Synthesis, characterization, and nonlinear optical responses of nickel(ii) complexes with phenanthroline-based ligands

Article abstract of DOI:10.1080/00958972.2013.805322

Three nickel(II) complexes with phenanthroline-based ligands were synthesized and characterized by UV-visible, IR, MS, and elemental analysis. Their off-resonance third-order nonlinear optical (NLO)properties were measured using a femtosecond laser and th

Full text of DOI:10.1080/00958972.2013.805322

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Synthesis, characterization, and
nonlinear optical responses of nickel(II)
complexes with phenanthroline-based
ligands
Zhi-Bin Cai a , Li-Fen Liu a , Yu-Qian Hong a & Mao Zhou b
a College of Chemical Engineering and Materials Science ,
Zhejiang University of Technology , Hangzhou , P.R. China
b Zhejiang Poly Pharmaceutical Co. Ltd. , Hangzhou , P.R. China
Published online: 17 Jun 2013.
To cite this article: Zhi-Bin Cai , Li-Fen Liu , Yu-Qian Hong & Mao Zhou (2013) Synthesis,
characterization, and nonlinear optical responses of nickel(II) complexes with phenanthroline-based
ligands, Journal of Coordination Chemistry, 66:13, 2388-2397, DOI: 10.1080/00958972.2013.805322
To link to this article: http://dx.doi.org/10.1080/00958972.2013.805322
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Journal of Coordination Chemistry, 2013
http://dx.doi.org/10.1080/00958972.2013.805322
Synthesis, characterization, and nonlinear optical responses
of nickel(II) complexes with phenanthroline-based ligands
ZHI-BIN CAI*†, LI-FEN LIU†, YU-QIAN HONG† and MAO ZHOU‡
†College of Chemical Engineering and Materials Science, Zhejiang University
of Technology, Hangzhou, P.R. China
‡Zhejiang Poly Pharmaceutical Co. Ltd., Hangzhou, P.R. China
(Received 8 November 2012; in final form 18 April 2013)
Three nickel(II) complexes with phenanthroline-based ligands were synthesized and characterized
by UV–visible, IR, MS, and elemental analysis. Their off-resonance third-order nonlinear optical
(NLO)properties were measured using a femtosecond laser and the degenerate four-wave mixing
technique. The third-order NLO susceptibilities χ(3) were 3.45–4.37 ꢀ 10ꢁ13 esu. The second-order
hyperpolarizabilities γ of the molecules were 3.46–4.36 ꢀ 10ꢁ31 esu. The response times were
50–74 fs. The influence of the molecular structure on the third-order optical nonlinearity was
analyzed. The results show that highly polarizable delocalized π-conjugated electron system is the
key factor leading to strong third-order optical nonlinearity.
Keywords: Nonlinear optics; DFWM technique; Nickel(II) complex; Synthesis
1. Introduction
Third-order nonlinear optical (NLO) materials have been the focus of research from both
fundamental and practical points of view for the possibility of their applications in the
domain of optoelectronics and photonics. A variety of materials have been investigated for
third-order nonlinear optics, among which organometallic and coordination materials are
especially interesting because compared with purely organic materials, they offer additional
effects on the NLO responses by introducing variations on the nature, the oxidation state,
and coordination sphere of the metal, as well as on the characteristics of the attached
ligands [1–8].
Third-order optical nonlinearities in organic materials usually arise from the delocalized
π-conjugated electron systems [9–14]. Thus, coordination to a metal of π-conjugated organic
molecules may produce a significant increase in their hyperpolarizabilities γ due to the
extensive electronic delocalization and polarization. 1,10-Phenanthroline (phen) is a classic
chelating bidentate ligand for transition metal ions with a rigid, planar, hydrophobic, and
electron-poor π-conjugated system. Taking advantage of these structural features, metal com-
plexes with phen-based ligands have been actively studied for their catalytic, redox, photo-
chemical, and photophysical properties [15–19]. They have very important applications to
*Corresponding author. Email: caizbmail@126.com
Ó 2013 Taylor & Francis

