Structure and spectral properties of dinuclear zinc complex containing semicarbazonate ligands

Article abstract of DOI:10.1016/j.saa.2010.12.029

The dinuclear Zn²⁺ complex [Zn(HSSC)OAc]₂·2DMF (H₂SSC = salicylaldehyde semicarbazone; HOAc = acetic acid; DMF = N,N-dimethylfomamide) was prepared and structurally characterized by single crystal X-ray. The basic structural unit of the complex is a dinuclear complex [Zn(HSSC)OAc]₂ in which the semicarbazone ligand adopts the phenol-imine form. The deprotonated phenol group forms a one-atom bridge between the two zinc centers, and both of the zinc centers are five-coordinated. The local coordination environment of Zn²⁺ can be approximately considered as square pyramidal. UV spectral studies show that the H ₂SSC provides strong binding of Zn²⁺ in a 1:1 ratio in solution. The conditional binding constant of the complex is lg K_Zn-L = 12.89 ± 0.76 in 0.05 M Tris-HCl buffer at pH 7.4. The H₂SSC exhibits an enhanced fluorescence effect by the addition of Zn²⁺, and affords an excellent selectivity for Zn²⁺ under physiological conditions.

Full text of DOI:10.1016/j.saa.2010.12.029

Spectrochimica Acta Part A 78 (2011) 1245–1249
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Structure and spectral properties of dinuclear zinc complex containing
semicarbazonate ligands
∗
Wang Jing-Lin, Feng Jiao, Xu Mei-Ping, Yang Bin-Sheng
Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Molecular Science, Shanxi University, No 36 Wucheng Rd, Taiyuan 030006, China
a r t i c l e i n f o
a b s t r a c t
The dinuclear Zn2+ complex [Zn(HSSC)OAc] ·2DMF (H SSC = salicylaldehyde semicarbazone;
Article history:
2
2
Received 22 December 2009
Received in revised form 2 December 2010
Accepted 11 December 2010
HOAc = acetic acid; DMF = N,N-dimethylfomamide) was prepared and structurally characterized by
single crystal X-ray. The basic structural unit of the complex is a dinuclear complex [Zn(HSSC)OAc]2 in
which the semicarbazone ligand adopts the phenol-imine form. The deprotonated phenol group forms
a one-atom bridge between the two zinc centers, and both of the zinc centers are five-coordinated.
Keywords:
UV spectra
2+
The local coordination environment of Zn can be approximately considered as square pyramidal. UV
2
+
spectral studies show that the H2SSC provides strong binding of Zn in a 1:1 ratio in solution. The
Fluorescence spectra
2+
conditional binding constant of the complex is lg KZn–L = 12.89 ± 0.76 in 0.05 M Tris–HCl buffer at pH 7.4.
Zn
2
+
The H2SSC exhibits an enhanced fluorescence effect by the addition of Zn , and affords an excellent
H2SSC
Crystal structure
2
+
selectivity for Zn under physiological conditions.
©
2010 Elsevier B.V. All rights reserved.
1
. Introduction
fied as appealing ligands for the construction of cluster complexes,
especially when an alkoxide can be served as a bridge between
metal centers [14–17].
No other metal has as many functions in biological processes
as the metal zinc [1,2]. In the majority of cases, the zinc ion
plays myriad roles as structural and catalytic cofactors, neural
signal transmitters or modulators, regulators of gene expression,
apoptosis, enzyme regulation, and neurotransmission [3–5]. The
design and synthesis of receptors that are of selectively binding
The H SSC has been used in the synthesis of mononuclear
2
complexes and multinuclear clusters of transition metals, such as
2
+
2+
+
Cu [18–21], Ni , as well as VO [22] complexes. To the best of our
2
2+
knowledge, the dinuclear Zn complex of H SSC ligand have not
2
been reported. In this paper, the synthesis, structural characteriza-
2
+
2+
and sensing Zn have drawn considerable attention [6]. In general,
tion, and spectral properties of dinuclear Zn complex containing
2+
Zn is tightly associated with proteins and peptides [7]. However,
free” zinc ions still exist in most cells, where their concentra-
semicarbazonate ligands are investigated. The H SSC was adopted
2
“
as a zinc ion chelator because it can afford an excellent selectivity
for Zn2+ over Mg , Cd , Ca , Al , Na and K .
