Four new nickel(II) complexes based on an asymmetric Salamo-type ligand: Synthesis, structure, solvent effect and electrochemical property

Article abstract of DOI:10.1016/j.ica.2016.02.043

Four new solvent-induced Ni(II) complexes with chemical formulae {[NiL(MeOH)(μ-OAc)]₂Ni}·2MeOH (1), {[NiL(EtOH)(μ-OAc)]₂Ni} (2), {[NiL(i-PrOH)(μ-OAc)]₂Ni} (3) and {[NiL(DMF)(μ-OAc)]₂Ni}·2DMF·0.44H₂O (4), where H₂L = 5-methoxy-4′-chloro-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol, have been synthesized and characterized by elemental analyses, ¹H NMR, FT-IR, UV-Vis spectra and X-ray crystallography. X-ray crystallographic analyses of the Ni(II) complexes reveal that they crystallize in the triclinic system, space group P1ˉ, and consists of three Ni(II) ions, two deprotonated L^2- units, two μ-acetato ligands and two coordinated solvent molecules. In each of the Ni(II) complexes, the Ni(II) ions are hexa-coordinated with a slightly distorted octahedral coordination geometries. Although the molecule structures of the Ni(II) complexes are similar each other, obtained in different solvents, the supramolecular structures are entirely different. The complexes 1 and 3 possess a self-assembled infinite 2D and 1D supramolecular structures via the intermolecular hydrogen bonds, respectively. But the Ni(II) complexes 2 and 4 are formed 0D structures by intramolecular hydrogen bonds. Cyclic voltammetry is used to characterize electrochemical property of the Ni(II) complex 1.

Full text of DOI:10.1016/j.ica.2016.02.043

Inorganica Chimica Acta 445 (2016) 140–148
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Four new nickel(II) complexes based on an asymmetric Salamo-type
ligand: Synthesis, structure, solvent effect and electrochemical property
⇑
Wen-Kui Dong , Jian-Chun Ma, Li-Chun Zhu, Yang Zhang, Xia-Liang Li
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Four new solvent-induced Ni(II) complexes with chemical formulae {[NiL(MeOH)(
l
l
-OAc)] Ni}ꢀ2MeOH
2
Received 10 October 2015
Received in revised form 14 January 2016
Accepted 12 February 2016
Available online 2 March 2016
(
0
1), {[NiL(EtOH)(
l
-OAc)]
2
Ni} (2), {[NiL(i-PrOH)(
l
-OAc)]
2
Ni} (3) and {[NiL(DMF)(
-OAc)]
2
Ni}ꢀ2DMFꢀ
0
0
.44H O (4), where H
2
2
L = 5-methoxy-4 -chloro-2,2 -[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphe-
1
nol, have been synthesized and characterized by elemental analyses, H NMR, FT–IR, UV–Vis spectra and
X-ray crystallography. X-ray crystallographic analyses of the Ni(II) complexes reveal that they crystallize
ꢀ
2ꢁ
in the triclinic system, space group P1, and consists of three Ni(II) ions, two deprotonated L units, two
-acetato ligands and two coordinated solvent molecules. In each of the Ni(II) complexes, the Ni(II) ions
Keywords:
Asymmetric Salamo-type ligand
Ni(II) complex
Synthesis
Crystal structure
Electrochemical property
l
are hexa-coordinated with a slightly distorted octahedral coordination geometries. Although the mole-
cule structures of the Ni(II) complexes are similar each other, obtained in different solvents, the
supramolecular structures are entirely different. The complexes 1 and 3 possess a self-assembled infinite
2D and 1D supramolecular structures via the intermolecular hydrogen bonds, respectively. But the Ni(II)
complexes 2 and 4 are formed 0D structures by intramolecular hydrogen bonds. Cyclic voltammetry is
used to characterize electrochemical property of the Ni(II) complex 1.
Ó 2016 Elsevier B.V. All rights reserved.
1
. Introduction
counter ions or small neutral molecules, the solvent systems and
so on. When the same ligand is allowed to react with the same
N
2
O
2
Salen-type ligands are easily obtained by the reaction of
salicylaldehyde or its derivatives with diamines, coordinated to
transition metal ions in a N tetradentate fashion to obtain
metal salt in different solvents with the same exterior conditions,
the performance of the ligands, the coordinated small neutral
molecules and the solvent systems often play important roles in
the formation of the molecular structure of the complexes [7]. In
order to study the electrochemical properties and further investi-
gate solvent effect of Salamo-type complexes, we have designed
and synthesized four solvent-induced Ni(II) complexes by the com-
2 2
O
stable mononuclear complexes [1,2]. In addition, there are a num-
ber of report on the synthesis of transition metal homometallic tri-
and polynuclear complexes consisting of two or more molecules of
Salen-type [3–6] or Salamo-type [7,8] ligands. In these complexes,
l
2
-phenoxo bridging plays an important role in assembling transi-
plexation of a N
(CH COO) O, under the same exterior conditions in four differ-
ꢀ4H
ent solvents.
2 2 2
O asymmetric Salamo-type ligand H L with Ni
tion metal ions and two ligands. Although transition metal com-
plexes of Salen or its derivatives have been extensively studied in
catalysts [9–12], nonlinear optical materials [13,14], magnetic
materials [15–17], electrochemical conduct [18,19], and biological
fields [20]. The novel structures of Salen-type complexes are also
fascinating, which may lead to a better property.
3
2
2
2. Experimental section
In the recent years, a part of our research program concentrated
on the syntheses of Salamo-type complexes by the structural
motifs of substituent groups [21–26]. The structural motifs of com-
plex molecules rest on several factors, such as the property of the
central atoms, the performance of the ligands, the coordinated
2.1. Materials and methods
5-Chlorosalicylaldehyde and 4-methoxybenzaldehyde of 98%
purity have been used without further purification. 1,3-Dibromo-
prophane and other reagents were analytical grade reagents from
Tianjin Chemical Reagent Factory.
C, H, and N analyses were obtained using a GmbH VarioEL V3.00
automatic elemental analysis instrument. Elemental analysis for Ni
was detected by an IRIS ER/SꢀWP-1 ICP atomic emission spectrometer.
