Co(II) and Ni(II) bis(salamo)-based tetraoxime complexes: Syntheses, structural characterizations, fluorescence properties, and Hirshfeld analyses

Article abstract of DOI:10.1080/00958972.2021.1891227

Two new asymmetric complexes with the chemical structural formulas [{Co₂(L)(μ ₂-OH)}{Co₂(L)(OAc)(CH₃OH)}{Co₂(L)(μ ₂-OCH₃)}{Co₂(L)(μ ₂-OAc)}]?4CH₃

Full text of DOI:10.1080/00958972.2021.1891227

Journal of Coordination Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Co(II) and Ni(II) bis(salamo)-based
tetraoxime complexes: Syntheses, structural
characterizations, fluorescence properties, and
Hirshfeld analyses
Shuang-Zhu Guo, Ji-Fa Wang, Shan-Shan Feng & Li Zhao
To cite this article: Shuang-Zhu Guo, Ji-Fa Wang, Shan-Shan Feng & Li Zhao (2021) Co(II)
and Ni(II) bis(salamo)-based tetraoxime complexes: Syntheses, structural characterizations,
fluorescence properties, and Hirshfeld analyses, Journal of Coordination Chemistry, 74:7,
1181-1195, DOI: 10.1080/00958972.2021.1891227
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JOURNAL OF COORDINATION CHEMISTRY
021, VOL. 74, NO. 7, 1181–1195
2
https://doi.org/10.1080/00958972.2021.1891227
Co(II) and Ni(II) bis(salamo)-based tetraoxime complexes:
Syntheses, structural characterizations, fluorescence
properties, and Hirshfeld analyses
Shuang-Zhu Guo, Ji-Fa Wang, Shan-Shan Feng and Li Zhao
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, PR China
ABSTRACT
ARTICLE HISTORY
Two new asymmetric complexes with the chemical structural formu-
Received 10 November 2020
Accepted 5 January 2021
las [fCo
2
(L)(l
2
-OH)gfCo
2
(L)(OAc)(CH
3
OH)gfCo
2
(L)(l
2
2
-OCH
2
3
)gfCo
2
(L)
(
l -OAc)g]ꢀ4CH OH and [Ni (L)(l -OAc)(CH OH)]ꢀCH Cl ꢀ3CH OH have
2
3
2
2
3
3
KEYWORDS
been synthesized from cobalt(II) acetate, nickel(II) acetate, and a bis(-
salamo)-based tetraoxime ligand derived from 3-bromo-5-chlorosali-
cylicaldehyde and 4-tert-butyl-2,6-diformylphenol, respectively, and
characterized by elemental analyses, IR, UV–vis, fluorescence spectra,
and single-crystal X-ray diffraction analyses. The Co(II) complex unit cell
contained four crystallographically independent and chemically differ-
ent heterotrinuclear complexes (molecules A, B, C, and D). The crystal
structure included eight Co(II) ions, four completely deprotonated lig-
Bis(salamo)-based ligand;
synthesis; crystal structure;
Hirshfeld surface analysis;
fluorescence property
3ꢁ
and (L) moieties, one bridging hydroxide, one monodentate acetate,
one bridging methoxy, one bidentate chelating acetate, one coordi-
nated methanol, and four crystallization methanol molecules. The Ni(II)
complex had a dinuclear structure. The crystal structure of the Ni(II)
complex included two Ni(II) ions, one completely deprotonated ligand
3ꢁ
(L) , one bidentate bridging acetate, one coordinated methanol, one
crystallized dichloromethane, and three crystallized methanol mole-
cules. Hirshfeld surface analyses showed that the complexes are stable.
Furthermore, the fluorescence quenching of the Co(II) and Ni(II) com-
plexes with H L further confirmed the above experimental results.
3
CONTACT Li Zhao
University, Lanzhou, Gansu 730070, PR China
ß 2021 Informa UK Limited, trading as Taylor & Francis Group
zhaoli_72@163.com
School of Chemical and Biological Engineering, Lanzhou Jiaotong

