Structurally characterized homotrinuclear Salamo-type nickel(II) complexes: Synthesis, solvent effect and fluorescence properties

Article abstract of DOI:10.1002/aoc.4379

Four new solvent-induced Ni(II) complexes with chemical formulae [{NiL(μ₂-OAc)(MeOH)}₂Ni]·2MeOH (1), [{NiL(μ₂-OAc)}₂(n-PrOH)(H₂O)Ni]·n-PrOH (2), [{NiL(μ₂-OAc)(DMF)}₂Ni] (3) and [{NiL(μ₂-OAc)(DMSO)}₂Ni]·2DMSO (4), (H₂L?=?4-Nitro-4′-chloro-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol) have been synthesized and characterized by elemental analyses, FT-IR, UV–Vis spectra and X-ray crystallography. X-ray crystal structure determinations revealed that each of the Ni(II) complexes 1–4 consists of three Ni(II) atoms, two completely deprotonated (L)^2? units, two μ₂-acetate ions and two coordinated solvent molecules (solvents are methanol, n-propanol, water, N,N-dimethylformamide and dimethyl sulphoxide, respectively). Although the four complexes 1–4 were synthesized in different solvents, it is worthwhile that the Ni(II) atoms in the four complexes 1–4 adopt hexa–coordinated with slightly distorted octahedral coordination geometries, and the ratios of the ligand H₂L to Ni(II) atoms are all 2: 3. The complexes 1–4 possess self-assembled infinite 1D, 3D, 1D and 2D supramolecular structures via the intermolecular hydrogen bonds, respectively. In addition, fluorescence behaviors were investigated in the complexes 1–4.

Full text of DOI:10.1002/aoc.4379

Received: 10 February 2018
DOI: 10.1002/aoc.4379
Revised: 8 March 2018
Accepted: 9 March 2018
F U L L P A P E R
Structurally characterized homotrinuclear Salamo‐type
nickel(II) complexes: Synthesis, solvent effect and
fluorescence properties
Quan‐Peng Kang | Xiao‐Yan Li | Qing Zhao | Jian‐Chun Ma | Wen‐Kui Dong
School of Chemical and Biological
Four new solvent‐induced Ni(II) complexes with chemical formulae [{NiL(μ2‐
Engineering, Lanzhou Jiaotong
University, Lanzhou 730070, P. R. China
OAc)(MeOH)}2Ni]·2MeOH (1), [{NiL(μ2‐OAc)}2(n‐PrOH)(H2O)Ni]·n‐PrOH (2),
[{NiL(μ2‐OAc)(DMF)}2Ni] (3) and [{NiL(μ2‐OAc)(DMSO)}2Ni]·2DMSO (4),
Correspondence
(H2L
=
4‐Nitro‐4′‐chloro‐2,2′‐[(1,3‐propylene)dioxybis(nitrilomethylidyne)]
Wen‐Kui Dong, School of Chemical and
Biological Engineering, Lanzhou Jiaotong
University, Lanzhou 730070, China.
Email: dongwk@126.com
diphenol) have been synthesized and characterized by elemental analyses, FT‐
IR, UV–Vis spectra and X‐ray crystallography. X‐ray crystal structure determi-
nations revealed that each of the Ni(II) complexes 1–4 consists of three Ni(II)
atoms, two completely deprotonated (L)2− units, two μ2‐acetate ions and two
coordinated solvent molecules (solvents are methanol, n‐propanol, water, N,
N‐dimethylformamide and dimethyl sulphoxide, respectively). Although the
four complexes 1–4 were synthesized in different solvents, it is worthwhile that
the Ni(II) atoms in the four complexes 1–4 adopt hexa–coordinated with slightly
distorted octahedral coordination geometries, and the ratios of the ligand H2L to
Ni(II) atoms are all 2: 3. The complexes 1–4 possess self‐assembled infinite 1D,
3D, 1D and 2D supramolecular structures via the intermolecular hydrogen
bonds, respectively. In addition, fluorescence behaviors were investigated in
the complexes 1–4.
Funding information
National Natural Science Foundation of
China, Grant/Award Number: 21761018;
Program for Excellent Team of Scientific
Research in Lanzhou Jiaotong University,
Grant/Award Number: 201706
KEYWORDS
fluorescence property, salamo‐type Ni(II) complex, solvent effect, structure, synthesis
1 | INTRODUCTION
and luminescence properties.[28–32] It is significant to
introduce appropriate functional groups into the organic
Salen‐like complexes have been extensively investigated
in the past decades since the synthesis of Salen (N, N
′–bis(salicylaldehydo)ethylenediamine) was first repor-
ted.[1–5] Moreover, the potential catalytic behavior of
the Salen‐type species, especially in the areas of
asymmetric catalysis,[6,7] was gradually recognized on
the basis of wide research works. The transition
metal complexes with Salen‐type ligands have excellent
properties, such as biological fields,[8–14] unusual mag-
netic[15–17] and electrochemical behaviors,[18] supramo-
lecular architectures,[19–23] molecular recognitions[24–27]
parts of the ligands to regulate the characteristics of these
metal complexes.[33–36] With respect to these complexes,
phenoxo bridging plays an important role in assembling
metal ions and Salen‐type ligands. There are also reports
of changes in the length of methylene chains of Salen com-
plexes, which includes trialkylene, tetralkylene, or longer
alkylene chains.[37] The chain length of methylene of the
Salen‐type complex will lead to different coordination
environment of the central metal ions.