⇑
Corresponding author. Tel.: +86 931 4938703; fax: +86 931 4956512.
E-mail address: dongwk@126.com (W.-K. Dong).
http://dx.doi.org/10.1016/j.ica.2016.02.043
020-1693/Ó 2016 Elsevier B.V. All rights reserved.
0

W.-K. Dong et al. / Inorganica Chimica Acta 445 (2016) 140–148
141
Melting points were obtained by the use of a microscopic melting
point apparatus made in Beijing Taike Instrument Limited Com-
pany and were uncorrected. IR spectra were recorded on a VER-
TEX70 FT-IR spectrophotometer, with samples prepared as KBr
2
H L (37.88 mg, 0.1 mmol) at room temperature. The color of the
mixed solution turned to pale green immediately. After stirring
for 10 min at room temperature, the mixture was filtered and the
filtrate was allowed to stand at room temperature for a week,
the solvent partially evaporated and green block-like single crys-
tals suitable for X-ray crystallographic analysis were obtained.
ꢁ1
ꢁ1
(
500–4000 cm ) and CsI (100–500 cm ) pellets. UV–Vis absorp-
tion spectra were recorded on a Shimadzu UV-2550 spectrometer.
1
H NMR spectra were determined by German Bruker AVANCE DRX-
Yield, 29.99 mg (51%). UV–Vis (ethanol): kmax
352 nm (77800 and 26200 L M cm ). IR (KBr, cm ) 3588(b),
2936(w), 1611(vs), 1539(s), 1420(s), 1301(s), 1213(s), 525(w),
(
e
max) 246 and
ꢁ1
ꢁ1
ꢁ1
4
00 spectrometer. The electrochemical property was measured by
the use of a PGSTAT128N Autolab.
4
(C44
75(w), 415(w). Anal. Calc. for {[NiL(MeOH)(
Ni 18): C, 44.94; H, 4.80; N, 4.76; Ni, 14.97. Found:
C, 44.73; H, 4.87; N, 4.61; Ni, 14.78%.
l
-OAc)]
2
Ni}ꢀ2MeOH
2
.2. Synthesis and characterization of H
2
L
H56Cl
2
N
4
3
O
0
0
Major synthetic route of 5-methoxy-4 -chloro-2,2 -[(1,3-propy-
lene)dioxybis(nitrilomethylidyne)]diphenol (H L) are given in
2
2.3.2. {[NiL(EtOH)(
The single crystal of the Ni(II) complex 2 was obtained by a sim-
ilar procedure, an ethanol solution (3 ml) of Ni(OAc)
ꢀ4H
(3.72 mg, 0.015 mmol) was added dropwise to a acetone solution
(1 ml) of H L (3.79 mg, 0.01 mmol). The pale green mixture was fil-
tered and the filtrate was allowed to stand at room temperature for
a week, the solvent partially evaporated and green block-like single
crystals suitable for X-ray crystallographic analysis were obtained.
2
l-OAc)] Ni} (2)
Scheme 1. 1, 3-Bis(aminooxy)prophane was synthesized according
to an analogous method reported earlier [27].
2
2
O
2 2 2
The N O Salamo-type ligand H L was synthesized according a
literature procedure [28]. A solution of 2-hydroxy-5-chloroben-
zaldehyde O-(2-(aminooxy)ethyl) oxime (0.490 g, 2 mmol) in etha-
nol (10 mL) was added to a solution of 4-methoxybenzaldehyde
2
(
6
0.304 g, 2 mmol) in ethanol (10 mL). The mixture was stirred at
0 °C for 5 h. After cooling to room temperature, the precipitates
Yield, 2.67 mg (47%). UV–Vis (ethanol): kmax (emax) 246 and 352 nm
ꢁ
1
ꢁ1
ꢁ1
were collected. The product was dried in vacuo, and a colorless
(94700 and 30600 L M cm ). IR (KBr, cm ) 3566(b), 2939(w),
flocculent solid was obtained. Yield, 0.462 g (61%). M.p. 108–
1611(vs), 1535(s), 1420(s), 1300(s), 1215(s), 518(w), 473(w), 419(w).
Anal. Calcd. for {[NiL(EtOH)(l-OAc)] Ni} (C44H50Cl N Ni O16):
2 2 4 3
C, 46.44; H, 4.43; N, 4.92; Ni, 15.47. Found: C, 46.33; H, 4.48; N,
4.39; Ni, 15.32%.
1
1
CH
09 °C. H NMR (400 MHz, CDCl
3
, d, ppm): 2.13–2.16 (m, 2H,
), 4.26–4.32 (m, 4H, CH ), 6.48 (dd,
J = 16 Hz, 2H, ArH), 6.91 (d, J = 24 Hz, 1H, ArH), 7.04 (d, J = 28 Hz,
H, ArH), 7.12 (d, J = 16 Hz, 1H, ArH), 7.22 (dd, J = 20 Hz, 1H,
ArH), 8.12 (d, J = 8 Hz, 2H, CH@N), 9.82 (s, 1H, OH), 9.98 (s, 1H,
2
), 3.81 (s, 3H, CH
3
2
1
2
2.3.3. {[NiL(i-PrOH)(l-OAc)] Ni} (3)
OH). UV–Vis (ethanol): kmax
(
e
max) 274 and 311 nm (31300 and
The single crystal of the Ni(II) complex 3 was obtained by a sim-
ꢁ1
ꢁ1
ꢁ1
2
2
1
0500 L M
cm ). IR (KBr, cm ) 3435(b), 3117(w), 2978(w),
ilar procedure, an i-propanol solution (3 ml) of Ni(OAc) ꢀ4H O
2
2
872(w), 1628(s), 1609(s), 1508(s), 1483(s), 1369(m), 1269(s),
211(s). Anal. Calc. for C18 19ClN : C, 57.07; H, 5.06, N; 7.40.
(3.72 mg, 0.015 mmol) was added dropwise to a acetone solution
H
2
O
5
(1 ml) of H L (3.79 mg, 0.01 mmol). The pale green mixture was fil-
2
Found: C, 57.13; H, 5.10,N; 7.49%.
tered and the filtrate was allowed to stand at room temperature for
a week, the solvent partially evaporated and green block-like single
crystals suitable for X-ray crystallographic analysis were obtained.