Nickel(II) complexes
2389
molecule/ion recognition and sensing [20, 21], DNA binding/cleavage [22, 23], molecular
self-assembling [24, 25], etc. Recent studies also indicate that some metal complexes with
phen-based ligands are promising candidates for NLO materials. However, the vast majority
of such studies have focused on quadratic optical nonlinearities [26–30] and, to a far lesser
extent, on third-order responses.
The nickel ion has an unfilled d-electron shell, which allows the possibility of low
energy charge transfer transitions. Several studies show that as an excellent template, it
can gather π-conjugated organic molecules to form two-dimensional (2-D) or three-dimen-
sional (3-D) third-order NLO materials [31–38].
Based on the above consideration, in this paper, we selected phen, 2-(o-hydroxy-
phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (OHPIP), and 2-(p-hydroxyphenyl)-1H-
imidazo[4,5-f][1,10]phenanthroline (PHPIP) as ligands for Ni(II). Three nickel(II) com-
plexes, [Ni(phen)2OHPIP]2+ (1), [Ni(OHPIP)3]2+ (2), and [Ni(PHPIP)3]2+ (3), were
obtained (figure 1). Their structures were characterized by UV–visible, IR, MS, and ele-
mental analysis. By using a femtosecond laser, the off-resonance third-order optical nonlin-
earities of the complexes were measured with the degenerate four-wave mixing (DFWM)
technique. The results show that these complexes possess large and ultrafast third-order
NLO responses. The relationships between molecular structure and optical property were
analyzed. This is the first report on the NLO properties of these complexes and complexes
2 and 3 are new.
2. Results and discussion
2.1. Synthesis and characterization
The synthetic routes to 1–3 are outlined in scheme 1.
Imidazole syntheses employing 1,2-diamino compounds are widely used, but in this
paper, the imidazoles (OHPIP, PHPIP) were prepared from α-diketone by its reaction with
aldehydes and ammonium acetate in glacial acetic acid. Ammonium acetate serves as the
source of ammonia. The initial reaction is the formation of 1,10-phenanthroline-5,6-dii-
mine, which then undergoes an aldol-type condensation with o(p)-hydroxybenzaldehyde.
This is followed by 1,5-hydrogen shift and subsequent loss of water to form the desired
imidazoles.
The nickel(II) complexes were synthesized by the reaction of NiCl2·6H2O with the cor-
responding ligands (phen, OHPIP, and PHPIP), in the appropriate molar ratios, using
methanol as solvent. They were isolated as perchlorates and purified by recrystallization in
relatively high yield. The elemental analyses of these complexes were in agreement with
their molecular formulas. The strong stretching absorption around 1110 cmꢁ1 in FTIR
spectra indicated the existence of ClO4ꢁ. In the ESI-MS spectra, both signals [M–2ClO4]2+
and [M–2ClO4–H]+ were observed. Their values were consistent with the expected molec-
1
ular weights. Due to their paramagnetic properties, 1–3 could not be characterized by H
NMR spectra.
2.2. Absorption spectra
UV–visible absorption spectra of 1–3 and the ligands (OHPIP, PHPIP) in DMF are
displayed in Supplementary material. The maximum absorption peaks are at 274, 279, and
290 nm for 1–3, respectively, attributed to intraligand π–π⁄ transitions. The band at 330 nm

2390
Z.-B. Cai et al.
2+
N
HO
N
N
N
N
Ni
N
N
H
N
1
NH
HO
N
2+
N
HO
N
N
N
N
N
Ni
N
H
N
N
NH
HO
2
HO
NH
N
N
2+
N
N
N
N
N
OH
Ni
N
H
N
N
NH
3
HO
Figure 1. Structures of the nickel(II) complexes 1–3.

Nickel(II) complexes
2391
HO
OH
N
N
CHO
O
N
O
N
NH4Ac / HAc
N
H
N
OHPIP
N
N
HO
CHO
OH
NH4Ac / HAc
N
H
N
PHPIP
phen
[ Ni(phen)2OHPIP ] 2+
OHPIP
1
[ Ni(OHPIP)3 ] 2+
OHPIP
PHPIP
.
NiCl2 6H2O
2
[ Ni(PHPIP)3 ] 2+
3
Scheme 1. Synthesis of 1–3.
for 1 and 2 is related to ligand-to-ligand charge transfer (LLCT); 3 shows only a weak
LLCT shoulder at 400 nm. Above 500 nm, they are essentially transparent. The laser wave-
length (800 nm) used in DFWM is out of the absorption region. Thus their off-resonance
third-order optical nonlinearities can be measured. A good nonlinearity–transparency trade-
off which is very important for practical applications of NLO materials is obtained.
2.3. Third-order NLO properties
The third-order NLO susceptibility χ(3) is measured via comparison with that of a reference
sample CS2, calculated from the DFWM signal (I), the linear refractive index (n), the
sample thickness (L), and absorption correction factor using the following equation [39]:

2392
Z.-B. Cai et al.
ꢀ ꢁ
ꢀ ꢁ
Is 1=2Lr ns 2 aL expðaL=2Þ
vðs3Þ
¼
vðr3Þ
ð1Þ
Ir
Ls nr 1 ꢁ expðꢁaLÞ
where the subscripts “s” and “r” represent the parameters for the sample and CS2, and α
aL expðaL=2Þ
indicates the linear absorption coefficient. The fraction
comes from the sample
1ꢁexpðꢁaLÞ
absorption and equals approximately 1, while the sample has little absorption around the
employed laser wavelength. The values of χr(3) and nr for CS2 are 6.7 ꢀ 10ꢁ14 esu and
1.632, respectively [40].
The second-order hyperpolarizability γ of a molecule in isotropic media is related to the
solution χ(3) by [41]:
c ¼ vð3Þ=Nf 4
ð2Þ
where N is the number density of the solute per milliliter, related to the molar concentra-
tion c by N = NAc with NA being Avogadro’s number; f 4 is the local field correction factor
which is [(n2 + 2)/3]4 (n is the linear refractive index of solution, measured by 2WAJ Abbe
refractometer).
The dependence of DFWM signal intensity on the delay time of the input beam is
shown in figure 2. The curves are obtained via fitting the time convolution between auto-
ꢂ
ꢃ
t
correlation function of pulse and single exponent decline function exp
. The fitting
ꢁT2
expressions are shown in equation (3) and equation (4). The response times of the samples
can be obtained from figure 2.
ꢀ
ꢁ
4 ln 2t2
T2
IðtÞ ¼ exp ꢁ
ð3Þ
ð4Þ
ꢀ
ꢁ
Z
Z
t
SðsÞ ¼ exp ꢁ
dt
Iðt ꢁ t0ÞIðtÞdt0
T2
The values of χ(3), γ, and response times for the samples are deduced and calculated
from the experimental results which are listed in table 1. From table 1 and it is found that
1–3 show large second-order molecular hyperpolarizabilities γ, on the order of 10ꢁ31 esu,
which are comparable with those of some known NLO organometallic and coordination
materials [42–47].
For 1, Ni(II) is six-coordinate octahedral, ligated by six nitrogens from two phen and
one OHPIP. OHPIP consists of imidazole-fused phen and o-hydroxyphenyl radical in the
2-position. Phen possesses a planar and rigid π-conjugated electron system, which can be
polarized in the light induction and exhibits a relatively large γ of 1.76 ꢀ 10ꢁ31 esu [48].
The γ value of 1 is approximately twice that of phen, mainly due to the incorporation of
Ni(II) with an open d-shell involving low energy charge transfer transitions. The d orbitals
interact strongly with π-electron orbitals of the ligands, resulting in a larger polarizable
system and better NLO responses.
Compared with 1, 2 and 3 feature extended π-conjugated ligands containing three
2-(hydroxyphenyl)imidazole-fused phen units rather than one. The electron-donating
hydroxy on the benzene ring can effectively push electrons onto the ring system. Such

Nickel(II) complexes
2393
6
5
4
3
2
1
1
2
3
0
-150
-100
-100
-100
-50
-50
-50
0
50
50
50
100
100
100
150
150
150
Time delay (fs)
7
6
5
4
3
2
1
0
-150
0
Time delay (fs)
7
6
5
4
3
2
1
0
-150
0
Time delay (fs)
Figure 2. DFWM signal vs. delay time for 1–3 in DMF solution.