Recently, Salamo‐type ligand as a novel Salen‐type
analogue has been studied in modern coordination
Appl Organometal Chem. 2018;e4379.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4379

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KANG ET AL.
chemistry and organometallic chemistry. Salamo‐type
ligand (R–CH=N–O–(CH2)n–O–N=CH–R) is one of the
most versatile ligands. It is expected that the large electro-
negativity of oxygen atoms will strongly influences the
electronic properties of the N2O2 coordination sphere,
leading to different structures and characteristics of the
complexes. Owing to the special structures of Salamo‐
type complexes, a study was shown that it is at least 104
times more stable than Salen‐type complexes.[38] Herein,
we report the syntheses, crystal structures and solvent
effects of four homotrinuclear complexes, [{NiL(μ2‐OAc)
reported Salen‐type ligands.[43] Meanwhile, the free
ligand H2L exhibited a typical Ar–O stretching frequency
at 1263 cm−1, while those of complexes 1–4 appeared at
1256, 1253, 1250 and 1250 cm−1, respectively. The Ar–O
stretching frequencies are shifted to lower frequencies,
indicating that Ni–O bonds are formed between the Ni(II)
atoms and oxygen atoms of phenolic groups.[44]
The far‐infrared spectra of the Ni(II) complexes 1–4
were obtained from 100–550 cm−1 to identify frequencies
due to the Ni–O and Ni–N bonds. The bands appeared at
513, 519, 519 and 525 cm−1 in the Ni(II) complexes 1–4
could be attributed to ν(Ni–N), while the bands appeared
at 474, 487, 474 and 468 cm−1 were assigned to ν(Ni–O),
which is in consistent with the literature frequency
values.[45,46]
(MeOH)}2Ni]·2MeOH
(1),
[{NiL(μ2‐OAc)}2(n‐PrOH)
(H2O) Ni]·n‐PrOH (2), [{NiL(μ2‐OAc)(DMF)}2Ni] (3) and
[{NiL(μ2‐OAc)(DMSO)}2Ni]·2DMSO (4), the complexes
1–4 were characterized by elemental analyses, IR, UV–
Vis spectra and X‐ray single crystallography.
2.2 | UV–vis absorption spectra
2 | RESULTS AND DISCUSSION
2.1 | IR spectra analyses
UV–vis absorption spectra of H2L and its corresponding
complexes 1–4 were determined in 1.0 × 10−5 M ethanol
solution, as shown in Figure 2. Absorption spectra of the
complexes 1–4 showed that the complexes 1–4 have sim-
ilar absorption spectra, but are different from the spec-
trum of H2L. UV–vis spectrum of H2L exhibited three
absorptions at ca. 219, 267 and 311 nm. The absorptions
at 219 and 267 nm can be assigned to π–π* transitions
of the benzene rings, while the absorption at 311 nm
can be attributed to intraligand π–π* transitions of C=N
groups.[47–49] Compared with the absorption peak of the
free ligand, the corresponding absorption peaks of the
complexes 1–4 are bathochromically shifted and were
observed at ca. 230–233 nm, indicating the phenolic
oxygen and oxime nitrogen atoms are involved in coordi-
nation to the Ni(II) atoms. The absorption peaks at ca.
267 and 311 nm were absent in the complexes 1–4.
IR spectra of H2L and its corresponding Ni(II) complexes
1–4 exhibited various bands in the region of 400–4000 cm−1
region (Figure 1). It is obvious that the typical ν(O–H)
absorption band was near 3084 cm−1 in the spectrum of
H2L. A typical C=N stretching band of the free ligand
H2L appeared at 1605 cm−1, and those of complexes 1–4
appeared at 1606, 1608, 1606 and 1613 cm−1, respec-
tively.[39,40] The C=N stretching frequencies are shifted
to high frequencies, indicating that the Ni(II) atoms are
coordinated by oxime nitrogen atoms of deprotonated
(L)2− moieties. Therefore, conclusion could be made that
the ligand H2L has coordinated with Ni(II) atoms.[41,42]
The typical Ar–O stretching frequency is a strong band
at 1231–1263 cm−1, which is similar to previously
FIGURE 2 UV–vis spectra of H2L and its complexes 1–4 in
FIGURE 1 Infrared spectra of H2L and its complexes 1–4
ethanol (c = 1.0 × 10−5 M)

KANG ET AL.
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Meanwhile, new absorption peaks were observed at ca.
