Structural characterization and second-order nonlinear optical properties of zinc halide thiosemicarbazone complexes

Article abstract of DOI:10.1016/S0277-5387(02)01004-5

Three zinc(II) halide complexes ZnL₂X₂ (X = Cl, Br, I; L = 4-methoxylbenzaldehyde thiosemicarbazone) have been synthesized and characterized by spectroscopic techniques. The complexes exhibit powder SHG efficiency approximately ten t

Full text of DOI:10.1016/S0277-5387(02)01004-5

Polyhedron 21 (2002) 1217Á1222
/
www.elsevier.com/locate/poly
Structural characterization and second-order nonlinear optical
properties of zinc halide thiosemicarbazone complexes
Yu-Peng Tian a,*, Wen-Tao Yu b, Cun-Yuan Zhao c, Min-Hua Jiang b, Zhi-Gang Cai d,
Hoong Kun Fun e
a Department of Chemistry, Anhui University, Hefei 230039, People’s Republic of China
b Institute of Crystal Material and State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, People’s Republic of China
c The State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, People’s Republic of China
d Ultrafast Laser Spectroscopic Laboratory Institute of Laser & Spectroscopy, Zhongshan University, Guangzhou 510275, People’s Republic of China
e X-ray Crystallography Unit, School of Physics, University Sains Malaysia, 11800 USM, Penang, Malaysia
Received 15 November 2001; accepted 20 March 2002
Abstract
Three zinc(II) halide complexes ZnL2X2 (Xꢀ
and characterized by spectroscopic techniques. The complexes exhibit powder SHG efficiency approximately ten times higher than
that of urea. The molecular hyperpolarizabilities are calculated to be ꢁ2.6ꢂ 4.6ꢂ
10ꢁ30 esu for the free ligand L, and ꢁ 10ꢁ30, ꢁ
6.2ꢂ 10.1ꢂ
10ꢁ30, ꢁ 10ꢁ30 esu for the three zinc complexes, respectively. The former two complexes crystallize in the
/
Cl, Br, I; Lꢀ/4-methoxylbenzaldehyde thiosemicarbazone) have been synthesized
/
/
/
/
/
/
/
/
noncentrosymmetric space group Aba2, whilst ZnL2I2 crystallizes in the centrosymmetric space group P21/c and does not exhibit
any SHG efficiency. The zinc(II) atom in these complexes is tetrahedrally coordinated by two neutral sulfur atoms from the
corresponding thiosemicarbazones and two halide anions. The relationships between the molecular structures and nonlinear optical
properties were studied based on theoretical calculation and experimental determination methods. # 2002 Elsevier Science Ltd. All
rights reserved.
Keywords: Zinc; Halide complexes; Thiosemicarbazones; Ligand
1. Introduction
SHG materials with nonlinearity superior to that of
inorganic materials have been investigated [6,7]. How-
ever, only a few organic compounds with large hyper-
polarizability (b) have been developed into useful bulk
crystalline materials for practical applications [8,9].
Ideally the large nonlinearities of p-conjugated or-
ganics and favorable crystal growth characteristics and
mechanical properties of ionic salts would be combined
Nonlinear optical materials exhibiting efficient sec-
ond-harmonic generation (SHG) at short wavelengths
are needed in the fields of high-density optical recording,
laser printing, and optical measurement systems and for
other applications [1,2]. Compact all-solid-state devices
based on the frequency doubling of diode-pumped laser
have the potential to meet industrial needs such as
efficiency, reliability, and low costing. Recently efficient
continuous-wave (cw) green and blue SHG was demon-
strated with inorganic crystals such as KTP [3], KNbO3
[4], and b-barium borate (BBO) [5]. The properties of
these inorganic devices [5] have made them suitable for
practical use. On the other hand, numerous organic
into a single NLO crystal [10Á17]. Extended p-conju-
/
gated networks in organic systems with the largest
nonlinearities invariably have significant absorption in
the visible portion of the spectrum. Consequently, for
SHG into the blue-near-UV regions, more transparent
and less extensively delocalized organics must be con-
sidered (e.g. urea), albeit at the expense of decreasing the
nonlinearity. Semiorganics have the potential for com-
bining the high optical nonlinearity and chemical
flexibility of organics with the physical ruggedness of
inorganics. Also, for obtaining the materials with large
* Corresponding author. Tel.: ꢃ
5107342.
