Unprecedented fluorescent dinuclear CoII and ZnII coordination compounds with a symmetric bis(salamo)-like tetraoxime

Article abstract of DOI:10.3390/molecules23051141

Two unprecedented homometallic Co^II and Zn^II coordination compounds, [M₂(L)(OCH₃)][M₂(L)(OAc)] (M^II = Co^II (1) and Zn^II (2)), with a novel symmetric bis(salamo)-like t

Full text of DOI:10.3390/molecules23051141

molecules
Article
II
II
Unprecedented Fluorescent Dinuclear Co and Zn
Coordination Compounds with a Symmetric
Bis(salamo)-Like Tetraoxime
Lin-Wei Zhang, Ling-Zhi Liu, Fei Wang and Wen-Kui Dong * ID
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, 730070, China;
zhanglinwei@mail.lzjtu.cn (L.-W.Z.); llz1009663202@126.com (L.-Z.L.); wangfei3986@163.com (F.W.)
*
Correspondence: dongwk@126.com; Tel.: +86-931-493-8755
Academic Editor: Gregor Drummen
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀ
ꢁꢂꢃꢄꢅꢆ
Received: 31 March 2018; Accepted: 8 May 2018; Published: 10 May 2018
II
Abstract:
Two unprecedented homometallic Co and ZnII coordination compounds,
M (L)(OCH )][M (L)(OAc)] (M = Co (1) and Zn (2)), with a novel symmetric bis(salamo)-like
II
II
II
[
2 3 2
tetraoxime ligand H L were synthesized and characterized by elemental analyses, infrafred (IR),
3
ultraviolet–visible spectroscopy (UV-Vis), fluorescent spectra and single-crystal X-ray diffraction
analyses. The unit cell of the two coordination compounds contains two crystallographically and
chemically independent dinuclear coordination compounds. In the two coordination compounds,
three metal ions are five-coordinated, formed two square pyramidal and a trigonal bipyramidal
geometries, and the other metal ion is a hexacoordinate octahedral configuration. In addition,
the coordination compound
1 forms a 3D supramolecular structure, and the coordination compound
2
forms a 0D dimer structure by the inter-molecular hydrogen bond interactions. Meanwhile,
the fluorescence spectra of the coordination compounds 1 and 2 were also measured and discussed.
Keywords: bis(salamo)-like tetraoxime; coordination compound; synthesis; structure; fluorescence property
1
. Introduction
As we know, salen-like ligands play an important role in the field of inorganic chemistry [1–8].
They are synthesized by the interaction of diamines with salicylaldehyde or its derivatives, and can
coordinate to transition metal ions in a tetradentate fashion to obtain mono- or polynuclear metal
coordination compounds [
as nonlinear optical materials [13], catalysts [14], biological systems [15], magnetic materials [16],
supramolecular buildings [17 26], and so on. In order to improve the structure of salen-like ligands
9–12]. These coordination compounds have been extensively investigated
–
and strengthen the coordination ability, in recent years, our research has mainly concentrated on the
syntheses of salamo-like ligands and their metal coordination compounds. A new study has shown that it
4
◦
is at least 10 times more stable against the metathesis reaction in H O/MeCN (5:95) at 40 C than salen-like
2
coordination compounds due to the unique structure of salamo-like coordination compounds [27]. In our
previous studies on salamo-type metal complexes, we exchanged salicylaldehyde for its derivatives to
obtain some new salamo-like transition metal coordination compounds with different structures [28
The structural motifs of these coordination compounds may be affected by the performance of the ligands,
the property of the central atoms, solvent effect, anion effect and so forth [33 42]. In addition, some practical
photophysical properties of transition metal coordination compounds with salamo-like bisoxime ligands
have been reported in succession [43 50]. The N O tetradentate motif can coordinate easily with transition
metal ions. Therefore, salamo-like ligands can form mono-, di- or trinuclear metal coordination compounds
–32].
–
–
2
2
II
II
with transition metal ions. Meanwhile, some Co and Zn salamo-like coordination compounds have
been reported earlier [51–57].
Molecules 2018, 23, 1141; doi:10.3390/molecules23051141
www.mdpi.com/journal/molecules

