Syntheses, crystal structures, antibacterial activities of Cu(II) and Ni(II) complexes based on terpyridine polycarboxylic acid ligand

Article abstract of DOI:10.1016/j.molstruc.2019.02.072

Six metal complexes [Cu(Htpt)]_n (1), {[Cu(H_1.5tpt)Cl_0.5(H₂O)_0.5]·1/5H₂O}_n (2), {[Cu(H₂tpt)(H₂O)]·1/2SO₄·2H₂O}_n (3), [Cu(Htpt)]_n (4), {[Ni₂(Htpt)₂(H₂O)₂]·CH₃CN}_n (5), [Ni(H₂tpt)₂]·3H₂O (6) based on a multidentate 4-(2,4,6-tricarboxyphenyl)-2,2′,6,2″-terpyridine ligand (H₃tpt) have been prepared by hydrothermal synthesis method and structurally characterized. 1, 2 and 3 show 1-D chain structures, the chains are further linked via π···π interactions or hydrogen bonds to generate 3-D supramolecular structures. 4 displays a 2-D binodal (3,3)-connected fes net with a Schl?fli symbol of (4·8²)(4·8²), which has been reported. 5 also exhibits a 2-D (3,3)-connected hcb topology with Schl?fli symbol of (6³·6³). 6 is a mononuclear structure. The microbiological properties of 1–6 were studied. 1–6 showed pretty good antibacterial activities towards B. subtilis compared to other bacterial strains. 5 exhibits the smallest MIC value of 1 μg/mL which may be related to the presence of easily-leaving solvent water molecules, thereby exposing more active sites easily.

Full text of DOI:10.1016/j.molstruc.2019.02.072

Accepted Manuscript
Syntheses, crystal structures, antibacterial activities of Cu(II) and Ni(II) complexes
based on terpyridine polycarboxylic acid ligand
Xiaoting Wang, Ruiying Li, Aogang Liu, Caipeng Yue, Shimin Wang, Jiajia Cheng,
Jinpeng Li, Zhongyi Liu
PII:
S0022-2860(19)30202-9
DOI:
https://doi.org/10.1016/j.molstruc.2019.02.072
MOLSTR 26229
Reference:
To appear in: Journal of Molecular Structure
Received Date: 7 January 2019
Revised Date: 17 February 2019
Accepted Date: 18 February 2019
Please cite this article as: X. Wang, R. Li, A. Liu, C. Yue, S. Wang, J. Cheng, J. Li, Z. Liu, Syntheses,
crystal structures, antibacterial activities of Cu(II) and Ni(II) complexes based on terpyridine
polycarboxylic acid ligand, Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/
j.molstruc.2019.02.072.
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Graphical abstract: Synopsis
Syntheses, crystal structures, antibacterial activities of Cu(II) and
Ni(II) complexes based on terpyridine polycarboxylic acid ligand
Xiaoting Wang,a Ruiying Li,a Aogang Liu,a Caipeng Yue,b Shimin Wang,c Jiajia
Cheng,a Jinpeng Li*,a Zhongyi Liua
Six complexes have been synthesized and characterized. 1-3 display 1-D chain
structures. 4 and 5 exhibit 2-D frameworks and 6 is a mononuclear structure. The
antibacterial activities of 1-6 against four strains bacteria have been examined. The
relationship between the structures of complexes and antibacterial activities was
studied.
* Corresponding author. E-mail: ljp-zd@zzu.edu.cn.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Syntheses, crystal structures, antibacterial activities of Cu(II) and
Ni(II) complexes based on terpyridine polycarboxylic acid ligand
Xiaoting Wang,a Ruiying Li,a Aogang Liu,a Caipeng Yue,b Shimin Wang,c Jiajia
Cheng,a Jinpeng Li*,a Zhongyi Liua
aCollege of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001,
Henan, P. R. China
bSchool of Life Sciences, Zhengzhou University, Zhengzhou, 451191, Henan, P. R. China
cCollege of Material and Chemistry Engineering, Henan Institute of Engineering, Zhengzhou,
451191, PR China
Abstract
Six metal complexes [Cu(Htpt)]n (1), {[Cu(H1.5tpt)Cl0.5(H2O)0.5]·1/5H2O}n (2),
{[Cu(H2tpt)(H2O)]·1/2SO4·2H2O}n (3), [Cu(Htpt)]n (4), {[Ni2(Htpt)2(H2O)2]·CH3CN}n (5),
[Ni(H2tpt)2]·3H2O (6) based on a multidentate 4-(2,4,6-tricarboxyphenyl)-2,2',6,2''-terpyridine
ligand (H3tpt) have been prepared by hydrothermal synthesis method and structurally
characterized. 1, 2 and 3 show 1-D chain structures, the chains are further linked via π···π
interactions or hydrogen bonds to generate 3-D supramolecular structures. 4 displays a 2-D
binodal (3,3)-connected fes net with a Schläfli symbol of (4·82)(4·82), which has been reported. 5
also exhibits a 2-D (3,3)-connected hcb topology with Schläfli symbol of (63·63). 6 is a
mononuclear structure. The microbiological properties of 1-6 were studied. 1-6 showed pretty
good antibacterial activities towards B. subtilis compared to other bacterial strains. 5 exhibits the
smallest MIC value of 1 ꢀg/mL which may be related to the presence of easily-leaving solvent
water molecules, thereby exposing more active sites easily.
