Influence of axial ligands on diverse properties in three trinickel string complexes

Article abstract of DOI:10.1080/15533174.2012.680096

Three new trinickel string complexes, [Ni₃(dpa)4(3-nba) ₂](1), [Ni₃(dpa)4(4-nba)₂]·(CH ₃OH) (2), and [Ni₃(dpa)4(3,5-dnba)₂](3) where dpa^- is the anion of 2,2-dipyridylamine, 3-nba^- is 3-nitrobenzoate anion, 4-nba is 4-nitrobenzoate anion, and 3,5-dnba^- is 3,5-dinitrobenzoate anion, were synthesized in good yield and characterized by X-ray crystallography, infrared spectra, elemental analysis, magnetic susceptibility, cyclic voltammogram (CV), UV-vis spectra, fluorescence spectra, and TG analysis. The magnetic susceptibilities suggested that the terminal Ni atoms in all three complexes are in high-spin state while the central Ni atom is in a low-spin state. The CVs of complexes 1-3 showed reversible one-electron redox waves at E1/₂ = 1.1395 V for 1, 1.108 V for 2, and 1.109 V for 3 corresponding to Ni₃ ⁷⁺/Ni₃ ⁶⁺. The Ni-Ni distances in three complexes are somewhat different, indicating the axial nitrobenzoate ligands have significant effect on the structural assembly. Supplemental materials are available for this article. Go to the publisher's online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry to view the supplemental file.

Full text of DOI:10.1080/15533174.2012.680096

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Influence of Axial Ligands on Diverse Properties in
Three Trinickel String Complexes
Jing Zhang a & Long-Guan Zhu a
a Department of Chemistry , Zhejiang University , Hangzhou , P. R. , China
Accepted author version posted online: 29 May 2012.Published online: 28 Aug 2012.
To cite this article: Jing Zhang & Long-Guan Zhu (2012) Influence of Axial Ligands on Diverse Properties in Three Trinickel
String Complexes, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:8, 1071-1077, DOI:
10.1080/15533174.2012.680096
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:1071–1077, 2012
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.680096
Influence of Axial Ligands on Diverse Properties in Three
Trinickel String Complexes
Jing Zhang and Long-Guan Zhu
Department of Chemistry, Zhejiang University, Hangzhou, P. R. China
nearly 30 complexes and such replacement can largely in-
fluence electronic structures, electrochemistry, and magnetic
properties,[6,18] while the axial ligands in previous reports are
mainly limited in the simple anions, such as SCN−, CN−, F−,
NO3−, N(CN)2−, and so on (CSD, Version 5.31, August 2010,
UK). Herein we report three trinickel string complexes with
axial nitrobenzoate ligands, namely [Ni3(dpa)4(3-nba)2] (1),
[Ni3(dpa)4(4-nba)2]·(CH3OH) (2), and Ni3(dpa)4(3,5-dnba)2
(3) where 3-nba− is 3-nitrobenzoate anion, 4-nba− is 4-
nitrobenzoate anion, and 3,5-dnba− is 3,5-dinitrobenzoate an-
ion. The nitrobenzoate ligands used in this work are shown in
Scheme 1.
Three new trinickel string complexes, [Ni3(dpa)4(3-nba)2](1),
[Ni3(dpa)4(4-nba)2]·(CH3OH) (2), and [Ni3(dpa)4(3,5-dnba)2](3)
where dpa− is the anion of 2,2ꢀ-dipyridylamine, 3-nba− is 3-
nitrobenzoate anion, 4-nba− is 4-nitrobenzoate anion, and 3,5-
dnba− is 3,5-dinitrobenzoate anion, were synthesized in good yield
and characterized by X-ray crystallography, infrared spectra, el-
emental analysis, magnetic susceptibility, cyclic voltammogram
(CV), UV-vis spectra, fluorescence spectra, and TG analysis. The
magnetic susceptibilities suggested that the terminal Ni atoms in
all three complexes are in high-spin state while the central Ni atom
is in a low-spin state. The CVs of complexes 1–3 showed reversible
one-electron redox waves at E1/2 = 1.1395 V for 1, 1.108 V for
2, and 1.109 V for 3 corresponding to Ni37+/Ni36+. The Ni-Ni dis-
tances in three complexes are somewhat different, indicating the
axial nitrobenzoate ligands have significant effect on the structural
assembly.
