Received: 19 May 2022
Revised: 13 July 2022
Accepted: 15 July 2022
DOI: 10.1002/aoc.6828
FULL PAPER
Two mono- and dinuclear Bi(III) complexes combined with
crystallographic, spectroscopic, and antibacterial activities,
MEP/HSA, and TD/DFT calculations
Lan-Qin Chai
| Yong-Mei Chai
School of Chemistry and Chemical
Engineering, Lanzhou Jiaotong
University, Lanzhou, China
Correspondence
Lan-Qin Chai, School of Chemistry and
Chemical Engineering, Lanzhou Jiaotong
University, Lanzhou 730070, China.
Email: chailanqin@163.com and
chailq@mail.lzjtu.cn
Funding information
Foundation of a Hundred Youth Talents
Training Program of Lanzhou Jiaotong
University, Grant/Award Number:
152022; Fundamental Research Funds of
Gansu Province Universities, Grant/
Award Number: 214152
| Xiao-Fang Zhang
Two mono- and dinuclear Bi(III) complexes, [Bi(L)2(NO3)2]NO3 (1) and
[Bi2(L)2Cl8] (2) (L = (2-(2-pyridyl)-4-methyl-1,2-dihydroquinazoline-N3-oxide),
were obtained via complexation of L with Bi(III) nitrate pentahydrate and
Bi(III) chloride. L and both complexes were characterized by elemental analyses and spectroscopic methods including FT-IR, UV–Vis, and fluorescence
spectroscopy. Specifically, it clearly manifested that both complexes had good
fluorescence emission and showed different fluorescence behaviors in diverse
solvents. Both Bi(III) complexes were further determined by X-ray crystallography, and it was found that the ratio of ligand to metal was 2:1 in 1, whereas
2 was 1:1. Their coordination geometric configurations were significantly different, such as octa-coordinated complex 1 formed an infinite 1-D chain-like,
funnel-shaped 2-D network, and ladder-like 3-D supramolecular framework,
whereas hexa-coordinated complex 2 with a binuclear structure exhibited two
slightly distorted octahedral geometric structures; meanwhile, symmetric units
came into being an infinite 2-D layer even and meter-shaped 3-D supramolecular skeleton. The optimal geometries, frontier molecular orbital energies, and
molecular electrostatic potential diagrams of both complexes were calculated
using DFT/B3LYP. The electronic distribution of HOMO-LUMO rationalized
the results of UV–Vis spectra with the help of TD-DFT calculations. Furthermore, all samples demonstrated excellent antibacterial activities against
Escherichia coli and Staphylococcus aureus. In addition, non-covalent interactions of complexes and their contributions were quantified with Hirshfeld
surfaces using CrystalExplorer17 program.
KEYWORDS
antimicrobial activity, Hirshfeld surface analysis, molecular electrostatic potential (MEP),
spectroscopic behavior, TD/DFT calculation
1 | INTRODUCTION
Schiff base ligands have outstanding significance in the
field of coordination chemistry because of their structure
containing imine or azomethine groups (–RC=N–). It
Appl Organomet Chem. 2022;e6828.
https://doi.org/10.1002/aoc.6828
can stabilize metal ions in various oxidation states and
form stable complexes with them owing to the existence
of lone pairs of electrons from nitrogen atoms.[1,2] These
metal complexes lay the foundation for the development
of magnetic,[3] catalysis,[4] spectroscopy,[5,6] adhesive
wileyonlinelibrary.com/journal/aoc
© 2022 John Wiley & Sons Ltd.