Keywords: complexes; crystal structure; antibacterial activity
*
Corresponding author. E-mail: ljp-zd@zzu.edu.cn
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1. Introduction
In the past few years, much interest has been focused on the design and synthesis
of coordination polymers not only for their interesting molecular topologies but also
for the fact that they exhibit excellent antibacterial activity, which can provide
important reference in the design of more efficient antibacterial drugs [1-8]. Factors
effecting the antibacterial activity of metal complex are directly related to chelation
effect between metal ions and ligands, and the influence of the metal ions on the cell
process. The chelation effect reduces the polarity of the metal ions mainly by partial
sharing of positive charge with the donor groups and possible π-electron
delocalization over the whole chelate rings enhancing the lipophilicity of the
complexes [9-10]. This increased lipophilicity may lead to breakdown of the
permeability barrier of the cells and thus block the normal cell processes [11]. Earlier
articles [12-13] revealed that bidentate or tridentate ligands having more lipophilicity
showed higher antimicrobial activity than monodentate ligands, and according to the
theory of similarity and intermiscibility, two different types of ligands in complexes
have the better antibacterial activity than single ligand. Moreover, another factor
affecting the activity is nature of metal ions. Extensively studied transition metals for
antimicrobial activity includes silver, copper, nickel, and cobalt complexes, which
show different antibacterial properties [14-21]. On the other hand, although
complexes with well-defined structure are suitable for exploring the structure-activity
relationship, the corresponding reports are limited due to the influence of many
complicated factors [22]. It is very important to explore the relationship between the
structures of complexes and antibacterial activities, which can provide theoretical
guidance for us to design and synthesize complexes with excellent antibacterial
activity.
Based on above-mentioned considerations, we selected a terpyridine chelating
ligand with multiple aromatic rings named H3tpt (Scheme 1) to prepare four Cu(II)
and two Ni(II) complexes. The antibacterial activities of six complexes were
performed against four bacterial strains. Herein, we further explore the relationship
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between the structures of six complexes and their biological properties. It should be
noted that the structure of 4 has been reported previously [23].
2. Experimental section
2.1 Materials and general methods
The H3tpt ligand and other reagents were commercially sourced and utilized
without further purification. The water used in the experiment was deionized water.
Solid UV-vis spectra were obtained in the 200-800 nm range on an Agilent Cary 5000
spectrophotometer. Infrared data for ligand and complexes were measured on a
Bruker Tensor 27 infrared spectrometer using a potassium bromide disks in the region
of 400-4000 cm-1. Thermogravimetric measurements (TGA, 30~800ºC) were
recorded on a Netzsch STA409PC differential thermal analyzer using air atmosphere
at a heating rate of 10ºC/min. Elemental analyses (C, H and N) were carried out on a
FLASH EA 1112 elemental analyzer. Powder X-ray diffraction (PXRD) was
measured on PANalytical X’Pert PRO MPD system.
2.2 Preparation of the complexes
2.2.1 Synthesis of [Cu(Htpt)] n (1)
Polymer 1 was synthesized hydrothermally in a Teflon-lined stainless steel
container by heating a mixture of H3tpt (8.8 mg, 0.02 mmol), CuCl2·6H2O (5.1 mg,
0.03 mmol) and 2,2’-bipy (4.7 mg, 0.03 mmol) in 3 mL of H2O/CH3CN (1:2) mixed
solvent at 130°C for 3 days, and then cooled to room temperature at a rate of 5oC/h.
Blue crystals of 1 were isolated from the filtrate (yield: 60% based on copper). Anal.
Calcd for C24H13CuN3O6: C, 57.26; H, 2.58; N, 8.35. Found: C, 57.36; H, 2.78; N,
8.47%. IR spectra (KBr/pellet, cm-1): 3394m, 1714s, 1604s, 1474s, 1403s, 1347s,
1170m, 1022m, 913w, 800m, 655w, 562w.
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2.2.2 Synthesis of {[Cu(H1.5tpt)Cl0.5(H2O)0.5]·1/5H2O}n (2)
2 was synthesized by a hydrothermal procedure similar to that described for 1
except using 4,4’-bipy (4.7 mg, 0.03 mmol) instead of 2,2’-bipy. Blue crystals of 2
were isolated from the filtrate. Yield: 73%. Anal. Calcd for C48H29.8ClCu2N6O13.4: C,
53.95; H, 2.79; N, 7.86. Found: C, 54.15; H, 2.89; N, 7.97%. IR spectra (KBr/pellet,
cm-1): 3409s, 3087m, 1714s, 1615s, 1567s, 1472s, 1419s, 1245s, 1112s, 1021m, 912m,
800s, 681m, 455w.
2.2.3 Synthesis of {[Cu(H2tpt)(H2O)]·1/2SO4·2H2O}n (3)
A mixture of H3tpt (8.8 mg, 0.02 mmol), CuBr2 (6.7 mg, 0.03 mmol),
H2O/CH3CN (1:2, 3 mL) and two drops of concentrated sulfuric acid was sealed in a
Teflon-lined stainless steel vessel (25 mL), then heated to 120°C for 72 h, followed by
cooling to room temperature at a rate of 5ºC/h. Blue stick crystals of 3 were isolated
from the filtrate. The yield of the product 3 was 57%. Anal. Calcd for
C48H40Cu2N6O22S: C, 47.52; H, 3.30; N, 6.93. Found: C, 47.63; H, 3.43; N, 7.04%. IR
spectra (KBr/pellet, cm-1): 3428s, 1713s, 1617s, 1557s, 1474s, 1370s, 1325m, 1251m,
1097m, 914w, 798m, 618w, 417w.