EXPERIMENTAL
Materials and Equipments
Supplemental materials are available for this article. Go to the
publisher’s online edition of Synthesis and Reactivity in Inorganic,
Metal-Organic, and Nano-Metal Chemistry to view the supplemen-
tal file.
3-Nitrobenzoic acid, 4-nitrobenzoic acid, and 3,5-
dinitrobenzoic acid were purchased from commercial sources
and their sodium salts were prepared by addition of
NaOH. The 2,2’-dipyridylamine (Hdpa), [Ni3(dpa)4Cl2], and
[Ni3(dpa)4(ClO4)2] were synthesized according to previously
reported methods.[19–22] IR spectra were performed with a Nico-
let Nexus 470 infrared spectrophotometer (USA) as KBr pellets
in the range of 400–4000 cm−1. Elemental analyses (C, H, and
N) were performed on a Flash EA 1112 analyzer (Italy). Ther-
mogravimetric analyses (TGA) were carried out using a Delta
Series TA-SDT Q600 (USA) in a N2 atmosphere in the tempera-
ture range between room temperature and 800◦C at a heating rate
of 10◦C min−1 using Al2O3 crucibles. The fluorescent spectra
were determined on a powdered sample in the solid state at room
temperature using a Shimadzu RF-50 spectrometer (Japan).
Molar magnetic susceptibilities were recorded in the range of
2–300 K on a SQUID system (USA) with a 3000 gauss external
magnetic field. Cyclic voltammograms were recorded by a CHI
600C potentiostat (USA), which was conducted with a home-
made three-electrode cell equipped with a BAS glassy carbon
(0.07 cm2) disk as the working electrode, a homemade platinum
plate (12 cm2) as the auxiliary electrode, and a Ag/AgCl (satu-
rated) reference electrode. These electrodes were separated from
each other by placing in a L-tube filled with electrolyte solution.
Potentials were reported versus Ag/AgCl (saturated) and refer-
enced to the ferrocene–ferrocenium ([Cp2Fe]/[Cp2Fe]+) couple
that occurs at E1/2 = +0.54 V versus Ag/AgCl (saturated). The
Keywords crystal structure, cyclic voltammetric property, magnetic
property, metal string complex
INTRODUCTION
Metal string complexes as an active field in coordination
chemistry have been an immense growth since 1991 when
the first trinickel string complex, [Ni3(dpa)4Cl2] (dpa− = the
2,2ꢁ-dipyridylamine anion), was structurally determined.[1–15]
The growing research on metal string complexes is benefit for
electrical, optical, magnetic, and superconducting materials.[16]
The detailed study of [Ni3(dpa)4Cl2] showed that terminal
five-coordinated nickel atoms have two unpaired electrons re-
spectively with antiferromagnetic coupling while the central
nickel atom is d8, square-planar, and diamagnetic.[17] The ax-
ial replacement of the trinickel string complexes has produced
Received 13 September 2010; accepted 26 December 2011.
This work was supported by the Zhejiang Provincial Natural Sci-
ence Foundation of China (grant No. Z407036), the National Natural
Science Foundation of China (grant No. 20573092).