2394
Z.-B. Cai et al.
Table 1. The values of χ(3), γ, and response times for 1–3.
Sample
n
χ(3) (10ꢁ13 esu)
γ (10ꢁ31 esu)
Response time (fs)
1
2
3
1.4308
1.4326
1.4325
3.45
4.37
4.03
3.46
4.36
4.02
50
64
74
extended π-conjugated ligands with acceptor and donor, strengthen intramolecular charge
transfer, and hence lead to higher γ values.
Comparison of γ value for 2 with that for 3 indicates that the position of hydroxy affects
the NLO responses. For OHPIP, the benzene ring is almost coplanar with the imidazole
ring owing to the formation of an intramolecular hydrogen bond between the ortho
hydroxy and nitrogen of the imidazole ring. The extended coplanarity facilitates electronic
communication and charge transfer transitions, so the γ value of 2 with OHPIP is larger
than that of 3 with PHPIP.
Normally, the time domain response of the sample should contain several processes of
different time scales. The third-order NLO response time induced by delocalized electrons
is believed to be 10ꢁ14–10ꢁ15 s. The response time induced by molecular reorientation is
10ꢁ11–10ꢁ12 s, that induced by electrostriction is 10ꢁ8–10ꢁ9 s and that induced by
heat absorption is 10ꢁ1–10ꢁ7 s. From figure 2, we obtain the response times of 1–3 to be
50–74 fs, which is commonly accepted to be the contribution from transient motion of the
π-conjugated electron distribution.
3. Conclusions
Three nickel(II) complexes with phen-based ligands were synthesized and characterized by
UV–visible, IR, MS, and elemental analysis. Their off-resonance third-order NLO proper-
ties were investigated by DFWM with the laser duration of 80 fs at 800 nm. The large and
ultrafast NLO responses for these complexes are due to highly polarizable electronic
networks in their delocalized π-conjugated systems. In addition, they are also transparent
and stable, thereby making them promising candidates for NLO materials.
4. Experimental
4.1. Materials
1,10-Phenanthroline-5,6-dione was prepared according to the literature method [49]. Other
materials were commercially available and of reagent grade. All of them were used
without purification.
4.2. Physical measurements
1
FTIR spectra were recorded on a Vector 22 spectrometer using KBr pellets. H NMR spec-
tra were collected on an AVANCE III 500 MHz apparatus, with TMS as internal standard

Nickel(II) complexes
2395
and DMSO-d6 as solvent. UV–visible spectra were recorded on a Shimadzu UV-2550
UV–visible spectrometer. Elemental analyses were conducted on a Thermo Finnigan Flash
EA 1112 apparatus. Mass spectra were taken on a Therm LCQ TM Deca XP plus ion trap
mass spectrometer instrument. Melting points were measured on an X-4 micromelting
point apparatus without correction.
4.3. Synthesis
4.3.1. 2-(o-Hydroxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (OHPIP). A mix-
ture of 1,10-phenanthroline-5,6-dione (1.05 g, 5 mmol), o-hydroxybenzaldehyde (0.73 g,
6 mmol), ammonium acetate (7.7 g, 100 mmol), and glacial acetic acid (16 mL) was heated
under reflux with stirring for 3 h. The cooled solution was diluted with H2O and neutral-
ized with concentrated aqueous ammonia. The precipitate was collected and recrystallized
1
from DMF to give yellow granular crystals. Yield: 1.3 g, 83.3%. m.p. > 300 °C. H NMR
(500 MHz, DMSO-d6), δ (ppm): 13.98 (s, 1H), 12.75 (s, 1H), 9.09 (dd, 2H, J1 = 4.4 Hz,
J2 = 1.5 Hz), 8.98 (dd, 2H, J1 = 7.8 Hz, J2 = 1.5 Hz), 8.21–8.23 (m, 1H), 7.89 (dd, 2H,
J1 = 7.8 Hz, J2 = 4.4 Hz), 7.41–7.45 (m, 1H), 7.11–7.14 (m, 2H).
4.3.2. 2-(p-Hydroxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (PHPIP). This
ligand was synthesized as above using p-hydroxybenzaldehyde. The product was yellow
needle crystals. Yield: 1.35 g, 86.5%. m.p. > 300 °C (Lit. m.p. > 300 °C [50]). 1H NMR
(500 MHz, DMSO-d6), δ (ppm): 13.52 (s, 1H), 9.98 (s, 1H), 9.03 (dd, 2H, J1 = 4.4 Hz,
J2 = 1.5 Hz), 8.91 (dd, 2H, J1 = 8.8 Hz, J2 = 1.5 Hz), 8.12 (d, 2H, J = 7.8 Hz), 7.83 (dd, 2H,
J1 = 8.8 Hz, J2 = 4.4 Hz), 6.99 (d, 2H, J = 7.8 Hz).
4.3.3. [2-(1H-Imidazo[4,5-f][1,10]phenanthrolin-2-yl-κN7,κN8)phenol]bis(1,10-phena-
nthroline-κN1,κN10)-nickel(2+) (1). A mixture of nickel dichloride hexahydrate (0.24 g,
1 mmol), phen (0.4 g, 2.2 mmol), and methanol (20 mL) was heated under reflux with stir-
ring for 2 h. A solution of OHPIP (0.37 g, 1.2 mmol) in methanol (15 mL) was then added
and further stirred under reflux for 3 h. The reaction mixture was cooled to room tempera-
ture and a saturated aqueous sodium perchlorate solution was added. The precipitate was
collected and recrystallized from DMF twice to give a light yellow crystalline powder.
Yield: 0.67 g, 70.6%. FTIR (KBr), ν (cmꢁ1): 3431 (νNH, νOH), 3071 (ν=CH), 1626, 1515,
1485, 1409, 1102 (νClO4), 813 (δ=CH), 729 (δ=CH), 623 (δClO4). ESI-MS (CH3CN): m/z
728.9 ([M–2ClO4–H]+), 365.3 ([M–2ClO4]2+). Anal. Calc. for C43H28Cl2N8NiO9·H2O: C,
54.46; H, 3.19; N, 11.82. Found: C, 54.46; H, 3.58; N, 12.09%.
4.3.4. Tris[2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl-κN7,κN8)phenol]-nickel(2+)
(2). A mixture of nickel dichloride hexahydrate (0.24 g, 1 mmol), OHPIP (1.03 g,
3.3 mmol), and methanol (30 mL) was heated under reflux with stirring for 3 h. The reac-
tion mixture was cooled to room temperature and a saturated aqueous sodium perchlorate
solution was added. The precipitate was collected and recrystallized from DMF twice to
give a yellow crystalline powder. Yield: 0.78 g, 63.9%. FTIR (KBr), ν (cmꢁ1): 3435 (νNH
,
ν
OH), 3076 (ν=CH), 1627, 1514, 1485, 1409, 1120 (νClO4), 812 (δ=CH), 734 (δ=CH), 623
(δClO4). ESI-MS (CH3CN): m/z 993.5 ([M–2ClO4–H]+), 498.0 ([M–2ClO4]2+). Anal. Calc.