1
182
S.-Z. GUO ET AL.
1. Introduction
Salen and its derivatives (–CH ¼ N–(CH) –N ¼ CH–) are used in various fields due to
n
their excellent properties and interesting structures [1]. Some complexes can be
applied to molecular recognitions [2–5], catalysts [6–8], supramolecular architectures
[9–14], magnetic materials [15], and fluorescence materials [16–19]. These ligands can
form mononuclear or multinuclear complexes with d-block transition metal ions.
Supramolecular chemistry has received attention in coordination chemistry, and for
salen-based ligands, supramolecular structures were formed mainly with C–HꢀꢀꢀO,
C–Hꢀꢀꢀp or pꢀꢀꢀp interactions [20, 21]. To improve the properties of salen-based ligands,
two salicylaldehyde molecules with an alkoxyl bridging unit as a linker formed a new
structural configuration (–CH ¼ N–O–(CH) –O–N ¼ CH–) of a salamo-based ligand.
n
Salamo-based ligands and their new complexes have received attention [22–25]. These
salamo-based ligands exhibit very high stability compared to the parent salen-based
ligands and can be used for construction of new materials. In our previous studies, sal-
amo-based ligands and their complexes have been synthesized [26–28]. However, few
studies have been reported on bis(salamo)-based ligands and their complexes [29].
Bis(salamo)-based complexes have good application prospects, especially in sensors
and supramolecular structures.
To explore the structure and optical properties of the transition metal complexes,
here, the Co(II) and Ni(II) bis(salamo)-based complexes derived from 3-bromo-5chloro-
salicylicaldehyde and 4-tert-butyl-2,6-diformylphenol were synthesized. The structural
characterizations, fluorescence, and Hirshfeld analyses of the Co(II) and Ni(II) com-
plexes
[fCo (L)(l -OH)gfCo (L)(OAc)(CH OH)gfCo (L)(l -OCH )gfCo (L)(l -
2
2
2
3
2
2
3
2
2
OAc)g]ꢀ4CH OH and [Ni (L)(l -OAc)(CH OH)]ꢀCH Cl ꢀ3CH OH of the bis(salamo)-based
3
2
2
3
2
2
3
tetraoxime ligand H L are reported.
3
2. Experimental
2.1. Materials and physical measurements
All chemical reagents were analytically pure and used without purification. The GmbH
VarioEL V3.00 automatic element analyzer was used for C, H, and N analysis. Elemental
analyses for Co(II) and Ni(II) were performed using an IRIS ER/SꢀWP-1 ICP atomic emis-
sion spectrometer. Determination of melting point was done by a microscopic melting
1
point instrument made by Beijing Tektronix Instruments Co. Ltd (Peking, China). H
NMR spectra were measured on a Bruker AV 500 MHz spectrometer. FT-IR spectra were
ꢁ
1
ꢁ1
recorded by using KBr (500–4000 cm ) and CsI (100–500 cm ) pellets on a
VERTEX70 FT-IR spectrophotometer (Bruker, Billerica, MA, USA). UV–visible absorption
and fluorescence spectra were determined using Shimadzu UV-3900 (Shimadzu, Japan)
and Hitachi F-7000 (Hitachi, Tokyo, Japan) spectrometers, respectively. The X-ray sin-
gle-crystal structure determinations were carried out on a Bruker Smart Apex CCD dif-
fractometer. The Crystal Explorer program was used for Hirshfeld surface analyses of
the Co(II) and Ni(II) complexes, according to similar methods previously
reported [29–34].

JOURNAL OF COORDINATION CHEMISTRY
1183
Scheme 1. Synthetic route to H3L.
2
.2. Preparation of H3L
,2-Bis(aminooxy)ethane was prepared by the method reported [35–39]. Yield: 72.5%.
Anal. calcd. for C H N O (%): C, 26.08; H, 8.76; N, 30.42. Found: C, 26.63; H, 8.41; N,
1
2
8 2 2
3
0.26. The preparation route to the bis(salamo)-based tetraoxime ligand (H L) is shown
3
in Scheme 1.
The bis(salamo)-based tetraoxime ligand (H L) was obtained according to the previ-
3
ꢂ
ous method [40]. Yield: 81.8%, M. p.: 124–126 C. Anal. calcd. for C H N O Br Cl (%):
30
30
4
7
2
2
1
C, 45.65; H, 3.83; N, 7.10. Found: C, 46.79; H, 3.55; N, 6.96. H NMR (400 MHz, CDCl ) d:
3
1
0.56 (s, 2H), 9.94 (s, 1H), 8.40 (s, 2H), 8.13 (s, 2H), 7.51 (d, J ¼ 2.4 Hz, 2H), 7.48 (d,
J ¼ 8.4 Hz, 2H), 7.10 (d, J ¼ 2.4 Hz, 2H), 4.49 (m, 8H), 1.30 (s, 9H).
2.3. Syntheses of the Co(II) and Ni(II) complexes
To a methanol solution (4 mL) of Co(OAc) ꢀ4H O (4.98 mg, 0.02 mmol) was added a
2
2
solution of H L (7.98 mg, 0.01 mmol) in 4 mL of dichloromethane. The color of the mix-
3
ture immediately turned pale pink and then stirring was continued for 10 min at room
temperature. Next, the mixed solution was filtered by absorbent cotton, the bottle
sealed with foil, and allowed to sit for about one week to evaporate. Finally, a pink
block-shaped single crystal suitable for X-ray diffraction analysis was obtained. Yield:
6
4.5%. Anal. calcd. for C130H138Br C Co N O (%): C, 39.47; H, 3.17; N, 5.93; Co, 13.75.
8 l8 8 16 39
Found: C, 39.74; H, 2.94; N, 5.79; Co, 13.56.
The Ni(II) complex was prepared by the same method. To a methanol solution
(
0
4 mL) of Ni(OAc) ꢀ4H O (4.96 mg, 0.02 mmol) was added a solution of H L (7.98 mg,
2
2
3
.01 mmol) in 4 mL of dichloromethane. The color of the mixture immediately turned
pale green and then stirring was continued for 10 min at room temperature. Next, the
mixed solution was filtered by absorbent cotton, the bottle sealed with foil, and
allowed to sit for about one week to evaporate. Finally, a green block-shaped single
crystal suitable for X-ray diffraction analysis was obtained. Yield: 69.8%. Anal. calcd. for
C H Br Cl N Ni O (%): C, 39.87; H, 4.28; N, 6.14; Ni, 15.62. Found: C, 40.13; H, 3.96;
3
7
48
2
4
4
2 13
N, 6.07; Ni, 15.49.