370–376 nm in the complexes 1–4, may be due to
L → M charge‐transfer transitions, which are characteris-
tic of the transition metal complexes with Salen‐type
N2O2 coordination spheres.
2.3 | Descriptions of the crystal structures
Selected bond lengths (Å) and angles (°) are presented in
Table S1. Hydrogen bonds in the Ni(II) complexes 1–4 are
given in Table S2.
2.3.1 | Crystal structures of the Ni(II)
complexes 1 and 4
The X‐ray crystal structure analyses of the complexes 1
and 4 revealed that they have the similar symmetrical
trinuclear molecular unit [{NiL(μ2‐OAc)(solvent)}2Ni]·
2solvent (the solvents are MeOH and DMSO in the com-
plexes 1 and 4, respectively), as shown in Figures 3 and
4, respectively. While the different solvents observed lead
to the formation of the typical solvent‐induced the Ni(II)
complexes.[50]
The crystal structure of the Ni(II) complex 1 is shown
in Figure 3. The complex 1 crystallizes in the triclinic sys-
tem, space group P–1 with Z = 1. The molecular structure
of complex 1 consists of three Ni(II) atoms, two
completely deprotonated (L)2− units, two μ2‐acetate
ions, two coordinated methanol molecules and two non‐
coordinated methanol molecules resulting in a trinuclear
Ni(II) complex. The terminal Ni(II) atom (Ni2 or Ni2#1) is
hexa‐coordinated by two oxime nitrogen (N1 and N2) and
two phenolic oxygen (O3 and O4) atoms of the
deprotonated Salamo‐type (L)2− unit, one oxygen atom
(O5) from the coordinated μ2‐acetate ion and the other
oxygen atom (O7) from the coordinated methanol mole-
cule. The dihedral angle between the coordination planes
of N1–Ni2–O3 and N2–Ni2–O4 is 7.80(2)°, indicating the
coordination geometry around the terminal Ni(II) atom is
a slightly distorted octahedron.
However, the coordination sphere of the central Ni(II)
(Ni1) atom is completed by four phenoxo oxygen (O3, O4,
O3#1 and O4#1) atoms from two deprotonated (L)2− moi-
eties and two μ2‐acetato oxygen (O6 and O6#1) atoms. Ni1
is bridged by Ni2 and Ni2#1 through two bridging μ2‐ace-
tate ions in a similar μ–O–C–O fashion.[51,52] As a result
the central Ni1 atom finally has an O2O2O2 coordination
environment. Then all of the hexa‐coordinated Ni(II)
atoms of the complex 1 have slightly distorted octahedral
geometries. The crystal structure of the complex 4 is very
similar to that of the complex 1 (Figure 4).
FIGURE 3 (a) Molecular structure and atom numberings of the
complex 1 with 30% probability displacement ellipsoids (hydrogen
atoms are omitted for clarity); (b) Coordination polyhedrons for
Ni(II) atoms of the complex 1
The intramolecular and intermolecular hydrogen
bonding interactions of the complex 1 are given in

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KANG ET AL.
FIGURE 5 View of the intramolecular hydrogen bonds of the
complex 1
interactions, respectively, which plays a vital role in con-
structing and stabilizing the complexes 1 and 4 mole-
cules. As shown in the Figures 6 and 8, the neighboring
complex molecules are further linked into an infinite 1D
and 2D supramolecular structure by three and a pairs of
intermolecular hydrogen bonds, respectively. (In complex
1: O7–H7A···O10, C O10–H10···O6, C19–H19B···O9; in
complex 4: C8–H8A···O5A) (Table S2).[53–56]
2.3.2 | Crystal structure of the Ni(II) com-
plex 2
The X‐ray crystallographic analysis of the complex 2
revealed an asymmetric trinuclear structure. It crystal-
lizes in the orthorhombic system, space group P212121
with Z = 4. The molecule consists of three Ni(II) atoms,
two completely deprotonated (L)2− units, two μ2‐acetate
ions, one coordinated n‐propanol molecule, one crystal-
lizing water molecule and one non‐coordinated n‐
propanol molecule.
As shown in Figure 9. Two terminal Ni(II) atom (Ni1
or Ni3) is located at the N2O2 coordination spheres of
Salamo moieties, while the third one (Ni2) is located in
the central cavity. The three Ni(II) atoms were bridged
by the two μ2‐acetate groups. Two terminal Ni(II) (Ni1
or Ni3) atom is hexa‐coordinated by two oxime nitrogen
(N1, N2 or N4, N5) atoms, two deprotonated phenoxo‐
oxygen (O1, O4 or O7, O10) atoms of the (L)2− units,
one oxygen (O13 or O15) atom of one μ2‐acetate ion,
and other oxygen (O19 or O17) atom comes from the
coordinated water or n‐propanol molecule that the axial
FIGURE 4 (a) Molecular structure and atom numberings of the
complex 4 with 30% probability displacement ellipsoids (hydrogen
atoms are omitted for clarity); (b) Coordination polyhedrons for
Ni(II) atoms of the complex 4
Figures 5 and 6, and those of the complex 4 are given in
Figures 7 and 8, respectively. In the crystal structures of
the complexes 1 and 4, the structures are connected by
three and four pairs of intramolecular hydrogen bonding

KANG ET AL.