E-mail address: yptian@mars.ahu.edu.cn (Y.-P. Tian).
/
86-551-5107105; fax: ꢃ86-551-
/
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 0 0 4 - 5

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Y.-P. Tian et al. / Polyhedron 21 (2002) 1217Á1222
/
x2, optimization of both the molecular, first hyperpolar-
izability and their orientation in the bulk should be
considered. Towards this end, we have explored a class
of crystals in which urea or urea analogs have been
stoichiometrically incorporated into an inorganic salt
Table 1
Decomposition temperature of the ligand (L) and its zinc halide
complexes (heating rate 20 8C minꢁ1 under nitrogen)
Complex
m.p. (8C)
Td (8C)
L
172
209
200
201
201
235
223
221
[18Á20]. In continuation of these studies, we reported
/
ZnL2Cl2
ZnL2Br2
ZnL2I2
herein the design, synthesis, crystal structure and non-
linear optical properties of zinc halide complexes derived
from 4-methoxylbenzaldehyde thiosemicarbazone. The
structure of the complexes is shown in Scheme 1.
suitable for X-ray structure analysis were obtained by
slowly evaporating an ethanol solution in air. IR data
2. Experimental
(KBr disc): 3158 (s, Nꢀ
/
H), 1607, 1535 (s, Cꢁ
/
N), 980
cmꢁ1 (s, Cꢁ
/
S). UVÁVis: lmax (log o): 326 nm (3.69).
/
All chemicals used were of analytical grade. The
solvents were purified by conventional methods.
Found: C, 39.3; H, 4.4; N, 15.0; C18H24N6O2S2ZnCl2
Calc.: C, 39.0; H, 4.1; N, 15.2%.
2.1. Physical measurements
2.2.3. Preparation of ZnL2Br2
The complex was synthesized by the same procedure,
but from ZnBr2 (yield: 73%). IR data (KBr disc): 3159
Elemental analysis data were obtained using a
PerkinÁ
/
Elmer 240 analyzer. Infrared spectra were
400 cmꢁ1
(s, Nꢀ
/
H), 1604, 1532 (s, Cꢁ
/
N), 985 cmꢁ1 (s, Cꢁ
/
S).
recorded from KBr discs in the range 4000Á
/
UVÁVis: lmax (log o): 328 nm (3.72). Found: C, 33.5; H,
/
on a Nicolet FT IR-170SX instrument. Electronic
absorption spectra were obtained on a Shimadzu UV-
3.6; N, 13.2; C18H24N6O2S2ZnBr2 Calc.: C, 33.4; H, 3.4;
N, 13.0%.
3100 spectrophotometer in DMF solution (1.0ꢂ
10ꢁ4
/
mol dmꢁ3). Solid-state electronic spectra were obtained
by the reflection technique on a Shimadzu UV 240
spectrophotometer using MgO as the reference material.
DSC and TG of the compounds were carried out using a
2.2.4. Preparation of ZnL2I2
The complex was synthesized by the same procedure,
but from ZnI2 (yield: 69%). IR data (KBr disc): 3289 (s,
Nꢀ
/
H), 1598, 1548 (s, Cꢁ
/
N), 1020 cmꢁ1 (s, Cꢁ
/
S). UVÁ
/
PerkinÁElmer DSC-2C Differential Scanning Calori-
/
Vis: lmax (log o): 334 nm (3.71). Found: C, 19.4; H, 2.9;
N, 7.4; C18H24N6O2S2ZnI2 Calc.: C, 19.1; H, 2.7; N,
7.4%.
meter and TGS-2 Thermogravimetric Analyzer. The
samples were heated at the rate of 20 K minꢁ1 in an
inert nitrogen atmosphere. The decomposition tempera-
ture of the free ligand and its zinc complexes are shown
in Table 1.
2.3. X-ray crystallography and structure solution
The relevant crystal data and structural parameters
are summarized in Table 2. Selected bond distances and
angles are shown in Tables 3 and 4, respectively. The
intensities of ZnL2Cl2 was collected at 294 K on a MSC/
2.2. Synthesis
2.2.1. Preparation of the ligand
4-Methoxylbenzaldehyde thiosemicarbazone (L) was
prepared by reacting equimolar amounts of 4-methox-
ylbenzaldehyde and thiosemicarbazone in hot ethanol.
