Synthesis, crystal structure, luminescence and electrochemical properties of a Salamo-type trinuclear cobalt(II) complex

Article abstract of DOI:10.1515/znb-2017-0191

A trinuclear Co(II) complex, [{CoL(C₄H₉OH)}₂-(OAc)₂Co]·C₃H₇NO, was synthesized by the reaction of a Salamo-type chelating ligand (H₂L=4,42′-dinitro-2,2′-[1,2-ethylenedioxybis(nit

Full text of DOI:10.1515/znb-2017-0191

Z. Naturforsch. 2018; 73(3–4)b: 203–210
Zong-Li Ren, Jing Hao, Ping Hao, Xiu-Yan Dong, Yang Bai and Wen-Kui Dong*
Synthesis, crystal structure, luminescence and
electrochemical properties of a Salamo-type
trinuclear cobalt(II) complex
https://doi.org/10.1515/znb-2017-0191
chemistry aiming at potential applications of Salen-
type compounds and their transition metal complexes
[42–47].
Received October 27, 2017; accepted November 29, 2017
Abstract: A trinuclear Co(II) complex, [{CoL(C4H9OH)}2-
(OAc)2Co]ꢀ·ꢀC3H7NO, was synthesized by the reaction of
a Salamo-type chelating ligand (H2Lꢀ=ꢀ4,42′-dinitro-2,2′-
[1,2-ethylenedioxybis(nitrilomethylidyne)]diphenol) with
cobalt(II) acetate tetrahydrate in n-butanol, and char-
acterized by elemental analyses, X-ray crystallography,
FT-IR and UV/Vis spectra. In the Co(II) complex, there
are two ligand L2− units, two μ2-acetate ions, two coor-
dinated n-butanol molecules and one non-coordinated
N,N-dimethylformamide molecule. The Co(II) atoms in
the structure of the Co(II) complex adopt slightly dis-
torted octahedra geometries. Furthermore, through inter-
molecular C–Hꢀ·ꢀ·ꢀ·ꢀO, O–Hꢀ·ꢀ·ꢀ·ꢀO and C–Hꢀ·ꢀ·ꢀ·ꢀπ interactions,
infinite layer-like, plane-like and 3D supramolecular
structures are constructed. The fluorescence and electro-
chemical properties of the Co(II) complex have also been
investigated.
Compared with Salen-type ligands, synthesis of
Salamo-type ligands is more difficult. With an O-alkylox-
ime unit (–CHꢀ=ꢀN–O–(CH)2–O–Nꢀ=ꢀCH–) instead of the
(–CHꢀ=ꢀN–(CH)2–Nꢀ=ꢀCH–) group, the high electronegativ-
ity of the oxygen atoms is expected to affect strongly the
electronic properties of the N2O2 coordination sphere,
which can lead to the novel properties and structures of
the resulting complexes. Furthermore, this variety can
give better ways to control and monitor coordination
in the context of the infinite supramolecular structures
[48–57]. In order to study the structural features, the
spectral characteristics and electrochemical properties of
transition metal complexes with Salamo-type bisoxime
ligands, we herein report one trinuclear Co(II) complex
with 4,4′-dinitro-2,2′-[1,2-ethylenedioxybis(nitrilomethyli
dyne)]diphenol (H2L).
Keywords: complex; crystal structure; property; Salamo-
type ligand; synthesis.
2 Experimental section
2.1 Materials and physical measurements
1 Introduction
All chemicals were of analytical reagent grades and were
used without further purification. C, H and N analyses
were obtained using a VarioEL V3.00 automatic elemen-
tal analysis instrument. Elemental analyses for Co(II) ions
were performed by an IRIS ER/S-WP-1 ICP atomic emission
spectrometer. IR spectra were recorded on a VERTEX70
FT-IR spectrophotometer, with samples prepared as KBr
(500–4000 cm−1) pellets. Melting points were obtained by
the use of an X4 microscopic melting point apparatus pro-
duced by Beijing Taike Instrument Limited Company and
were uncorrected. Fluorescent spectra were taken on an
LS-55 fluorescence photometer. X-ray single crystal struc-
ture determinations were carried out on a Bruker Smart
Apex CCD diffractometer. Cyclic voltammetry measure-
ments were performed using a Chi 660 voltammetric ana-
lyzer in DMF containing 0.05 mol L−1 tetrabutylammonium
perchlorate.