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FIGURE 6 Part of the infinite 1D
supramolecular chain of the complex 1
four phenoxo oxygen (O1, O4, O7 and O10) atoms from
two deprotonated (L)2− units and double μ2–acetate oxy-
gen (O14 and O16) atoms that adopt a similar μ–O–C–O
fashion. As a result the central Ni2 atom finally has an
O2O2O2 coordination environment. The primary Ni–O dis-
tances are in the normal ranges (Ni2–O1 = 2.062(7), Ni2–
O4 = 2.078(8), Ni2–O7 = 2.083(7), Ni2–O10 = 2.086(8),
Ni2–O14 = 1.993(8) and Ni2–O16 = 2.071(8) Å) (Table S1).
As depicted in Figure 10, in the complex 2, eleven
pairs of intramolecular hydrogen bonds are formed,
which plays a vital role in constructing and stabilizing
the complex 2 molecules.[53–56] The complex 2 is further
linked by intermolecular hydrogen bonding interactions
form a 3D supramolecular structure (Figure 11).
2.3.3 | Crystal structure of the Ni(II) com-
plex 3
The results of the X‐ray structural study revealed that the
complex 3 crystallizes in the triclinic system and P–1
space group. As depicted in Figure 12. The molecular
structure of complex 3 consists of three Ni(II) atoms,
two completely deprotonated (L)2− units, two μ2‐acetate
ions and two coordinated DMF molecules.
FIGURE 7 View of the intramolecular hydrogen bonds of the
complex 4
The terminal Ni(II) (Ni2 or Ni2#3) atom is hexa‐
coordinated by two oxime nitrogen (N1, N2 or N1#3,
N2#3) atoms and two phenoxo oxygen (O1, O4 or O1#3,
O4#3) atoms, the four atoms are all from one deprotonated
(L)2− units, one oxygen (O8 or O8#3) atom from the μ2‐
acetate ions and one oxygen (O9 or O9#3) atom from the
coordinated DMF molecules. The central Ni(II) (Ni1)
atom is also hexa‐coordinated via four phenoxo oxygen
atoms from two (L)2− units, and two oxygen (O7 or
O7#3) atoms from μ2‐acetate ions, The Ni1 and Ni2 (or
Ni1 and Ni2#3) atoms are connected through μ2‐acetate
ions in a familiar μ–O–C–O fashion. The coordination
environment around all the Ni(II) atoms are best
described as slightly distorted octahedral geometries.
As depicted in Figure 13, in the complex 3, there are
eight pairs of intramolecular (C2–H2···O7, C8–H8B···O3,
C10–H10B···O2, C10–H10B···O8, C16–H16···O1, C16–
H16···O7, C20–H20···O7 and C22–H22B···O9) hydrogen
bonds are formed, which performs a crucial role in
positions. The dihedral angle between coordination
planes of N1–Ni1–O1 and N2–Ni1–O4 is 7.73(5)°. The
dihedral angle between coordination planes of N4–Ni3–
O7 and N5–Ni3–O10 is 7.94(2)°. These indicate that the
Ni(II) (Ni1 or Ni3) atom forms a slightly distorted octahe-
dral geometry. The primary Ni–N and Ni–O distances are
in the normal ranges (Ni1–N1
= 2.054(9), Ni1–
N2 = 2.052(11), Ni1–O1 = 2.036(7), Ni2–O4 = 2.034(8),
Ni2–O19 = 2.108(2) and Ni2–O13 = 2.007(2) Å)
(Table S1). The bond length between the Ni(II) atom
and the apical oxygen (O19) atom is 2.108(2) Å, which
is obviously longer than the distances between the
Ni(II) atom and the basal oxygen and nitrogen atoms.
This significant elongation has been observed previously
in the Ni(II) complexes with Salamo‐type ligands. The
Ni3 atom is similar to Ni1 atom.
In addition, the central Ni(II) (Ni2) atom is also
located in a hexa‐coordinated environment, The coordi-
nation sphere of the central Ni(II) atom (Ni2) contains

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KANG ET AL.
FIGURE 8 Part of the infinite 2D
supramolecular network of the complex 4
constructing and stabilizing supramolecular structure.