2.3. Synthesis of the Ni(II) complexes 1, 2, 3 and 4
Yield, 2.69 mg (46%). UV–Vis (ethanol): kmax (emax) 246 and 352 nm
ꢁ1
ꢁ1
ꢁ1
Four solvent-induced Ni(II) complexes 1, 2, 3 and 4 are obtained
(69,500 and 22,300 L M cm ). IR (KBr, cm ) 3564(b), 2941(w),
by the reaction of Salamo-type ligand H
2
L with Ni(OAc)
2
ꢀ4H
2
O in a
2833(w), 1607(vs), 1537(s), 1422(s), 1301(s), 1217(s), 519(w),
2
:3 M ratio in mixed solution of acetone and methanol, ethanol,
475(w), 419(w). Anal. Calcd. for {[NiL(i-PrOH)(
Ni 16): C, 47.30; H, 4.83; N, 4.80; Ni, 15.08. Found:
C, 47.11; H, 4.90; N, 4.73; Ni, 14.90%.
2
l-OAc)] Ni}
i-propanol or (methanol and DMF), respectively. The Ni(II) com-
plex 4 also can be obtained by the reaction of the Ni(II) complexes
(C46
H56Cl
2
N
4
3
O
1, 2 or 3 with DMF solvent, respectively. The single crystals of the
Ni(II) complexes 1, 2, 3 and 4 suitable for X-ray diffraction analysis
were obtained by solvent partially evaporated.
2.3.4. {[NiL(DMF)(
The single crystal of the Ni(II) complex 4 was obtained by a sim-
ilar procedure, a methanol solution (3 ml) of Ni(OAc)
ꢀ4H
(3.72 mg, 0.015 mmol) was added dropwise to a mixture solution
of acetone and DMF (1 ml) of H L (3.79 mg, 0.01 mmol). The pale
l
-OAc)] Ni}ꢀ2DMFꢀ0.44H O (4)
2
2
2
2
O
2
.3.1. {[NiL(MeOH)(
l
-OAc)]
2
Ni}ꢀ2MeOH (1)
A
methanol solution (3 ml) of Ni(OAc)
2
ꢀ4H
2
O
(37.24 mg,
2
0
.15 mmol) was added dropwise to a acetone solution (1 ml) of
green mixture was filtered and the filtrate was allowed to stand
O
O
C
O
C
C
2 2 2
NH NH ·H O
Br
Br
2
N
OH
N
O
O
N
H
2
N
O
O
NH
2
C
O
C
O
C
O
CHO
OH
O
O
O
N
O
CHO
OH
N
NH
2
N
H
2
N
O
O
NH
2
MeO
Cl
Cl
OH
Cl
OH
HO
OMe
2
Scheme 1. The synthetic route of H L.

1
42
W.-K. Dong et al. / Inorganica Chimica Acta 445 (2016) 140–148
at room temperature for a week, the solvent partially evaporated
and green block-like single crystals suitable for X-ray crystallo-
graphic analysis were obtained. Yield, 2.76 mg (41%). UV–Vis
DMF solution with adding 0.1 M tetrabutylammonium perchlorate
(TBAP) as supporting electrolyte. The potentials were recorded
ꢁ1
between ꢁ1.0 and +1.5 V at 100 mV s scan rate.
. Results and discussion
.1. IR spectra analyses
(
ethanol):
k
max
(
e
max
)
246 and 352 nm (65000 and 22300
ꢁ
1
ꢁ1
ꢁ1
L M cm ). IR (KBr, cm ) 3616(b), 2835(w), 1645(s), 1607(vs),
3
1
537(s), 1472(s), 1422(s), 1300(s), 1217(s), 521(w), 476(w), 417
w). Anal. Calc. for {[NiL(DMF)( -OAc)]
Ni}ꢀ2DMFꢀ0.44H
Ni 18.44): C, 46.33; H, 5.15; N, 8.31; Ni, 13.06.
(
(
l
2
2
O
3
C
52
H68.88Cl
2
N
8
3
O
Found: C, 46.13; H, 5.29; N, 8.27; Ni, 12.98%.
2
IR spectra of H L and its corresponding Ni(II) complexes 1, 2, 3
and 4 are shown the characteristic C@N stretching band. The free
ligand H L appears at 1609 cm , while the C@N bands of the
2
ꢁ
1
2.4. Crystal structure determination
The single crystals of the Ni(II) complexes 1, 2, 3 and 4 with
approximate dimensions of 0.19 ꢂ 0.23 ꢂ 0.25, 0.19 ꢂ 0.24 ꢂ
0
.26, 0.23 ꢂ 0.25 ꢂ 0.31 and 0.17 ꢂ 0.18 ꢂ 0.22 mm were placed
on a Bruker Smart diffractmeter equipped with Apex CCD area
detector, respectively. The diffraction data were collected using a
graphite monochromated Mo K
a radiation (k = 0.71073 Å) at 293
(
2), 296(2), 294.58(10) and 296(2) K, respectively. The structures
were solved by using the program SHELXS-97 and Fourier difference
2
techniques, and refined by full-matrix least-squares method on F
using SHELXL-97 [29]. Anisotropic thermal parameters were used for
the nonhydrogen atoms and isotropic parameters for the hydrogen
atoms. Hydrogen atoms were added geometrically and refined
using a riding model. Crystallographic data and refinement for all
of the Ni(II) complexes are summarized in Table 1.
2.5. Cyclic voltammetry
The electrochemical measurement was carried out at 25 °C in a
standard three-electrode cell, consisting of a glassy carbon (GC)
disc ( = 5 mm) as working electrode, a platinum wire as auxiliary
U
Fig. 1. Cyclic voltammetry of the Ni(II) complex
1
in DMF + TBAP 0.1 M at
ꢁ3
ꢁ1
100 mV s scan rate on GC electrode at 25 °C.
and a Hg/HgO as reference. The sample was made of 1.0 ꢂ 10
M
Table 1
X-ray crystallographic data collection, solution and refinement parameters for the Ni(II) complexes 1, 2, 3 and 4.
