Syntheses, characterizations and third-order NLO properties of a series of Ni(II), Cu(II) and Zn(II) complexes using a novel S-benzyldithiocarbazate ligand

Article abstract of DOI:10.1016/j.poly.2016.09.025

A novel dithiocarbazate derivative ligand based on triphenylamine with D-π-A model (HL) and its corresponding transition metal complexes were designed, synthesized and fully characterized. The crystal structures of NiL₂and CuL₂have been confirmed by single crystal X-ray diffraction analysis, indicating that the coordinates to metal-ion to form a five-membered chelated ring with an excellent square-planar conformation, which further form high electron delocalization. Crystal structure determination also confirmed that the structures of NiL₂and CuL₂are isostructural. Open and closed aperture Z-scan measurements were devoted to explore the third-order nonlinear optical (NLO) properties with the aid of femtosecond pulse laser from 680 to 1080 nm. The results revealed that complexes NiL₂and CuL₂possessed large 2PA cross-sections 11235.33 and 12018.99 GM, as well as optical power limiting properties.

Full text of DOI:10.1016/j.poly.2016.09.025

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Polyhedron 121 (2017) 53–60
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Syntheses, characterizations and third-order NLO properties
of a series of Ni(II), Cu(II) and Zn(II) complexes using a novel
S-benzyldithiocarbazate ligand
Hui Liu a,1, Liangtao Wu a,1, Fei Li a, Xingyu Wang a, Hui Pan a, Yanhan Ni a, Jiaxiang Yang a, Shengli Li a,
Yupeng Tian a,b, , Jieying Wu a,
⇑
⇑
a Department of Chemistry, Key Laboratory of Functional Inorganic Materials Chemistry of Anhui Province, Anhui University, Hefei 230601, PR China
b State Key Laboratory of Coordination Chemistry, 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:
Received 4 August 2016
Accepted 13 September 2016
A novel dithiocarbazate derivative ligand based on triphenylamine with D-p-A model (HL) and its corre-
sponding transition metal complexes were designed, synthesized and fully characterized. The crystal
structures of NiL2 and CuL2 have been confirmed by single crystal X-ray diffraction analysis, indicating
that the coordinates to metal-ion to form a five-membered chelated ring with an excellent square-planar
conformation, which further form high electron delocalization. Crystal structure determination also con-
firmed that the structures of NiL2 and CuL2 are isostructural. Open and closed aperture Z-scan measure-
ments were devoted to explore the third-order nonlinear optical (NLO) properties with the aid of
femtosecond pulse laser from 680 to 1080 nm. The results revealed that complexes NiL2 and CuL2 pos-
sessed large 2PA cross-sections 11235.33 and 12018.99 GM, as well as optical power limiting properties.
Ó 2016 Elsevier Ltd. All rights reserved.
Keywords:
S-benzyldithiocarbazate ligand
Ni(II), Cu(II) and Zn(II) complexes
Z-scan technique
Third-order nonlinear
Optical limiting
1. Introduction
be of practical interest with applications ranging from anticancer
agent [13], catalysis [14], diagnostic imaging [15,16], bioimaging
Nonlinear optical (NLO) materials have attracted great interests
due to their applications in signal processing [1–3], ultrafast opti-
cal communication, data storage, optical limiting [4,5], optical
switching [6–8], logic devices, bioimaging [9,10] etc. Therefore, a
variety of new NLO materials were designed and synthesized to
meet the applications. Generally, NLO materials can be classified
as, inorganic, organic, polymer, hybrid and metal complex [11,12]
materials, among which the metal complexes were paid high
attention due to the combination of advantages of both inorganic
and organic materials. Furthermore, with the developments of
optoelectronic technique and practical applications of NLO materi-
als, novel NLO material design and synthesis were concentrated on
the ultrafast optical communication and optical limiting within
near-infrared region.
[17–19], inhibitor and chemosensors [20]. The metal complexes
always benefit from particularities of the five-membered chelated
ring [21] using S, N coordinated atoms, whose unique and fascinat-
ing moieties bring obvious delocalization effect, also make the
structure much more stable as far as the whole molecule is
concerned.