Furthermore, every molecule links other molecules
via intermolecular hydrogen bonds (C21–H21C···O5A)
forming a 1D supramolecular structure (Table S2)
(Figure 14).[53–56]
To sum up, here we reported four homotrinuclear
Salamo‐type Ni(II) complexes. In previous reports, the
Salamo‐type Ni(II) complexes are essentially mono‐,[57,58]
di‐,[29] tri‐,[43] and hepta‐nuclear,[59] and the ratios of the
ligand to Ni atoms are 1:1, 2:2, 2:3 and 2:7. Here we have
successfully designed and synthesized a different ligand
by changing the synthetic routes of Salamo‐type ligands,
including introducing asymmetric aldehydes or changing
the length of methylene chains. The corresponding com-
plexes were synthesized by the introduction of different
solvents, in order to further promote the study of its struc-
ture and properties.
introduced. However, they possessed different supramo-
lecular structure characteristics. The Ni(II) complexes 1–
4 self‐assemble into infinite 1D, 3D, 1D and 2D supramo-
lecular structures through intermolecular hydrogen
bonding interactions, respectively. In the Ni(II) com-
plexes 1–4, the solvent effect clearly showed the changes
in bond distances (Å) and angles (°) (Table S1). It is note-
worthy that the bond lengths from the oxygen (O7 and
O17) atoms of the coordinated solvent molecules (metha-
nol or n‐propanol) to the terminal Ni(II) atoms in the
Ni(II) complexes 1 and 2 are 2.112(5) and 2.161(8) Å,
respectively, due to larger steric hindrance of the n‐
propanol than the methanol. Thus, solvent effects could
explain their slight differences in crystal structures.
Experiments show that the methanol, n‐propanol and
acetone solution systems are suitable for the growth of
complexes 1–4 single crystals, about two weeks later the
single‐crystal obtained can be used to analysis. When
only methanol and acetone solution system, the methanol
molecules can coordinate to the two terminal Ni(II) atoms
in the axial position, while DMF or DMSO molecule can
replace methanol and coordinate to the axial positions
of the two terminal Ni(II) atoms when DMF or DMSO
molecule is added into the system. In the n‐propanol
and acetone solution systems, water was added and it
2.4 | Solvent effect
The four Ni(II) complexes could been synthesized by
the reaction of the Salamo–type ligand H2L with
Ni(OAc)2·4H2O in different solvents. The complexes 1–4
presented similar stoichiometry ratio and molecular
structures when different solvent molecules were

KANG ET AL.
7 of 13
FIGURE 10 View of the intramolecular hydrogen bonds of the
complex 2
FIGURE 11 Part of the infinite 3D supramolecular structure
showing the hydrogen bonding interactions of the complex 2
FIGURE 9 (a) Molecular structure and atom numberings of the
complex 2 with 30% probability displacement ellipsoids (hydrogen
atoms are omitted for clarity); (b) Coordination polyhedrons for
Ni(II) atoms of the complex 2
2.5 | Fluorescence properties
was found that n‐propanol and water molecules are
involved in the coordination of two terminal Ni(II) atoms.
A series of reaction processes show that the coordination
ability of DMF or DMSO > methanol, n‐propanol ≈ water.
The fluorescence properties of H2L and its corresponding
complexes 1–4 were investigated at room temperature
(Figure 15). The ligand H2L exhibited an intense emission
peak at 472 nm upon excitation at 365 nm, which should

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KANG ET AL.
FIGURE 13 View of the intramolecular hydrogen bonds of the
complex 3
FIGURE 14 Part of the infinite 1D supramolecular chain of the
complex 3
FIGURE 15 Emission spectra of H2L and its complexes 1–4 in
ethanol (1.0 × 10−3 M) upon excitation at 365 nm
be assigned to the intraligand π‐π* transition. The emis-
sion spectra of the complexes 1–4 showed main peaks at
492, 496, 490 and 494 nm (λex = 365 nm), respectively.
The four Ni(II) complexes 1–4 exhibited similar fluores-
cence emissions because of their similar molecular struc-
tures. Meanwhile, it can be seen that the complexes 1–4
exhibited a bathochromically‐shifted with respect to the
Salamo‐type ligand H2L. We tentatively assigned it to a
ligand‐to‐metal charge transfer (LMCT).[39,57,60,61] In
addition, compared with the free ligand, the emission
intensities of the Ni(II) complexes 1–4 were reduced
FIGURE 12 (a) Molecular structure and atom numberings of the
complex 3 with 30% probability displacement ellipsoids (hydrogen
atoms are omitted for clarity); (b) Coordination polyhedrons for
Ni(II) atoms of the complex 3

KANG ET AL.
9 of 13
significantly, indicating that the Ni(II) ions have the
properties of fluorescent quenching.
four‐circle (complexes 2–4) diffractometer. Fluorescence
spectra were carried out on F‐7000 FL spectrophotometer.