2.2.4 Synthesis of [Cu(Htpt)]n (4)
A mixture of H3tpt (8.8 mg, 0.02 mmol) and CuSO4·5H2O (7.5 mg, 0.03 mmol) in
solvent of H2O/DMF (1:2, 3mL) was placed in a 25 mL Teflon-lined stainless steel
container, and heated to 130°C for 3 days, then cooled to room temperature. Blue
crystals of 4 were isolated from the filtrate (yield: 60% based on copper). The
structure of 4 has been reported previously [23].
2.2.5 Synthesis of {[Ni2(Htpt)2(H2O)2]·CH3CN}n (5) and [Ni(H2tpt)2]·3H2O (6)
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H3tpt (8.8 mg, 0.02 mmol), NiCl2·6H2O (4.8 mgꢀ0.02 mmol) and 3 mL
H2O/CH3CN (1:2 volume ratio) were mixed in a 25 mL Teflon-lined stainless steel
container. The mixture was stirred for 10 min at room temperature and sealed, which
was heated at 130°C for 3 days and then slowly cooled to room temperature at the rate
of 5°C/h. Finally, blue sheet crystals of 5 (yield: 42% based on nickel) and yellow
block crystals of 6 (yield: 26% based on nickel) were isolated from the filtrate and
washed by water. Anal.Calcd of crystals 5 for C50H33N7Ni2O14: C, 55.90; H, 3.07; N,
9.13. Found: C, 55.98; H, 3.12; N, 9.35%. IR spectra (KBr/pellet, cm-1): 3415m,
3069s, 1705s, 1656s, 1601s, 1472s, 1402s, 1348m, 1269s, 1159w, 793s, 680m, 559w,
417w. Anal. Calcd of crystals 6 for C48H34NiN6O15: C, 57.98; H, 3.42; N, 8.45. Found:
C, 58.12; H, 3.37; N, 8.65%. IR spectra (KBr/pellet, cm-1): 3415s, 3065s, 1710s,
1601s, 1570m, 1551m, 1469w, 1423m, 1247s, 1164m, 1015w, 916w, 793w, 768w,
691w.
2.3 Crystal structure determination
X-ray diffraction data were collected with a Bruker APEXII CCD diffractometer
at temperature of 298 ± 1K using Mo-Kα ray (λ=0.71073 Å) for 1-2, 5-6 and Cu-Kα
ray ( =1.5418 Å) for 3 and 4. All crystal structures were solved by direct methods
λ
with the SHELXS-97 crystallographic software package [24]. Crystal structures of 2,
3, 4, 6 were refined by full-matrix least-squares technique based on F2 with the
SHELXL-2014 crystallographic software package [25]. The structures of 1 and 5
were first refined with the SHELXL-2015 crystallographic software package [26].
Finally, the structures of 1 and 5 were refined with Olex 2 crystallographic software
package [27]. The data of 1, 2, 4, 5 were corrected with SQUEEZE to remove the
solvent molecules due to severe crystallographic disorder [28]. All atoms were refined
anisotropically except hydrogen atoms. A summary of the crystallographic data and
processing parameters is presented in Table 1 and Table 2. Table S1 show selected
bond lengths and angles of 1-6.
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2.4 Antibacterial activity
To measure bacteriostatic activities of 1-6 and ligand against Gram-positive
Bacillus subtilis CMCC(B) 63501, Staphylococcus aureus ATCC 29213,
Gram-negative Escherichia coli ATCC 25922, Salmonella enteritidis ATCC 13076,
inhibition zone were performed using the agar diffusion technique [29-30]. The
nutrient agar medium and 6mm diameter paper discs were used. DMSO was used as
solvent to dissolve the compounds and also used as control. The filter paper discs
were soaked in different solution of the compounds and then placed in the Petri dishes
previously seeded with the test organisms. The experiment for each compound has
been done in triplicate. The plates were incubated for 18 hours at 37oC and the
inhibition zone around each disc was measured in mm using vernier caliper. The
average zone of inhibition in millimeter was determined from the readings taken in
triplicate (Table 3). Typical inhibition zones of obtained complexes 1(a), 3(b), 5(c),
6(d) against B. subtilis are shown in Fig. S1. Activity was determined by measuring
the diameter of the zone of inhibition in mm. An inhibition zone diameter over 7 mm
indicates that the tested compound is active against the bacteria under investigation.
From the results of the inhibition zone experiments, it is found that all complexes
inhibit Bacillus subtilis, whereas no compounds show obvious inhibitory effect
towards E. coli, S. aureus, S. enteritidis. Therefore, the minimum inhibitory
concentration (MIC) of 1-6 for Bacillus subtilis was conducted using agar dilution
methods [11]. MIC was the minimum sample concentration that completely inhibited
the growth of bacteria in the pores [31]. Each compound was dissolved in DMSO at
different concentrations of 128, 64, 32, 16, 8, 4, 2, 1, 0.5 ꢀg/mL. A preculture of
Bacillus subtilis was grown in LB (Luria Broth) for 18 h at the most favorable
temperature. This culture was used as a control to examine if the growth of bacteria
tested is normal. In a similar second culture, 100 ꢀL of the bacteria as well as DMSO
at the desired concentration were added. The MIC endpoint is the lowest
concentration of complex that produces inhibition of bacterial growth. In addition,
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two percent of DMSO without active ingredients was used as a positive control to
assess the MIC values of the strains. Kanamycin, Gatifloxacin, Norfloxacin,
Ciprofloxacin, Sparfloxacin and Streptomycin served as standard bactericides
[5,12,32-33]. The MIC values for all complexes and representative commercial
antibiotics are expressed as ꢀg/mL in Table 4.