2396
Z.-B. Cai et al.
for C57H36Cl2N12NiO11·1.5H2O: C, 56.04; H, 3.22; N, 13.76. Found: C, 56.03; H, 3.43;
N, 13.48%.
4.3.5. Tris[4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl-κN7,κN8)phenol]-nickel(2+)
(3). This complex was synthesized using a procedure similar to that described for 2, with
PHPIP instead of OHPIP. The product was a yellow crystalline powder. Yield: 0.77 g,
61.7%. FTIR (KBr), ν (cmꢁ1): 3404 (νNH, νOH), 3080 (ν=CH), 1611, 1508, 1483, 1452,
1116 (νClO4), 813 (δ=CH), 734 (δ=CH), 624 (δClO4). ESI-MS (CH3CN): m/z 993.2 ([M–
2ClO4–H]+), 497.3 ([M–2ClO4]2+). Anal. Calc. for C57H36Cl2N12NiO11·3H2O: C, 54.83;
H, 3.39; N, 13.46. Found: C, 54.92; H, 3.04; N, 13.23%.
4.4. Nonlinear optical measurements
The third-order NLO properties were measured using femtosecond DFWM technique, with
a Ti: Sapphire laser. The pulse width was determined to be 80 fs on a SSA25 autocorrela-
tor. The operating wavelength was centered at 800 nm. The repetition rate of the pulses
was 1 kHz. During the measurement, the laser was very stable (rms < 0.1%). The input
beam was split into two beams k1 and k2 with nearly equal energy by using a beam split-
ter, then focused on the sample. The beam k2 passed through a delay line driven by a step-
ping motor in order that the optical path length difference between the k2 and k1 beams
could be adjusted during the measurement. The angle between the beams k1 and k2 was
about 5°. When k1 and k2 were overlapped spatially in the sample, the generated signal
beam k3 or k4 passed through an aperture, recorded by a photodiode and then analyzed by
a Lock-in amplifier and computer.
The experiments were performed at 22 °C. The samples dissolved in DMF at
5 ꢀ 10ꢁ4 mol Lꢁ1 were placed in a 1 mm thick quartz cell. The solvent DMF has no non-
linear signal under the light intensity adopted. So the third-order optical nonlinearities mea-
sured come from the complexes themselves.
Acknowledgment
We are grateful to the National Natural Science Foundation of China for financial support
(Grant No. 21103151).
References
[1] G. Li, Y.L. Song, H.W. Hou, L.K. Li, Y.T. Fan, Y. Zhu, X.R. Meng, L.W. Mi. Inorg. Chem., 42, 913 (2003).
[2] Z.B. Liu, Y. Zhu, Y.Z. Zhu, J.G. Tian, J.Y. Zheng. J. Phys. Chem. B, 111, 14136 (2007).
[3] Z.H. Chen, C. Zhong, Z. Zhang, Z.Y. Li, L.H. Niu, Y.J. Bin, F.S. Zhang. J. Phys. Chem. B, 112, 7387
(2008).
[4] C.E. Powell, M.P. Cifuentes, M.G. Humphrey, A.C. Willis, J.P. Morrall, M. Samoc. Polyhedron, 26, 284
(2007).
[5] R. Rangel-Rojo, K. Kimura, H. Matsuda, M.A. Mendez-Rojas, W.H. Watson. Opt. Commun., 228, 181
(2003).
[6] S. Kar, T.A. Miller, S. Chakraborty, B. Sarkar, B. Pradhan, R.K. Sinha, T. Kundu, M.D. Ward, G.K. Lahiri.
Dalton Trans., 3, 2591 (2003).
[7] H. Akdas-Kilig, J.P. Malval, F. Morlet-Savary, A. Singh, L. Toupet, I. Ledoux-Rak, J. Zyss, H.L. Bozec.
Dyes Pigm., 92, 681 (2011).
[8] H.S. Nalwa. Mater. Lett., 33, 23 (1997).