2+
2+
2+
3+
+
+
tion varies from the subfemtomolar range in bacterial cells to the
millimolar range in some vesicles. These ions are released dur-
ing synaptic activity or depolarization, modulating the function
of certain ion channels and receptors [8,9]. Many sensors, probes
and receptors have also emerged as useful Zn2 sensing tools [10],
but ions recognition motifs are often structurally complicated and
require laborious multi-step organic syntheses for their assembly.
Therefore, the development of simple and easily synthesized metal-
specific receptors is strongly desired [11]. Over the past few years,
some research efforts have been made on developing these recep-
tors using urea/thiourea and thiouronium as a binding site [12,13],
such as the semicarbazones (SCs) and thiosemicarbazones (TSCs).
These ligands containing NOO or NOS donors have been identi-
2. Experimental
+
2.1. Instrumentation
IR spectra were recorded on a Shimadzu FT-IR-8300 instru-
−
1
ment using KBr discs in the 400–4000 cm . UV–vis spectra were
measured with a HP8453 UV–vis spectrophotometer. Fluorescence
spectra were measured with a Cary Eclipse fluorescence spec-
trophotometer, with the slit widths of excitation and emission were
set to 2.5 nm and 5 nm, respectively. Chemical analyses for car-
bon, hydrogen, and nitrogen were determined by microanalysis
using a Perkin-Elmer 240B elemental analyzer. The crystal data
were collected on a BRUKER SMART APEX CCD DIFFRACTOME-
∗ Corresponding author. Tel.: +86 351 7016358.
E-mail address: yangbs@sxu.edu.cn (Y. Bin-Sheng).
TER equipped with a fine-focus sealed tube employing graphite
monochromatised Mo K␣ radiation (ꢀ = 0.71073 A˚ ). The structures
1
386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.12.029

1
246
W. Jing-Lin et al. / Spectrochimica Acta Part A 78 (2011) 1245–1249
were solved using SHELXS-97 and the model was refined using
SHELXL-97.
2.2. Materials and methods
All chemicals and solvents used in this work were of analyti-
cal grade available commercially and were used without further
purification.
UV spectra were recorded on a Hewlett Packard 8453 spec-
trometer. The sample cuvette containing H SSC was titrated with a
2
2
+
solution of Zn to determine the value of the molar absorptivity of
the Zn–HSSC complex to be used in the calculation. The sample was
also titrated with a solution of Zn2 that contained various concen-
trations of EDTA as a competing ligand to measure the equilibrium
constants. During the titration process, the sample was maintained
+
◦
at 25 C by using a jacketed cell holder connected to an external
circulating water bath (Huber).
2
.3. Synthesis of H SSC
2
H SSC was prepared by a reaction of semicarbazide hydrochlo-
2
ride with salicyl aldehyde in a molar ratio of 1:1 in water (yield:
2%). Anal. Calc. for H SSC(C H N O ): C, 53.63; H, 5.06; N, 23.45.
8
2
8
9
3
2
−
1
Found: C, 53.74; H, 5.07; N, 22.97%. IR (KBr):ꢁ(OH) 3472 cm , ꢁ
Fig. 1. Structure of [Zn(HSSC)OAc] ·2DMF obtained by single-crystal X-ray diffrac-
2
−1
−1
−1
(
C
O) 1697 cm , ꢁ (C N) 1622 cm , ꢁ (C–O) 1267 cm .
tion, DMF are omitted for clarity.
2
.4. Synthesis of [Zn(HSSC)OAc] ·2DMF
3.2. UV difference spectra
2
H SSC (0.179 g, 1 mmol) dissolved in methanol (20 ml) was
Fig. 3 depicts UV difference spectra upon titrating a fixed con-
centration of H2SSC with Zn(OAc)2. Four extrema can be found:
two maxima at 244, 353 nm and two minimum at 272 and 311 nm.