Many chemists have focused their studies mainly on the
investigation of the syntheses and crystal structures of
metal complexes having the Salen ligand and its ana-
logues [1–7]. These complexes can be used in lumines-
cence materials [8–13], biochemistry [14–21], magnetic
devices [22–25], optical sensors [26–30], catalysis [20, 31],
and supramolecular architectures [32–41]. Electrochemi-
cal properties are also important in modern coordination
*Corresponding author: Wen-Kui Dong, School of Chemical and
Biological Engineering, Lanzhou Jiaotong University, Lanzhou,
Gansu 730070, P. R. China, e-mail: dongwk@126.com
Zong-Li Ren, Jing Hao, Xiu-Yan Dong and Yang Bai: School of
Chemical and Biological Engineering, Lanzhou Jiaotong University,
Lanzhou, Gansu 730070, P. R. China
Ping Hao: Lanzhou University Second Hospital, Lanzhou, Gansu
730030, P. R. China
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204ꢀ ꢀZ.-L. Ren et al.: Trinuclear cobalt(II) complex
Scheme 1:ꢀSynthetic route to the Salamo-type ligand H2L.
2.2 Synthesis and characterization of the
ligand H2L
atoms were added in idealized positions. Details of the
data collection and the refinement are collected in Table 1.
CCDC 1567223 contains the supplementary crystallo-
The preparation step involved in the synthesis of H2L is graphic data for this paper. These data can be obtained
given in Scheme 1. 4,4′-Dinitro-2,2′-[1,2-ethylenedioxybis free of charge from The Cambridge Crystallographic Data
(nitrilomethylidyne)]diphenol (H2L) was prepared by the Centre via www.ccdc.cam.ac.uk/data_request/cif.
modification of the reported method [58–60]. A mixture
of 5-nitrosalicylicaldehyde (341.6 mg, 2.01 mmol) and
1,2-bis(aminoxy)ethane (93.4 mg, 1.00 mmol) in ethanolic 3 Results and discussion
solution was stirred at 55°C for 5 h. After cooling to room
temperature, the precipitate was filtered, and washed
3.1 IR spectra of H2L and its Co(II) complex
successively with ethanol and ethanol/hexane (1:4). The
product was dried under vacuum to give 298 mg of color-
The FT-IR spectra of H2L and its corresponding
less microcrystals. Yield: 85%. m.p. 202–203°C. – Elemen-
Co(II) complex show various bands in the range of
tal analysis for C16H14N4O8: calcd. C 49.24, H 3.62, N 14.35;
found C 49.12, H 3.75, N 14.12.
Table 1:ꢀCrystal data and structure refinements for the Co(II)
complex.
2.3 Synthesis of the Co(II) complex
Co(II) complex
ꢂ
[{CoL(C4H9OH)}2(OAc)2Co]ꢁ·ꢁ
C3H7NO
C50H64Co3N10O24
1365.90
291(2)
0.71073
Monoclinic
P21/c
A solution of Co(OAc)2·4H2O (2.47 mg, 0.01 mmol) in
n-butanol (3 mL) was added to a solution of H2L (3.52 mg,
0.01 mmol) in chloroform (3 mL) at room temperature.
The resulting solution immediately turned yellow, and
was stirred for 2 h at ambient temperature. The solution
was filtered and the filtrate was allowed to stand at room
temperature for about 4 weeks. The solvent was partially
evaporated to obtain several red prismatic single crystals
suitable for X-ray crystallographic analysis. – Elemental
Formula
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
Formula weight, gꢁ·ꢁmol−1
Temperature, K
Wavelength, Å
Crystal system
Space group
Unit cell dimensions
a, Å
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
10.850(4)
15.993(2)
17.724(2)
102.41(3)
3003.7(13)
2
b, Å
c, Å
analysis for C50H64Co3N10O24: calcd. C 43.97, H 4.72, N 10.25, β, °
Co 12.94; found C 43.76, H 4.89, N 10.09, Co 12.71.