4.2 | Crystal structure determinations of
the complexes 1–4
3 | CONCLUSIONS
The crystal and structure refinement data for the com-
plexes 1–4 are given in Table 1. The single crystals of the
Ni(II) complexes 1–4 with approximate dimensions of
0.18 × 0.15 × 0.11, 0.13 × 0.11 × 0.04, 0.31 × 0.26 × 0.25
and 0.31 × 0.25 × 0.24 mm were placed on a SuperNova,
Dual (Cu at zero) Eos. diffractometer or Bruker Smart
diffractmeter equipped with Apex CCD area detector,
respectively. The diffraction data were collected using a
In summary, as a result of the introduction of different
solvent molecules, four new homotrinuclear Ni(II) com-
plexes 1–4 with an asymmetric Salamo‐type N2O2 ligand,
were successfully designed and synthesized. X‐ray crystal
structure analyses of the Ni(II) complexes revealed that
the structures of the Ni(II) complexes 1–4 are basically
similar to each other. The Ni(II) complexes 1–4 differ
only by the solvent molecules coordinated to central
Ni(II) ions. Two terminal Ni(II) ions are located at the
N2O2 coordination spheres of Salamo moieties, The ter-
minal Ni(II) and central Ni(II) atoms are connected
through μ2‐acetate ions in a familiar μ–O–C–O fashion.
All the hexa‐coordinated Ni(II) atoms of the Ni(II) com-
plexes 1–4 have slightly distorted octahedral coordination
polyhedrons. Significantly, these Ni(II) complexes possess
basically similar structures, but the supramolecular
structures are entirely different. The Ni(II) complexes
1–4 possess self‐assembling infinite 1D, 3D, 1D and 2D
supramolecular structures via the intermolecular hydro-
gen bonds, respectively. The fluorescent spectra exhib-
ited that the complexes 1–4 have weaked fluorescent
emissions.
graphite monochromated Mo Ka radiation (λ
=
0.71073 Å) at 296(2), 150.00(10), 294(2) and 294.54(10)
K, respectively. The structures were solved by using the
program SHELXS‐2014[62] and Fourier difference tech-
niques, and refined by full‐matrix least‐squares method
on F2 with SHELXL‐2014.[63] Anisotropic thermal param-
eters were used for the nonhydrogen atoms and isotropic
parameters for the hydrogen atoms. Hydrogen atoms
were added geometrically and refined using a riding
model.
4.3 | Synthesis and characterization of
H2L
The main reaction steps involved in the synthesis of H2L
is given in Scheme 1. 1,3‐Bis(aminooxy)prophane was
synthesized according to an analogous method reported
earlier.[64]
4 | EXPERIMENTAL SECTION
4.1 | Materials and methods
The Salamo‐type N2O2 ligand H2L was synthesized
according to an analogous method reported earlier.[38,65]
To an ethanol solution (80 ml) of 5‐chlorosalicylaldehyde
(626.0 mg, 4.0 mmol) was added an ethanol solution
(50 ml) of 1,3‐bis(aminooxy)prophane (637.0 mg,
6.0 mmol). The mixture solution was heated at 50–55 °C
for 6 h. The solution was concentrated in vacuo and the
residue was purified by column chromatography (SiO2,
chloroform/ethyl acetate, 10:1) to afford colorless floccu-
lent crystalline solid of 2‐[O‐(1‐ethyloxyamide)]oxime‐4‐
chlorophenol (655.0 mg, 2.68 mmol). Yield, 66.9%. Anal.
calc. For C10H13ClN2O3 (%): C, 49.09; H, 5.36; N, 11.45.
Found (%): C, 49.31; H, 5.47; N, 11.22.
5‐Chlorosalicylaldehyde and 5‐nitrosalicylaldehyde of
98% purity have been used without further purification.
1,3‐Dibromoprophane and other reagents were analytical
grade reagents from Tianjin Chemical Reagent Factory.
Carbon, hydrogen and nitrogen analyses were ob-
tained using a GmbH VarioEL V3.00 automatic elemental
analysis instrument. Elemental analyses for Ni(II) were
carried out by an IRIS ER/SWP‐1 ICP atomic emission
spectrometer. Melting points were measured by the use
of a microscopic melting point apparatus made by Beijing
Taike Instrument Limited Company. IR spectra were
recorded on a VERTEX70 FT‐IR spectrophotometer,
with samples prepared as KBr (400–4000 cm−1) pellets.
UV–Vis absorption spectra were recorded on a Hatachi
U‐3900H spectrometer. 1H NMR spectra were determined
by German Bruker AVANCE DRX‐400 spectrometer. X‐
ray single crystal structure determinations for the com-
plexes 1–4 were carried out on a Bruker Smart Apex
CCD (complex 1) or SuperNova Dual Eos (Cu at zero)
A
solution of 2‐[O‐(1‐ethyloxyamide)]oxime‐4‐
chlorophenol (489 mg, 2.0 mmol) in ethanol (15 ml)
was added to solution of 5‐nitrosalicylaldehyde
a
(334 mg, 2.0 mmol) in ethanol (10 ml). The mixture was
stirred at 55–60 °C for 6 h. After cooling to room temper-
ature, the precipitate was filtered off and an orange red
powder crystalline solid was obtained. Yield, 541 mg
1
(68.8%). M.p. 117–118 °C. H NMR (400 MHz, CDCl3) δ

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KANG ET AL.