1
184
S.-Z. GUO ET AL.
Table 1. Crystallographic data and refinement parameters for the Co(II) and Ni(II) complexes.
Compound
Co(II) complex
Ni(II) complex
Cl Ni
1175.83
0.19 ꢃ 0.17 ꢃ 0.14
Block-shaped
Triclinic
Empirical formula
Molecular weight
Crystal size (mm)
Habit
Crystal system
Space group
Unit cell dimension
a (Å)
C
130
H138Br
8 8
Cl8Co N
16
O
39
C
37
H48Br
2
4
N
4
2 13
O
3942.88
0.17 ꢃ 0.14 ꢃ 0.13
Block-shaped
Triclinic
P ꢁ 1
P ꢁ 1
18.0197(7)
19.1060(6)
27.2929(10)
93.5740(10)
101.5930(10)
117.4090(10)
8040.9(5)
2
13.1303(8)
13.4410(7)
14.5785(7)
73.053(2)
87.189(2)
70.724(2)
2320.0(2)
2
b (Å)
c (Å)
ꢂ
a ( )
ꢂ
b ( )
ꢂ
c ( )
3
V (Å )
Z
D
–
3
calc (g cm )
1.628
3.001
3948
1.683
2.828
1192
–
1
l (mm )
F(0 0 0)
ꢂ
h Range for data collection ( )
Index ranges
2.244–26.763
ꢁ22 ꢄ h ꢄ 22,
2.528–26.831
ꢁ16 ꢄ h ꢄ 16,
ꢁ17 ꢄ k ꢄ 16,
ꢁ18 ꢄ l ꢄ 18
28,060
ꢁ
24 ꢄ k ꢄ 24,
ꢁ
34 ꢄ l ꢄ 34
158,098
99.7
Reflections collected
Completeness to (%)
Data/restraints/parameters
99.1
34168/63/1931
0.0487, 0.0987
0.0878, 0.1168
1.501, ꢁ0.999
9878/10/576
0.0633, 0.1547
0.0931, 0.1738
1.214, ꢁ1.584
Final R
, wR
Largest diff. peak and hole (e Å
1
, wR
indices (all data)
2
indices
R
1
2
–
3
)
2.4. X-ray structure determinations of the Co(II) and Ni(II) complexes
Crystal data of the Co(II) and Ni(II) complexes were obtained via a Bruker Smart Apex
CCD diffractometer at 100.03(10) K and 293(2) K (Mo Ka radiation (k ¼ 0.71073 Å)) [27,
41]. The cell parameters of the Co(II) and Ni(II) complexes were determined by the
least squares method. The LP factor and semi-empirical absorption corrections were
applied to the intensity data. The structures were measured by direct methods
(SHELXS-2015) [42]. All hydrogen atoms were added theoretically and all non-hydro-
gen atoms were refined by full matrix least squares anisotropy. The positions of hydro-
gen atoms were calculated and fixed isotropically in the final refinement. The key
crystal data and structural parameters of the Co(II) and Ni(II) complexes are given in
Table 1.
3
. Results and discussion
.1. IR spectra analyses
Infrared spectra of H L and its Co(II) and Ni(II) complexes exhibited different bands
3
3
ꢁ
1
from 4000–400 cm (Figure 1). The main infrared peaks for H L and its Co(II) and
3
Ni(II) complexes are listed in Table 2.
ꢁ
1
An O–H stretching vibration of free H L was observed at 3437 cm , while the cor-
3
responding stretch was not present in the Co(II) and Ni(II) complexes, due to deproto-
nation of H L and coordination of the Co(II) and Ni(II) ions occurred [43–45]. The Co(II)
3
ꢁ
1
and Ni(II) complexes exhibited stretching vibration bands at 3411 and 3415 cm that