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The aim of the present work is the structural characterization of the homometallic coordination
compounds and based on a symmetric bis(salamo)-like tetraoxime ligand. Herein, the ligand
H L and its corresponding dinuclear coordination compounds and were prepared successfully.
1
2
1
2
3
Interestingly, the obtained 2:1 (metal-to-ligand stoichiometry) type coordination compounds are unusual in
the previously reported bis(salamo)-type metal coordination compounds, in which most of them possess
3:1 (metal-to-ligand stoichiometry) type of structures [43,57]. Furthermore, the supramolecular features
and luminescent spectra of the coordination compounds 1 and 2 are discussed.
2
. Results and Discussion
2
.1. Crystal Structures of the Coordination Compounds 1 and 2
X-ray crystallographic analyses reveal that the structure of the coordination compound
2 is
similar to that of the coordination compound
1. The coordination compounds 1 and 2 form novel
dinuclear structures, which are different from the common trinuclear structures of bis(salamo)-like
metal coordination compounds reported earlier [58
compounds and
Selected bond lengths and angles are listed in Tables 1 and S1.
–
62]. The crystal structures of the coordination
II
1
2
and the coordination polyhedrons of the M atoms are shown in Figures 1 and 2.
Table 1. Selected bond lengths (Å) for the coordination compounds 1 and 2.
Coordination Compound 1
Bonds Lengths (Å)
Bonds Lengths (Å)
Bonds Lengths (Å)
Co1-O1
Co1-O8
Co1-N2
Co1-N1
Co1-O4
Co2-O7
Co2-O8
1.952(3)
1.961(3)
2.033(3)
2.045(3)
2.071(3)
1.954(3)
1.961(3)
Co2-N3
Co2-O4
Co2-N4
Co3-O12
Co3-N5
Co3-N6
Co3-O9
2.060(3)
2.069(3)
2.083(4)
2.021(3)
2.047(4)
2.063(3)
2.074(3)
Co3-O16
Co3-O17
Co4-O15
Co4-O9
Co4-N7
Co4-O12
Co4-N8
2.138(3)
2.198(3)
1.917(3)
2.022(3)
2.027(3)
2.086(3)
2.139(3)
Coordination Compound 2
Bonds Lengths (Å)
Bonds Lengths (Å)
Bonds Lengths (Å)
Zn1-O17
Zn1-O14
Zn1-O15
Zn1-N1
Zn1-N2
Zn2-O14
Zn2-O15
1.954(5)
2.082(4)
1.978(4)
2.088(6)
2.101(5)
2.057(4)
1.991(5)
Zn2-O16
Zn2-N3
Zn2-N4
Zn3-O4
Zn3-O3
Zn3-O7
Zn3-O8
1.951(5)
2.103(6)
2.111(5)
2.047(4)
2.056(4)
2.205(5)
2.138(5)
Zn3-N6
Zn3-N5
Zn4-O4
Zn4-O9
Zn4-O3
Zn4-N8
Zn4-N7
2.115(5)
2.103(5)
2.096(4)
1.941(4)
2.027(4)
2.031(5)
2.180(5)
The coordination compounds 1 and 2 crystallize in the triclinic crystal system, space group P-1,
and the unit cell of the two coordination compounds contains two crystallographically and chemically
independent dinuclear coordination compounds (A and B molecules) (As shown in Figures 1 and 2).
II
In the two coordination compounds, A molecule consisting of two M atoms, one heptadentate
3
−
L) unit and one µ -bridged methoxyl group, and B molecule is composed of two M atoms,
2
II
(
3
−
one heptadentate (L) unit and one chelating acetate ion. In molecules A and B, the purpose of
the acetate ion and methoxyl group is to compensate for the charge and make the whole molecule
neutral. The obtained 2:1 (metal-to-ligand stoichiometry) type dinuclear coordination compounds are
unprecedented in the reported bis(salamo)-like metal coordination compounds, which always possess
3
:1 (metal-to-ligand stoichiometry) type of structures [43,57].