The minimum at 272 and 311 nm can be attributed to the per-
turbations of azomethine C N and the keto-amine transition of
2
slowly added to a solution of Zn(Ac) ·2H O (0.170 g, 1 mmol) in
2
2
methanol (20 ml) in a flask and stirred for ∼3 h. A milky white
precipitate was obtained from the resulting reaction solution, sep-
arated by filtration, and then washed with methanol, THF and dried
(
yield: 70%). Anal. Calc. for Zn(HSSC)OAc (C10H11N O Zn): C, 39.69;
O C–C C–(NH), respectively. The transition corresponding to the
3
4
H, 3.66; N, 13.89. Found: C, 39.62; H, 3.69; N, 13.95%. IR (KBr pellet):
band 311 nm has more characteristic of O C–C C–(NH) than that
of (HO)–C C–C N (phenol-imine), indicating that the nitrogen has
more affinity for hydrogen than oxygen [25]. In solution, H2SSC
−1
−1
−1
.
ꢁ
(C O) 1670 cm , ꢁ (C N) 1603 cm , ꢁ (C–O) 1278 cm
The milky white powder was dissolved in DMF, and was
kept at room temperature. After several weeks, crystals of the
[
Zn(HSSC)OAc] ·2DMF appeared in DMF, and were ready for X-ray
2
Table 1
diffraction.
Summary of the structure determination for [Zn(HSSC)OAc]2·2DMF.
Parameter
[Zn(HSSC)OAc]2·2DMF
3
. Results and discussion
Formula
C26H36N8O10Zn2
CCDC number
726079
3.1. Description of crystal structures
Mr
T/K
751.37
298(2)
Crystal system
Space group
a/Å
b/Å
c/Å
Monoclinic
P2(1)/c
11.0879(16)
11.6801(19)
12.367(2)
90
91.698(2)
90
1600.9(5)
2
1.559
1.565
Single-crystal X-ray diffraction was used to establish the struc-
ture of [Zn(HSSC)OAc] ·2DMF (see Fig. 1). The crystallographic data
2
are listed in Table 1. The basic structural unit is the dimer com-
plexes [Zn(HSSC)OAc]2 in which the semicarbazone ligand has a
deprotonated phenol group. Z-Configuration is adopted by coordi-
nating its N(2) and O(1) atoms to one zinc ion and its deprotonated
hydroxyl O(2) atom forms a one-atom bridge between the two zinc
centers. The coordination number of each zinc ion can be up to 5,
˛/deg.
ˇ/deg.
ꢂ/deg.
Volume/Å
Z
3
−
−3
by coordinating of O(3) in OAc ion. The coordination polyhedron
Density (calculated)/Mg m
Absorption coefficient/mm
F(0 0 0)
−
1
2
+
around each Zn can be described as a distorted square pyramidal.
Selected interatomic dimensions are given in Table 2.
776
Crystal size/mm
0.23 × 0.19 × 0.10
Although self-assembly directed by dinuclear zinc species was
mainly assisted by coordinating bond-based approach [23], some
non-covalent interactions, such as hydrogen bond, aromatic ␲–␲
stack, and metal–metal interactions also have an important impact
on the structures of the complexes [24]. The dimer is further assem-
bled through N–H· · ·O interactions with adjacent dimers to form
Theta range for collection/deg.
Reflections collected/unique
Absorption correction
Refinement method
Data/restraints/parameters
Goodness-of-fit on F
Final R indices/I > 2ꢃ(I)
R indices (all data)
1.84–25.01
7439/2819 [R(int) = 0.0408]
Semi-empirical from equivalents
Full-matrix least-squares on F2
2819/0/208
2
1.001
R1 = 0.0394, wR2 = 0.1043
R1 = 0.0580, wR2 = 0.1117
0.460 and −0.399
2
D network (Fig. 2). The hydrogen bonding data of the complex are
−
3
Largest diff. peak and hole/e Å
listed in Table 3.