TABLE 1 Crystallographic data and refinement parameters for the complexes 1–4
Complex
1
2
3
4
Empirical formula
Formula weight
T (K)
C42H50Cl2Ni3N6O20
1205.91
C44H52Cl2Ni3N6O19
1215.94
C44H48Cl2Ni3N8O18
1223.93
C46H58Cl2Ni3N6O20S4
1390.19
296 (2)
150.00(10)
0.71073
294 (2)
294.54(10)
0.71073
Wavelength (Å)
Crystal system
Space group
a (Å)
0.71073
0.71073
triclinic
orthorhombic
P212121
triclinic
monoclinic
P 21/c
P–1
P–1
10.922 (12))
11.263 (12)
11.375 (12)
84.896 (15)
74.300 (16)
69.704 (16)
1263 (2)
20.6301 (14)
20.3857 (12)
12.1769 (9)
90
9.2381 (10)
12.816 (2)
13.749 (3)
69.663 (18)
83.488 (13)
83.725 (11)
1512.2 (5)
1
13.5766 (13)
16.0286 (15)
15.7655 (13)
90
b (Å)
c (Å)
α (°)
β (°)
90
96.941 (8)
90
γ (°)
V (Å3)
90
5121.1 (6)
4
3405.6 (5)
2
Z
1
Dcalc (g·cm−3
)
1.585
1.577
1.344
1.356
μ (mm−1
)
1.294
1.276
1.081
1.088
F (000)
622
2512
630
1436
Crystal size (mm)
θ Range (°)
0.18 × 0.15 × 0.11
1.86–27.71
0.13 × 0.11 × 0.04
3.402–26.022
0.31 × 0.26 × 0.25
3.40–26.013
0.31 × 0.25 × 0.24
3.304–25.680
Index ranges
−6 ≤ h ≤ 14
−14 ≤ k ≤ 14
−14 ≤ l ≤ 14
−15 ≤ h ≤ 25
−25 ≤ k ≤ 23
−8 ≤ l ≤ 1
−11 ≤ h ≤ 11
−14 ≤ k ≤ 15
−16 ≤ l ≤ 16
−16 ≤ h ≤ 16
−19 ≤ k ≤ 14
−19 ≤ l ≤ 19
Reflections collected
Unique reflections
8336
5766
15394
9615
10420
5925
19674
6283
Rint
0.0732
0.0750
0.0952
0.1439
Completeness to (%) (θ)
Data/restraints/ parameters
Goodness of fit (GOF)
Final R1, wR2 indices
R1, wR2 indices (all data)
Residuals peak / hole (e Å−3
99.2 (25.24)
5766 / 44 / 354
0.921
99.6 (26.00)
9615 / 131 / 746
0.970
99.4 (25.24)
5925 / 64 / 380
0.968
97.3 (25.24)
6283 / 86 / 429
0.975
0.0723, 0.1729
0.1627, 0.2166
1.078 and − 1.10
0.0728, 0.0861
0.1483, 0.1179
0.730 and − 0.519
0.0801, 0.1493
0.1703, 0.2008
0.763 and − 0.533
0.0839, 0.1816
0.1769, 0.2485
0.905 and − 0.609
)
J = 4.0 Hz, 1H, ArH), 8.16 (s, 1H, ArH), 8.19 (s, 1H,
CH=N), 8.26 (s, 1H, CH=N), 9.77 (s, 1H, OH), 10.65 (s,
1H, OH). IR (KBr; cm−1): 3084 [w, ν(O–H)], 1613
[s,ν(C=N)], 1263 [s, ν(Ar–O)]. UV–vis [EtOH], λmax
(nm) [1.0 × 10−5 M] 219, 267 and 311. Anal. calc. For
C17H16ClN3O6 (%): C, 51.77; H, 4.21; N, 10.59, Found
(%): C, 51.95; H, 4.10; N, 10.37.
SCHEME 1 The synthetic route to H2L
4.4 | Syntheses of the Ni(II) complexes 1–4
2.18 (t, J = 6.0 Hz, 2H, CH2), 4.35 (m, 4H, CH2), 6.91 (d,
J = 4.0 Hz, 1H, ArH), 7.04 (d, J = 6.0 Hz, 1H, ArH), 7.13
(s, 1H, ArH), 7.23 (dd, J = 8 Hz, 1H, ArH), 8.14 (d,
Four solvent‐induced the Ni(II) complexes 1–4 are
obtained via the reaction of asymmetric Salamo‐

KANG ET AL.