Rigaku RAXIS-IIC imaging plate diffractometer using
˚
0.71073 A) from a rotating anode
Mo Ka radiation (lꢀ
/
operating at 50 kV, 90 mA (2umax
ꢀ
/
55.28); 60 oscilla-
tion frames in the range of 0Á1808, expose 8 min per
/
2.2.2. Preparation of ZnL2Cl2
frame for those compounds. Absorption corrections
were made using the ABSCOR program based on Four-
ier-coefficient fitting to the intensities of symmetry-
Ethanol solution of (0.42 g, 2 mmol) and zinc chloride
(0.69 g, 2 mmol) were mixed. The colorless crystalline
solid formed after refluxing for 4 h was isolated and
dried in vacuo over P4O10. Yield: 0.78 g ( 90%). Crystals
equivalent reflections [21Á23].
/
The structures of ZnL2Cl2 was solved by direct
methods. All non-hydrogen atoms were refined anistro-
pically by full-matrix least-squares. Hydrogen atoms
˚
Hꢀ0.96 A),
were placed in calculated positions (Cꢀ
/
/
assigned fixed isotropic thermal parameters and allowed
to ride on their respective parent atoms. The contribu-
tions of these hydrogen atoms were included in the
structure-factor calculations. All the computations were
Scheme 1.

Y.-P. Tian et al. / Polyhedron 21 (2002) 1217Á
/1222
1219
Table 2
Crystallographic data for zinc complexes
The data for [ZnL2I2] were collected on a Siemens
SMART CCD area detector diffractometer equipped
with Mo Ka radiation using v-scan mode. The data
collection covered over a hemisphere of reciprocal space
by a combination of three sets of exposures; each set had
a different f angle (0.888 and 1808) for the crystal and
each exposure of 30 s covered 0.38 in v. The crystal-to-
detector distance was 4 cm and the detector swing angle
ZnL22Cl2
ZnL22I2
Empirical formula
Mw
C18H22N6O2S2Cl2Zn C18H22N6O2S2I2Zn
554.81
colorless
737.71
colorless
Crystal color
Crystal dimensions
(mm)
0.40ꢂ0.30ꢂ0.30
0.40ꢂ0.40ꢂ0.14
was ꢁ358. Coverage of the unique set is over 99%
/
Temperature (K)
Crystal system
Space group
293
orthorhombic
Aba2
293
monoclinic
P21/c
complete. Crystal decay was monitored by repeating
thirty initial frames at the end of data collection and
analyzing the duplicate reflections and was found to be
negligible.
The unit cell parameters were determined using
SMART (Siemens, 1996a) [26]. The three sets of data
collected were reduced using the program SAINT (Sie-
mens, 1996b) [27]. The structure was solved with direct
methods using the program SHELXTL (Sheldrick, 1997)
[28]. All the non-hydrogen atoms were located from the
trial structure and then refined anisotropically with
˚
a (A)
11.971(2)
22.153(4)
9.090(2)
90.00 (1)
2374.5(8)
4
14.0113(2)
14.9098(1)
13.2814(1)
110.718(1)
2595.14(5)
4
˚
b (A)
˚
c (A)
b (8)
3
V (A )
˚
Z
m (Mo Ka) (mmꢁ1
)
1.463
1.552
3.512
1.888
Dcalc (g cmꢁ3
F(000)
Unique reflections
)
1136
4278
1424
23102
Observed reflections 2305 (I ꢀ3s(I))
9539
0.0369, 0.0791
1.052
R, Rw
Goodness-of-fit
Drmin, Drmax
0.0400, 0.1129
1.060
SHELXTL using full-matrix least-squares procedure. A
2
weighting scheme of wꢀ
/
1/[s2(Fo )ꢃ
/
(0.0422P)2ꢃ
/
ꢁ0.549, 0.421
ꢁ1.541, 1.569
2
2
2.1119P], where Pꢀ
/
(Fo ꢃ2Fc )/3 was applied. The
/
hydrogen atom positions were fixed geometrically at
calculated distances.