Nickel(II) complexes
2397
[9] C. Videlot-Ackermann, T. Isoshima, A. Yassar, T. Wada, H. Sasabe, D. Fichou. Synth. Met., 156, 154
(2006).
[10] S.C. Yin, H.Y. Xu, W.F. Shi, L. Bao, Y.C. Gao, Y.L. Song, B.Z. Tang. Dyes Pigm., 72, 119 (2007).
[11] D. Udayakumar, A.J. Kiran, A.V. Adhikari, K. Chandrasekharan, G. Umesh, H.D. Shashikala. Chem. Phys.,
331, 125 (2006).
[12] H.Y. Xu, S.C. Yin, W.J. Zhu, Y.L. Song, B.Z. Tang. Polymer, 47, 6986 (2006).
[13] J.M. Lu, S.J. Ji, N.Y. Chen, Z.R. Sun, X.L. Zhu, W.P. Shi, Z.G. Wang. J. Appl. Polym. Sci., 89, 2611
(2003).
[14] P. Poornesh, K. Ravi, G. Umesh, P.K. Hegde, M.G. Manjunatha, K.B. Manjunatha, A.V. Adhikari. Opt.
Commun., 283, 1519 (2009).
[15] A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser, A. Von Zelewsky. Coord. Chem. Rev., 84, 85
(1988).
[16] N. Armaroli. Chem. Soc. Rev., 30, 113 (2001).
[17] D.V. Scaltrito, D.W. Thompson, J.A. O’Callaghan, G.J. Meyer. Coord. Chem. Rev., 208, 243 (2000).
[18] J. Bossert, C. Daniel. Coord. Chem. Rev., 252, 2493 (2008).
[19] A. Lavie-Cambot, M. Cantuel, Y. Leydet, G. Jonusauskas, D.M. Bassani, N.D. McClenaghan. Coord. Chem.
Rev., 252, 2572 (2008).
[20] A. Chakraborty, R. Gunupuru, D. Maity, S. Patra, E. Suresh, P. Paul. Inorg. Chem. Commun., 13, 1522
(2010).
[21] X.Y. Xu, H.N. Xiao. J. Lumin., 132, 2251 (2012).
[22] P.K. Sasmal, A.K. Patra, A.R. Chakravarty. J. Inorg. Biochem., 102, 1463 (2008).
[23] Q.X. Wang, W.Q. Li, F. Gao, S.X. Li, J.C. Ni, Z.Y. Zheng. Polyhedron, 29, 539 (2010).
[24] R.F. D’Vries, N. Snejko, E. Gutiérrez-Puebla, M. Iglesias, M.A. Monge. Inorg. Chim. Acta, 382, 119 (2012).
[25] B. Das, J.B. Baruah. Polyhedron, 31, 361 (2012).
[26] A. Valore, M. Balordi, A. Colombo, C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, T. Benincori,
G. Rampinini, F. Sannicolò, F. Demartin. Dalton Trans., 39, 10314 (2010).
[27] C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, A. Valore, F. Demartin, F.D. Angelis, A. Sgamellotti,
S. Fantacci. Inorg. Chim. Acta, 361, 4070 (2008).
[28] A. Valore, E. Cariati, C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, F.D. Angelis, S. Fantacci,
A. Sgamellotti, A. Macchioni, D. Zuccaccia. Chem. Eur. J., 16, 4814 (2010).