Compound code
1
2
3
4
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
44
H
56Cl
2
N Ni
4 3
O
18
C
44
H
50Cl
2
N
4 3
Ni O
16
C
46
H
56Cl
2
4
N Ni
3
O
16
C
52 2 8 3 18.44
H68.88Cl N Ni O
1175.95
293(2)
0.71073
triclinic
P1ꢀ
1137.91
296(2)
0.71073
triclinic
P1ꢀ
1167.97
294.58(10)
0.71073
triclinic
P1ꢀ
1348.10
296(2)
0.71073
triclinic
P1ꢀ
9.585(4)
9.388(4)
10.893(3)
10.926(3)
12.438(3)
103.25(2)
105.99(2)
110.83(2)
1238.7(7)
1
11.1521(14)
11.8576(15)
12.3578(16)
72.564(2)
76.515(2)
76.383(2)
1491.8(3)
1
b (Å)
c (Å)
11.594(5)
12.634(5)
69.802(6)
82.727(6)
84.221(7)
1304.6(9)
1
12.479(6)
13.992(6)
65.285(6)
82.914(7)
68.341(6)
1383.0(11)
1
a
(°)
b (°)
(°)
c
3
Cell volume (Å )
Z
D
l
calc (g cmꢁ3)
1.497
1.247
1.366
1.172
1.566
1.301
1.500
1.104
ꢁ
1
(mm
)
F(000)
610
588
606
702
Crystal size (mm)
h Range (°)
0.19 ꢂ 0.23 ꢂ 0.25
0.19 ꢂ 0.24 ꢂ 0.26
0.23 ꢂ 0.25 ꢂ 0.31
0.17 ꢂ 0.18 ꢂ 0.22
1.7–25.5
1.9–25.0
3.3–26.0
1.8–27.8
Index ranges
ꢁ11 6 h 6 11, ꢁ14 6 k 6 7,
ꢁ11 6 h 6 7, ꢁ14 6 k 6 14,
ꢁ16 6 l 6 16
9273
4740 (0.063)
97.2 (25.010)
4740/210/316
ꢁ13 6 h 6 13, ꢁ13 6 k 6 9,
ꢁ15 6 l 6 15
7888
4855 (0.095)
99.2 (26.022)
4855/3/329
ꢁ11 6 h 6 14, ꢁ9 6 k 6 15,
ꢁ15 6 l 6 16
9981
6882 (0.023)
97.7 (27.760)
6882/9/392
ꢁ
15 6 l 6 14
Collected reflections
Unique reflections (Rint
Completeness (%) (h)
Data/
7382
)
4790 (0.018)
98.9 (25.498)
4790/0/321
restraints/parameters
Goodness-of-fit on (GOF) 1.091
F
1.020
0.984
1.033
2
Final R
R Indices (all data)
1
Indices [I > 2
r(I)]
R
R
1
= 0.0440, wR
= 0.0600, wR
2
= 0.1190
= 0.1268
R
R
1
= 0.0822, wR
= 0.1057, wR
2
2
= 0.1965
= 0.2099
R
R
1
= 0.0906, wR
= 0.1700, wR
2
2
= 0.1737
= 0.2286
R
R
1
1
= 0.0509, wR
= 0.0883, wR
2
= 0.1284
= 0.1513
1
2
1
1
2
Residuals peak/hole (e/
Å )
1.14 and ꢁ0.38
1.30 and ꢁ0.71
1.28 and ꢁ0.82
0.82 and ꢁ0.84
3

W.-K. Dong et al. / Inorganica Chimica Acta 445 (2016) 140–148
143
Ni(II) complexes 1, 2, 3 and 4 are observed at 1611, 1611, 1607 and
The far-infrared spectra of the Ni(II) complexes 1, 2, 3 and 4 are
also obtained in the region 500–100 cm in order to identify fre-
quencies due to the Ni–O and Ni–N bonds. IR spectra of the Ni(II)
ꢁ
1
ꢁ1
1
607 cm , respectively. The shift of this C@N absorption by about
ꢁ1
3
and 2 cm on going from the free ligand H
2
L to the Ni(II) com-
plexes 1, 2, 3 and 4.
The Ar–O stretching frequencies appear as a very strong band
complexes 1, 2, 3 and 4 show m(Ni–N) (or m(Ni–O)) vibrational
absorption frequencies at 475, 473, 475 and 476 (or 415, 419,
ꢁ1
ꢁ1
within 1269–1211 cm range as reported for similar Salen-type
419 and 417) cm , respectively, which are consistent with the lit-
ꢁ
1
ꢁ1
ligands [30]. These bands occur at 1269 cm for H
2
L, 1213 cm
erature frequency values [32,33]. These bands are observed as new
bands for the Ni(II) complexes 1, 2, 3 and 4 and are not present in
the spectrum of the free ligand H L.
2
ꢁ1
for the Ni(II) complex 1, 1215 cm for the Ni(II) complex 2 and
217 cm for the Ni(II) complexes 3 and 4. The Ar–O stretching
ꢁ1
1
frequency is shifted to lower frequency, indicating that the Ni–O
bonds are formed between the Ni(II) ions and oxygen atoms of
phenolic groups [31]. In addition, the O–H stretching bands can
3.2. UV–Vis spectra analyses
ꢁ1
2
be found at 3435 cm in the free ligand H L and the broad absorp-
ꢁ1
tion centered on 3588, 3566, 3564 and 3616 cm in the Ni(II)
complexes 1, 2, 3 and 4, respectively, which are the evidence for
the existence of alcohols or water molecules.
