-M. Che, K.-K. Cheung, N. Zhu, Chem. Eur. J.
7 (2001) 4180.
[43] B. Kolp, D. Abeln, H. Stoeckli-Evans, A. von Zelewsky, Eur. J. Inorg. Chem.
(2001) 1207.
[44] F.N. Castellano, I.E. Pomestchenko, E. Shikhova, F. Hua, M.L. Muro, N.
Rajapakse, Coord. Chem. Rev. 250 (2006) 1819.
[45] J.A.G. Williams, Top. Curr. Chem. 281 (2007) 205.
[46] W. Lu, M.C.W. Chan, N. Zhu, C.-M. Che, Z. He, K.-Y. Wong, Chem. Eur. J. 9 (2003)
6155.
[47] J. Ni, L.-Y. Zhang, H.-M. Wen, Z.-N. Chen, Chem. Commun. (2009) 3801.
[48] H.Y. Chang, T. Sivakumar, K.M. Ok, P.S. Halasyamani, Inorg. Chem. 47 (2008)
8511.
[49] M.J. Polking, M.-G. Han, A. Yourdkhani, V. Petkov, C.F. Kisielowski, V.V. Volkov,
Y. Zhu, G. Caruntu, A.P. Alivisatos, R. Ramesh, Nat. Mater. 11 (2012) 700.
[50] J.P. Singh, G. Dixit, R.C. Srivastava, H.M. Agrawal, K. Asokan, J. Phys. D Appl.
Phys. 44 (2011) 435306.
[51] F.-H. Zhao, Y.-X. Che, J.-M. Zheng, Inorg. Chem. 51 (2012) 4862.
[52] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798.
[53] D.-P. Li, C.-H. Li, J. Wang, L.-C. Kang, T. Wu, Y.-Z. Li, X.-Z. You, Eur. J. Inorg.
Chem. (2009) 4844.
[1] A. Sheikholeslami, P.G. Gulak, Proc. IEEE 88 (2000) 667.
[2] S.H. Lim, A.C. Rastogi, S.B. Desu, J. Appl. Phys. 96 (2004) 5673.
[3] R.C.G. Naber, C. Tanase, P.W.M. Blom, G.H. Gelinck, A.W. Marsman, F.J.
Touwslager, S. Setayesh, D.M. de Leeuw, Nat. Mater. 4 (2005) 243.
[4] S. Mathews, R. Ramesh, T. Venkatesan, J. Benedetto, Science 276 (1997) 238.
[5] Y. Yuan, T.J. Reece, P. Sharma, S. Poddar, S. Ducharme, A. Gruverman, Y. Yang, J.
Huang, Nat. Mater. 10 (2011) 296.
[6] H. Huang, Nat. Photonics 4 (2010) 134.
[7] K. Asadi, P. de Bruyn, P.W.M. Blom, D.M. de Leeuw, Appl. Phys. Lett. 98 (2011)
183301.
[8] T. Hang, W. Zhang, H.-Y. Ye, R.-G. Xiong, Chem. Soc. Rev. 40 (2011) 3577.
[9] W. Zhang, R.-G. Xiong, Chem. Rev. 112 (2012) 1163.
[10] W. Zhang, H.-Y. Ye, R.-G. Xiong, Coord. Chem. Rev. 253 (2009) 2980.
[11] S. Horiuchi, Y. Tokura, Nat. Mater. 7 (2008) 357.
[12] S. Horiuchi, Y. Tokunaga, G. Giovannetti, S. Picozzi, H. Itoh, R. Shimano, R.
Kumai, Y. Tokura, Nature 463 (2010) 789.
´
[13] M. Szafranski, J. Phys. Chem. B 115 (2011) 8755.
[14] X.-L. Li, K. Chen, Y. Liu, Z.-X. Wang, T.-W. Wang, J.-L. Zuo, Y.-Z. Li, Y. Wang, J.S.
Zhu, J.-M. Liu, Y. Song, X.-Z. You, Angew. Chem., Int. Ed. 46 (2007) 6820.
[15] Z. Sun, T. Chen, J. Luo, M. Hong, Angew. Chem., Int. Ed. 51 (2012) 3871.
[16] Y. Sui, D.-P. Li, C.-H. Li, X.-H. Zhou, T. Wu, X.-Z. You, Inorg. Chem. 49 (2010)
1286.
[17] J. Liu, X.-P. Zhang, T. Wu, B.-B. Ma, T.-W. Wang, C.-H. Li, Y.-Z. Li, X.-Z. You,
Inorg. Chem. 51 (2012) 8649.
[18] M.-Y. Yuen, V.A.L. Roy, W. Lu, S.C.F. Kui, G.S.M. Tong, M.-H. So, S.S.-Y. Chui, M.
Muccini, J.Q. Ning, S.J. Xu, C.-M. Che, Angew. Chem., Int. Ed. 47 (2008) 9895.
[19] J.K. Bera, K.R. Dunbar, Angew. Chem., Int. Ed. 41 (2002) 4453.
[20] W.B. Connick, D. Geiger, R. Eisenberg, Inorg. Chem. 38 (1999) 3264.
[21] K.M.-C. Wong, V.W.-W. Yam, Acc. Chem. Res. 44 (2011) 424.
[22] C. Yamamoto, H. Nishikawa, M. Nihei, T. Shiga, M. Hedo, Y. Uwatoko, H. Sawa,
H. Kitagawa, Y. Taguchi, Y. Iwasa, H. Oshio, Inorg. Chem. 45 (2006) 10270.
´
´
[23] A. Guijarro, O. Castillo, A. Calzolari, P.J.S. Miguel, C.J. Gomez-Garcia, R. di Felice,
F. Zamora, Inorg. Chem. 47 (2008) 9736.
[24] P. Deplano, M.L. Mercuri, L. Marchiò, L. Pilia, M. Salidu, A. Serpe, F. Congiu, S.
Sanna, Eur. J. Inorg. Chem. (2005) 1829.
[25] M. Ziegler, A. von Zelewsky, Coord. Chem. Rev. 177 (1998) 257.