Address correspondence to Long-Guan Zhu, Department of Chem-
istry, Zhejiang University, Hangzhou 310027, P. R. China. E-mail:
chezlg@zju.edu.cn
1071

1072
J. ZHANG AND L.-G. ZHU
X-Ray Structural Determination
Suitable crystals of 1–3 were selected for data collection by
a Bruker Smart CCD area detector with graphite monochrom-
atized Mo-Kα radiation (λ = 0.71073 Å). The data were inte-
grated by use of the SAINT program (University of Go¨ttingen,
Germany)[23] and the Lorentz and polarization effects were cor-
rected. The absorption corrections were done by the SADABS
program (University of Go¨ttingen, Germany).[24] Three struc-
tures were solved initially by Patterson methods and then com-
pleted by full matrix least squares on F2 followed by difference
Fourier synthesis using the SHELXL-97 program (University
of Go¨ttingen, Germany)[25] in the WinGX environment.[26] All
non-hydrogen atoms were anisotropic. H atoms on solvent in
2 were not determined. Other H atoms on carbon atoms were
placed in idealized positions and refined as riding atoms, with
C-H = 0.93 Å and Uiso(H) = 1.2Ueq(C). The drawings of these
three molecules were realized with the help of ORTEP-3 for
Windows.[27] Crystallographic information for complexes 1–3
is summarized in Table 1.
SCH. 1. Axial ligands used in synthesis of three trinickel string complexes
1–3.
values of E1/2 are taken as (Epa + Epc)/2, where Epa and Epc are
the anodic and cathodic peak potentials, respectively.
Preparation of [Ni3(dpa)4(3-nba)2] (1)
Complex 1 was synthesized by three-layer-solution method
in a slender tube with the diameter of 0.8 cm. The bottom
layer was 5 mL of water containing 0.02 mol/L sodium 3-
nitrobenzoate. The middle layer was 5 mL of mixture sol-
vents of water and methanol with the volume ratio of 3:2.
The upper layer was 5 mL of methanol containing 0.01 mol/L
[Ni3(dpa)4(ClO4)2]. Dark purple crystals were obtained af-
ter standing for 14 days. Yield: 69%. Anal. Calcd. for
C54H40N14O8Ni3: C, 54.55; H, 3.39; N, 16.49%. Found: C,
54.27; H, 3.37; N, 16.25%. IR (KBr, cm−1): 1632 m, 1604 s,
1593 s, 1551 m, 1526 m, 1469 s, 1460 m, 1426 s, 1384 w, 1346
s, 1313 m, 1283 w, 1243 w, 1154 m, 1122 w, 1104 w, 1074 w,
1050 w, 1016 m, 923 w, 895 w, 821 w, 765 m, 742 m, 723 m,
712 w, 671 w, 640 w, 519w.
RESULTS AND DISCUSSION
Structural Analysis
Each of three complexes has a trinickel core of [Ni3(dpa)4]2+
,
which typically exhibits a linear trinickel chain helically
wrapped by four all syn dpa− ligands (Figures 1–3). The two ax-
ial sites of the trinickel core are occupied by two nitrobenzoate
ligands. In each complex, the center Ni atom adopts a square pla-
nar geometry while two terminal Ni atoms have square pyrami-
dal geometries. Ni-O bond lengths in 1–3 are similar (Table 2).
The Ni-N(inner) and Ni-N(terminal) bond lengths are also simi-
lar in 1–3 (Table 2). It is very interesting that the Ni-Ni distances
in 1–3 are different, indicating the axial ligands have significant
effect on the structural assembly. Complex 1 has the largest Ni-
Ni distances while complex 3 has the shortest Ni-Ni separations.
In the previous report the d value defined by the distance from
the Ni atom to the center of the idealized square base given by
four dpa− N donors can be used to measure the distortion of the
square-pyramidal for terminal Ni atoms and the larger d values
for terminal Ni ions away from the square planes, the longer Ni-
Ni distances.[28] But in our three complexes this rule is not true.
The d values are 0.2689(9) and 0.2845(8) Å in 1, 0.2696(11)
and 0.2830(11) Å in 2, and 0.2858(18) and 0.2983(18) Å in 3,
indicating the distortion of the coordination geometry for the Ni
atom is not always strongly related to the Ni-Ni distances.
It is intriguing that C-H. . .π weak interactions occur in com-
plexes 1, 2, and 3. In 1, the distance between C19–H19 and
Cg1 (the ring of N3/C6–C10) is 2.75Å, and 2.99Å for C33-H33
and Cg2 (the ring of C49–C54); in 2, the distance of C9-H9
and Cg3 (the ring of N4/C11–C15) is 2.81 Å, and 2.99 Å for
C5-H53 and Cg4 (the ring of N3/C6-C10); in 3, the distance
between C3-H3 and Cg5 is 2.84 Å, where Cg5 is the ring of
N4/C11–C15, and 2.64 Å for C39-H39 and Cg6 where Cg6 is
the ring of N9/C26-C30. The existence of C-H. . .π interactions
can stabilize the assembly of these complexes.