The absorption spectra of H L and its corresponding Ni(II) com-
plexes 1, 2, 3 and 4 in ethanol solution show that the spectra of the
Ni(II) complexes 1, 2, 3 and 4 are similar to each other, but are dif-
2
ferent from the spectrum of the ligand H
2
L. The UV–Vis spectrum
Table 2
of the free ligand H L exhibits two absorption peaks at ca. 274
2
Electrochemistry data (vs Hg/HgO) of the Ni(II) complex 1.
and 311 nm. The absorption peak at 274 nm can be attributed to
⁄
E
pa
E
(V)
pc
D
(V)
E
E
(V)
1/2
I
(
pa
I
(
pc
I
pa/Ipc
the
p–p
transition of the benzene rings and the absorption peak
(V)
lA)
lA)
⁄
at 311 nm can be assigned to the intra-ligand
the C@N bonds [34]. Compared with the absorption peak of the
p–p
transition of
Ni(II)(salamo)/Ni
I)(salamo)
Ni(III)(salamo)/Ni
II)(salamo)
–
–
0.141
–
–
6.53 1.899
(
0.575 0.434
1.152
0.505 12.40
–
free ligand H
2
L, a new absorption peak is observed at 352 nm in
–
–
–
35.26
–
⁄
the Ni(II) complexes 1, 2, 3 and 4, which are assigned to the n–
charge transfer transition from the filled p
phenolic oxygen to the vacant d-orbital of the Ni(II) ions [35]. It is
noteworthy that the same UV–Vis absorption spectra of the Ni(II)
p
(
p
orbital of the bridging
E
pa and Epc are the anode and cathode electrode potential, respectively. E1/2 = 1/2
pa + Epc),
E = |Epa ꢁ Epc|.
(E
D
Table 3
Selected bond lengths (Å) and bond angles (°) for the Ni(II) complexes 1, 2, 3 and 4.
Complex 1
Complex 2
Complex 3
Complex 4
Bond
Distance
Bond
Distance
Bond
Distance
Bond
Distance
Ni2–N1
Ni2–N2
Ni2–O3
Ni2–O4
Ni2–O7
Ni2–O9
Ni1–O3
Ni1–O4
Ni1–O6
2.109(3)
2.124(3)
2.031(2)
2.045(2)
2.033(2)
2.110(3)
2.075(2)
2.104(2)
2.129(2)
Ni2–N1
Ni2–N2
Ni2–O6
Ni2–O1
Ni2–O2
Ni2–O7
Ni1–O1
Ni1–O2
Ni1–O8
2.113(6)
2.081(7)
2.013(6)
2.021(5)
2.034(5)
2.118(5)
2.082(5)
2.084(5)
2.102(5)
Ni1–O1
Ni1–O4
Ni1–O6
Ni1–O7
Ni1–N1
Ni1–N2
Ni2–O1
Ni2–O4
Ni2–O8
2.018(6)
1.991(5)
2.199(6)
2.040(6)
2.076(7)
2.047(7)
2.101(6)
2.071(5)
2.023(5)
Ni2–N1
Ni2–N2
Ni2–O4
Ni2–O3
Ni2–O2
Ni2–O8
Ni1–O1
Ni1–O3
Ni1–O4
2.056(3)
2.059(3)
2.026(3)
2.031(2)
2.042(3)
2.174(3)
2.055(2)
2.078(2)
2.106(2)
Bond
Angle
Bond
Angle
Bond
Angle
Bond
Angle
O3–Ni1–O3#
O3–Ni1–O4#
O3–Ni1–O4
O3–Ni1–O6#
O3–Ni1–O6
180.0
O2–Ni1–O2
O2–Ni1–O1#
O2–Ni1–O1
O1–Ni1–O1#
O2–Ni1–O8
180.0
O1–Ni1–O6
O1–Ni1–O7
O1–Ni1–N1
O1–Ni1–N2
O4–Ni1–O1
O4–Ni1–O6
O4–Ni1–O7
O4–Ni1–N1
O4–Ni1–N2
O7–Ni1–O6
O7–Ni1–N1
O7–Ni1–N2
N1–Ni1–O6
N2–Ni1–O6
N2–Ni1–N1
88.9(2)
93.1(2)
87.0(2)
167.9(2)
81.8(2)
92.5(2)
90.5(2)
168.3(2)
87.3(3)
176.5(2)
93.4(3)
92.0(3)
83.9(3)
86.5(3)
103.6(3)
180.0
102.0(2)
78.0(2)
180.0
91.0(2)
89.0(2)
91.3(2)
88.7(2)
180.0
O1–Ni1–O1#
O1–Ni1–O3#
O1–Ni1–O3
180.0
103.99(9)
76.01(9)
89.01(9)
90.99(9)
180.0
89.01(9)
90.99(9)
89.01(9)
180.0
109.41(12)
89.95(11)
86.07(10)
78.30(9)
92.52(10)
90.64(10)
86.23(10)
164.11(10)
90.59(11)
88.05(11)
89.53(11)
93.92(10)
174.94(10)
86.74(12)
164.52(11)
102.80(19)
77.20(19)
180.0
91.97(19)
88.9(2)
91.1(2)
88.03(19)
88.9(2)
180.0
90.9(2)
93.2(2)
79.7(2)
93.2(3)
86.2(2)
164.6(2)
88.9(2)
166.2(2)
86.5(2)
107.7(3)
176.0(2)
92.9(2)
86.4(2)
88.2(2)
87.1(2)
92.50(10)
87.50(10)
180.00(2)
89.82(10)
79.63(9)
100.37(9)
90.18(10)
79.63(9)
180.00(11)
82.65(10)
92.34(11)
90.67(10)
87.32(12)
168.90(13)
94.49(12)
168.61(11)
86.67(11)
91.71(12)
102.97(13)
91.41(10)
90.00(10)
176.24(11)
85.49(11)
84.63(12)
#
O3 –Ni1–O3
#
O1–Ni1–O4
#
#
#
#
O4–Ni1–O4
O1 –Ni1–O8
O3 –Ni1–O4
O4–Ni1–O6#
O4–Ni1–O6
O1–Ni1–O8
O3–Ni1–O4#
O1–Ni1–O4
O3–Ni1–O4
O2–Ni1–O8#
#
#
O4 –Ni1–O6
O1–Ni1–O8
#
O8–Ni1–O8#
O6–Ni2–O1
O6–Ni2–O2
O1–Ni2–O2
O6–Ni2–N2
O1–Ni2–N2
O2–Ni2–N2
O6–Ni2–N1
O1–Ni2–N1
O2–Ni2–N1
N2–Ni2–N1
O6–Ni2–O7
O1–Ni2–O7
O2–Ni2–O7
N2–Ni2–O7
N1–Ni2–O7
#
O6 –Ni1–O6
O4 –Ni1–O4
N1–Ni2–N2
N1–Ni2–O9
O3–Ni2–N2
O3–Ni2–O4
O4–Ni2–O3
O4–Ni2–O2
O3–Ni2–O2
O4–Ni2–N1
O3–Ni2–N1
O2–Ni2–N1
O4–Ni2–N2
O3–Ni2–N2
O2–Ni2–N2
N1–Ni2–N2
O4–Ni2–O8
O3–Ni2–O8
O2–Ni2–O8
N1–Ni2–O8
N2–Ni2–O8
#
O3 –Ni2–O7
#
O3–Ni2–O9
O4–Ni2–N1
O4–Ni2–N2
O4–Ni2–O9
O1 –Ni2–O1
O4–Ni2–O1#
O4–Ni2–O1
#
O4 –Ni2–O4
#
O8–Ni2–O1#
O8–Ni2–O1
O8–Ni2–O4#
O8–Ni2–O4
O7 –Ni2–N1
#
O7 –Ni2–N2
#
O7 –Ni2–O4
#
O7 –Ni2–O9
#
O9–Ni2–N2
O3–Ni2–N1
O8 –Ni2–O8
#
#
O8 –Ni2–O4
88.7(2)
Symmetry transformations used to generate equivalent atoms: #1: 1 ꢁ x, 1 ꢁ y, ꢁz, : 1 ꢁ x, ꢁy, 1 ꢁ z, : ꢁx, 1ꢁy, 1 ꢁ z and : 2 ꢁ x, 2 ꢁ y, 1 ꢁ z for the Ni(II) complexes 1, 2,
#2
#3
#4
3
and 4, respectively.