Table 3
˚
Selected bond lengths (A) and angles (8) for ZnL2Cl2 complex
2.4. Nonlinear optical property measurements
Bond lengths
Zn(1)ꢀCl(1)
Zn(1)ꢀS(1)
N(1)ꢀC(1)
N(2)ꢀC(1)
N(3)ꢀC(2)
2.262(1)
2.361(1)
1.321(5)
1.343(4)
1.263(5)
Zn(1)ꢀCl(2)
Zn(1)ꢀS(2)
S(1)ꢀC(1)
2.262(1)
2.361(1)
1.715(3)
1.383(4)
The second order nonlinear optical intensities are
estimated by measuring powder samples of 76Á154 mm
/
N(2)ꢀN(3)
diameter in the form of pellet. The thickness of a pellet is
about 0.8 mm. The experimental arrangement for the
nonlinear optical properties utilizes a M200 high power
Mode-Locked Nd:YAG laser with 200 ps pulse at a
repetition rate of 5 Hz. The selected wavelength is 1064
nm. After the selection of the wavelength, the laser beam
is split into two parts, one to generate the second
harmonic signal in the sample and the other to generate
the second harmonic signal in the reference (urea pellet).
According to the principle proposed by Kurtz and Perry
[29], SHG efficiency can be estimated as 7.6 and 13.2
times higher than that of urea for complexes ZnL2Cl2
and ZnL2Br2, respectively. However, no SHG response
was observed for ZnL2I2.
Bond angles
Cl(1)ꢀZn(1)ꢀCl(2)
Cl(2)ꢀZn(1)ꢀS(1)
S(1)ꢀC(1)ꢀN(1)
S(1)ꢀC(1)ꢀN(2)
108.08(12) Cl(1)ꢀZn(1)ꢀS(2)
109.11(4)
109.11(4)
104.63(6)
118.4(3)
112.99(5)
120.4(3)
121.2(3)
Cl(2)ꢀZn(1)ꢀS(2)
S(1)ꢀZn(1)ꢀS(2)
N(1)ꢀC(1)ꢀN(2)
Table 4
˚
Selected bond lengths (A) and angles (8) for ZnL2I2 complex
Bond lengths
I(1)ꢀZn(1)
N(2)ꢀN(1)
N(1)ꢀC(8)
N(3)ꢀC(9)
2.6056(4)
1.397(3)
1.283(4)
1.313(4)
Zn(1)ꢀS(1)
N(2)ꢀC(9)
S(1)ꢀC(9)
2.3897(8)
1.334(4)
1.732(3)
Bond angles
3. Results and discussion
I(2)ꢀZn(1)ꢀS(2)
N(3)ꢀC(9)ꢀN(2)
S(1)ꢀC(9)ꢀN(2)
I(2)ꢀZn(1)ꢀS(1)
108.97(2)
119.2(3)
117.7(2)
111.03(2)
I(1)ꢀZn(1)ꢀI(2)
S(1)ꢀC(9)ꢀN(3)
S(1)ꢀZn(1)ꢀS(2)
I(1)ꢀZn(1)ꢀS(1)
114.14(1)
123.1(2)
105.30(3)
107.46(2)
3.1. Spectroscopic characterization
The new Schiff base ligand L was prepared by the
reaction of thiosemicarbazide with 4-methoxylbenzalde-
hyde in a 1:1 molar ratio. The ligand can, in principle,
carried out using the SHELXTL-PC program package
[24]. Analytical expressions of neutral-atom scattering
factors were employed, and anomalous dispersion
corrections were incorporated [25].
exhibit thioneÁ
thioamide ꢀHNꢀ
n(Sꢀ
H) band at 2570 cmꢁ1 is absent from the IR
/thiol tautomerism, since it contains a
/
/
CꢁS functional group [30Á32]. The
/
/
/

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Y.-P. Tian et al. / Polyhedron 21 (2002) 1217Á
/1222
spectra of the Schiff-base, but n(Nꢀ/H) at approximately
3150 cmꢁ1 is present, indicating that in the solid state
the ligand remains as the thione tautomer. After
refluxing the free ligand and zinc halide in ethanol
solution, a colorless crystalline solid was formed. It has
been shown [33] that the thiosemicarbazide molecule
itself exists in the trans configuration and while com-
plexing in this configuration, it behaves as a mono-
dentate ligand, bonding only through the sulfur atom.