Preparation of [Ni3(dpa)4(4-nba)2]·(CH3OH) (2)
Complex 2 was synthesized similarly to 1 except for the use
of sodium 4-nitrobenzoate instead of sodium of 3-sulfobenzoate.
Dark purple crystals were obtained after standing for 10 days.
Yield: 65%. Anal. Calcd. for C55H44N14O9Ni3: C, 54.10; H,
3.63; N, 16.06%. Found: C, 53.69; H, 3.49; N, 15.83%. IR
(KBr, cm−1): 1631 m, 1604 s, 1593 s, 1551 m, 1518 m, 1469 s,
1460 w, 1425 s, 1384 m, 1359 s, 1338 s, 1314 m, 1284 w, 1243
w, 1154 m, 1106 w, 1053 w, 1015 m, 923 w, 894 w, 878 w, 821
w, 795 w, 764 m, 740 m, 724 m, 640 w, 518w.
Preparation of [Ni3(dpa)4(3,5-dnba)2] (3)
Complex 3 was synthesized similarly to 1 except for the
use of sodium 3,5-dinitrobenzoate instead of sodium of 3-
sulfobenzoate. After 10 days later, dark purple block crystals
were obtained in the interface of the solution. Yield: 57%. Anal.
Calcd. for C54H38N16O12Ni3: C, 50.71; H, 2.99; N, 17.52%.
Found: C, 49.95; H, 3.28; N, 16.55%. IR (KBr, cm−1): 1640
m, 1604 s, 1594 m, 1540 s, 1469 s, 1460 w, 1426 s, 1384 w,
1354 s, 1313 m, 1284 w, 1243 w, 1154 s, 1122 m, 1109 w, 1077
w, 1050 w, 1016 s, 920 w, 894 m, 764 s, 741 m, 725 m, 715
w, 640 w, 623 w, 517 w. These three complexes are soluble in
dichloromethane, DMF, and DMSO, while slightly soluble in
methanol, ethanol, and acetonitrile.

TRINICKEL STRING COMPLEXES
1073
TABLE 1
Crystallographic data and refinement parameters for complexes 1–3
1
2
3
Empirical formula
Formula
C54H40N14O8Ni3
1189.07
C55H44N14O9Ni3
1221.17
C54H38N16O12Ni3
1279.08
Crystal color/shape
Crystal size/mm
Space group
a/Å
Dark purple/block
0.22 × 0.20 × 0.19
Monoclinic, P21/c
13.7121(2)
16.6521(2)
26.1180(3)
90
Dark purple/ block
0.48 × 0.24 × 0.22
Monoclinic, C2/c
32.5693(4)
14.0185(2)
23.9065(4)
90
Dark purple/ block
0.42 × 0.38 × 0.22
Orthorhombic, P212121
13.3173(5)
16.7141(8)
24.4641(10)
90
b/Å
c/Å
α/◦
β/◦
121.465(1)
90
5086.76(12)
4
1.553
295(2)
1.171
3.2–25.2
16319
97.490(1)
90
10821.9(3)
8
1.499
295(2)
1.104
3.5–25.2
24494
9705
6882
90
90
5445.4(4)
4
1.560
295(2)
1.106
3.2–25.2
16531
8846
γ /◦
V/Å3
Z
D/g·cm−3
T/K
µ/mm−1
θ range/◦
Measured reflections
Unique reflections
Observed reflections
F(000)
8676
6304
2440
5606
2616
4992
R1 and wR2 (I > 2σ (I))
R1 and wR2(all data)
Number of variable
Goodness of fit(GOF)
Largest difference peak and hole/e Å−3
0.026, 0.058
0.043, 0.060
712
0.917
0.334, –0.275
0.034, 0.087
0.053, 0.091
720
0.960
0.418, –0.264
0.038, 0.050
0.074, 0.054
766
0.853
0.367, –0.301
FIG. 1. View of the molecular structure of complex 1. Hydrogen atoms are omitted for clarity. Displacement ellipsoids are shown at the 40% level.