1
44
W.-K. Dong et al. / Inorganica Chimica Acta 445 (2016) 140–148
Table 4
Intra- and inter-molecular hydrogen geometries (Å, °) for the Ni(II) complexes 1, 2, 3 and 4.
Complex
D–H
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
\DHA
A
Symmetry codes
1
O9–H9
0.86
0.82
0.97
0.97
0.97
0.93
1.76
1.90
2.47
2.43
2.56
2.51
2.605(4)
2.715(4)
2.857(6)
3.329(6)
3.474(6)
3.201(5)
169
171
103
154
158
132
O10
O6
O2
O7
O10
O6
x, y, ꢁ1 + z
x, y, 1 + z
O10–H10
C8–H8A
C10–H10
C10–H10B
C16–H16
1 ꢁ x, 1 ꢁ y, ꢁz
1 + x, y, ꢁ1 + z
2
3
4
C2–H2
C8–H8A
C10–H10A
C10–H10A
C16–H16
C16–H16
0.93
0.97
0.97
0.97
0.93
0.93
2.59
2.53
2.56
2.43
2.55
2.54
3.276(10)
2.879(14)
2.895(13)
3.346(11)
3.154(11)
3.269(10)
131
101
100
157
123
135
O8
O3
O4
O6
O8
O2
1 ꢁ x, ꢁy, 1ꢁz
O6–H6
C2–H2
C5–H5
C8–H8B
C14–H14
C14–H14
0.86
0.93
0.93
0.97
0.93
0.93
2.17
2.53
2.50
2.37
2.56
2.57
3.010(8)
166
124
135
151
132
124
O2
O8
O3
O7
O1
O8
ꢁx, 1 ꢁ y, ꢁz
ꢁx, 1ꢁy, 1ꢁz
ꢁx, 1 ꢁ y, ꢁz
3.141(11)
3.228(11)
3.251(12)
3.259(11)
3.189(11)
ꢁx, 1 ꢁ i, 1ꢁz
ꢁx, 1ꢁy, 1ꢁz
C8–H8A
0.97
0.91
0.93
0.93
0.96
2.52
2.51
2.60
2.43
2.34
3.323(5)
3.277(6)
3.171(6)
3.344(5)
2.759(7)
140
142
120
168
106
O2
O2
O1
O1
O8
C10–H10B
C16–H16
C20–H20
C21–H21A
2 ꢁ x, 2ꢁy, 1ꢁz
2ꢁx, 2ꢁy, 1ꢁz
complexes 1, 2, 3 and 4 clearly indicate that the structures of the
four Ni(II) complexes are similar to each other.
currents, Ipa/Ipc = 1.899 (Ipa = ꢁ12.40, Ipc = 6.53) and
D
E = |Epa ꢁ Epc
|
= 0.141 V, in agreement with a quasi-reversible electron-transfer
process [37]. The second couple potentials is attributed to the Ni
(II/I)(salamo) process, but the anodic peak is not observed, indicat-
ing a irreversible redox process. The cathodic peak potential is
observed at Epc = 1.152 V which corresponded to the process Ni
(III)(salamo) + e ? Ni(II)(salamo) [38]. In this system, the Ni(II)
(salamo) complex is more stable than the Ni(III)(salamo) one.
3.3. Cyclic voltammetry
Fig. 1 shows cyclic voltammograms (CVs) of the Ni(II) complex
1
in DMF. The electrochemistry data (vs Hg/HgO) of the Ni(II) com-
plex 1 are shown in Table 2. It is easy to see that the plots of the
Ni(II) complex 1 exhibiting two redox pairs. The first anodic/
cathodic couple potentials (Epa = ꢁ0.575, Epc = ꢁ0.434) is attribu-
ted to the Ni(II)(salamo)/Ni(I)(salamo) process (Ni(II)(salamo)
3.4. Description of the crystal structures
+
e M Ni(I)(salamo)) [36]. The ratio of anodic to cathodic peak
Selected bond lengths (Å) and bond angles (°) are presented in
Table 3. Hydrogen bonds in the Ni(II) complexes 1, 2, 3 and 4 are
given in Table 4.
Fig. 2. Crystal structure of the Ni(II) complex 1. The hydrogen atoms and solvent
Fig. 3. Crystal structure of the Ni(II) complex 2. The hydrogen atoms are omitted for
molecules are omitted for clarity.
clarity.