Molecules 2018, 23, 1141
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Figure 1.
atoms are omitted for clarity). (
(
a
) Molecule structure and atom numberings of the coordination compound
1
(hydrogen
II
b) Coordination polyhedrons for Co atoms of the coordination
compound 1.
II
In each of the A molecules, all of the M atoms are located in the N O coordination spheres of
2
2
the salamo-type ligand (L)3 unit, the
−
µ
2
-bridged methoxyl groups bridge two M atoms in a familiar
M-O-M fashion (Figures 1a and 2a). Meanwhile, two M atoms of the coordination compounds
II
II
1
and
2
are pentacoordinated and adopt distorted trigonal bipyramidal (Co1 and Zn1) and square pyramidal (Co2
and Zn2) geometries (Figures 1b and 2b), which were deduced by calculating the values of = 0.62
τ
,
Co1
τ
= 0.41,
τ
= 0.63 and
τ
= 0.41, respectively [63]. From the calculation results, we can see that
Zn2
Co2
Zn1
the
values of Co2 and Zn2 are less than 0.5, forming square pyramidal configurations. The structures of
the B molecules are different from those of the A molecules, the Co4 and Zn4 atoms of the coordination
compounds and are pentacoordinated and adopt distorted square pyramidal geometries, which were
deduced by calculating the values of = 0.49 and = 0.48, respectively. The Co4 and Zn4 atoms
τ values of Co1 and Zn1 are greater than 0.5, forming trigonal bipyramidal configurations, and the
τ
1
2
τ
τ
Zn4
Co4
3−
are located in the N O coordination spheres of the salamo-type ligand (L) unit, and coordinate to
2
2
one phenoxo oxygen (O9) atom, respectively. The Co3 and Zn3 atoms coordinate to N O atoms of the
2
2
deprotonated ligand (L)3 units as well as two oxygen atoms from one chelating acetate ion, and have
−
a hexacoordinated environment and adopt distorted octahedral coordination geometries (By means of

Molecules 2018, 23, 1141
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continuous shape measures (CShM), when the value of CShM is the smallest, the ideal structure is the
octahedron configuration, CShM = 3.03270 and 3.72885 for Co3 and Zn3 atoms) [64].
Figure 2.
atoms are omitted for clarity). (
(
a
) Molecule structure and atom numberings of the coordination compound
2
(hydrogen
II
b
) Coordination polyhedrons for Zn atoms of the coordination
compound 2.
The supramolecular structures of the coordination compounds
1
and
2 are very different from
each other. In the crystal structure of the coordination compound
1, there are eight significant
intermolecular hydrogen bonds (C9-H9A···O13, C10-H10···O15, C40-H40A···Br8, C61-H61A···Br2,
C36-H36···Br7, C8-H8A···Br8, C39-H39B···Br6 and C43-H43···O7) and one intramolecular hydrogen
bond (C49-H49A···O16). The units are interlinked by the intermolecular C9-H9A···O13, C10-H10···O15,
C40-H40A···Br8, C61-H61A···Br2 and C43-H43···O7 hydrogen bonds into a 2D layered supramolecular
structure, which are further assembled into an infinite 3D network structure with the help
of intermolecular C36-H36···Br7, C8-H8A···Br8 and C39-H39B···Br6 hydrogen bond interactions
(
(
Figure 3). For the coordination compound 2, there is a pairs of intermolecular hydrogen bond
3
−
C55-H55···O10). The oxygen (O10) atom of the (L) unit is hydrogen bonded to the C55–H55 group
of another coordination compound
2
molecule, linking a 0D dimer structure (Figure 4). In addition,
A and B molecules are connected steadily by intermolecular C-H···O hydrogen bond interactions.
Putative hydrogen bond interactions for the coordination compounds 1 and 2 are shown in Table 2.