1074
J. ZHANG AND L.-G. ZHU
FIG. 2. View of the molecular structure of complex 2. Hydrogen atoms and methanol are omitted for clarity. Displacement ellipsoids are shown at the 40% level.
complex the central Ni atom is low spin state and two terminal
Ni atoms with unpaired electrons are high spin state.[6]
The magnetic data were modeled using the approximate Eq.
1 according to previous reports.[6,18,29,30]
Magnetic Susceptibility
The variable temperature magnetic data for complexes 1, 2,
and 3 in range of 2–300 K with an applied field of 3000 gauss
of χMT versus T plot are shown in Figure 4 and S1–S2 and
the fitting parameters are listed in Table 3. At 300 K, χMT are
1.03 emu·K·mol−1 for 1, 0.98 emu·K·mol−1 for 2, and 1.03
emu·K·mol−1 for 3, indicating that there are two unpaired elec-
2Ng2β2(eJ/kT + 5e3J/kT
kT (1 + 3eJ/kT + 5e3J/kT
)
)
χ =
[1]
trons in these three complexes (S = 1) according to the the-
ꢀ
oretical formula µeff
=
n(n+2), while they decrease as the
temperature is lowered, and below 50 K χMT tends to zero, giv-
ing a S = 0 ground state. Moreover, magnetic susceptibilities
of these three complexes are similar to those of trinickel string
complexes with axial chloro ligands,[6,18] indicating that in each
where N is Avogadro’s number, g is the Lande´ factor, β is
the electron Bohr magneton, κ is the Boltzmann constant, J is
the exchange parameter, and T is the absolute temperature.
FIG. 3. View of the molecular structure of complex 3. Hydrogen atoms are omitted for clarity. Displacement ellipsoids are shown at the 40% level.

TRINICKEL STRING COMPLEXES
1075
TABLE 2
Ni2-N2
Ni2-N8
1.896(3)
1.872(3)
Ni2-N5
Ni2-N11
1.874(3)
1.882(3)
Selected bond lengths (Å) and angles for complexes 1–3
Ni3-N3
Ni3-N9
2.110(3)
2.090(3)
Ni3-N6
Ni3-N12
2.095(3)
2.103(3)
Complex 1
Ni1-O1
Ni1-Ni2
1.991(3)
Ni3-O7
Ni2-Ni3
2.008(3)
Ni1-N1
Ni1-N7
Ni2-N2
Ni2-N8
Ni3-N3
Ni3-N9
Ni1-O1
Ni1-Ni2
N1-Ni1-N4
N1-Ni1-N10
N4-Ni1-N7
N4-Ni1-O1
N7-Ni1-O1
N2-Ni2-N5
N2-Ni2-N11
2.0977(18) Ni1-N4
2.1107(18) Ni1-N10
1.8861(17) Ni2-N5
1.8981(17) Ni2-N11
2.0814(16) Ni3-N6
2.0837(16) Ni3-N12
1.9926(14) Ni3-O5
2.0522(16)
2.4151(8)
86.46(14)
89.54(13)
89.08(13)
94.31(14)
104.09(13)
88.68(15)
88.96(14)
177.64(16)
87.42(13)
85.97(13)
91.94(13)
99.68(12)
105.00(13)
177.16(3)
2.4177(7)
164.42(14)
91.13(13)
163.97(14)
90.67(13)
101.29(13)
179.47(16)
91.63(16)
90.73(15)
163.15(13)
91.70(12)
163.50(14)
90.04(13)
95.61(12)
2.0787(16)
1.8773(15)