Gerbeleu et al. [34] have shown that bonding may also
occur through the hydrazine nitrogen and the amide
nitrogen, if the sulfur center is substituted. In most of
the complexes studied the thiosemicabazone function
coordinates to the metal ion in the cis configuration [35],
Fig. 1. Molecular structure and atom numbering of ZnL2Cl2. The
thermal ellipsoids are drawn at the 50% probability level.
as a bidentate ligand bonding through the thioneÁthiol
/
sulfur atom and hydrazine nitrogen atom in bidentate
manner. The most common stereo chemistries encoun-
tered in bidentate thiosemicarbazone complexes are
centrosymmetric octahedral and square-planar, so in
order to obtained a noncentrosymmetric complex mo-
lecule, it is necessary to ensure that the thiosemicarba-
zone behaves as a monodentate sulfur ligand. HSAB
consideration dictates that the softer acid character of
Zn(II), Cd(II)and Hg(II) exhibit higher stability con-
stants with this class of sulfur ligands, because of the
Fig. 2. Packing diagram for ZnL2Cl2 viewed approximately along the
c axis.
formation of strong s-bonds as well as d(p)Ád(p) bonds
/
by donation of a pair of electrons to ligands. So it can be
expected that the zinc halide complexes might be
monodentate S-bonded. The explanation was supported
˚
best plane being ca. 0.074 A). The dihedral angle
between the two ligand planes is 75.78.
The thiosemicarbazone moiety in the complex shows
by the IR and UVÁ
which are quite similar to those of the corresponding
ligand L, especially with the presence of n(NꢀH) at
approximately 3150 cmꢁ1
/Vis spectra of the zinc complexes,
E configuration about both C(2)ꢀ
/
N(3) and C(1)ꢀ/N(2).
The hydrogen atoms attached to the imine nitrogen
atoms N(2) and N(5) are also in cis-configuraion with
the sulfur atoms. The six hydrogen atoms attached to
amino nitrogen atoms N(1), N(2), N(4) and N(5) have
the potential to form donor hydrogen bonds. The two
hydrogen atoms attached to the imine nitrogen atoms
N(2) and N(5) form intramolecular hydrogen bond with
the chloride atoms Cl(1) and Cl(2) (distances of 3.235(7)
/
.
3.2. Thermal stabilities for the ligand and its zinc
complexes
Thermal stabilities for the ligand and its zinc com-
plexes were determined by DSC and TG. The data for
them are given in Table 1. From the table, it can be seen
that both melting point and decomposition temperature
of the complexes are higher than those of their free
ligand. So it can be concluded that coordination of the
ligand to the metal ion results in greater thermal
stability.
˚
and 3.215(7) A for N(2)Á Á ÁCl(1) and N(5)Á Á ÁCl(2),
respectively and angles around corresponding hydrogen
atoms are 152.9(4)8 and 152.4(4)8, respectively). Ana-
lyses of intermolecular contacts indicated that the
hydrogen atoms attached to amino nitrogen atoms
N(1) and N(4) formed donor hydrogen bonds of the
types N(1)ꢀ
/
H(1b)Á Á ÁO(2a) (ꢁ
/
0.5ꢃ
/
x, ꢁ
/
0.5ꢃ
/
y, 1ꢃ
/
z)
and N(4)ꢀH(4b)Á Á ÁO(1b) (ꢁ
/
/
0.5ꢃ
/
x, 0.5ꢃ
/
y, zꢁ
/
1). The
3.3. Crystal structure for ZnL2Cl2
NÁ Á ÁO separations are approximately 3.02 and the Nꢀ
/
HÁ Á ÁO angles are approximately 1548. There are also
two intermolecular contacts which can be considered as
hydrogen bonds, although the contacts are approxi-
The ORTEP drawing of ZnL2Cl2, with numbering
scheme is shown in Fig. 1. The unit cell contents of
the complex is shown in Fig. 2. The coordination
geometry of the zinc atom is distorted tetrahedral with
the two sulfur atoms from the neutral thiosemicarba-
zone ligand forming bond angles around the Zn(1) in the
˚
˚
mately 3.40 A. [3.397(8) A, N(1) and Cl(2c) (ꢁ
/
0.5ꢃ
z); 3.405(8) A, N(4)Á Á ÁCl(1d) (ꢁ0.5ꢃ
0.5ꢃ
/x,
˚
0.5ꢁ
/
y, 0.5ꢃ
/
/
/x,
0ꢃ0.5ꢁ
/
/
y, ꢁ
/
/z)], since the bond angles around the
range of 104.58Á
atom N(1) is almost planar (mean deviations from the
/
113.28. The ligand (except the amino
corresponding hydrogen atoms are 158.2(5)8 and
158.8(5)8, respectively.