W. Jing-Lin et al. / Spectrochimica Acta Part A 78 (2011) 1245–1249
1247
Table 2
Bond lengths [Å], angles [deg.] and torsion angles [deg.] for [Zn(HSSC)OAc]2·2DMF.
´
Bond
d, A˚
Angle
ω, deg.
Angle
ω, deg.
Zn(1)–O(3)
Zn(1)–O(2)#1
Zn(1)–O(2)
Zn(1)–N(2)
Zn(1)–O(1)
Zn(1)–Zn(1)#1
N(2)–C(2)
1.957(3)
2.013(2)
2.063(2)
2.097(3)
2.106(3)
3.1514(9)
1.283(5)
1.244(4)
1.348(4)
O(3)–Zn(1)–O(2)#1
O(3)–Zn(1)–O(2)
O(2)#1–Zn(1)–O(2)
O(3)–Zn(1)–N(2)
O(2)#1–Zn(1)–N(2)
O(2)–Zn(1)–N(2)
O(3)–Zn(1)–O(1)
O(2)#1–Zn(1)–O(1)
O(2)–Zn(1)–O(1)
106.56(11)
110.16(11)
78.74(10)
120.36(12)
133.07(11)
84.56(11)
95.24(11)
101.05(10)
153.69(10)
N(2)–Zn(1)–O(1)
76.48(11)
114.06(9)
39.94(7)
38.79(7)
111.97(9)
135.18(8)
O(3)–Zn(1)–Zn(1)#1
O(2)#1–Zn(1)–Zn(1)#1
O(2)–Zn(1)–Zn(1)#1
N(2)–Zn(1)–Zn(1)#1
O(1)–Zn(1)–Zn(1)#1
O(1)–C(1)
O(2)–C(4)
Symmetry codes: #1 −x + 1, −y + 1, −z + 1.
244 nm
0
0
.3
.0
353 nm
h
g
f
e
d
c
b
a
-0.3
311 nm
72 nm
2
250
300
350
400
Wavelength (nm)
Fig. 3. UV difference spectra produced by the addition of Zn to H2SSC in 0.05 M
◦
−5
Tris–HCl buffer at pH 7.4 and 25 C. H2SSC (3.69 × 10 M) 2.0 mL; the volume (␮L)
−
4
of Zn (7.37 × 10 M): (a) 0; (b) 20; (c) 40; (d) 60; (e) 80; (f) 100; (g) 120; (h) 140.
lg KZn–L = 12.89 ± 0.76, was calculated according to the literature
[
27,28].
Fig. 2. The hydrogen bonds in the crystal packing of [Zn(HSSC)OAc]2, hydrogen
atoms are omitted for clarity.
Fig. 5 shows that the UV difference spectral response of
−
5
H SSC (4.00 × 10 M) upon introducing chlorides of biologically
2
+
+
2+
2+
3+
2+
2+
significant Na , K , Ca , Mg , Al , and Zn , including Cd
exists as a tautomeric equilibrium of phenol-imine (O–H· · ·N) and
keto-amine (O· · ·H–N) forms. The peak at 244 nm is attributed to
perturbations of the ␲–␲* transitions of the aromatic ring, the band
−
5
(
12.0 × 10 M). It can be seen that there are dramatic modifica-
2+ 2+ 2+
tions upon addition of Zn , slight changes for Mg and Cd , scarce
variations for Al3+, Ca , Na , and K .