Molecules 2018, 23, 1141
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◦
Table 2. Putative hydrogen bond interactions (Å, ) for the coordination compounds 1 and 2.
Coordination Compound 1
D-X···A
d(D-X)
d(X···A)
d(D···A)
∠D-X···A
Symmetry Code
C9-H9A···O13
C10-H10···O15
C40-H40A···Br8
C43-H43···O7
C49-H49A···O16
C8-H8A···Br8
C61-H61A···Br2
C36-H36···Br7
C39-H39B···Br6
0.97
0.93
0.97
0.93
0.97
0.97
0.96
0.93
0.97
2.44
2.43
2.90
2.60
2.46
3.92
2.99
3.81
2.96
3.231(6)
3.130(5)
3.776(6)
3.477(6)
3.379(6)
3.019(5)
3.280(6)
3.044(5)
3.895(5)
138
132
151
158
159
154
99
−x,1−y,1−z
140
161
Coordination Compound 2
D-X···A
d(D-X)
d(X···A)
d(D···A)
∠D-X···A
Symmetry Code
C6-H6···O16
C11-H11···O16
C22-H22A···O8
C44-H44···O9
C55-H55···O10
0.93
0.93
0.97
0.93
0.93
2.52
2.57
2.43
2.40
2.59
3.394(8)
3.439(7)
3.374(8)
3.070(9)
3.297(9)
157
156
163
129
133
[1−x,1−y,1−z]
Figure 3. The 3D supramolecular structure of the coordination compound
1 with inter-molecular
hydrogen bondings (hydrogen atoms, except those forming hydrogen bonds, are omitted for clarity).
Figure 4. The 0D dimer structure of the coordination compound
2 with inter-molecular hydrogen
bondings (hydrogen atoms, except those forming hydrogen bonds, are omitted for clarity).

Molecules 2018, 23, 1141
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2
.2. IR Spectra
IR spectra of H L and its corresponding coordination compounds
1
and
2
exhibit various bands in
3
−
1
−1
the region of 400–4000 cm . Main IR bands/cm for the ligand H L and its coordination compounds
3
1
and 2 are presented in Table 3.
Table 3. Main IR bands (cm 1) for the ligand H L and its coordination compounds 1 and 2.
−
3
Coordination Compound
ν
ν
ν
ν
(Co–N)
(C=N)
(Ar–O)
(Co–O)
H3L
1
2
1611
1619
1621
1265
1258
1261
447
453
512
519
−
1
The free ligand H L shows a characteristic C=N stretching band at 1611 cm , while the
3
−
1
C=N stretching bands of the coordination compounds
1
and
2
appear at 1619 and 1621 cm
,
−
1
respectively [65]. For the ligand H L, the Ar-O stretching band appears at 1265 cm , which is
3
−
1
observed at 1258 and 1261 cm for the coordination compounds
and Ar–O stretching frequencies are shifted to lower frequencies, indicating that the M–N and M–O
bonds are formed [66]. For the coordination compound , the (Co–O) and (Co–N) frequencies are
observed at 447 and 512 cm , respectively [67]. Meanwhile, the (Zn–O) and (Zn–N) bonds at 453
. As pointed out by Percy and Thornton [68], the M-O
and M-N frequency assignments are at times difficult.
1 and 2. The characteristic C=N
1
ν
ν
−
1
ν
ν
−
1
and 519 cm for the coordination compound
2
2
.3. Ultraviolet–Visible Spectroscopy (UV-Vis) Spectra
The UV-Vis absorption spectra of H L and its coordination compounds
1
and
MeOH solution, as shown in Figure 5. It can be seen that the absorption peaks of
and are obviously different from those of the H L upon coordination.
The electronic absorption spectrum of H L consists of one relatively intense peak centered at 330 nm,
2 were determined
3
−
5
−1
in 1
×
10 mol
·
L
the coordination compounds
1
2
3
3
assigned to the
π
–
π
* transition of the oxime groups [69
,
70]. Compared with the absorption peak of the
and appear
at 380 and 378 nm, which are bathochromically shifted by 50 and 48 nm, respectively, indicating the
free ligand H L, the corresponding absorption peaks of the coordination compounds
1
2
3
II
II
coordination of the Co and Zn ions with the ligand H L.
3
Figure 5. Ultraviolet–visible spectroscopy UV-Vis absorption spectra of H L and its coordination
3
compounds 1 and 2 in MeOH (1 × 10− M).
5