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type ligand H2L with Ni(OAc)2·4H2O in a 2:3 molar
ratio in absolute methanol, n‐propanol, water, N,N‐
dimethylformamide and dimethyl sulphoxide solvents,
respectively.
evaporated and several pale green block‐shaped single
crystals suitable for X‐ray crystallographic analysis were
obtained. Yield, 2.86 mg (46.7%). UV–vis [EtOH], λmax
(nm) [1.0 × 10−5 M]: 230, 373. IR (KBr; cm−1): 1652
[s, ν(C=O)], 1606 [s, ν(C=N)], 1577 [s, νas(COO−)], 1419
[s, νs(COO−)], 1250 [w, ν(Ar–O)]. Anal. calc. For
C44H48Cl2N8Ni3O18 (%): C, 43.18; H, 3.95; N, 9.16; Ni,
14.39. Found (%): C, 43.09; H, 3.90; N, 9.21; Ni, 14.53.
4.4.1 | Synthesis of the complex 1
A solution of Ni(OAc)2·4H2O (3.73 mg, 0.015 mmol) in
methanol (3 ml) was added dropwise to a solution of
H2L (3.90 mg, 0.010 mmol) in acetone (1 ml). The color
of the mixed solution changed to pale green immediately.
After stirring for 10 min at room temperature, the mix-
ture was filtered and the filtrate was allowed to stand at
room temperature for about two weeks. Through partial
solvent evaporation, several pale green block‐shaped sin-
gle crystals suitable for X‐ray diffraction analysis were
obtained after two weeks. Yield, 3.45 mg (57.2%). UV–
vis [EtOH], λmax (nm) [1.0 × 10−5 M]: 231, 376. IR
(KBr; cm−1): 1606 [s, ν(C=N)], 1576 [s, νas(COO−)],
1425 [s, νs(COO−)], 1256 [w, ν(Ar–O)]. Anal. calc. For
C42H50Cl2N6Ni3O20 (%): C, 41.83; H, 4.18; N, 6.97; Ni,
14.60. Found (%): C, 41.68; H, 4.15; N, 7.03; Ni, 14.63.
4.4.4 | Synthesis of the complex 4
A solution of Ni(OAc)2·4H2O (3.74 mg, 0.015 mmol) in
methanol (2 ml) was added dropwise to a mixture solu-
tion of acetone (1.0 ml) and DMSO (0.5 ml) of H2L
(3.95 mg, 0.010 mmol). The color of the mixed solution
changed to pale yellow immediately. After stirring for
10 min at room temperature, the mixture was filtered
and the filtrate was allowed to stand in the dark at room
temperature for about two weeks, the solvent partially
evaporated and several pale yellow block‐shaped single
crystals suitable for X‐ray crystallographic analysis were
obtained. Yield, 3.03 mg (43.5%). UV–vis [EtOH], λmax
(nm) [1.0 × 10−5 M]: 231, 371. (1.0 × 10−5 M). IR (KBr;
cm−1): 1613 [s, ν(C=N)], 1576 [s, νas(COO−)], 1425 [s,
νs(COO−)], 1250 [w, ν(Ar–O)]. Anal. calc. for
C46H58Cl2N6Ni3O20S4 (%): C, 39.74; H, 4.21; N, 6.05; Ni,
12.67. Found (%): C, 39.69; H, 4.09; N, 5.92; Ni, 12.73.
4.4.2 | Synthesis of the complex 2
A solution of Ni(OAc)2·4H2O (3.75 mg, 0.015 mmol) in
n‐propanol (2 ml) was added dropwise to a mixture
solution of acetone (1.0 ml) and water (0.5 ml) of H2L
(3.96 mg, 0.010 mmol). The color of the mixed solution
changed to pale green immediately. After stirring for
15 min at room temperature, The mixture was filtered
and the filtrate was allowed stand in the dark at room
temperature for about two weeks, Through partial sol-
vent evaporation, several pale green block‐shaped single
crystals suitable for X‐ray diffraction analysis were
obtained after two weeks. Yield, 3.09 mg (50.9%). UV–
vis [EtOH], λmax (nm) [1.0 × 10−5 M]: 232, 375. IR
(KBr; cm−1): 1652 [s, ν(C=O)], 1608 [s, ν(C=N)], 1557
[s, νas(COO−)], 1419 [s, νs(COO−)], 1253 [w, ν(Ar–O)].
Anal. calc. For C44H52Cl2N6Ni3O19 (%): C, 43.46; H,
4.31; N, 6.91; Ni, 14.48. Found (%): C, 43.39; H, 4.27;
N, 6.98; Ni, 14.56.
ACKNOWLEDGEMENTS
This work was supported by the National Natural
Science Foundation of China (21761018) and the
Program for Excellent Team of Scientific Research in
Lanzhou Jiaotong University (201706), which is grate-
fully acknowledged.
ORCID
Wen‐Kui Dong http://orcid.org/0000-0003-1249-5808
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CCDC 1814381–1814384 contains the supplementary
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How to cite this article: Kang Q‐P, Li X‐Y, Zhao
Q, Ma J‐C, Dong W‐K. Structurally characterized
homotrinuclear Salamo‐type nickel(II) complexes:
Synthesis, solvent effect and fluorescence
properties. Appl Organometal Chem. 2018;e4379.
https://doi.org/10.1002/aoc.4379
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SUPPORTING INFORMATION
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