2+
+
+
−
at 353 nm is attributed to ( O)–C C–C N in the complex. The peak
2+
Fig. 6 depicts the dependency of difference spectral sub-
at 311 nm disappeared with the increase of Zn concentration,
indicating that the deprotonated chelator has been of phenol-imine
characteristics after metal binding [26].
traction (ꢄA353 − ꢄA ) on different metal ions. The values of
311
2+
2+
2+
ꢄA353 − ꢄA311 are 0.47, 0.067 and 0.026 for Zn , Mg and Cd
,
The absorbance at 353 nm at each point in the titration pro-
cess was divided by the analytical concentration of H SSC to give a
2
2
.5
value of ꢄε. Titration curves were prepared by plotting ꢄε versus
R, which was defined as the ratio of total Zn2 to the analyti-
+
a
2+
cal concentration of H SSC. Titration of H SSC by adding Zn is
2.0
2
2
shown in Fig. 4 curve (a). The plot has a break near R = 1, show-
ing the 1:1 ligand stoichiometry of the Zn–HSSC complex. From
the slope of the line at R ≤ 1 the molar absorptivity (ꢄεZn) of
1
.5
3
−1
−1
M . To determine
Zn–HSSC complex is (2.12 ± 0.06) × 10 cm
b
the binding constant of Zn–HSSC, the solution of H SSC was also
1.0
2
ε
Δ
titrated with Zn–EDTA. EDTA serves as a competitive ligand, thus
the observed absorptivity decreases as the [EDTA]/[Zn2 ] = 0.25,
as shown in Fig. 4 curve (b). The conditional binding constant,
+
0
0
.5
.0
Table 3
Hydrogen bonds for [Zn(HSSC)OAc]2·2DMF.
0.0
0.5
1.0
1.5
2.0
2
+
[
Zn ]/[H SSC]
D–H
d(D–H) d(H· · ·A) ∠DHA
d(D· · ·A)
A
2
N(1)–H(1)
N(3)–H(3A) 0.860
N(3)–H3B 0.860
0.860
2.074
2.150
2.148
144.32 2.817
140.66 2.867
146.76 2.906
O(4) [x, −y + 3/2, z + 1/2]
O(5) [x, y, z + 1]
O(4) [x, −y + 3/2, z + 1/2]
◦
Fig. 4. Titration curves of H2SSC in 0.05 M Tris–HCl buffer at pH 7.4 and 25 C with
the solution of Zn(OAc)2 that contained EDTA. H2SSC (3.69 × 10 M) 2 mL; Zn2+
−5
−
4
(
7.37 × 10 M), Rt = [EDTA]/[Zn]. (a) Rt = 0; (b) Rt = 0.25.

1
248
W. Jing-Lin et al. / Spectrochimica Acta Part A 78 (2011) 1245–1249
150
4
55 nm
353 nm
i
h
0
0
.2
.0
g
1
00
f
e
d
c
b
a
L=H SSC
2
50
L+Zn
L+Mg
L+Cd
L+Ca
L+Al
L+Na
L+K
-
0.2
311 nm
0
4
00
450
500
550
3
00
350
400
Wavelength (nm)
Wavelength (nm)
Fig. 7. Fluorescence emission spectra of adding Zn(OAc)2 to an aqueous solu-
tion of H SSC in 0.05 M Tris–HCl buffer at pH 7.4 and 25 C, ꢀex = 350 nm. H SSC
(3.69 × 10 M) 2.0 mL; the volume (␮L) of Zn (7.37 × 10 M): (a) 0; (b) 10; (c) 20;
(d)30; · · ·.
−5
◦
Fig. 5. UV difference spectra of H2SSC (4.00 × 10 M) in the absence and presence
2
−5
2
−5
−4
of selected metal chlorides (12.0 × 10 M) in 0.05 M Tris–HCl buffer at pH 7.4 and
◦
2
5
C.
respectively. Obviously, the change in the ꢄA
− ꢄA
of H SSC
3
53
311 2
enhancement (4.5-fold) at 455 nm was detected after the addition
is more pronounced in the presence of Zn2 than other metal ions.
+
of Mg2+ (3.69 × 10 M) due to its lower binding affinity to H SSC.
−5
2
Therefore, the analysis of ꢄA353 − ꢄA , with respect to difference
311
Among transitional metal ions, Cd2+, Mn , Co , Ni , Cu , and
2+
2+
2+
2+
2+
spectral changes at 353 and 311 nm, is possible to determine Zn
.