Considering above, we first rationally synthesized a novel
ligand HL (as shown in Scheme 1) and their complexes ML2
(M = Ni, Cu and Zn) (as shown in Scheme 2). Specifically, this idea
was based on the following considerations: (1) triphenylamine
containing conjugated system, bearing favorable optical properties
and having potential applications as an electron donor, meantime,
diethoxyl possesses synergistic effect for enhancing electron-
donating [22]; (2) S-benzyldithiocarbazate unit has strong coordi-
nation activity with transition metal ions to develop stable com-
Dithiocarbazate and thiocarbazone derivative ligands contain-
ing S, N atoms and their transition-metal complexes, remain to
plexes, forming a long
p-conjugated system after deprotonation
[23]; (3) Ni(II), Cu(II) and Zn(II) can arouse stronger charge transfer
within the metal complexes [24–25]. As a systematic work, near-IR
nonlinear optical properties should be investigated by the Z-scan
technique. Finally, optical limiting effects in near-infrared region
were also been observed.
⇑
Corresponding authors at: Department of Chemistry, Key Laboratory of
Functional Inorganic Materials Chemistry of Anhui Province, Anhui University,
Hefei 230601, PR China (Y. Tian).
E-mail addresses: yptian@ahu.edu.cn (Y. Tian), jywu1957@163.com (J. Wu).
Hui Liu and Liangtao Wu contributed equally to this work.
1
http://dx.doi.org/10.1016/j.poly.2016.09.025
0277-5387/Ó 2016 Elsevier Ltd. All rights reserved.

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54
H. Liu et al. / Polyhedron 121 (2017) 53–60
Scheme 1. Synthetic routes for ligand HL.
Scheme 2. Synthetic routes for the Ni(II), Cu(II) and Zn(II) complexes.
2.2.2. Synthesis of benzyl hydrazinecarbodithioate
2. Experimental
KOH (11.4 g, 200 mmol) was dissolved in 70 mL 90% ethanol
solution, 10.0 g (312 mmol) of hydrazine hydrate was added. In
the ice-bath, when CS2 (15.2 g, 200 mmol) was dropped, the mix-
ture was kept in 0 °C, and obtained the yellow oil in the bottom.
It was then separated and dissolved into 60 mL 40% cold ethanol.
Benzyl chloride (25.0 g, 197 mmol) was added dropwise with ice-
cooling. When white solid precipitated it was filtered, washed
and recrystallized by benzene.
2.1. Materials and instruments
All chemicals were commercially available and all solvents
were purified by conventional methods before use. Elemental anal-
yses were performed with a Perkin Elmer 240C elemental analyzer.
The 1H NMR spectra were recorded at 25 °C on a Bruker Avance
400 M spectrometer, and the chemical shift are reported as parts
per million from TMS (d). Coupling constants J are given in Hertz
(Hz). Mass spectra were acquired on a Micromass GCT-MS (EI
source). Fourier transform infrared spectra (FT-IR) were recorded
2.2.3. Synthesis of benzyl 2-(4-(bis(4-ethoxyphenyl)amino)
benzylidene)hydrazine-carbodithioate (HL)
on
a
NEXUS-870 (Nicolet) spectrophotometer in the
A mixture of hydrazinecarbodithioate (4.12 g, 20.8 mmol) and
4-(bis(4-ethoxyphenyl)amino)benzaldehyde (7.51 g, 20.8 mmol)
in 40 mL ethanol, refluxed for 3 h. Upon cooling down, suction-fil-
tration and recrystallization, yellow crystals were obtained as pro-
duct 9.11 g, yield 81%. Anal. Calc. for C31H31N3O2S2: C, 68.73; H,
5.77; N, 7.76. Found: C, 68.65; H, 5.92; N, 7.78%. IR (KBr, cmꢀ1):
3258(m), 2977(m), 1594(s), 1504(s), 1476(s), 1431(w), 1391(w),
1320(m), 1292(m), 1240(s), 1172(m), 1114(m), 1045(s), 829(s),
706(m); 1H NMR (400 MHz, CDCl3) d 10.16 (s, 1H), 7.72 (s, 1H),
7.43 (dd, J = 14.6, 7.9 Hz, 4H), 7.37–7.18 (m, 4H), 7.05 (d,
J = 8.8 Hz, 4H), 6.82 (dd, J = 8.6, 5.7 Hz, 5H), 4.54 (s, 2H), 4.01 (q,
J = 7.0 Hz, 4H), 1.41 (t, J = 7.0 Hz, 6H). MALDI-TOF: m/z, cal:
541.73, found: 542.67 [M+H]+, 361.26.