3. Results and Discussion
3.1 Structural description of [Cu(Htpt)]n (1)
Crystal data of the compound reveals that 1 crystallizes in the triclinic system, P-1
space group, which exhibits one dimensional double-chain structure. The asymmetric
unit of 1 possesses one crystallographically unique Cu(II) cation, one Htpt2- ligand. As
shown in Fig. 1a, each five-coordinated Cu(II) ion is in a slightly distorted
square-pyramidal environment with a Addison trigonality factor τ=0.269 [34]. The
Cu(II) ion is coordinated by three nitrogen atoms [Cu1-N1A: 2.014(4) Å, Cu1-N2A:
1.941(3) Å, Cu1-N3A: 2.034(4) Å] and two oxygen atoms [Cu1-O2: 2.230(4) Å,
Cu1-O6B: 1.926(3) Å] (Scheme 2a). The oxygen atoms (O3, O4) of the carboxylate
groups in 1 are disordered. The surrounding bond angles of 1 are shown in Table S1.
The bond lengths and bond angles around Cu(II) ion are in the normal range [35-36].
The Htpt2- ligands connect neighboring Cu(II) ions by N/O chelation to yield limitless
1-D double chains (Fig. 1b). As shown in Fig. 1c, adjacent parallel 1-D double chains
form a 2-D supramolecular layer through π···π interactions between pyridine rings
(average face-to-face distances of 3.484(1) Å, and centroid-to-centroid distances of
3.996(6) Å) [37-38]. Additionally, the 2-D layers are further bridged through the
weaker C-H···O hydrogen bonds in 1 {H/O distances (bond angles): 2.180(4) Å
[143.23(1)o] for C4-H4···O5, 2.638 Å (123.01o) for C9-H9···O4} along a direction.
They are in the normal range of C-H···O hydrogen bonds [39-40]. The 2D planar
structure is further stacked into a 3-D supramolecular structure by another π···π
interaction between inter-molecular pyridine rings [interplanar separations: 3.355(2)
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Å; centroid-centroid separations: 3.524(4) Å]. Both the above interactions extend the
above 1-D double chains into 3-D supramolecular structure.
3.2 Structural description of {[Cu(H1.5tpt)Cl0.5(H2O)0.5]·1/5H2O}n (2)
Single-crystal X-ray diffraction analysis reveals that 2 is a 1-D structure and
crystallizes in the triclinic crystal system, space group P-1. The asymmetric unit of 2
possesses one crystallographically unique Cu(II) cations, one H1.5tpt1.5- ligand
including a H5 and half a H2, half a Cl- anion and half a coordinated water molecule
located in the same coordination site, 1/5 lattice water molecule. The disorder occurs
on the oxygen atoms and chlorine atoms (O6, Cl1, O8) in 2. As shown in Fig. 2a, each
Cu(II) ion is five-coordinated with a slightly distorted square-pyramidal environment
(τ=0.0833) involving three nitrogen atoms (N1, N2, N3), one oxygen atoms (O3A)
from the H1.5tpt1.5- ligand, half a coordinated Cl atom (Cl1) and half an oxygen atoms
(O8) located in the same coordination site (Scheme 2b). The bond lengths of Cu-O3A
and Cu-O8 are 1.941(1) and 2.194(2) Å and the Cu-N bond lengths are 1.942(1),
2.040(2) and 2.041(1) Å, respectively. The bond length of Cu-Cl1 is 2.586(3) Å. The
above bond lengths are within the range reported for square-pyramidal environments
[41]. The surrounding bond angles of Cu(II) are shown in Table S1. They are in the
normal range [41]. Neighboring Cu(II) ions are linked to form a 1-D single chain
through H1.5tpt1.5- ligands. Furthermore, these 1-D chains are assembled together by
C-H···O hydrogen bonds {H/O distances (bond angles): 2.470(3) Å [137.939(1)o] for
C3-H3···O4} to form a 2-D layer (Fig. 2b). The 2-D layers are further outspread to
3-D structure by the intermolecular C-H···O hydrogen bonds (Fig. 2c) {H/O distances
(bond angles): 2.599(9) Å [161.333(1)o] for C9-H9···O5}, which agree well with
those reported in the literature [42-43].
3.3 Structural description of {[Cu(H2tpt)(H2O)]·1/2SO4·2H2O}n (3) and [Cu(Htpt)]n
(4)
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The crystal data shows that 3 crystallizes in the orthorhombic crystal lattice with
space group Pbcn. As shown in Fig. 3a, 3 consists of one Cu(II) ion, one H2tpt- ligand,
2-
one coordinated water molecule, half a SO4 anion and two lattice water molecules.