Molecules 2018, 23, 1141
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In the UV-Vis titration experiment of the coordination compound
1
, with the increasing
2+
concentration of Co , the absorbance of the solution at 380 nm enhanced, and at 330 nm reduced.
The absorption peak reached the highest value after Co2+ was added up to 2 equiv. The spectroscopic
2+
3−
titration indicates that the ratio of the replacement reaction was 2:1 (Co : L ). Similar changes also
appear in the coordination compound 2, obtaining the same conclusion (Figure 6).
Figure 6. UV-Vis spectral changes of the coordination compounds
different amounts of Co and Zn ions (MeOH (1 × 10 M)).
1 (a) and 2 (b) upon addition of
II
II
−5
2
.4. Fluorescence Spectra
The fluorescence spectra of H L and its corresponding coordination compounds
1 and 2 were
3
investigated at room temperature and are shown in Figure 7. The free ligand H L exhibits a relatively
3
strong emission peak at ca. 462 nm upon excitation at 370 nm, and it should be assigned to the
*
intraligand
π
–
π
transition. The coordination compound
1
shows lower photoluminescence with
maximum emission at ca. 454 nm. Compared with the ligand H L, emission intensity of the
3
II
coordination compound
1
reduces obviously, indicating that the Co ions have a quality of fluorescent
quenching, which makes the conjugated system larger and also indicates it may be a purple device.
On the other hand, the coordination compound
ca. 460 nm. The intense peak is likely due to the coordination of H L with the Zn ions, which
2
shows an obvious fluorescence enhancement at
II
3
breaks the intramolecular hydrogen-bonding interactions of H L and increases the coplanarity of the
3
conjugated system.

Molecules 2018, 23, 1141
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Figure 7. Emission spectra of H L (c = 1
and 2 in dilute MeOH solutions at room temperature.
×
10-5 M, λex = 370 nm) and its coordination compounds
1
3
In addition, the fluorescence titration experiment of the coordination compound
Figure 8. The fluorescence intensity of the solution hardly changed after the Zn ions were added up to
2
is shown in
II
2
equiv, which shows the same conclusion compared with the UV-Vis titration experiment. Meanwhile,
II
coordination of the Zn ions evidently increases the fluorescence intensity of the ligand H L.
3
−
5
Figure 8. Fluorescence spectrum changes of H L (c = 1
of different amounts of Zn ions.
×
10 M, λex = 370 nm) solution upon addition
3
II
3
. Experimental
3
.1. Materials and Physical Measurements
All chemicals were of analytical reagent grade and were used without further purification. C, H,
and N analyses were obtained using a GmbH VarioEL V3.00 automatic elemental analysis instrument
Berlin, Germany). Elemental analyses for Co and Zn were detected by an IRIS ER/S WP-1 ICP atomic
(
·
emission spectrometer (Berlin, Germany). Melting points were measured via a microscopic melting point
apparatus (Beijing Taike Instrument Limited Company, Beijing, China). H-NMR spectra were determined
1