1.8841(16)
2.1133(17)
2.0721(17)
2.0052(14)
2.4360(3)
N1-Ni1-N4
N1-Ni1-N10
N4-Ni1-N7
N4-Ni1-O1
N7-Ni1-O1
N2-Ni2-N5
N2-Ni2-N11
N5-Ni2-N11
N3-Ni3-N6
N3-Ni3-N12
N6-Ni3-N9
N6-Ni3-O7
N9-Ni3-O7
Ni1-Ni2-Ni3
N1-Ni1-N7
N1-Ni1-O1
N4-Ni1-N10
N7-Ni1-N10
N10-Ni1-O1
N2-Ni2-N8
N5-Ni2-N8
N8-Ni2-N11
N3-Ni3-N9
N3-Ni3-O7
N6-Ni3-N12
N9-Ni3-N12
N12-Ni3-O7
2.4278(3)
86.12(7)
90.35(7)
87.71(7)
101.54(6)
89.99(7)
88.70(7)
89.94(7)
Ni2-Ni3
N1-Ni1-N7
N1-Ni1-O1
163.69(6)
106.04(7)
N4-Ni1-N10 166.01(6)
N7-Ni1-N10
N10-Ni1-O1
N2-Ni2-N8
N5-Ni2-N8
N8-Ni2-N11
N3-Ni3-N9
N3-Ni3-O5
N6-Ni3-N12 164.64(6)
N9-Ni3-N12
N12-Ni3-O5
92.02(7)
92.45(6)
178.43(7)
89.95(7)
91.42(7)
163.93(6)
107.28(6)
N5-Ni2-N11 178.42(8)
N3-Ni3-N6
N3-Ni3-N12
N6-Ni3-N9
N6-Ni3-O5
N9-Ni3-O5
87.45(6)
89.69(7)
92.05(7)
96.20(6)
88.75(6)
Electrochemistry
86.55(6)
99.06(7)
The redox properties of trinickel complexes are key to their
application as molecular devices. The bistable states for the loss
and gain of electrons are the base of molecular switches.[31] It
has been known that the axial ligands can significantly influence
the HOMO energy of the trinickel string complexes.[18,30] The
cyclic voltammograms of complexes 1–3 are shown in Figure 5.
All three complexes exhibit reversible one-electron redox waves
at E1/2 = 1.1395 V for 1, 1.108 V for 2, and 1.109 V for 3 cor-
responding to Ni37+/Ni36+. It is clear that axial nitrobenzoate
ligands have some effect on the redox potentials of 1–3 com-
pared with that of [Ni3(dpa)4Cl2].[32] Complexes 2 and 3 have
similar oxidation potentials, while complex 1 has the highest
oxidation potential.
Ni1-Ni2-Ni3 178.360(15)
Complex 2
Ni1-N3
Ni1-N9
Ni2-N2
Ni2-N8
Ni3-N1
Ni3-N7
Ni1-O1
Ni1-Ni2
N3-Ni1-N6
N3-Ni1-N12
N6-Ni1-N9
N6-Ni1-O1
N9-Ni1-O1
N2-Ni2-N5
N2-Ni2-N11
2.0758(19) Ni1-N6
2.082(2) Ni1-N12
1.8884(18) Ni2-N5
1.8959(19) Ni2-N11
2.085(2)
2.103(2)
1.886(2)
1.894(2)
2.093(2)
2.079(2)
2.065(2)
Ni3-N4
Ni3-N10
2.122(2)
2.0123(19) Ni3-O5
1.9933(18)
2.4248(4)
164.90(8)
101.50(8)
2.4194(4)
89.72(8)
89.96(8)
87.69(8)
104.45(8)
93.55(9)
89.88(8)
89.88(9)
Ni2-Ni3
N3-Ni1-N9
N3-Ni1-O1
UV-Vis Spectroscopy
N6-Ni1-N12 165.30(8)
UV-vis spectra of three complexes 1–3 were recorded in
CH2Cl2 at room temperature and are shown in Figure 6. A
comparison of the UV-vis spectra of complexes 1–3 shows that
they have some differences (Table 4). Complex 3 has the largest
ε value and the absorption strength order of molar absorptivity
is 3 > 1 > 2.