JOURNAL OF COORDINATION CHEMISTRY
1185
Figure 1. Infrared spectra of H L and its Co(II) and Ni(II) complexes.
3
ꢁ
1
Table 2. The major IR spectral data of H L and its Co(II) and Ni(II) complexes (cm ).
3
Compound
ꢀ
(O–H)
ꢀ
(C¼N)
ꢀ
(Ar–O)
ꢀ
(M–O)
ꢀ
(M–N)
H
3
L
3437
3411
3415
1604
1598
1603
1271
1275
1273
–
445
449
–
513
509
Co(II) complex
Ni(II) complex
belonged to coordinated and crystallized methanol molecules [40]. A characteristic
ꢁ
1
C ¼ N stretch of H L was found at 1604 cm . Upon complexation, the bands in the
3
ꢁ
1
Co(II) and Ni(II) complexes were at 1598 and 1603 cm , respectively, indicating that
the nitrogen of C ¼ N groups coordinated to Co(II) and Ni(II) [39, 40]. The Ar–O stretch
ꢁ
1
ꢁ1
was at 1271 cm for free H L; the Ar–O stretches were at 1275 and 1273 cm in the
3
Co(II) and Ni(II) complexes, respectively [23]. The Ar–O stretching frequencies shifted
ꢁ
1
3
–5 cm from free H L, which may be due to formation of M–O bonds between Co(II)
3
3ꢁ
and Ni(II) ions and the phenolic oxygens of (L) [33]. In order to determine the fre-
quency of M–O and M–N bonds, far-IR spectra of the Co(II) and Ni(II) complexes were
ꢁ
1
ꢁ1
from 500–100 cm , showing appearance of new bands at 445 and 449 cm from
M–O vibrations [39]. For the Co(II) and Ni(II) complexes, the typical M–N vibration
ꢁ
1
bands were discovered at 513 and 509 cm , respectively [43–45]. The above experi-
mental results indicated that the Co(II) and Ni(II) ions were coordinated to the N- and
3
ꢁ
O-donors of (L) . The results mentioned above are consistent with single-crystal X-ray
diffraction structure.
3.2. UV–Vis absorption spectral analyses
The UV–Vis absorption spectra of H L and its Co(II) and Ni(II) complexes (methanol,
3
ꢁ
5
5
ꢃ 10 M) were measured at 298 K from 250 to 550 nm (Figure 2). The absorption
peaks of free H L and its Co(II) and Ni(II) complexes were significantly different. Free
3
H3L showed obvious absorption peaks at 334 nm. The absorption spectrum can be

1
186
S.-Z. GUO ET AL.
Figure 2. UV–vis spectra of H L and its Co(II) and Ni(II) complexes.
3
ꢅ
attributed to the p–p transition of the oxime nitrogens of H L [46–48]. Compared
3
with H L, the peak of H L at 334 nm disappeared in the Co(II) and Ni(II) complexes,
3
3
indicating that N of oxime groups participated in coordination with Co(II) and Ni(II)
40]. New absorption peaks of Co(II) and Ni(II) complexes appeared at 377 and 379 nm,
[
which can be attributed to the L ! M (LMCT) charge transfer transition, characteristic
of transition metal complexes with N O coordination sphere [49–51].
2
2
3.3. Description of the crystal structures of the Co(II) and Ni(II) complexes
3.3.1. Crystal structure of Co(II) complex
The crystal structure, atom numbering, and coordination polyhedra of the Co(II) com-
plex are presented in Figure 3. [fCo (L)(l -OH)gfCo (L)(OAc)(CH OH)gfCo (L)(l -
2
2
2
3
2
2
OCH )gfCo (L)(l -OAc)g]ꢀ4CH OH has an octa-nuclear structure involving oxime oxy-
3
2
2
3
gen coordination which is different from the structures of the bis(salamo)-type
metal(II) complexes reported earlier [29]. It crystallized in the monoclinic crystal sys-
tem, space group P ꢁ 1. The unit cell contained four crystallographically independent
and chemically different binuclear complexes (molecules A, B, C, and D). The crystal
3
ꢁ
structure included eight Co(II) ions, four completely deprotonated (L) moieties, one
bridging hydroxide, one monodentate acetate, one bridging methoxy, one bidentate
chelating acetate, one coordinated methanol, and four crystallization methanol mole-
cules. In molecule A, Co1 and Co2 were located in the two N O cavities (O1, O4, N1,
2
2
3
ꢁ
N2 and O4, O7, N3, N4) of the bis(salamo)-based (L)
moiety, respectively.
Meanwhile, Co1 and Co2 also combined with O8 of the bridging hydroxide to form a
slightly distorted tetragonal cone and trigonal bipyramidal geometries (s ¼ 0.302 and
1
s ¼ 0.578) [36]. In molecule B, the five-coordinate Co3 was located in the N O cavity
2
2 2
(O9, O12, N5, and N6) and also coordinated to O28 of the bridging phenoxy group to
form a slightly distorted tetragonal cone (s ¼ 0.006). Interestingly, the six-coordinate
3
Co4 was located in the N O cavity (O12, O15, N7, and N8) and furthermore, combined
2
2