Each Cu(II) ion is five-coordinated to form a slightly distorted square-pyramidal
geometry (τ=0.031). One oxygen donors (O4A) from the other H2tpt- ligand, an
oxygen donor (O11) of the water molecule and three nitrogen donors (N2, N3, N5) of
the pyridine from the ligand are coordinated with the Cu(II) ion (Scheme 2c). The
bond distances of Cu1-N2, Cu1-N3, and Cu1-N5 are 2.045(3), 2.036(3), 1.936(2) Å
while the bond lengths of Cu1-O4A and Cu1-O11 are 1.934(2), 2.244(3) Å,
respectively (Table S1). They are in the normal range [44-45]. In 3, the Cu(II) ions are
connected by H2tpt- ligand to give rise to a 1-D zigzag chain in the ab plane, in which
the Cu1···Cu1 distance is 7.895(1) Å (Fig. 3b). Moreover, two types of π···π stacking
interactions can be seen in 3. One is between adjacent pyridine rings with a
centroid-to-centroid distance of 3.670(2) Å and face-to-face distance of 3.400(0) Å,
which give rise to a 2-D infinite packing structure (Fig. 3c); the other is between
neighboring benzene rings with a centroid-to-centroid distance of 3.854(2) Å and
face-to-face distance is 3.370(1) Å, which further extend the 2-D structure into a 3-D
supramolecular architecture.
Single-crystal X-ray diffraction reveals that 4 is a two-dimensional structure and
crystallizes in monoclinic system with space group P21/n. It should be noted the
structure of 4 has been reported previously [23]. Hence, the description of the crystal
structure is omitted.
3.4 Structural description of {[Ni2(Htpt)2(H2O)2]·CH3CN}n (5)
The crystal data shows that 5 is the monoclinic system, P21/c space group. As
illustrated in Fig. 4a, the independent unit of 5 is composed of two
similar-coordinated Ni(II) cations, two Htpt2- ligands, two coordinated water
molecules, one lattice CH3CN molecule. The O11 and O12 atoms of carboxylate
groups in 5 present disordered state. Both Ni1 and Ni2 in distorted octahedron
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geometries are coordinated by three nitrogen atoms and three oxygen atoms. In Ni1,
one equatorial coordination site is occupied by N1, N2, N3 from Htpt2- ligand and
O13 from one coordinated water molecule (Scheme 2a). The apical position is
occupied by O4B and O7C from two Htpt2- ligands. Similar to Ni1, Ni2 is coordinated
by three nitrogen atoms (N4, N5, N6) from Htpt2- ligand adopting chelating
coordination and an oxygen atom (O14) from coordinated water molecule at the
equatorial positions. In addition, Ni2 is coordinated by two other oxygen atoms
(O11A, O1) from two Htpt2- ligands in monodentate mode at the axial positions. The
bond distances of Ni1-N1, Ni1-N2, Ni1-N3 are 1.948(5), 2.074(7), 2.050(7) Å, and
the Ni1-O13 is 1.987(5) Å, Ni1-O7C is 2.059(6) Å, Ni1-O4B is 2.025(6) Å. The bond
distances of Ni2-N4, Ni2-N5, Ni2-N6 are 1.956(5), 2.079(7), 2.054(7) Å, and the
Ni2-O1 is 2.033(5) Å, Ni2-O11A is 2.059(1) Å, Ni2-O14 is 1.992(5) Å. The bond
angles around Ni(II) ion are shown in Table S1. They are in the normal range [46]. In
5, adjacent Ni(II) atoms are connected through Htpt2- ligand adopting chelating mode
to give rise to 1-D zigzag chain which Ni1···Ni2 distance is 13.160(7) Å. The 1-D
zigzag chains are further linked by the carboxyl oxygen atoms of Htpt2- ligands to
form a 2-D planar structure in which the adjacent Ni1···Ni1 distance is 8.976(0) Å
(Fig. 4b).
For achieving further insight into the structure of 5, we can simplify Htpt2- ligands
and Ni(II) ions from the topological point of view. The structure of 5 is binodal with
three-connected [Ni(II) ion] and three-connected (Htpt2- ligands) nodes, and exhibits a
fascinating 2-D topology network (Fig. 4c). Thus, the overall structure of 5 can be
described as a (3,3)-connected hcb net with a Schläfli symbol of (63·63) calculated by
the TOPOS program [47-49].
3.5 Structural description of [Ni(H2tpt)2]·3H2O (6)
Single-crystal X-ray diffraction analysis reveals that 6 crystallizes in the
monoclinic system, P21/c space group. The independent unit of 6 contains one Ni(II)
ion, two H2tpt- ligands and three lattice water molecules. It should be pointed out that
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the disorder occurs on the oxygen atoms (O1, O2, O7, O8) of carboxylate groups. The
six-coordinated Ni(II) ion is in a distorted octahedral environment involving four
nitrogen atoms (N2, N4, N5, N6) from two ligands at the equatorial positions and two
nitrogen atoms (N1, N3) at the axial positions (Scheme 2d). The bond lengths of
Ni1-N1, Ni1-N2, Ni1-N3, Ni1-N4, Ni1-N5, Ni1-N6 are 2.098(2), 1.988(2), 2.097(3),
1.984(2), 2.132(2), 2.120(2) Å, respectively. And the bond angles around Ni(II) are
shown in Table S1. They are consistent with the reported Ni(II) complexes [50-51].
As illustrated in Fig. 5a, six terpyridyl nitrogen atoms from two H2tpt- ligands connect
one Ni(II) ion to form [Ni(Htpt)2] molecule. The adjacent [Ni(Htpt)2] molecules form
2-D structure through the stronger C-H···O hydrogen bonds in the ac plane (Fig. 5b).
The H···O distances (bond angles) of the O-H···O hydrogen bonds are 2.496(5) Å
[128.507(1)°] for C19A-H1A···O11, 2.364(5) Å [155.795(5)°] for C38-H38···O9.