4000–50 cmꢀ1 region (mid-IR: 4000–400 cmꢀ1
, with powder
sample on KBr plate; far-IR: 600–50 cmꢀ1, with powder sample
on PE film stained with paroline). UV–Vis absorption spectra were
recorded on a UV-265 spectrophotometer. Fluorescence measure-
ments were carried out by
spectrophotometer.
a Hitachi F-7000 fluorescence
2.2. Synthesis of target molecules
2.2.1. Preparation of HL
Compounds 1 and 2 were synthesized according to reported
methods [26].

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H. Liu et al. / Polyhedron 121 (2017) 53–60
55
2.2.4. Preparation of complexes ML2 (M = Ni, Cu and Zn)
up to energy of about 5 eV, were taken into account for the calcu-
lation of the absorption spectra.
1.0 mmol ligand (HL) was added into the 20 mL ethanol solu-
tion of 0.5 mmol M(OAc)2, then refluxed for 4 h. After cooling to
room temperature, filtered and washed with ethanol for three
times, dry product was obtained in vacuum.
2.5. Third-order nonlinear optical properties
Synthesis of complex NiL2, a brown power with a yield of 85%.
Anal. Calc. for C62H60NiN6O4S4 (1140.13): C, 65.31; H, 5.30; N,
7.37. Found: C, 65.35; H, 5.32; N, 7.36%. Found: C, 65.35; H, 5.32;
N, 7.36%. IR (KBr, cmꢀ1): 2978(s), 2931(s), 1599(m), 1566(w),
1504(w), 1435(m), 1323(m), 1244(w), 1182(m), 1026(m), 960
(m), 823(m), 710(s), 582(s), 523(s). MALDI-TOF: m/z, cal:
1140.13, found: 1139.29 [M+].
Synthesis of complex CuL2, a brown power with a yield of 85%.
Anal. Calc. for C62H60CuN6O4S4 (1144.98): C, 65.04; H, 5.28; N,
7.34. Found: C, 65.10; H, 5.25; N, 7.36%; IR (KBr, cmꢀ1): 2978(s),
1601(m), 1570(w), 1504(w), 1468(w), 1433(m), 1387(m), 1302
(m), 1242(w), 1174(m), 1119(m), 1026(m), 960(m), 858(s), 825
(m), 725(s), 579(m), 526(s). MALDI-TOF: m/z, cal: 1144.98, found:
1143.27 [M+].
NLO properties were measured by the Z-scan technique with a
femtosecond laser pulse and Ti: 95 Sapphire System (680–
1080 nm, 80 MHz, 140 fs, Chameleon II) as the light source. The
beam was spatially filtered to remove higher-order modes and
tightly focused using a 5 cm focal length lens. The incident average
power of 100 mW was adjusted by a Glan prism. The thermal heat-
ing of the sample with high repetition rate laser pulse was
removed by the use of a mechanical chopper running at 10 Hz. A
1 mm cell of the sample in CH2Cl2 at 1.0 ꢁ 10ꢀ3ꢂmolꢂLꢀ1 was put
in the light path, and all measurements were carried out at room
temperature.
3. Results and discussion
Synthesis of complex ZnL2, a brown power with a yield of 85%.
Anal. Calc. for C62H60ZnN6O4S4: C, 64.93; H, 5.27; N, 7.33. Found:
C, 64.96; H, 5.28; N, 7.38%. IR (KBr, cmꢀ1): 2970(s), 1577(m),
1504(w), 1475(m), 1387(m), 1234(m), 1242(w), 1176(m), 1115
(m), 1045(m), 951(m), 825(m), 698(s), 604(s), 525(s). MALDI-
TOF: m/z, cal: 1146.84, found: 1145.29 [M+].