JOURNAL OF COORDINATION CHEMISTRY
1187
Figure 3. (a) The X-ray crystal structure of the Co(II) complex (hydrogens are omitted for clarity).
b) The structures of molecules A, B, C, and D in the Co(II) complex. (c) Coordination configurations
(
for Co(II) ions.
with O18 and O16 of the coordinated methanol molecule and the monodentate acet-
ate anion to form an octahedral configuration. In molecule C, Co5 and Co6 were
located in the two N O cavities (O19, O22, N9, N10 and O22, O25, N11, N12) of the
2
2
3
ꢁ
bis(salamo)-based (L) moiety, respectively. The Co5 and Co6 were bridged with O26
of the methoxy group to form slightly distorted tetragonal cone and triangular bipyra-
midal geometries (s ¼ 0.274 and s ¼ 0.699). In molecule D, the five-coordinate Co7
5
6
was located in the N O cavity (O27, O30, N13, and N14) and also coordinated to O33
2
2
of the phenoxy group to form a slightly distorted tetragonal cone (s ¼ 0.039). Co8
7
was located in the N O cavity (O30, O33, N15, and N16) and coordinated further with
2
2
O34 and O35 from the bidentate chelating acetate group to form an octahedral
configuration.
The molecular structure of the Co(II) complex is shown in Figure 3(a). For the con-
venience of observation, the configurations of A, B, C, and D are shown in Figure 3(b).
The coordination configurations of Co(II) ion in the Co(II) complex are shown in

1
188
S.-Z. GUO ET AL.
CF iog ( uI I )r eco 4m .p Il ne tx e. rmolecular hydrogen bonding, C–Hꢀꢀꢀp, and pꢀꢀꢀp stacking interactions of the
Figure 5. (a) The crystal structure of the Ni(II) complex (hydrogens are omitted for clarity). (b)
Coordination configuration for Ni(II) ions.
Figure 3(c). Furthermore, four couples of significant intramolecular hydrogen bonds
(
C18–H18ꢀꢀꢀO16, C18–H18ꢀꢀꢀO17, C116–H11AꢀꢀꢀO34, C52–H52BꢀꢀꢀO16) were observed in
the Co(II) complex. Two C–Hꢀꢀꢀp interactions (C33–H33ꢀꢀꢀCg28, C63–H63ꢀꢀꢀCg3) and five
pꢀꢀꢀp stacking interactions (Cg6ꢀꢀꢀCg8, Cg10ꢀꢀꢀCg20, Cg11ꢀꢀꢀCg13, Cg28ꢀꢀꢀCg3 and
Cg28ꢀꢀꢀCg7) are shown in Figure 4.
3.3.2. Crystal structure of the Ni(II) complex
The crystal structure and coordination configuration of the Ni(II) complex are shown in
Figure 5. Significant bond lengths and angles are summarized in Table 3. Ni(II) com-
plex [Ni (L)(l -OAc)(CH OH)]ꢀCH Cl ꢀ3CH OH has a dinuclear structure, crystallized in
2
2
3
2
2
3
the monoclinic crystal system P ꢁ 1 space group. The crystal structure included two
3
ꢁ
Ni(II) ions, one (L) moiety, one bidentate bridging acetate, one coordinated metha-
nol, a crystallization dichloromethane, and three crystallization methanol molecules.
Ni1 or Ni2 was located in the N O cavities (O1, O4, N1, N2 or O4, O7, N3, N4) of the
2
2
bis(salamo)-based ligand. The six-coordinate Ni1 was also coordinated with O8 of the
bidentate bridging acetate and O7 from the bridging phenoxy group. The six-coordin-
ate Ni2 was also coordinated to O9 of the bidentate bridging acetate and O10 from
the coordinated methanol to form an octahedral configuration.
The molecular structure of the Ni(II) complex is shown in Figure 5(a). The coordin-
ation configuration of Ni(II) in the Ni(II) complex is shown in Figure 5(b). Furthermore,