W.-K. Dong et al. / Inorganica Chimica Acta 445 (2016) 140–148
145
3
.4.1. Structure of the Ni(II) complex 1
X-ray crystallographic analysis of the Ni(II) complex 1 reveals a
symmetric trinuclear structure. It crystallizes in the triclinic sys-
ꢀ
2ꢁ
tem, space group P1, and consists of three Ni(II) ions, two L units,
two -acetato ligands, two coordinated methanol and two non-
l
coordinated methanol molecules. Selected bond lengths and angles
are listed in Table 3.
As shown in Fig. 2, the two terminal Ni(II) ions (Ni2 and Ni2#1
)
are both located in the cis-N
tonated L units, and carboxylate oxygen atom O7 from the
2
O
2
coordination cavity of the depro-
2ꢁ
l
-
acetato bridge and oxygen atom O9 from the methanol ligand,
coordinated to Ni2 in axial positions. The dihedral angle between
the coordination planes of N1–Ni2–O4 and N2–Ni2–O3 is 2.81
(
2)°, indicating slight distortion octahedral geometry from the
#
1
square planar structure. Because Ni2 and Ni2 are symmetry
related, they have identical geometries. In addition, the coordina-
tion sphere of the central Ni(II) ions (Ni1) is completed by quadru-
-phenoxo oxygen atoms from two L2 moieties and two
ꢁ
ple four
l
l
-acetato oxygen atoms which adopt a familiar
All of the six oxygen atoms coordinate to Ni1 constituting an octa-
hedral geometry: one -acetato ligand serves as bridging group for
l–O–C–O fashion.
l
Fig. 4. Crystal structure of the Ni(II) complex 3. The hydrogen atoms are omitted for
clarity.
#
1
Ni1 and Ni2 and another coordinates to Ni1 and Ni2 , in both
cases via Ni–O–C–O–Ni bridges. The bond angles of O7–Ni2–O9
#
1
#1
#1
(
or O7 –Ni2 –O9 ) is 174.94(10)°, while the bond angles of
#
1
O6–Ni1–O6 is 180.0°, showing that the center Ni(II) has a lower
distortion than the terminal Ni(II) in octahedral coordination
geometry. Thus, all the hexa-coordinated Ni(II) ions of the Ni(II)
complex 1 have a slightly distorted octahedral coordination poly-
hedron. Furthermore, the distances of Ni1 and Ni2 (or Ni2# ) atoms
to the six donors are in the range of 2.031(2)–2.129(2) Å. The dis-
tance of Ni1ꢀ ꢀ ꢀNi2 is 3.134(3) Å, indicating weak inter-metal inter-
action, which is significantly longer than all of the Ni–O and Ni–N
bonds. The Ni–N bonds (2.109(3) and 2.124(3) Å) around the ter-
1
#
1
minal Ni(II) (Ni2 and Ni2 ) ions are slightly longer than Ni–O
bonds (2.031(2) and 2.045(2) Å).
3.4.2. Structure of the Ni(II) complexes 2, 3 and 4
X-ray crystal structure analyses of the Ni(II) complexes 2, 3 and
reveal that the structures of the Ni(II) complexes 2, 3 and 4 are
4
similar to the Ni(II) complex 1. The Ni(II) complexes 2, 3 and 4
ꢀ
crystallize in the triclinic system, space group P1, and consists of
three Ni(II) ions, two L2 units, two
ꢁ
l-acetato ligands, two coordi-
nated solvent molecules (The solvent molecules are ethanol, i-pro-
panol and DMF in the Ni(II) complexes 2, 3 and 4, respectively) and
non-coordinated solvent molecules (two H O and one DMF in the
2
Fig. 5. Crystal structure of the Ni(II) complex 4. The hydrogen atoms and solvent
molecules are omitted for clarity.
Ni(II) complex 4). All the hexa-coordinated Ni(II) ions of the
Ni(II) complexes 2, 3 and 4 have a slightly distorted octahedral
coordination polyhedron. Crystal structures are shown in
Figs. 3–5, respectively.
In the Ni(II) complexes 2, 3 and 4, all the terminal Ni(II) ions lie
in a hexa-coordinated environment and adopt slightly distorted
coordination environment as that of the central Ni(II) ion in the
Ni(II) complex 1. Two phenoxo oxygen atoms bridge the terminal
and central Ni(II) ions with a separation of 3.108(2), 3.067(2) and
3
.063(2) Å in the Ni(II) complexes 2, 3 and 4, respectively, which
are not sufficiently short to imply strong inter-metal bonding
interaction.
2 2
octahedral coordination geometry, where the inner N O cavities
2ꢁ
of the pentadentate L units as the basal planes, and two oxygen
atoms from the coordinated solvent molecules (ethanol, i-propanol
and DMF, respectively) occupies the axial positions. The primary
bond lengths (Ni–O and Ni–N) of the Ni(II) complexes 2, 3 and 4
are listed in Table 3. The dihedral angle between the two coordina-
tion planes of N1–Ni2–O2 and N2–Ni2–O19 (N1–Ni1–O1 and N2–
Ni1–O4 or N1–Ni2–O4 and N2–Ni2–O3) is 6.07(2) in the Ni(II)
complex 2 (6.46(2) or 6.58(2)° in the Ni(II) complex 3 or 4, respec-
tively), which are larger than the Ni(II) complex 1, showing that the
terminal Ni(II) ions have a higher distortion than the Ni(II) complex
3.4.3. Supramolecular interaction of the Ni(II) complexes 1, 2, 3 and 4
The molecular structures of four solvent-induced Ni(II) com-
plexes 1, 2, 3 and 4 are similar each other, but the supramolecular
structures are entirely different owed to the inter- and intramolec-
ular hydrogen bonds (Table 4). In the crystal structure of the Ni(II)
complex 1, there are three pairs of intramolecular hydrogen bond-
ing (C8–H8Aꢀ ꢀ ꢀO2, C10–H10Aꢀ ꢀ ꢀO7 and C16–H16ꢀ ꢀ ꢀO6) and three
pairs of intermolecular hydrogen bonding (O9–H9ꢀ ꢀ ꢀO10, O10–
H10ꢀ ꢀ ꢀO6 and C10–H10Bꢀ ꢀ ꢀO10) interactions. The oxygen (O10)
atoms of the non-coordinated methanol molecules are hydrogen-
bonded to the C10–H18B groups of another complex molecule,
1
in octahedral geometry. The central Ni(II) ions are hexa-coordi-
nated, surrounded by six oxygen atoms from the two [NiL(solvent)]
units and two oxygen atoms from -acetato ligands, with the same
l

1
46
W.-K. Dong et al. / Inorganica Chimica Acta 445 (2016) 140–148
Fig. 6. Infinite 2D supramolecular structure of the Ni(II) complex 1 showing inter-molecular hydrogen bonds.