Moreover, adjacent 2-D layers are further connected by C-H···O hydrogen bonds
{H/O distances (bond angles): 2.353(5) Å [148.827(2)º] for C16-H16···O3; 2.383(5)
Å [148.431(4)º] for C22-H22···O2} to form 3-D supramolecular structure in the bc
plane. The lengths of C-H···O hydrogen bonds agree well with those reported in the
literatures [52-54].
The PXRD patterns of 5 and 6 are shown in Figure S2. It could be seen that
result of the most peak positions was concordant to the simulated from single crystal
data, indicating that the synthesized complexes possess high phase purity.
3.6 UV/vis absorbance properties and IR spectroscopy
The solid-state UV-vis absorption spectroscopy of complexes 1-3, 5-6 and H3tpt
ligand have been studied (Fig. S3). It is obvious that the H3tpt ligand shows the
absorption band around 335 nm, which can be assigned to the intraligand π-π*
transition. Similarly, all complexes show weak shoulder band around 335 nm, which
suggest that the coordination of the metal ions hardly alters the intrinsic electronic
properties of the H3tpt ligand [55-56]. Compared to the H3tpt ligand, all the Cu(II)
complexes display similar spectral feature containing a broad absorption band around
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686 nm. The absorption band of 5 in the vision region was observed at ca. 618 nm.
These bands in the absorption spectra can be attributed to the d-d transition of the
Cu(II) and Ni(II) [55-56].
The IR spectra of H3tpt ligand, 1-3 and 5-6 are shown in Fig. S4. The vibrational
bands present at 3410 and 3094 cm-1 should be ascribed to the ν(O-H) and ν(C-H) in
ligand. The bands around 3400 cm-1 in complexes could be attributed to the ν(O-H) of
the carboxyl groups, which indicates carboxyl groups in complexes are not fully
involved in the coordination. The bands of H3tpt at 1712 cm-1 and 1597 cm-1 are
attributed to the stretching vibration of the C=O bonds of carboxyl groups and C=N
bonds of the pyridine rings. The characteristic shifting bands of ν(C=O) and ν(C=N)
(shown in Table S2) in complexes is indicative of the coordination state between the
central ions and H3tpt. The absorption peaks in the range of 1112-1269 cm-1 are
assigned to C-O stretching vibrations for H3tpt and the complexes. In addition, in all
complexes, strong bands observed in the range of 1601-1656 cm-1 are associated with
asymmetric stretching vibrations ν(COO-)as of the carboxylic acid groups, while the
peaks in the range of 1347-1423 cm-1 are attributed to symmetric stretching vibrations
ν(COO-)s of the carboxylic acid groups [57-59].
3.7 Thermogravimetric analysis
The thermal properties of 1-3, 5-6 were characterized by thermogravimetric
analysis (TGA) (Figure S5). The metal coordination complexes were heated in a
temperature range of 30-800°C in an air atmosphere. The thermal decomposition of
as-prepared complexes proceeds with two degradation steps. The first step of
decomposition can be attributed to the loss of solvent molecules at 50-200°C for 1
and at 30-200°C for 5, and the loss of lattice water molecules, coordinated water
molecules, and coordinated Cl ions at 135-205°C for 2. As for 3 and 6, the first step of
weight loss at 80-235°C and 70-180°C corresponds to the loss of lattice water
molecules. The second decomposition stage involves the removal of the ligand,
resulting in the collapse of the crystal structure. For 1-3, the residue is CuO with
12

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weight loss of 86.29% (Calcd. 84.18%), 84.87% (Calcd. 85.09%), 83.55% (Calcd.
86.87%), respectively. As for 5-6, the total weight loss amounts to 89.79% (Calcd.
93.04%), 89.86% (Calcd. 92.48%) leaving NiO as a residue. Table S3 reports the
calculated and experimental weight losses, and the temperature range of
decomposition for these complexes studied.
3.8 Antibacterial activity
The search for agents with antibacterial activity is an important field of research
nowadays. Many researchers have reported the antibacterial activity of complexes due
to various molecular architectures and different metal center of complexes
[60-61,12,13]. In this work, from an insight of coordination chemistry, 1-6 containing
same ligand are suitable for the research of antibacterial mechanism and the
structure-function relationship. Herein, antibacterial activity of as-prepared 1-6 and
H3tpt ligand against two Gram(+) bacterial strains [Bacillus subtilis CMCC(B) 63501,
Staphylococcus aureus ATCC 29213] and two Gram(−) bacterial strains (Escherichia
coli ATCC 25922, Salmonella enteritidis ATCC 13076) was studied using the method
of the agar diffusion technique. As shown in Table 3, the diameters of inhibition zones
for 1-6 against B. subtilis are obviously larger than those of other bacterial strains,
which shows that all complexes demonstrate selective antibacterial activity.
Compared to the metallic salt and the corresponding ligands, all complexes show
antibacterial activity towards B. subtilis, which can be attributed to the chelation
theory where chelation of metal ions and ligands reduces the polarity of the metal ion
mainly because of partial sharing of its positive charge with the donor groups and
possible π-electron delocalization within the whole chelate ring [62-67]. Furthermore,
according to the theory of similarity and intermiscibility, the chelate process improves
lipophicity of central metal, which subsequently favours its permeation through the
lipid layer of cell membranes and further inhibit enzyme activity, which resulting in
excellent antibacterial activity [68-70].