Volume, Å3
Z
Dc, g cm−3
1.51
μ, mm−1
0.9
2.4 X-ray structure determination of the
Co(II) complex
F(000), e
1414
Crystal size, mm3
θ range, °
0.24ꢁ×ꢁ0.22ꢁ×ꢁ0.02
1.922–25.999
−10, 13/−18, 19/−21, 12
12 248
hkl range
A suitable single crystal of the Co(II) complex with approx-
imate dimensions of 0.24ꢀ×ꢀ0.22ꢀ×ꢀ0.02 mm3 was placed on
a Bruker Smart 1000 CCD area detector. The diffraction
data were collected using a graphite monochromated
Reflections collected
Independent reflections/Rint
Completeness to θmax, %
Data/restraints/parameters
5908/0.0239
99.8
5908/1/398
0.0475/0.1291
0.0655/0.1358
1.010
MoKα radiation (λꢀ=ꢀ0.071073 nm) at 291(2) K. The structure Final R1/wR2 [Iꢁ>ꢁ2σ(I)] [Iꢁ>ꢁ2σ(I)]
Final R1/wR2 (all data)
was solved the using the program Shelxs-97 and differ-
Goodness-of-fit (F2)
ence Fourier techniques, and refined by full-matrix least-
Δρmax/min, e Å−3
0.820/−0.484
squares methods on Fꢀ2 using Shelxl-97 [61]. Hydrogen
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Z.-L. Ren et al.: Trinuclear cobalt(II) complexꢃ
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400–4000 cm−1 so as to identify frequencies owing to the
Co–O and Co–N bonds (Fig. 1). The free ligand H2L shows a
characteristic Cꢀ=ꢀN stretching band at 1627 cm−1, while the
3.2 UV/Vis absorption spectra of H2L and its
Co(II) complex
Cꢀ=ꢀN stretching band of the Co(II) complex is observed at UV/Vis absorption spectra of H2L and its corresponding
1606 cm−1. The shift to lower frequency by ca. 21 cm−1 upon Co(II) complex in CH3OH solutions at 298 K are shown in
complexation shows a decrease in the Cꢀ=ꢀN bond order Fig. 2. The spectrum of H2L shows three absorption peaks
due to the coordinative bonds of the Co(II) atom with the at ca. 221, 267 and 322 nm [37–39]. The former two can be
oxime nitrogen lone pair [28]. The Ar–O stretching band assigned to the π–π* transition of the benzene rings, and
occurs at 1274 cm−1 for H2L, but is observed at 1242 cm−1 for the latter one to intra-ligand π–π* transitions of the Cꢀ=ꢀN
the Co(II) complex; shift to lower frequency indicates that bonds [40–42]. Upon the addition of Co(II) ions, the peaks
Co–O bonds are formed between the Co(II) atoms and the at 267 and 322 nm disappear. Furthermore, compared with
phenolic oxygen atoms [28]. Besides, an O–H stretching the absorption peaks of the free ligand, the correspond-
band appears at 3444 cm−1 in the Co(II) complex, which ing peaks of the Co(II) complex are observed at ca. 227 nm.
is evidence of the existence of the coordinated n-butanol The bathochromic shift indicates the coordination of the
molecules [36].
Co(II) ions with the ligand. The UV/Vis titration showed
Fig. 1:ꢀIR spectra of H2L and its corresponding Co(II) complex.
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206ꢀ ꢀZ.-L. Ren et al.: Trinuclear cobalt(II) complex
Fig. 2:ꢀUV/Vis absorption spectra of H2L and its Co(II) complex.
that the stoichiometry of complexation between them is
3:2. The appearances of four distinct isosbestic points at
330, 312, 280 and 261 nm are a significant evidence of a
complete deprotonation of the phenolic hydrogen present
in the Co(II) complex and a successful complexation
between the ligand and the Co(II) ions.