N9-Ni1-N12
N12-Ni1-O1
N2-Ni2-N8
N5-Ni2-N8
N8-Ni2-N11
N1-Ni3-N7
N1-Ni3-O5
N4-Ni3-N10 163.80(8)
N7-Ni3-N10
N10-Ni3-O5
88.80(8)
90.01(9)
179.48(9)
90.19(9)
90.06(9)
164.98(8)
93.72(8)
N5-Ni2-N11 179.34(9)
N1-Ni3-N4
N1-Ni3-N10
N4-Ni3-N7
N4-Ni3-O5
N7-Ni3-O5
88.37(8)
87.91(8)
89.12(8)
105.23(8)
101.22(9)
TABLE 3
Least squares fitting parameters of magnetic susceptibility data
90.41(9)
90.74(9)
Complex
g
J/cm−1
R (goodness of fit)
Ni1-Ni2-Ni3 176.634(19)
Complex 3
1
2
3
1.92
1.85
1.92
–95.23
–91.78
–94.93
0.99885
0.99867
0.9984
Ni1-N1
Ni1-N7
2.110(3)
2.078(3)
Ni1-N4
Ni1-N10
2.113(3)
2.094(3)

1076
J. ZHANG AND L.-G. ZHU
TABLE 4
UV-vis absorption spectral data for complexes 1–3 in CH2Cl2
Complex
λmax/nm (ε/dm3·mol−1·cm−1
)
1
2
3
200(45967)
201(55965)
200(58593)
237(59008)
229(49300)
239(74755)
260(51778)
265(65159)
324(51752)
322(56511)
324(56855)
350(49867)
350(52539)
350(55528)
545(5456)
543(7188)
546(7159)
FIG. 6. UV-vis spectra of complexes 1–3 in CH2Cl2.
cating the 3,5-dinitrobenzoate ligand has more influence on the
fluorescence than those of 3-nitrobenzoate and 4-nitrobenzoate
ligands. Further, the emission strength for complexes 1–3 has
an order of 3 > 1 > 2.
FIG. 4. Plot of χMT versus T for complex 1. The solid line represents least
squares fitting using Eq. 1.
Thermal Stability Behavior
Fluorescent Emission
TG analysis shows that complex 1 began to decompose at
313◦C. For complex 2, weight loss of 3.06% from room tem-
perature to 190◦C corresponds to the release of one methanol
molecule (calculated 2.67%). Complex 2 decomposed at 304◦C.
Complex 3 is stable up to 318◦C.
These three complexes have similar fluorescence properties
in solid state at room temperature with the λex = 220 nm. Three
emission peaks are observed at 418, 453, and 470 nm for 1; 417,
454, and 470 nm for 2; and 410, 453, and 470 nm for 3, respec-
tively. The maximum peak is at 470 nm in each complex. These
emission bands are mainly caused from dpa− by comparison of
the free ligand Hdpa. The emission peak at 410 nm in complex
3 is shifted compared with those of complexes 1 and 2, indi-
CONCLUSION
Three trinickel string complexes 1–3 were successfully syn-
thesized by layered-solution method and the introduction of
water into the reaction system led to the axial replacement of
trinickel string complexes by nitrobenzoate ligands. The differ-
ent nitrobenzoate axial replacement led to the tune of structural
parameters and diverse properties: (a) the 1,3-dinitrobenzoate
axial replacement gave the shortest Ni-Ni distances in 3 while
the 3-nitrobenzoate led to the longest Ni-Ni distances in 1; (b)
complex 1 has the highest redox potential and the largest J value;
(c) the distortion of the coordination geometries for Ni atoms are
not strongly related to the Ni-Ni distances; and (d) the absorp-
tion strength of UV-vis and emission strength of fluorescence
are 3 > 1 > 2.
SUPPLEMENTARY MATERIALS
CCDC 784781–784783 contain the supplementary crystallo-
graphic data for complexes 1–3. These data can be obtained free
FIG. 5. Cyclic voltammograms of 1–3 in CH2Cl2 with 1 M TBAP electrolyte.

TRINICKEL STRING COMPLEXES
1077
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