Fig. 7. Infinite 1D supramolecular structure of the Ni(II) complex 3 showing inter-molecular hydrogen bonds.
Fig. 9. 0D structure of the Ni(II) complex 4 showing intra-molecular hydrogen
bonds.
Fig. 8. 0D structure of the Ni(II) complex 2 showing intra-molecular hydrogen
bonds.

W.-K. Dong et al. / Inorganica Chimica Acta 445 (2016) 140–148
147
Cl
3
H CO
O
O
N
N
O
O
N
O
O
R-OH (1, 2, 3)
X
Ni
Ni
Ni
X
O
O
O
O
O
N
O
OMe
OCH
3
Cl
O
O
N
N
OH
OH
Ni(OAc)
2
·4H
2
O
DMF
Acetone
Cl
O
3
H CO
Cl
H
2
L
O
O
N
O
O
N
O
R-OH and DMF (4)
DMF Ni
Ni
Ni DMF
O
O
O
O
N
O
N
O
OCH
3
Cl
{[NiL(
X
)(μ-OAc)]
2
Ni}
X = MeOH (1), EtOH (2), i-PrOH (3), DMF(4)
Scheme 2. Controlled design of the solvent-induced Ni(II) complexes 1, 2, 3 and 4.
linking adjacent complex molecules into a infinite 2D supramolec-
ular structure (Fig. 6).
respectively. But the Ni(II) complexes 2 and 4 form 0D isolated
structures by intramolecular hydrogen bonds.
There are four pairs of intramolecular hydrogen bonds and two
pairs of intermolecular hydrogen bonds (Table 4) existing in the
Ni(II) complex 3. The Ni(II) complex 3 is further linked by a pairs
of intermolecular C5–H5ꢀ ꢀ ꢀO3 hydrogen bonding interactions
between the –CH group of the O-alkyl chain and the aromatic rings
of L unit and a pairs of intermolecular O6–H6ꢀ ꢀ ꢀO2 hydrogen
bonding interactions between the –CH group of the O-alkyl chain
and the coordinated i-propanol molecule to form a 1D infinite
chain (Fig. 7).
The influence of solvent effect is clearly revealed in selected
bond distances (Å) and bond angles (°) for the Ni(II) complexes 1,
2, 3 and 4 (Table 3). It is noteworthy that the bond lengths from
the oxygen atoms (O9, O7 and O6) of coordinated solvent mole-
cules (methanol, ethanol or i-propanol) to the terminal Ni(II) ions
in the Ni(II) complexes 1, 2 and 3 are 2.110(3), 2.118(5) and
2.199(6) Å, respectively, which present a regular elongation when
the steric hindrance successively becomes larger from methanol,
ethanol to i-propanol.
2ꢁ
However, there are not intermolecular hydrogen bonds in the
Ni(II) complexes 2 and 4 which are stabilized by six and five pairs
of intramolecular hydrogen bonding interactions (Table 4), respec-
tively, forming a 0D isolated molecular structures (Figs. 8 and 9).
4. Conclusions
We have designed and synthesized four solvent-induced trinu-
3.4.4. Solvent effect
2 2
clear Ni(II) complexes 1, 2, 3 and 4 with an asymmetric N O Sal-
As shown in Scheme 2, controlled design of the solvent-induced
amo-type ligand. X-ray crystal structure analyses of the Ni(II)
complexes reveal that the structures of the Ni(II) complexes 1, 2,
3 and 4 are similar each other. They all form symmetric trinuclear
Ni(II) complexes 1, 2, 3 and 4. Because of the coordination with dif-
ferent solvents (methanol, ethanol, i-propanol and DMF), the Ni(II)
complexes 1, 2, 3 and 4 present two kinds of synthetic route: all
the four Ni(II) complexes could been synthesized by the reaction
2
ꢁ
structure with three Ni(II) ions, two L
units, two l-acetato
ligands and two coordinated solvent molecules. All the hexa-coor-
dinated Ni(II) ions of the Ni(II) complexes 1, 2, 3 and 4 have a
slightly distorted octahedral coordination polyhedron. Signifi-
cantly, these Ni(II) complexes possess similar structures, but the
supramolecular structures are entirely different. The Ni(II) com-
plexes 1 and 3 possess a self-assembling infinite 2D and 1D
supramolecular structure via the intermolecular hydrogen bonds,
respectively. But the Ni(II) complexes 2 and 4 are formed 0D iso-
lated structures by intramolecular hydrogen bonds. Cyclic voltam-
metry is used to characterize electrochemical properties of the
Ni(II) complex 1. The cyclic voltammograms of the Ni(II) complex 1
of the Salamo-type ligand H
2
L with Ni(CH
3
COO)
2
ꢀ4H
2
O in different
solvents. The Ni(II) complex 4 also could been synthesized by the
Ni(II) complexes 1, 2 or 3 dissolved in DMF solvent, because of
the strong polarity and coordination ability of DMF which could
displace the coordinated alcohol molecules of the Ni(II) complexes
1
, 2 or 3. Although the molecule structures of the Ni(II) complexes
are similar each other, obtained in different mixture solutions, the
supramolecular structures are entirely different. The Ni(II) com-
plexes 1 and 3 possess a self-assembling infinite 2D and 1D
supramolecular structures via the intermolecular hydrogen bonds,

1
48
W.-K. Dong et al. / Inorganica Chimica Acta 445 (2016) 140–148
exhibits two redox pairs. There is a quasi-reversible electron-trans-
fer process which is found at anodic peak Epa = ꢁ0.575 V. But the
anodic peak is not observed at Epc = 1.152 V, indicating a irre-
versible redox process.
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[
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