Fig. 3:ꢀ(a) Molecular structure of the Co(II) complex (displacement
ellipsoids at 30% probability, the hydrogen atoms are omitted for
clarity). (b) The coordination polyhedra for Co(II) atoms of the Co(II)
complex.
3.4 Supramolecular interaction of the Co(II)
complex
3.3 Description of the crystal and molecular
structure of the Co(II) complex
Notably, supramolecular interactions exist in crystals of
the Co(II) complex. The hydrogen bond parameters are
The molecular structure of the Co(II) complex is shown summarized in Table 3. As is shown in Fig. 4, there are three
in Fig. 3. Selected bond lengths and angles are listed in pairs of intramolecular hydrogen bonding interactions
Table 2.
(C3–H3ꢀ·ꢀ·ꢀ·ꢀO2, C8–H8Aꢀ·ꢀ·ꢀ·ꢀO9 and C15–H15ꢀ·ꢀ·ꢀ·ꢀO10) [62–
The Co(II) complex crystallizes in the monoclinic, 64]. Besides, the structure is stabilized by intermolecular
space group P21/c with Zꢀ=ꢀ2. It consists of three Co(II) C–Hꢀ·ꢀ·ꢀ·ꢀO, O–Hꢀ·ꢀ·ꢀ·ꢀO and C–Hꢀ·ꢀ·ꢀ·ꢀπ hydrogen bond interac-
atoms, two deprotonated L2− units, two μ2-acetate ions, tion. As a result, a 3D supramolecular structure is formed
two coordinated n-butanol molecules and one non- (Fig. 5; Figs. S1 and S2 in the Supplementary Information).
coordinated N,N-dimethylformamide molecule resulting The 3D supramolecular structure of the Co(II) complex is
in a trinuclear Co(II) complex. As there are two of these composed of two parts. The first part is linked by inter-
complexes in the unit cell, the entire trinuclear aggregate molecular C–Hꢀ·ꢀ·ꢀ·ꢀO and O–Hꢀ·ꢀ·ꢀ·ꢀO hydrogen bonding
̅
has crystallographic inversion (ꢁ1) symmetry. All the six- interactions. The other part is composed of the C–Hꢀ·ꢀ·ꢀ·ꢀπ
coordinated Co(II) atoms lie in a slightly distorted octahe- interactions. The intermolecular hydrogen bonds of the
dral coordination environment. The two terminal Co(II) Co(II) complex not only make its structure variable but
(Co1 and Co1#1) atoms are located in the N2O2 coordina- also make it stable [65–68].
tion sphere of L2−. One oxygen atom (O9 or O9#1) comes
from the acetato bridge and the other oxygen atom (O11
or O11#1) comes from the n-butanol molecule. The coor- 3.5 Fluorescence properties of the Co(II)
dination sphere of the central Co(II) atom (Co2) contains
complex
four phenol oxygen atoms (O1, O6, O1#1 and O6#1) from two
L2− and two oxygen atoms (O10 and O10#1) from two bridg- The emission spectra of the Co(II) complex in dilute DMF
ing μ2-acetate anions. As do the ligands L, these acetate solution at ambient temperature are shown in Fig. 6. The
anions firmly link the peripheral Co(II) atoms with the H2L ligand exhibits an intense photoluminescence with
central one.