JOURNAL OF COORDINATION CHEMISTRY
1189
ꢂ
Table 3. Selected bond lengths (Å) and angles ( ) for the Co(II) and Ni(II) complexes.
Co(II) complex
Bond
Dist.
Bond
Dist.
Bond
Dist.
Co1–O4
Co1–O1
Co1–N2
Co1–O8
Co1–N1
Co2–O8
Co2–N4
Co2–O7
Co2–N3
Co2–O4
Co3–O15
Co3–O12
Co3–N5
Co3–O9
2.085(3)
1.946(3)
2.075(4)
1.968(4)
2.043(4)
1.967(4)
2.082(4)
1.960(3)
2.061(4)
2.077(4)
2.040(3)
2.069(3)
2.155(4)
1.931(3)
Co3–N6
Co4–O16
Co4–O18
Co4–O15
Co4–N8
2.017(4)
2.056(4)
2.117(4)
2.064(3)
2.096(4)
2.096(4)
2.073(3)
2.036(4)
1.973(3)
1.955(4)
2.075(5)
2.075(5)
1.949(4)
2.054(4)
Co6–O25
Co6–N12
Co6–O22
Co7–N14
Co7–N13
Co7–O30
Co7–O33
Co7–O27
Co8–N15
Co–O34
1.941(4)
2.053(4)
2.089(3)
2.018(4)
2.109(4)
2.058(3)
2.047(3)
1.936(4)
2.063(4)
2.126(4)
2.067(3)
2.079(4)
2.025(3)
2.215(4)
Co4–N7
Co4–O12
Co5–O22
Co5–O26
Co5–O19
Co5–N10
Co5–N9
Co8–O33
Co8–N16
Co8–O30
Co8–O35
Co6–O26
Co6–N11
Bond
Angles
Bond
Angles
Bond
Angles
O8–Co1–N1
O1–Co1–N2
O4–Co1–N2
O4–Co1–N2
N1–Co1–N2
O8–Co1–N2
O4–Co1–N1
O1–Co1–O8
O1–Co1–N1
O1–Co1–O4
O4–Co1–O8
O4–Co2–N3
O4–Co2–O8
N3–Co2–N4
O8–Co2–N4
O7–Co2–N3
O4–Co2–N4
O7–Co2–O8
O4–Co2–O7
O7–Co2–N4
O8–Co2–N3
O9–Co3–O12
O9–Co3–O15
O9–Co3–N5
O9–Co3–N6
O12–Co3–O15
O12–Co3–N5
O12–Co3–N6
O15–Co3–N5
O15–Co3–N6
N5–Co3–N6
O12–Co4–O16
105.0(2)
114.91(16)
81.54(14)
81.54(14)
153.86(9)
136.75(15)
171.87(14)
104.77(16)
90.38(14)
96.55(13)
77.40(15)
81.68(14)
77.61(15)
90.12(16)
101.84(17)
114.99(14)
167.68(13)
110.70(14)
103.35(14)
88.42(15)
132.97(15)
104.71(14)
103.78(14)
86.42(14)
119.93(14)
79.94(12)
168.20(14)
85.88(14)
93.75(13)
136.19(14)
92.00(15)
167.84(15)
O12–Co4–O18
O12–Co4–N7
O12–Co4–N8
O15–Co4–O16
O15–Co4–O18
O15–Co4–N7
O15–Co4–N8
O16–Co4–O18
O16–Co4–N7
O16–Co4–N8
O18–Co4–N7
O18–Co4–N8
N7–Co4–N8
N9–Co5–N10
O19–Co5–N10
O22–Co5–O26
O22–Co5–N9
O22–Co5–N10
O19–Co5–O22
O19–Co5–O26
O19–Co5–N9
O26–Co5–N9
O26–Co5–N10
O22–Co6–O26
O25–Co6–O26
O22–Co6–N11
O22–Co6–N12
O25–Co6–N12
O22–Co6–O25
O26–Co6–N12
N11–Co6–N12
O26–Co6–N11
86.74(14)
84.87(17)
97.63(14)
90.81(14)
97.26(14)
162.14(17)
83.95(14)
87.54(15)
105.85(18)
88.24(15)
89.97(18)
175.62(15)
90.08(19)
88.75(19)
111.25(18)
77.10(14)
157.78(19)
81.57(17)
113.26(14)
106.82(15)
88.88(19)
99.07(17)
141.3(2)
O25–Co6–N11
O27–Co7–N14
O27–Co7–N14
O30–Co7–O33
O30–Co7–N13
O30–Co7–N14
O33–Co7–N13
O33–Co7–N14
N13–Co7–N14
O27–Co7–O33
O27–Co7–O30
O30–Co8–O34
O30–Co8–O35
O30–Co8–N16
O30–Co8–C26
O30–Co8–N15
O30–Co8–O33
O33–Co8–N15
O33–Co8–N16
O33–Co8–C26
O34–Co8–O35
O34–Co8–N15
O34–Co8–N16
O34–Co8–C26
O35–Co8–N15
O35–Co8–N16
O35–Co8–C26
N15–Co8–N16
N15–Co8–C126
N16–Co8–C126
O33–Co8–O34
O33–Co8–O35
115.05(16)
121.04(14)
121.04(14)
80.46(12)
165.37(15)
85.64(13)
91.72(13)
136.25(15)
91.68(15)
102.67(13)
105.86(14)
149.98(15)
92.50(14)
105.20(15)
121.04(17)
86.17(13)
80.76(12)
165.94(14)
85.48(14)
85.18(15)
60.38(14)
108.27(14)
100.28(15)
30.46(16)
96.90(15)
160.26(15)
30.01(16)
93.01(16)
106.17(16)
130.41(17)
85.74(13)
88.88(14)
76.37(15)
107.93(15)
81.89(13)
174.68(14)
89.75(17)
94.58(14)
105.22(19)
93.50(15)
132.94(16)
Ni(II) complex
Bond
Dist.
Bond
Dist.
Bond
Dist.
Ni1–O1
Ni1–O4
Ni1–O7
2.027(4)
2.052(4)
2.088(4)
Ni1–O8
Ni2–O4
Ni2–O7
2.075(4)
2.076(4)
2.010(4)
Ni2–O9
Ni2–O10
2.029(4)
2.110(5)
Bond
Angles
Bond
Angles
Bond
Angles
O1–Ni1–O4
O1–Ni1–O7
O1–Ni1–O8
O1–Ni1–N1
O1–Ni1–N2
O4–Ni1–O7
O4–Ni1–O8
O4–Ni1–N1
O4–Ni1–N2
O7–Ni1–O8
86.74(17)
94.49(17)
173.11(17)
83.86(17)
91.7(2)
84.23(16)
86.47(17)
170.56(18)
89.5(2)
O7–Ni1–N1
O7–Ni1–N2
O8–Ni1–N1
O8–Ni1–N2
N1–Ni1–N2
O4–Ni2–O7
O4–Ni2–O9
O4–Ni2–O10
O4–Ni2–N3
O4–Ni2–N4
97.38(19)
171.0(2)
102.94(17)
89.5(2)
O7–Ni2–O9
O7–Ni2–O10
O7–Ni2–N3
O7–Ni2–N4
O9–Ni2–O10
O9–Ni2–N3
O9–Ni2–N4
O10–Ni2–N3
O10–Ni2–N4
N3–Ni2–N4
89.32(18)
92.64(18)
171.3(2)
85.24(18)
86.61(19)
91.83(18)
171.08(18)
96.1(2)
89.9(2)
85.60(17)
172.32(17)
97.63(14)
85.84(19)
100.69(19)
86.6(2)
94.62(19)
83.62(16)