In order to further compare their antimicrobial activities, 1-6 were selected against
13

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B. subtilis for minimum inhibitory concentration (MIC) studies. As present in Table 4,
compared with other copper complexes, 3 shows the excellent antibacterial
performance with an MIC value of 2 ꢀg/mL. Analyzing from the structure, 3 contains
easily-leaving coordinated water molecules, thereby exposing more active sites easily,
which may be an important factor exhibiting excellent antibacterial activity. Similarly,
compared with 6, 5 also exhibit outstanding activity because 5 has also easily-leaving
coordinated water molecule. Furthermore, the difference of metal ion may be one of
the reasons why 5 exhibits the higher antimicrobial activity than 3. In contrast, 6
showed weaker antibacterial activity compared to other complexes. This is probably
due to the fact that Ni(II) is coordinated by terpyridyl nitrogen atoms of two H3tpt
ligands adopting bis-tridentate chelating coordination mode, thus it is difficult to
expose the active site because of its stable structure. Our results preliminary reveal
that the antibacterial activities are related to complex structures. Namely, containing
easily-leaving coordinated water molecules in as-prepared complexes, thereby
exposing more active sites easily, is an important factor exhibiting excellent
antibacterial activity.
4. Conclusion
In summary, four Cu(II) complexes and two Ni(II) complexes based on H3tpt
ligand have been synthesized and characterized. Thermogravimetric analysis has been
used to determine the structural stability, which shows that the thermal decomposition
results in the metal oxides as residues. The antibacterial activities of as-prepared 1-6
against four strains have been studied, which reveals all complexes show selective
antibacterial activity against B. subtilis. Our study on antimicrobial activity
demonstrates that the complexes containing easily-leaving coordinated water
molecules exhibit excellent antibacterial activity. This work preliminarily reveals that
the antibacterial activities are related to complex structures. The mode of action and
antibacterial mechanism still need further exploration and validation.
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Acknowledgment:
We are thankful for financial support from National Natural Science Foundation
of China (Nos. J1210060), Science and technology research program of Henan
Province of China (162102210167, 172102210483), Key scientific research projects
of Henan Province of China (17A150020), Natural Science Foundation of Henan
Province of China (182300410216), National Undergraduate Innovation and
entrepreneurship training project (201810459007), College Science and Technology
Innovation Team of Henan Province (Nos. 16IRTSTHN001) and the Science &
Technology Innovation Talent Plan of Henan Province (Nos. 174200510018).
Appendix A. Supplementary data
Crystallographic data for the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplementary publication with
CCDC numbers 1861713-1861715 (1-3) and 1861716-1861717 (5-6). Copies of the
data can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: (44) 1223 336-033; e-mail: deposit@ccdc.cam.ac.uk).
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Captions:
Scheme 1. Structure of the H3tpt ligand.
Scheme 2. (a) Coordination modes found in 1 and 5. (b) Coordination modes found in 2. (c)
Coordination modes found in 3. (d) Coordination modes found in 6.
Table 1. Crystallographic data for 1-3.
Table 2. Crystallographic data for 4-6.
Table 3. Antimicrobial screening results of the H3tpt ligands, 1-6 and metal salts.
Table 4. Minimum inhibition concentration (MIC) values for 1-6 and some standard drugs.
Table S1. Selected bond distances (Å) and bond angles (deg) for 1-6.
Table S2. Selected IR frequencies of the H3tpt, 1-3 and 5-6.
Table S3: Theoretical & experimental weight loss of the complexes.
Figure S1. Typical inhibition zones of complexes 1(a), 3(b), 5(c), 6(d) against B. subtilis.
Figure S2. PXRD patterns for as-synthesized 5 and 6.
Figure S3. UV-vis absorption spectra at room temperature for the free the H3tpt, 1-3 and 5-6.
Figure S4. IR spectra of as-prepared complexes and the free ligand.
Figure S5. The TG curves for 1-3, 5-6.
20

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Figure 1. (a) The coordination environment of Cu(II) atom in 1 (A: 1-x, -y-1, -z+2; B: 2-x, -1-y,
3-z), all hydrogen atoms are omitted for clarity. (b) The 1-D double chains structure. (c) 2-D
structure resulting from π···π stacking.
Figure 2. (a) The coordination environment of Cu(II) atom in 2 (A: x, y, z+1), part of the
hydrogen atom is omitted for clarity. (b) The 2-D supramolecular network. (c) 3-D supramolecular
structure constructed by hydrogen-bonding interactions.
Figure 3. (a) The coordination environment of Cu(II) atom in 3 (A: -x+3/2, y-1/2, z), all hydrogen
atoms are omitted for clarity. (b) The 1-D zigzag chains structure. (c) 2-D structure resulting from
π···π stacking.
Figure 4. (a) The coordination environment of Ni(II) atom in 5 (A: x, -y+1/2, z+1/2; B: -1+x,
-y+1/2, z-1/2), all hydrogen atoms are omitted for clarity. (b) The 2-D planar network. (c) Views
of topology of 5 [The blue balls represent Ni(II) atoms, the pink balls represent the Htpt2- ligands,
respectively].
Figure 5. (a) The coordination environment of Ni(II) atom in 6, all hydrogen atoms are omitted
for clarity. (b) 2-D structure resulting from C-H···O hydrogen-bonding interactions.
21

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Table 1. Crystallographic data for 1-3.