Fe3+ induced a slight enhancement or quenching of the fluores-
cence intensity at 455 nm (Fig. 8). Although H SSC probably forms
2
3
.3. Fluorescence spectra
complexes with these metal cations, the fluorescence is weakened
due to electron or energy transfer between the metal cations and
the fluorophore, a known fluorescence quenching mechanism [29].
The fluorescence spectrum of H SSC in the range from 400 to
2
5
00 nm is shown in Fig. 7, curve a. There is a peak at 470 nm.
2+
After Zn was added to the solution, the fluorescence intensity
increased and accompanied by a blue shift of the maximum from
4. Conclusion
4
70 nm to 455 nm gradually (see Fig. 7, curve b, c, d, etc.). A signif-
In the work, a simple and easy-to-prepare Zn2+ receptor that
contains the acyl-hydrazones unit was prepared and structurally
characterized. Spectral measurements show that H2SSC can bind
icant fluorescence enhancement (14-fold) appears after 1 equiv. of
Zn was added. It is means that Zn exhibits a strong chelation
enhanced fluorescence effect (CEFE). Structure of [Zn(HSSC)OAc]2
2+
2+
−
2+
2+
(
Fig. 1) shows that HSSC is a plane structure. The binding of Zn
tightly to Zn in 1:1 ratio in 0.05 M Tris–HCl buffer at pH 7.4 and
◦
makes the rigidity of ligand increase, while the fluorescence of
H SSC is enhanced.
25 C. The conditional binding constant is lg KZn–L = 12.89 ± 0.76.
The H2SSC can afford Zn2+-selective fluorescence enhancement
2
Metal ion selectivity was also examined by fluorescence. The
under physiological conditions. The H2SSC should be useful for
studies on the biological functions of Zn2+
.
fluorescence of H SSC was not influenced by other cations, such as
2
+
+
2+
3+
Na , K , Ca , and Al , under physiological conditions, as shown
in Fig. 8. The phenomena are presumably due to the poor com-
plexation of metal ions with H SSC. However, a mild fluorescence
2
1
20
0
0
0
0
0
0
.5
.4
.3
.2
.1
.0
L=H SSC
2
8
4
0
0
0
L
K(I)
Na(I) Al(III) Ca(II) Cd(II) Mg(II) Zn(II)
Metal ions
Ions
−
5
Fig. 6. The subtraction (ꢄA353 − ꢄA311) of UV difference spectra response of H2SSC
Fig. 8. The relative fluorescence intensity of H2SSC (3.69 × 10 M) at 455 nm in the
−5
−5
(
4.00 × 10 M) vs. different metal ions (12.0 × 10 M) in 0.05 M Tris–HCl buffer at
presence of various cations. The data were measured in 0.05 M Tris–HCl buffer at
pH 7.4 and 25 C, ꢀex = 350 nm, [M ]/[H2SSC] = 1:1 or [M ]/[Zn ]/[H2SSC] = 1:1:1.
◦
◦
n+
n+
2+
pH 7.4 and 25 C.

W. Jing-Lin et al. / Spectrochimica Acta Part A 78 (2011) 1245–1249
1249
Acknowledgements
[11] A.E. Dennis, R.C. Smith, Chem. Commun. (2007) 4641.
[
[
[
[
[
[
[
[
12] T. Gunnlaugsson, A.P. Davis, G.M. Hussey, M. Glynn, Org. Biomol. Chem. 2 (2004)
1856.
This work was supported by the National Natural Science Foun-
dation of P.R. China (No. 20771068, 20901048) and the Natural
Science Foundation of Shanxi Province (No. 2010011011-1).
13] E.J. Cho, J.W. Moon, S.W. Ko, J.Y. Lee, S.K. Kim, J. Yoon, K.C. Nam, J. Am. Chem.
Soc. 125 (2003) 12376.
14] J.S. Casas, M.S. Garcia-Tasende, J. Sordo, Coord. Chem. Rev. 209 (2000)
1
97.