3.1. Synthesis and characterizations
As illustrated in the Schemes 1 and 2, through a series of steps,
namely, substitution, coupling, Vilsmier-Haack reaction and con-
densation of amino with aldehyde group, the ligand was synthe-
sized and a series of complexes were obtained by coordination
with metal ions. When it coordinated to the metal ion, five-mem-
bered chelated ring were constructed by the deprotonation, as rep-
resented in the single crystal structures of NiL2 and CuL2. The other
characterization data like 1H NMR, 13C NMR, IR and MALDI-TOF
could also confirmed. For the free ligand HL, 1H NMR spectral data
shows that a single peak (d = 7.72) appeared, indicating hydrogen
in vinyl group. The MALDI-TOF gives the found peak at 542.67
for [M+H]+, compared with the calculation at 541.73. The com-
plexes NiL2, CuL2 and ZnL2, which have been proved by the
MALDI-TOF, show peaks at 1139.29 [M+] (1140.13 calculated),
1143.27 [M+] (1144.98 calculated) and 1145.29 [M+] (1146.84 cal-
culated), respectively.
2.3. Crystal structure determination
The X-ray diffraction measurements were performed on a Bru-
ker SMART CCD area detector using graphite monochromated Mo
Ka
radiation (k = 0.71069 Å) at 298(2)K. Intensity data were col-
lected in the variable -scan mode. The structures were solved
x
by direct methods and difference Fourier syntheses. The non-
hydrogen atoms were refined anisotropically and hydrogen atoms
were introduced geometrically, and calculations were performed
with SHELXTL-97 program package.
2.4. TD-DFT studies
Thermostability properties were studied by the thermo-
gravimetry (TG) and derivative thermogravimetry (DTG) methods
from 20 to 800 °C with flowing N2 atmosphere. Fig. 1 shows the
TG and DTG curves, indicating that the decomposition temperature
of 10 wt% loss is 203.0 °C (HL), 256.3 °C (NiL2), 231.1 °C (CuL2),
238.0 °C (ZnL2). At 550 °C, the ligand and its complexes remain
33.3% (HL), 38.9% (NiL2), 40.9% (CuL2), 38.4% (ZnL2), respectively.
In summary, the TG and DTG data of the complexes much highly
exceed that of their free ligand, which mainly derive from the sta-
bility of five-chelated ring after complexation; the thermal stabili-
ties of all the three complexes exceed that of the ligand largely, and
among them, NiL2 behaves the best. Probably the biggest is that d8
Optimizations were carried out with B3LYP LANL2DZ without
any symmetry restraints, and the TD-DFT (B3LYP LANL2DZ) calcu-
lations were performed on the optimized structure. All calcula-
tions, including optimizations and TD-DFT, were performed with
the G03 software [27]. Geometry optimization of the singlet
ground state and the TD-DFT calculation of the lowest 25 sin-
glet–singlet excitation energies were calculated with a basis set
composed of 6-31G for C, H, N, O, S atoms and the Lanl2dz basis
set for the Cu and Ni atoms was download from the EMSL basis
set library. The lowest 25-spin allowed singlet–singlet transitions,
Fig. 1. TG diagrams (a) and DTG diagrams (b) of HL, NiL2, CuL2 and ZnL2.

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56
H. Liu et al. / Polyhedron 121 (2017) 53–60
Table 1
Crystal data and structure refinements for NiL2 and CuL2.
Comp
NiL2
CuL2
CCDC No.
1413276
C62H60NiN6O4S4
2221.61
293(2)
1497451
C62H60CuN6O4S4
1144.94
Empirical formula
Formula weight
T (K)
293(2)
Crystal system
Space group
Crystal size (mm)
a (Å)
b (Å)
c (Å)
triclinic
P1
triclinic
P1
ꢀ
ꢀ
0.30 ꢁ 0.20 ꢁ 0.20
7.586(5)
13.251(9)
15.625(11)
76.485(9)
84.076(9)
75.232(9)
1475.12
0.30 ꢁ 0.20 ꢁ 0.20
7.584(3)
13.557(4)
14.445(5)
87.204(4)
86.498(4)
75.938(4)
1437.1(8)
1
a
(°)
b (°)
c
(°)
V (Å3)
Z
1
Dcalc (Mg mꢀ3
)
1.283
0.522
1.323
0.578
(mmꢀ1
)
Fig. 2. Crystal structure of the complex NiL2.
l
F(000)
598
599
Final R indices [I > 2
r
(I)]
R1 = 0.0689,
wR2 = 0.2101
R1 = 0.0785,
wR2 = 0.2334
0.968
Goodness-of-fit (GOF) on 1.166
F2
and conjugation of metal complexes are also designed to expect
beneficial NLO properties.