maximum emission at ca. 435 nm when excited at 320 nm,
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Table 2:ꢀSelected bond lengths (Å) and angles (deg) for the Co(II) complex.a
Bond
ꢁ
ꢁ
Bond
ꢁ
ꢁ
Bond
ꢁ
Co1–O1
Co1–O6
Co1–O9
Co1–O11
ꢂ
ꢂ
ꢂ
ꢂ
2.042(2)ꢂ
2.065(2)ꢂ
2.065(2)ꢂ
2.107(2)ꢂ
Co2–O1
Co2–O6
Co2–O10
Co2–O1#1
ꢂ
ꢂ
ꢂ
ꢂ
2.161(2)ꢂ
2.109(2)ꢂ
2.052(2)ꢂ
2.161(2)ꢂ
Co1–N2
ꢂ
ꢂ
ꢂ
ꢂ
2.120(2)
2.110(3)
2.1089(19)
2.052(2)
Co1–N3
Co2–O6#1
Co2–O10#1
Angle
ꢁ
ꢁ
Angle
ꢁ
ꢁ
Angle
ꢁ
O1–Co1–O6
O1#1–Co2–O10#1
O1–Co1–O9
O6#1–Co2–O10#1
O1–Co1–O11
O1–Co1–N2
O9–Co1–N3
O9–Co1–N2
O1–Co1–N3
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
81.45(9)ꢂ
87.62(9)ꢂ
O11–Co1–N2
O1#1–Co2–O6#1
O11–Co1–N3
N2–Co1–N3
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
85.74(10)ꢂ
77.73(8)ꢂ
O6–Co1–O9
O6–Co1–O11
O6–Co1–N2
O1#1–Co2–O6
O6–Co1–N3
O1–Co2–O10#1
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
93.94(9)
89.35(9)
167.41(9)
102.27(8)
86.34(11)
92.38(9)
92.38(9)
87.23(8)
92.77(8)
91.89(9)ꢂ
87.41(10)ꢂ
104.98(12)ꢂ
77.73(8)ꢂ
87.23(8)ꢂ
89.13(9)ꢂ
86.88(10)ꢂ
92.26(10)ꢂ
91.14(10)ꢂ
167.35(12)ꢂ
O1–Co2–O6
O1–Co2–O10
O1–Co2–O6#1
O9–Co1–O11
87.62(9)ꢂ
102.27(8)ꢂ
176.66(9)ꢂ
92.77(8)ꢂ
O1#1–Co2–O10ꢂ
O6–Co2–O10
ꢂ
ꢂ
O6#1–Co2–O10 ꢂ
O6–Co2–O10#1
aSymmetry transformation used to generate equivalent atoms: #1ꢁ−ꢁx, 1ꢁ−ꢁy, 1ꢁ−ꢁz.
Table 3:ꢀHydrogen bonding interactions (Å, deg) for the Co(II) complex.a
D–H·ꢂ·ꢂ·A
d(D–H)
d(H·ꢂ·ꢂ·A)
d(D·ꢂ·ꢂ·A)
∠DHA
Symmetry code A
C3–H3·ꢁ·ꢁ·O2
0.93
0.97
0.93
0.93
0.93
0.97
0.97
0.97
0.97
0.96
0.96
0.96
0.93
2.37
2.45
2.56
2.60
2.16
2.36
2.39
2.49
2.49
2.54
2.28
2.59
2.48
2.89
2.80
2.687(4)
3.292(4)
3.228(4)
3.462(4)
3.003(4)
3.087(5)
3.300(5)
3.287(5)
3.206(5)
3.484(5)
3.109(6)
3.438(6)
3.027(5)
100
145
129
155
150
131
156
139
130
167
144
147
118
123
154
x, y, z
C8–H8A·ꢁ·ꢁ·O9
x, y, z
C15–H15··ꢁ·O10
O11–H11··ꢁ·O2
O11–H11··ꢁ·O3
C9–H9A·ꢁ·ꢁ·O8
−x, 1ꢁ−ꢁy, 1ꢁ−ꢁz
1ꢁ−ꢁx, 1/2ꢁ+ꢁy, 3/2ꢁ−ꢁz
1ꢁ−ꢁx, 1/2ꢁ+ꢁy, 3/2ꢁ−ꢁz
1ꢁ+ꢁx, y, z
1ꢁ−ꢁx, 1/2ꢁ+ꢁy, 3/2ꢁ−ꢁz
1ꢁ−ꢁx, 1/2ꢁ+ꢁy, 3/2ꢁ−ꢁz
1ꢁ−ꢁx, 1/2ꢁ+ꢁy, 3/2ꢁ−ꢁz
x, 3/2ꢁ−ꢁy, −1/2ꢁ+ꢁz
x, −1ꢁ+ꢁy, z
1ꢁ−ꢁx, −1/2ꢁ+ꢁy, 3/2ꢁ−ꢁz
x, y, z
1ꢁ−ꢁx, 1ꢁ−ꢁy, 1ꢁ−ꢁz
x, y, z
C9–H9B·ꢁ·ꢁ·O2
C17–H17A·ꢁ·ꢁ·O12
C18–H18A·ꢁ·ꢁ·O3
C22–H22C··ꢁ·O7
C24–H24A··ꢁ·O5
C24–H24B·ꢁ·ꢁ·O3
C25–H25·ꢁ·ꢁ·O2
C8–H8B··ꢁ·Cg1
C18–H18B·ꢁ·ꢁ·Cg2
aCg1 and Cg2 are the centroids of the C1–C6 and C11–C16 atoms, respectively.