1
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S.-Z. GUO ET AL.
NF i ig( I uI )r ec o m6 .p l Ien xt .r amolecular hydrogen bonding, C–Hꢀꢀꢀp, and pꢀꢀꢀp stacking interactions of the
Figure 7. Emission spectra of H L and its Co(II) and Ni(II) complexes.
3
a significant intramolecular hydrogen bond (C8–H8AꢀꢀꢀO8) was observed in the Ni(II)
complex. A C–Hꢀꢀꢀp interaction (C23–H23AꢀꢀꢀCg9) and two pꢀꢀꢀp stacking interactions
(Cg8ꢀꢀꢀCg10 and Cg10ꢀꢀꢀCg1) are shown in Figure 6.
3.4. Fluorescence properties
At room temperature, the fluorescence properties of H L and its Co(II) and Ni(II) com-
3
ꢁ
4
plexes were investigated in methanol solution (1.0 ꢃ 10 mol/L). The excitation wave-
length was 330 nm and the slit width was 10/20 nm [52, 53]. As shown in Figure 7,
ꢅ
H3L showed a strong fluorescence emission peak at 429 nm, attributed to the p–p
transition of the ligand [54]. Compared with H L, the fluorescence of the Co(II) and
3
Ni(II) complexes were quenched, which indicated that the Co(II) and Ni(II) atoms were
3
ꢁ
coordinated with (L) , thereby reducing the conjugated system.
3.5. Hirshfeld surface analyses
Hirshfeld surface analyses can investigate significant interactions between molecules in
the crystal environment and can also show the interface of the interaction between
molecules, judging the type of interaction from the color of different areas of the