Y.-P. Tian et al. / Polyhedron 21 (2002) 1217Á
/1222
1221
The data in Table 3 show that all the bond distances
in the side chain of the thiosemicarbazones are inter-
mediate between formal single and double bonds,
pointing to extensive electron delocalization over the
entire moiety. Examination of the structural data for
extensive electron delocalization in the whole system
with long conjugation length between the donor and
acceptor. The negative sign of bm can be explained by
the smaller dipole moment of the lowest excited state
than that of the ground one. The microscopic second-
order susceptibility b values of zinc complexes seems to
be twice as larger than that of the free ligands. This
suggests that the two ligands in complexes may con-
tribute equally to the microscopic second-order non-
linearity of complexes. The bu value can also be
understood by their contribution from lower-energy
transition. The linear absorption spectra of the ligand
and the zinc complexes in DMF solution exhibit only
one intense band near 325 nm. The optical transition
associated with this band is mainly the contribution of
thiosemicarbazones [36] and their metal complexes [37Á
40] shows that the N(1)ꢀC(1) and C(1)ꢀS(1) bonds in
Lꢁ are longer than those in the neutral form L (1.34 vs.
/
/
/
˚
1.31 and 1.73 vs. 1.71 A on average, respectively),
C(1) bond is shorter than that in L
whereas the N(2)ꢀ
/
˚
(1.35 vs. 1.33 A on average).
3.4. Crystal structure for ZnL2I2
The crystals contain individual ZnL22I2 neutral mole-
p*1
/
p and p*1
/
n transitions of nonbonding electron
cules.
A perspectives drawing with atom-labeling
pairs of N and S atoms according to the analysis of
molecular orbital components for the ligand and zinc
complexes, which are the excitation mainly responsible
for the NLO response [19].
Apart from the discussions above, the crystal struc-
tures and their alignment is important for the enhance-
scheme is shown in Fig. 3. Each metal atom is tetra-
coordinated by two monodentate L ligands bonded
through the S atoms, and two terminal iodine atoms
(Table 4). The Znꢀ
/
S and Znꢀ/I distances are almost
equal; thus the strong distortion in the tetrahedral
environment of the four donor atoms is explained on
the basis of strong stereo interactions between the two L
ment
noncentrosymmetric crystals of ZnL2Cl2 (molecular
dipole moment mꢀ0.39 D) and ZnL2Br2 (mꢀ1.27 D)
of
nonlinear
optical
response.
The
ligands in each complex. The Znꢀ
the complex is in the range of those found for metalꢀ
terminal bonds in other complexes [35]. ZnꢀI distances
are also in the range of those found in other Zn(II)
iodine complexes with terminal ZnꢀI bonds.
/S distance (Table 4) in
/
/
/S
serve to hold the molecules in the head-to-tail fashion
which give rise to effective dipolar orientation for near-
optimum second-order harmonic generation. However,
/
/
the complex ZnL2I2 (mꢀ2.29 D) showed no SHG
/
response due to its centrosymmetric space group in
crystallization, although it has the largest microscopic
second-order nonlinear susceptibility. As predicted by
PM3 method, the large ground dipolar moment of an
isolated molecule in these crystals can lead to strong
3.5. Nonlinear optical properties
Based on MNDO Hamitanian [41] and PM3 para-
metrization [42] with the MOPAC program package [43],
the molecular hyperpolarizability, bm, the vector com-
ponent along the dipole moment direction, of the
dipoleÁdipole interaction and then result in dimers or
/
organic ligand are calculated to be ꢁ
for the free ligand L, and ꢁ4.6ꢂ
10ꢁ30, ꢁ
10.1ꢂ
10ꢁ30 esu for the three zinc complexes, respec-
/
2.6ꢂ
/
10ꢁ30 esu
10ꢁ30
anti-paralleled molecular alignment in the crystal.
Therefore, the centrosymmetric crystals show vanishing
SHG efficiency.