which can be assigned to intraligand π–π* transitions. three-electrode cell, consisting of a glassy carbon (GC)
Compared with H2L, weaker fluorescence intensity of the disk (Uꢀ=ꢀ5 mm) as a working electrode, a platinum wire as
Co(II) complex is observed, indicating that the fluores- auxiliary and a Ag/AgCl electrode as reference. In DMF, the
cence characteristic has been influenced by the introduc- Co(II) complex displays two pairs of redox peaks resulting
tion of the Co(II) ions [41, 50].
from the redox reactionds of CoIII/CoII and CoII/CoI. The first
pair have potentials Epa1 of −0.762 V and Epc1 of −0.870 V
for the currents ipa1ꢀ=ꢀ49.101 μA and ipc1ꢀ=ꢀ−89.764 μA.
Another pair of redox peaks appear for the electron
transfer between CoII and CoI with potentials Epa2 of
−1.754 V and Epc2 of −1.269 V for currents ipa2ꢀ=ꢀ−9.520 μA,
3.6 Electrochemistry studies of the Co(II)
complex
The cyclic voltammogram of the Co(II) complex is shown ipc1ꢀ=ꢀ−88.079 μA. Also, these differences can be associ-
in Fig. 7. The cyclic voltammetry was performed within ated with the coordination environment around the metal
the potential range −1.5 to +1.5 V at the scanning rate of center. These characteristics suggest that the electrolysis
50 mV s−1 at ambient temperature (300 K) in a standard processes of the Co(II) complex are irreversible.
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208ꢀ ꢀZ.-L. Ren et al.: Trinuclear cobalt(II) complex
Fig. 7:ꢀCyclic voltammogram of the Co(II) complex in DMF solution at
293 K. Scan rate: 50 mV s−1.
Fig. 4:ꢀIntramolecular hydrogen bonding interactions of the Co(II)
complex.
4 Conclusions
We have designed and synthesized a supramolecular
trinuclear Co(II) complex with a Salamo-type ligand H2L.
The Co(II) complex has been characterized by physico-
chemical methods and single-crystal X-ray diffraction. In
the Co(II) complex, the three Co(II) atoms are hexa-coor-
dinated by the O and N atoms of two completely deproto-
nated L2− units, two μ2-acetato anions and two coordinated
n-butanol molecules. In addition, supramolecular struc-
tures ranging from chains to 3D arrays are formed by
abundant noncovalent interactions. The luminescent
properties of H2L and its Co(II) complex were also inves-
tigated, compared with H2L, the Co(II) complex exhibits
lower fluorescence intensity. Electrochemistry studies
suggest that electrolysis processes are irreversible.
Fig. 5:ꢀPart of the infinite layer-like of the Co(II) complex with
intermolecular hydrogen bondings (hydrogen atoms, except those
forming hydrogen bonds, are omitted for clarity).
5 Supporting information
Figs. S1 and S2 of the supramolecular structure are avail-
able online (https://doi.org/10.1515/znb-2017-0191).
Acknowledgments: This work was supported by the
National Natural Science Foundation of China (21361015
and 21761018) and the Program for Excellent Team of Sci-
entific Research in Lanzhou Jiaotong University (201706),
which are gratefully acknowledged.
References
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Fig. 6:ꢀFluorescence spectra of the Co(II) complex.
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210ꢀ ꢀZ.-L. Ren et al.: Trinuclear cobalt(II) complex
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