[29] C. Dragonetti, S. Righetto, D. Roberto, R. Ugo, A. Valore, S. Fantacci, A. Sgamellotti, F.D. Angelis. Chem.
Commun., 4116, (2007).
[30] S. Das, A. Jana, V. Ramanathan, T. Chakraborty, S. Ghosh, P.K. Das, P.K. Bharadwaj. J. Organomet. Chem.,
691, 2512 (2006).
[31] X.B. Sun, Y.L. Wang, Q. Ren, F.J. Zhang, Y. Gao, H.L. Yang, L. Feng, X.Q. Wang, D. Opt. Materials, 29,
1305 (2007).
[32] H. Fukui, H. Nagai, R. Kishi, T. Minami, H. Takahashi, T. Kubo, M. Nakano. Synth. Met., 159, 2416
(2009).
[33] Y.Z. Gu, F.X. Gan, S.Q. Wang, H. Opt. Communications, 197, 501 (2001).
[34] Z.F. Dai, X.L. Yue, B.X. Peng, Q.G. Yang, X.C. Liu. Chem. Phys. Lett., 317, 9 (2000).
[35] P.F. Zhang, Y.M. Xu, F.T. Zheng, Y. Yang. Laser Technol., 30, 155 (2006).
[36] Y.H. Wang, X.A. Zhang, P.H. Cheng, Y.Z. Gu. J. Henan Univ. (Nat. Sci.), 34, 19 (2004).
[37] Z.Y. Tian, W.T. Huang, D.B. Xiao, S.Q. Wang, Y.S. Wu, Q.H. Gong, W.S. Yang, J.N. Yao. Chem. Phys.
Lett., 391, 283 (2004).
[38] J. Tedim, S. Patrício, R. Bessada, R. Morais, C. Sousa, M.B. Marques, C. Freire. Eur. J. Inorg. Chem., 2006,
3425 (2006).
[39] Y. Pang, M. Samoc, P.N. Prasad. J. Chem. Phys., 94, 5282 (1991).
[40] M.E. Orczyk, M. Samoc, J. Swiatkiewicz, P.N. Prasad. J. Chem. Phys., 98, 2524 (1993).
[41] B.K. Mandal, B. Bihari, A.K. Sinha, M. Kamath, L. Chen. Appl. Phys. Lett., 66, 932 (1995).
[42] X.B. Sun, X.Q. Wang, Q. Ren, G.H. Zhang, H.L. Yang, L. Feng. Mater. Res. Bull., 41, 177 (2006).
[43] H.L. Yang, X.Q. Wang, Q. Ren, G.H. Zhang, X.B. Sun, L. Feng, S.F. Wang, Z.W. Wang. Opt. Commun.,
256, 256 (2005).
[44] J. Lu, C.H. Lü, J.H. Yu, J.Q. Xu, Y. Li, X. Zhang, T.G. Wang, Q.X. Yang. Polyhedron, 23, 755 (2004).
[45] M.P. Cifuentes, C.E. Powell, M.G. Humphrey, G.A. Heath, M. Samoc, B. Luther-Davies. J. Phys. Chem. A,
105, 9625 (2001).
[46] Y.C. Liu, Y.H. Kan, S.X. Wu, G.C. Yang, L. Zhao, M. Zhang, W. Guan, Z.M. Su. J. Phys. Chem. A, 112,
8086 (2008).
[47] H. Xiang, Z.Y. Tian, S.F. Wang, Z.W. Wang, Z. Li, H. Yang, J.N. Yao, Q.H. Gong. Chin. Phys. B, 17, 2535
(2008).
[48] Z.B. Cai, M. Zhou. Chin. J. Inorg. Chem., 27, 2383 (2011).
[49] W. Paw, R. Eisenberg. Inorg. Chem., 36, 2287 (1997).
[50] H.S. Zhuang, C.H. Guo, P. Chen, Q.E. Wang, G.N. Chen. Chem. Reagents, 25, 325 (2003).