/
/
/
6.2ꢂ
/
,
ꢁ
/
/
Several conclusions can be drawn from the experi-
mental determinations and theoretical calculations
above. Combining the conjugated thiosemicarbazide
containing donor group with a distorted inorganic
tetrahedral center, we may design and synthesize various
metal complexes, which possess a large second-order
microscopic and macroscopic nonlinear optical (NLO)
tively. The molecular hyperpolarizabilities bm of organic
ligands and their complexes are comparable with that of
p-nitroaniline (PNA, 6.3ꢂ
are much greater than that of urea (0.14ꢂ
/
10ꢁ30). The absolute values
/
10ꢁ30 esu).
This result is easily understood, since the ligand in the
free state and in the zinc complexes both present
property. For example, the complexes ZnL2X2 (XꢀCl,
/
Br, I) have larger molecular hyperpolarizability and
greater thermal stability than those of their free ligand.
It is interesting to find that the zinc halides are
deliquescent whereas the zinc halide thiosemicarbazone
complexes are moisture free. The molecules of ZnL2Cl2
and ZnL2Br2 are arranged noncentrosymmetrically in
the crystalline state to have macroscopic second-order
nonlinear optical response. Unfortunately, the mole-
cules of [ZnL2I2] crystallize centrosymmetrically, leading
to vanishing SHG activity. These are associated with
Fig. 3. Molecular structure and atom numbering of ZnL2I2. The
thermal ellipsoids are drawn at the 50% probability level.

1222
Y.-P. Tian et al. / Polyhedron 21 (2002) 1217Á1222
/
[13] V. Venkatarmanan, C.K. Subramanian, H.L. Bhat, J. Appl. Phys.
77 (1995) 6049.
their molecular dipole moment. The results above might
give us a general guideline in the synthesis of new
nonlinear optical materials. The complexes in this
report, are almost colorless, transparent and easy to
form crystals. They are also mechanically and thermally
stable, thereby making them suitable to be used as
potential or practical NLO materials.
[14] U.B. Ramabadra, R. Vuppuladhadium, D. Small, D.Z.E. Zel-
mon, G.C. Kennedy, Appl. Optics 35 (1996) 903.
[15] M.J. Gerald, A. Woodward, N.J. Taylor, T.B. Marder, Chem.
Mater. 10 (1998) 1355.
[16] (a) R. Andrel, I. Malfant, P.G. Lacroix, H. Gornitzka, Chem.
Mater. 11 (1999) 840;
(b) T. Renouard, H.L. Bozec, S. Brasselet, I. Ledoux, J. Zyss,
Chem. Commun. (1999) 871;
(c) A. Hilton, T. Renouard, O. Maury, I. Ledoux, J. Zyss, Chem.
Commun. (1999) 2521.
4. Supplementary material
[17] W.B. Hou, M.H. Jiang, D.R. Yuan, D. Xu, Mat. Res. Bull. 28
(1993) 645.
Crystallographic data have been deposited with the
CCDC (12 Union Road, Cambridge, CB2 1EZ, UK,
fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk;
www: http://www.ccdc.cam.ac.uk) and are available on
request quoting the deposition number CCDC145742
for ZnL2Cl2; CCDC145743 for ZnL2I2.
[18] D. Xu, M.G. Liu, M.H. Jiang, D.R. Yuan, Mat. Res. Bull. 29
(1994) 73.
[19] Y.P. Tian, C.Y. Duan, Z.L. Lu, X.Z. You, Inorg. Chem. 36
(1997) 1247.
[20] Y.P. Tian, F.X. Xie, Chin. Chem. Lett. 9 (1998) 215.
[21] K.L. Krause, G.N. Phillips, J. Appl. Crystallogr. 25 (1992) 146.
[22] T. Higashi, ABSCOR, Rigaku Corporation, Tokyo, 1995.
[23] G.M. Sheldrick, in: D. Sayre (Ed.), Computational Crystal-
lography, Oxford University Press, New York, 1982, pp. 506Á
514.
/
Acknowledgements
[24] J. Ibers, W.C. Hamilton (Eds.), International Tables for X-ray
Crystallography, Kynock Press, Birmingham (now distributed by
Kluwer Academic Press, Dordrecht), 1974, pp. 55, 99, 149.