Complexes
1
2
3
C24H13CuN3O6
C48H29.8ClCu2N6O13.4 C48H40Cu2N6O22S
Formula
Fw
502.91
293(2)
1067.51
293(2)
1212.00
273(2)
Temperature(K)
Wavelength(Å)
Crystal system
0.71073
triclinic
0.71073
triclinic
1.54178
rthorhombic
Space group
a(Å)
P-1
P-1
Pbcn
9.2864(14)
10.9212(16)
12.1185(18)
112.949(3)
107.104(3)
94.009(4)
1057.7(3)
2
8.1583(16)
11.151(2)
12.752(3)
77.00(3)
76.20(3)
85.53(3)
1097.4(4)
1
25.5176(5)
b(Å)
13.9277(3)
c(Å)
13.5555(3)
α
β
(deg)
(deg)
90
90
γ(deg)
90
V(Å3)
Z
4817.65(18)
4
Dc(g cm-3)
F(000)
1.579
510
1.615
542
1.671
2480
θ range for data
collection(deg)
3.36~28.460
30315/5326
5326/3/314
1.080
3.367~27.103
43225/4843
4843/14/346
1.044
3.464~68.424
51354/4435
4435/7/359
1.052
Reflections collected
/unique
Data/restraints/
params
Goodness-of-fit on
F2
Absorption
coefficient
1.081
1.108
2.323
Tmin/Tmax
0.6871, 0.7457
0.0819, 0.1429
0.6933, 0.7455
0.0399, 0.1106
0.6478, 0.7531
0.0490, 0.1366
Final R1a, wR2b
a R1 = ∑ Fo− Fc /∑Fo. b wR2 = [∑w(Fo  − Fc2)2/∑wFo  ] .
2
2 2 1/2
2
w1 = 1/[
σ
2(Fo)2 + 0.0594P2 + 1.9874P], where P = (Fo + 2Fc2)/3. w2 = 1/[
σ
2(Fo)2 + 0.0733P2 +
2
2
0.8069P], where P = (Fo + 2Fc2)/3. w3 = 1/[
σ
2(Fo)2 + 0.0863P2 + 4.7182P], where P = (Fo +
2Fc2)/3.

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Table 2. Crystallographic data for 4-6.
4
5
C50H33N7Ni2O14
1073.25
298(2)
6
C48H34N6NiO15
993.52
Complexes
Formula
C24H13CuN3O6
502.91
Fw
Temperature(K)
Wavelength(Å)
Crystal system
Space group
a(Å)
293(2)
293(2)
1.54178
Monoclinic
P21/n
0.71076
Monoclinic
P21/c
0.71073
Monoclinic
P21/c
13.276(3)
13.867(3)
16.406(3)
90
20.79(6)
14.59(4)
17.61(4)
90
11.7921(6)
16.3564(7)
23.2228(12)
90
b(Å)
c(Å)
α
β
(deg)
(deg)
111.90(3)
90
114.66(3)
90
100.938(2)
90
γ(deg)
V(Å3)
Z
2802.4(12)
4
4854(23)
4
4397.8(4)
4
Dc(g cm-3)
F(000)
1.192
1.469
1.501
1020
2200
2048
θ range for data
collection(deg)
3.676~71.998
2.904~25.249
3.065~24.804
Reflections collected
/unique
61376/5515
70946/8761
86061/7519
Data/restraints/
5515/0/308
0.825
8761/30/680
1.030
7519/13/664
1.083
Goodness-of-fit on F2
Absorption coefficient
Tmin/Tmax
1.424
0.851
0.523
0.5306, 0.7536
0.0394, 0.1229
0.6413, 0.7456
0.0612, 0.1367
0.6787, 0.7451
0.0464, 0.0975
Final R1a, wR2b
2
2 2 1/2
a R1 = ∑ Fo− Fc /∑Fo. b wR2 = [∑w(Fo  − Fc2)2/∑wFo  ] .
2
w4 = 1/[
σ
2(Fo)2 + 0.0978P2 + 3.4950P], where P = (Fo + 2Fc2)/3. w5 = 1/[
σ
2(Fo)2 + 0.0797P2 +
2
2
0.8482P], where P = (Fo + 2Fc2)/3. w6 = 1/[
σ
2(Fo)2 + 0.0366P2 + 5.1497P], where P = (Fo +
2Fc2)/3.

ACCEPTED MANUSCRIPT
Table 3. Antimicrobial screening results of the H3tpt ligands, 1-6 and metal salts.
Complexes and
metal salts
Inhibition zone diameter (mm)
Bacillus subtilis Staphylococcus
Salmonella
enteritidis
Escherichia coli
aureus
12.3
10
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
1
2
15.2
9.8
3
4
15
5
8
6
H3tpt
6.00
6.00
6.00
6.00
6.00
6.00
CuSO4·5H2O
CuCl2·6H2O
CuBr2
NiCl2·6H2O
Control: DMSO

ACCEPTED MANUSCRIPT
Table 4. Minimum inhibition concentration (MIC) values for 1-6 and some standard drugs.
Polymers and standard
MIC of Bacillus subtilis(ꢀg/mL)
4
8
1
2
2
3
16
1
4
5
64
-
6
Kanamycin*
Streptomycin*
Gatifloxacin*
Norfloxacin*
Ciprofloxacin*
Sparfloxacin*
10
4.0
2.5
1.1
2.0
* Standard drug.
- Dashes indicated zero inhibition, all microorganisms were resistant to DMSO.

ACCEPTED MANUSCRIPT
Scheme 1. Structure of the H3tpt ligand.

ACCEPTED MANUSCRIPT
Scheme 2. (a) Coordination modes found in 1 and 5. (b) Coordination modes found in 2. (c)
Coordination modes found in 3. (d) Coordination modes found in 6.