Molecules 2018, 23, 1141
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by German Bruker AVANCE DRX-400 spectroscopy (Bruker AVANCE, Billerica, MA, USA). Infrared
(
IR) spectra were recorded with a VERTEX-70 FT-IR spectrophotometer, with samples prepared as KBr
−1
(400–4000 cm ) (Bruker, Billerica, MA, USA). Ultraviolet–visible spectroscopy (UV-Vis) absorption
and fluorescence spectra were recorded on a Shimadzu UV-2550 spectrometer (Shimadzu, Tokyo,
Japan) and F-7000 FL spectrometer (Hitachi, Tokyo, Japan), respectively. X-ray single crystal structure
determinations were carried out on a Bruker APEX-II CCD diffractometer (Bruker AVANCE, Billerica,
MA, USA). Supplementary crystallographic data for this paper have been deposited at the Cambridge
Crystallographic Data Centre (1562395 and 1562396 for the coordination compounds
obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html.
1 and 2) and can be
3
.2. Preparation of Ligand H3L
,2-Bis(aminooxy)ethane was synthesized according to an analogous method reported earlier [71].
Yield, 78.2%. Anal. Calcd. for C H N O : C, 26.08; H, 8.76; N, 30.42. Found: C, 25.38; H, 8.20; N,
1
2
8
2
2
2
9.76%. The synthetic route to novel bis(salamo)-like tetraoxime ligand (H L) is shown in Scheme 1.
3
Scheme 1. Synthetic route to the bis(salamo)-like tetraoxime ligand H L.
3
Next,
the chloroform solution of 3,5-dibromosalicylaldehyde was added to
1
4
,2-bis(aminooxy)ethane by drop to obtain a monooxime compound 2-[O-(1-ethyloxyamide)]oxime-
,6-dibromophenol. Last, the monooxime compound was reacted with 4-tert-butyl-2,6-diformylphenol
(
2:1) in the ethanol solvent after purification by the recrystallization method so as to obtain the
◦
symmetric bis(salamo)-like tetraoxime ligand H L. Yield, 89.5%. m.p. 122–123 C. Anal. Calcd. for
C H N O Br : C, 41.03; H, 3.44; N, 6.38. Found: C, 40.85; H, 3.32; N, 5.99%. H-NMR (400 MHz,
3
1
30
30
4
7
4
DMSO)
δ
10.37 (s, 1H), 10.04 (s, 1H), 8.45 (d, J = 1.8 Hz, 4H), 8.29 (s, 1H), 7.59 (s, 2H), 7.57 (d, J = 2.6 Hz,
2
H), 7.51 (d, J = 2.6 Hz, 2H), 4.44 (s, 8H), 1.21 (s, 9H).
3
.3. Syntheses of the Coordination Compounds 1 and 2
The coordination compounds and were synthesized by the reaction of H L with
Co(OAc)2 4H O and Zn(OAc)2 2H O, respectively. A solution of Co(OAc)2
in methanol (2 mL) was added dropwise to a solution of H L (8.8 mg, 0.01 mmol) in dichloromethane
1
2
3
·
·
·
4H O (4.98 mg, 0.02 mmol)
2
2
2
3
(
3 mL). The color of the mixing solution turned to bronzing immediately, and then continuous stirring
for 0.5 h at room temperature. The mixture was filtered and the filtrate was allowed to stand at
room temperature for about two weeks. The solvent was partially evaporated and obtained brown,
block-shaped single crystals suitable for X-ray crystallographic analysis with a yield of 76.4%. Anal.
Calcd. for [Co (L)(OCH )][Co (L)(OAc)] (C H Br Co N O ): C, 36.27; H, 2.76; N, 5.53; Co, 12.18.
2
3
2
63 60
8
4
8
17
Found: C, 36.52; H, 2.64; N, 5.27; Co,11.85%.
The coordination compound was prepared by the same method as that of the coordination
compound . A solution of Zn(OAc)2 2H O (4.38 mg, 0.02 mmol) in methanol (2 mL) was added
dropwise to a solution of H L (8.8 mg, 0.01 mmol) in chloroform (3 mL). The color of the mixing
2
1
·
2
3