[25] Siemens, SAINT V4 Software Reference Manual, Siemens Analy-
tical X-Ray Systems, Inc., Madison, WI, USA, 1996b.
[26] Siemens, SMART Software Reference Manual, Siemens Analytical
X- Ray Systems, Inc., 1996a
This work was supported by a grant for the State Key
Program of China, National Natural Science Founda-
tion of China, the Ministry of Education of China, and
by research grant R&D No. 190-9609-2801 of the
Malaysian Government and Universiti Sains Malaysia.
[27] G.M. Sheldrick, SHELXTL V5.1 Software Reference Manual,
Bruker AXS, Inc, Madison, WI, USA, 1997.
References
[28] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798.
[29] M.A. Ali, S.E. Livingstone, Coord. Chem. Rev. 13 (1974) 101.
[30] M.J.M. Campbell, Coord. Chem. Rev. 15 (1975) 279.
[31] S.E. Livingstone, Q. Rev. 15 (1965) 386.
[1] (a) J. Zyss, I. Ledoux, Chem. Rev. 94 (1994) 77;
(b) W.E. Maerner, S.M. Silence, Chem. Rev. 94 (1994) 127.
[2] T. Verbiest, S. Houbrechts, M. Kauranen, A. Persoons, J. Mater.
Chem. 7 (1997) 2175.
[32] P. Dominao, M. Nardelli, P. Sgarabotto, Acta Crystallogr., Sect.
B 25 (1969) 343.
[33] N.V. Gerbeleu, M.D. Revenko, V.M. Leovats, Russ. J. Inorg.
Chem. 22 (1977) 1009.
[3] F. Averseng, C. Lepetit, P.G. Lacroix, J.P. Tuchagues, Chem.
Mater. 12 (2000) 2225.
[34] S. Padhye, G.B. Kauffman, Coord. Chem. Rev. 63 (1985) 127.
[35] E.W. Ainscough, A.M. Brodie, J.D. Ranford, J.M. Waters, J.
Chem. Soc., Dalton Trans. (1991) 1737.
[4] W.J. Kozlovsky, W. Lenth, E.E. Latta, A. Moser, G.L. Bona,
Appl. Phys. Lett. 56 (1990) 2291.
[5] H. Yamamoto, S. Funato, T. Sugiyama, J. Opt. Soc. Am. B 13
(1996) 837.
[36] B.M. Wu, C.W. Mak, J. Chem. Soc., Dalton Trans. (1996) 3485.
[37] K.V. Katti, P.R. Singh, C.L. Barnes, J. Chem. Soc., Dalton
Trans. (1993) 2135.
[6] H. Yamamoto, S. Funato, T. Sugiyama, J. Opt. Soc. Am. B 14
(1997) 1099.
[7] Y. Kitaoka, T. Sasaki, S. Nakai, Y. Goto, Appl. Phys. Lett. 59
(1991) 19.
[38] G.R. Clark, G. Palennik, J. Crystal Struct. Commun. 9 (1980)
499.
[8] H. Minemoto, Y. Ozaki, N. Sonoda, T. Sasaki, Appl. Phys. Lett.
63 (1993) 3565.
[39] J.S. Case, M.V. Castone, M.C. Rodriguez-Arguelles, A. Sanchez,
J. Sordo, J. Chem. Soc., Dalton Trans. (1993) 1253.
[40] M.B. Freeari, G.G. Fava, M. Lanfranchi, C. Pelizzi, P. Tarasconi,
J. Chem. Soc., Dalton Trans. (1991) 1951.
[9] S.R. Marder, J.W. Perry, W.P. Schaefer, Science 245 (1989) 626.
[10] U.B. Ramabadran, A.L. McPherson, D.E. Zelmon, J. Appl. Phys.
76 (1994) 1150.
[41] M.J.S. Dewar, W.J. Thiel, J. Am. Chem. Soc. 99 (1977) 4907.
[42] J.J.P. Stewart, J. Comp. Chem. 10 (1989) 209.
[43] J.J.P. Stewart, QCPE Program 455, 1983; Version 6.0, 1990.
[11] N.J. Long, Angew. Chem., Int. Ed. Engl. 34 (1995) 21.
[12] C. Dhenaut, I. Ledoux, I.D.W. Saue, J. Zyss, Nature 374 (1995)
339.