JOURNAL OF COORDINATION CHEMISTRY
1191
Figure 8. (a) Hirshfeld surface analyses mapped with curvedness, shape index, dnorm, d , and d of
e
i
the Co(II) complex. (b) Hirshfeld surface analyses mapped with curvedness, shape-index, dnorm, de,
and d of the Ni(II) complex.
i
interface [29–31]. The Hirshfeld surface analyses of the Co(II) and Ni(II) complexes are
illustrated in Figure 8.
The difference in Hirshfeld surface shape revealed the degree of intermolecular
bonding in the Co(II) and Ni(II) complexes. There are red triangle concave surfaces and

1
192
S.-Z. GUO ET AL.
Figure 9. Fingerprint plots of the Co(II) and Ni(II) complexes: full and resolved into full and
resolved into CꢀꢀꢀH, OꢀꢀꢀH, NꢀꢀꢀH, ClꢀꢀꢀH, BrꢀꢀꢀH, and HꢀꢀꢀH contacts showing the percentages of con-
tacts contributed to the total Hirshfeld surface area of molecules.
blue triangle convex surfaces corresponding to complementary regions in the Co(II)
and Ni(II) complexes. The dnorm surface can be used for the identification of very close
intermolecular interactions while the shape index is most sensitive to very subtle
changes in surface shape; the red triangles represent concave regions indicating pꢀꢀꢀp
stacked molecules and the blue triangles represent convex regions indicating the ring
atoms of these molecules inside these surfaces. In the Co(II) and Ni(II) complexes, pꢀꢀꢀp
interactions are evident on the Hirshfeld surface as a large flat region across the mol-
ecule, which is most clearly visible on the curvedness surfaces. The pattern of red and
blue triangles on the same region of the shape index surface is another characteristic
of pꢀꢀꢀp interactions. Blue triangles represent convex regions because of the benzene
ring carbons of the molecule inside the surface, while red triangles represent the con-
cave region formed by p–p stacking of carbons of benzene ring above it. The white

JOURNAL OF COORDINATION CHEMISTRY
1193
areas presented on the surface are due to the longer distance between the molecules,
not the existence of hydrogen bonds.
To provide context, the outlines of the full fingerprint are shown in gray and the
blue area shows the separate contact. Most of the fingerprints were occupied by gray
areas, and blue areas indicated different degrees of interaction between molecules, as
shown in Figure 9. In the Co(II) complex, the interactions of C–H/H–C, O–H/H–O, N–H/
H–N, Cl–H/H–Cl, Br–H/H–Br, and H–H/H–H accounted for 24.4%, 14,1%, 0.7%, 10.4%,
8.2%, and 41.5% of the total molecule Hirshfeld surfaces. In the Ni(II) complex, the
interactions of C–H/H–C, O–H/H–O, N–H/H–N, Cl–H/H–Cl, Br–H/H–Br, and H–H/H–H
accounted for 13.2%, 12.9%, 0.6%, 17.8%, 9.4%, and 41.5%, respectively. It was because
of the existence of these hydrogen bonds that the complexes can be stable.
4. Conclusion
Two new asymmetric bis(salamo)-based complexes, [fCo (L)(l -OH)gfCo (L)(OAc)
2
2
2
(
CH OH)gfCo (L)(l -OCH )gfCo (L)(l -OAc)g]ꢀ4CH OH
and
[Ni (L)(l -
3
2
2
3
2
2
3
2
2
OAc)(CH OH)]ꢀCH Cl ꢀ 3CH OH, were synthesized and characterized. The Co(II) complex
3
2
2
3
contained four crystallographically independent and chemically different binuclear
complexes (molecules A, B, C, and D). In molecule A, the Co1 and Co2 atoms formed a
slightly distorted tetragonal cone and trigonal bipyramidal geometries (s ¼ 0.302 and
1
s ¼ 0.578). In molecule B, Co3 formed a slightly distorted tetragonal cone (s ¼ 0.006)
2
3
and Co4 formed an octahedral configuration. In molecule C, Co5 and Co6 formed a
slightly distorted tetragonal cone and trigonal bipyramidal geometries (s ¼ 0.274 and
5
s ¼ 0.699). In molecule D, Co7 formed a slightly distorted tetragonal cone (s ¼ 0.039)
6
7
and Co8 formed an octahedral configuration. The Ni(II) complex possessed a dinuclear
structure; the six-coordinate Ni1 and Ni2 ions formed octahedral configurations.
Hirshfeld surface analyses further confirmed the intermolecular interactions in the
Co(II) and Ni(II) complexes. Compared with H L, the fluorescence of the Co(II) and Ni(II)
3
complexes quenched due to the formation of more stable complexes by coordination.
Supplementary data
CCDC-2033414 and 2033413 contains the supplementary crystallographic data for the Co(II) and
Ni(II) complexes. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK (Telephone: þ44–01223 762910; Fax: þ44–1223–336033; or E-mail: deposit
@
ccdc.cam.ac.uk).
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
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.

1
194
S.-Z. GUO ET AL.
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