Molecules 2018, 23, 1141
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solution turned to yellow immediately, and then continuous stirring for 0.5 h at room temperature.
The mixture was filtered and the filtrate was allowed to stand at room temperature for about two
weeks, the solvent was partially evaporated and obtained bright-yellow, block-shaped crystals. Yield,
7
1.6%. Anal. Calcd. for [Zn (L)(OCH )][Zn (L)(OAc)] (C H Br Zn N O ): C, 35.85; H, 2.79; N, 5.46;
2 3 2 63 60 8 4 8 17
Zn, 12.58 %. Found: C, 36.18; H, 2.71; N, 5.32; Zn, 12.36%.
3
.4. X-ray Structure Determination of the Coordination Compounds 1 and 2
X-ray diffraction data were collected on a Bruker APEX-II CCD diffractometer (296(2) K) for the
coordination compounds and using graphite monochromatized Mo-K radiation (λ = 0.71073 Å).
1
2
α
Unit cell parameters were determined by the least-squares analyses. The LP factor and Semi-empirical
absorption corrections were applied to the intensity data. The structures were solved by the direct
method (SHELXS-2016), and all hydrogen atoms were added theoretically. All non-hydrogen atoms
2
were refined anisotropically using a full-matrix least-squares procedure on F with SHELXL-2016
(Bruker AVANCE, Billerica, MA, USA). Anisotropic thermal parameters were assigned to all
non-hydrogen atoms. Contributions to scattering due to these highly disordered solvent molecules
were removed using the SQUEEZE routine of PLATON, the structures were then refined again using
the data generated. The hydrogen atoms were generated geometrically. Crystallographic data and
refinement parameters for the coordination compounds 1 and 2 are given in Table 4.
Table 4. Crystallographic data and refinement parameters for the coordination compounds 1 and 2.
Coordination Compound
1
2
Empirical formula
Molecular weight
Color
C H Br Co N O
C H Br Zn N O
63 60 8 4 8 17
6
3
60
8
4
8
17
2076.19
Brown
2101.95
Bright-yellow
Crystal size, mm
Habit
Crystal system
Space group
Unit cell dimension
a, Å
0.22 × 0.18 × 0.16
Block-shaped
Triclinic
0.22 × 0.18 × 0.17
Block-shaped
Triclinic
P-1
P-1
15.244(2)
18.674(3)
21.356(3)
109.512(4)
97.335(4)
109.429(4)
5205.4(14)
2
13.4501(6)
18.6963(9)
19.6467(8)
72.7450(10)
72.5280(10)
88.801(2)
b, Å
c, Å
◦
α,
β,
γ,
◦
◦
Volume, Å3
4487.9(3)
Z
2
−
3
Calculated density, mg·m
1.325
3.747
2036
1.555
4.675
2060
−
1
Absorption coefficient, mm
F (000)
◦
θ range for data collection,
h/k/l (min, max)
Reflections collected
Completeness
1.050 to 27.000
−19, 16/−22, 23/−27, 26
37,783
2.224 to 25.010
−11, 15/−22, 21/−23, 23
32,780
96.6%
99.4%
Data/restraints/parameters
Final R indices [I > 2σ(I)]
R indices (all data)
22,025/1/909
15,711/0/909
R = 0.0438, wR = 0.0932
R = 0.0523, wR = 0.1353
1
2
1 2
R = 0.0762, wR = 0.0977
R = 0.0888, wR = 0.1557
1
2
1
2
−
3)
Largest diff. peak and hole (e
·
Å
1.677, −0.861
1.434, −0.914
4
. Conclusions
We have designed and synthesized a novel symmetric bis(salamo)-like tetraoxime ligand
H L, and two unusual dinuclear coordination compounds and , [M (L)(OCH )][M (L)(OAc)]
= Co and Zn ). X-ray crystal structure analyses of the coordination compounds
1
2
3
2
3
2
II
II
II
(M
1 and 2

Molecules 2018, 23, 1141
11 of 15
reveal that the unit cell of the two coordination compounds contains two crystallographically and
chemically independent dinuclear metal coordination compounds. The supramolecular structures
of the coordination compounds
forms a 3D supramolecular structure and the coordination compound
by the inter-molecular hydrogen bond interactions. Furthermore, the fluorescence spectra of the
1
and
2
are different from each other, the coordination compound
1
2
forms a 0D dimer structure
II
II
coordination compounds
1 and 2 indicates that the coordination of Co and Zn ions leads to the
fluorescence quenching and enhancing of H L, respectively, which can be further studied as a new
3
type of fluorescent material.
Supplementary Materials: The following are available online at http://www.mdpi.com/1420-3049/23/5/1141/
s1.
Author Contributions: F.W. and L.-Z.L. performed most of the experiments. W.-K.D. designed the project.
F.W. and L.-W.Z. wrote the paper. All authors reviewed the manuscript.
Acknowledgments: 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
gratefully acknowledged.
Conflicts of Interest: There is no conflict of interest among all authors.
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Sample Availability: Samples of the compounds are available from the authors.
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2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
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