3.3. Linear optical properties and theoretical calculation
UV-Vis absorption spectra of HL and its complexes in ethyl acet-
ate are shown in the Fig. 4. UV–Vis absorption spectra of the four
compounds in varied solvents are exhibited in Fig. S1 and
Table S2 to further explore the solventchromism. From the Fig. 4,
NiL2 shows three bands while the others two bands. Comparing
the free ligand (HL) with its complexes, it is obviously observed
that the spectra of the complexes displayed the red-shift after
complexation. For detailed comparison of the spectra, shapes of
CuL2 and ZnL2 are resemble, and absorbance intensity of ZnL2 is
quite lower than that of CuL2 (Fig. S1). In addition, fluorescence
spectra of the compounds HL, NiL2, CuL2 and ZnL2 are shown in
Fig. S3.
Fig. 3. Crystal structure of the complex CuL2.
configuration of nickel(II) complex would be more stability when
applying tetra-coordinate mode with square plane construction.
To further investigate the molecular energy levels, theoretical
calculations were carried out. Electron distributions of the HOMO
and LUMO energy levels of NiL2 and CuL2 are shown in Fig. 5. As
listed in Table 2, the band at 463.2 nm of NiL2 can be attributed
3.2. Crystal structural descriptions
As shown in Figs. 2 and 3, the metal center possessed a distorted
square-planar coordination with centrosymmetrical geometry, the
ethoxy group (O1C22C23) was minor disorder and was refined
over two sites with partial occupancies in the ratio 0.50:0.50 in
the structure. The crystal data collections and refinement parame-
ters are listed in Table 1, which explicate that both complexes are
to the d
from metal ion d
phenyl ring. The absorbance at 417.8 nm of NiL2 is ascribed to
the
p⁄ ICT (H-1 ? L) transition, in which charge mobility is
p ?
p⁄ MLCT (H ? L + 1) transition, where the charge move
p
to the p⁄ level located in the bridge-linked
p
?
ꢀ
from the ethoxphenyl moieties to the chelated ring. Similarity
crystallized in a triclinic crystal system with the space group P1,
can be found in that of CuL2, where 424.3 nm also come from the
the selected bond lengths, bond angles and dihedral angles are
listed in Table S1. The N and S atoms from the ligand coordinate
to the metal ion to form a five-member chelated ring after depro-
tonation. The coordinated bond lengths of Ni–N and Ni–S are 1.935
(6) Å and 2.181(2) Å, Cu–N and Cu–S are 2.019(5) Å and 2.251(16)
Å, whose length range locates between normal C–N single and
double C@N bonds, indicating highly delocalization parts within
the metal complex molecules. The angles of S(1)–Ni(1)–N(2) is
85.62(16)°, S(1)–Ni(1)–S(1), 180.00° and N(2)–Ni(1)–N(2),
180.00°, S(1)–Cu(1)–N(2) is 84.46(12)°, S(1)–Cu(1)–S(1), 180.00°
and N(2)–Cu(1)–N(2), 180.00°, suggesting coplanar and distorted
square-planar coordination.
character
p ?
p⁄ ICT (H-1 ? L), with the same mobility of NiL2.
In summary, the calculations are correspondence with those from
above experiments.
3.4. Third-order nonlinear optical properties
The third-order NLO properties of complexes NiL2, CuL2 and
ZnL2 were investigated by the Z-scan technique with tunable fem-
tosecond laser system. While no NLO appearance has been found
with HL in the same measure condition, which imply that signifi-
cant increase of 2PA cross-section exist from the ligand to its com-
plexes. That may attribute to delocalization in the whole
molecules. Data from open aperture and closed aperture with solu-
tions of the three complexes are represented in the Fig. 5. As to all
compounds, the NLO response depends on the wavelength of laser,
On the one hand, triphenylamine is typical of electron-rich con-
jugated system, with remarkable electron-donating ability; on the
other hand, the propeller triphenylamine structure impedes the
accumulation of
p–p intermolecular. Therefore, the coplanarity