15] J.A. Hoshiko, G. Wang, J.W. Ziller, G.T. Yee, A.F. Heyduk, Dalton Trans. (2008)
712.
Appendix A. Supplementary data
5
16] M. Murugesu, M. Habrych, W. Wernsdorfer, K.A. Abboud, G. Christou, J. Am.
Chem. Soc. 126 (2004) 4766.
17] T.C. Stamatatos, K.A. Abboud, W. Wernsdorfer, G. Christou, Angew. Chem., Int.
Ed. 46 (2007) 884.
18] A.V. Gerasimenko, R.L. Davidovich, I.G. Bulimestru, A.P. Gulea, S.W. Ng, Acta
Crystallogr. E 61 (2005) m1816.
19] Yu.M. Chumakov, V.I. Tsapkov, V.N. Biyushkin, M.D. Mazus, N.M. Samus, Kristal-
lografiya 41 (1996) 873.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2010.12.029.
References
[
[
[
1] H. Vahrenkamp, Dalton Trans. (2007) 4751.
2] L.Q. Emily, W.D. Dylan, J.C. Christopher, Chem. Rev. 108 (2008) 1517.
3] G.K. Walkup, S.C. Burdette, S.J. Lippard, R.Y. Tsien, J. Am. Chem. Soc. 122 (2000)
[20] J. Patole, S. Dutta, S. Padhye, E. Sinn, Inorg. Chim. Acta 318 (2001) 207.
[21] J.-L. Wang, B. Liu, B.-S. Yang, S.-P. Huang, J. Struct. Chem. 49 (2008) 570.
[22] P. Noblía, E.J. Baran, L. Otero, P. Draper, H. Cerecetto, M. González, O.E. Piro, E.E.
Castellano, T. Inohara, Y. Adachi, H. Sakurai, D. Gambino, Eur. J. Inorg. Chem.
5
644.
4] B. Tang, H. Huang, K. Xu, L. Tong, G. Yang, X. Liu, L. An, Chem. Commun. (2006)
609.
[
(
2004) 322.
3
[
[
[
23] W. Huang, H.-B. Zhu, S.-H. Gou, Coord. Chem. Rev. 250 (2006) 414.
24] C. An, Y. Lu, Z. Shang, Z. Zhang, Inorg. Chim. Acta 361 (2008) 2721.
25] Y.-H. Lu, Y.-W. Lu, C.-L. Wu, Q. Shao, X.-L. Chen, R.N.B. Bimbong, Spectrochim.
Acta Part A 65 (2006) 695.
[
[
[
5] W. Jiang, Q. Fu, H. Fan, W. Wang, Chem. Commun. (2008) 259.
6] P.A. Gale, Coord. Chem. Rev. 240 (2003) 191.
7] K. Komatsu, K. Kikuchi, H. Kojima, Y. Urano, T. Nagano, J. Am. Chem. Soc. 127
(
2005) 10197.
[
[
[
[
26] J.D. Ranford, J.J. Vittal, Y.M. Wang, Inorg. Chem. 37 (1998) 1226.
27] L. Duan, Y.-Q. Zhao, B.-S. Yang, Spectrochim. Acta Part A 68 (2007) 165.
28] Z.-J. Wang, B.-S. Yang, Spectrochim. Acta Part A 65 (2006) 946.
29] A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, A.J. Huxley, C.P. McCoy, J.T.
Rademacher, T.E. Rice, Chem. Rev. 97 (1997) 1515.
[
[
8] L. Xue, H.-H. Wang, X.-J. Wang, H. Jiang, Inorg. Chem. 47 (2008) 4310.
9] E. Kawabata, K. Kikuchi, Y. Urano, H. Kojima, A. Odani, T. Nagano, J. Am. Chem.
Soc. 127 (2005) 818.
[10] E.M. Nolan, J.W. Ryu, J. Jaworski, R.P. Feazell, M. Sheng, S.J. Lippard, J. Am. Chem.
Soc. 128 (2006) 15517.