1 of 17
2 of 17
CHAI ET AL.
properties[7] and many important biological processes.[8]
Bismuth is one of the most stable and least toxic heavy
metal elements in the periodic table and also is well
known as the green metal. Due to their special physical
and chemical properties, plenty of novel structured bismuth complexes with the coordination numbers of 3–10
commonly have been synthesized in recent years. Corresponding to the disparate type of ligand and coordination
configuration of complex, it makes bismuth compounds
widely used in various aspects.[9,10] They can achieve
reversible phase changes and switchable photoluminescence (PL) under external stimuli.[11,12] On the other
hand, they can be used as drugs to kill Helicobacter pylori
and treat gastric ulcers and gastrointestinal diseases.[13]
Meanwhile, some bismuth complexes show high activity
against certain common bacteria (such as Staphylococcus
aureus, vancomycin-resistant enterococci, Escherichia
coli, and Pseudomonas aeruginosa).[14] The compounds
containing quinazoline ring structure have abundant
electron-rich donor centers and can form different types
of complexes with good physiological activity.[15,16]
Although these complexes have attracted much attention
owing to excellent applications, notable studies were still
done on single-crystal structure and theoretical calculations of quinazoline-type bismuth(III) complexes containing pyridine ring.
In continuation of our investigations on copper(II),
nickel(II), and cobalt(III) complexes based on some
quinazoline-type ligands previously,[17,18] herein we
firstly report on mononuclear [Bi(L)2(NO3)2]NO3 (1) and
dinuclear [Bi2(L)2Cl8] (2) complexes (L = 2-(2-pyridyl)4-methyl-1,2-dihydroquinazoline-N3-oxide) (Scheme 1).
The structures of Bi(III) complexes were determined by
X-ray single-crystal diffraction, which displayed the
ligand and metal were combined at ratios of 2:1 in 1 and
1:1 in 2. It was noteworthy that the octa-coordinated
complex 1 formed an infinite 1-D chain-like, 2-D funnelshaped, and 3-D ladder-like supramolecular skeleton.
Specially, six-coordinated complex 2 with dinuclear
structure constituted 2-D layered framework and 3-D
meter-shaped supramolecular structure. Remarkably, the
fluorescence effects were further investigated, in which
both complexes showed disparate fluorescence emission
SCHEME 1
Synthetic route of complexes 1 and 2
in multifarious solvents. The structures of both complexes were optimized using DFT calculations, and the
results of X-ray crystallography were verified by electrostatic potential (MEP) and Hirshfeld surface analysis
(HSA). Moreover, we further inspected the antibacterial
activities of all compounds including metal salts against
E. coli and S. aureus.
2 | EXPERIMENTAL
2.1 | Materials and instruments
2-Pyridinecarboxaldehyde and o-aminoacetophenone
were purchased from Energy Chemical. The chemicals
were directly used in experiments due to the purity of
chemical medicine may reach 98%. The infrared spectra
in the range of 400–4000 cm1 were measured by a
VERTEX-70 FT-IR spectrophotometer (KBr pellets). The
Shimadzu UV-2550 spectrometer was used to measure
the ground state absorption of samples in methanol solution at room temperature. Fluorescence spectra were
obtained on 970 CRT spectrofluorometer (Spectro Shanghai). 1H NMR spectrum at ambient temperature was
done on a Mercury Plus (400-MHz) spectrometer, with
CDCl3 as the solvent, and wherein ppm was the chemical
shift relative to TMS. IRIS ER/SWP-1 ICP atomic emission spectrometer was used for elemental analysis of Bi,
whereas the elemental analyses of C, H, and N were performed on the GmbH VariuoEL V3.00 automatic elemental analyzer. X-ray diffraction data of both complexes
were collected using an Agilent SuperNova Dual area
detector diffractometer. The micro melting point tester
(Beijing Taike Instrument Limited Company) measured
the melting point.
2.2 | Synthesis and structural
characterization of L
L 2-(2-Pyridyl)-4-methyl-1,2-dihydroquinazoline-N3-oxide
was synthesized by the method reported in the literature
recently.[19]
CHAI ET AL.
TABLE 1
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Molecular formula and elemental analyses of complexes 1 and 2
Found (calc.) %
Complexes
Yield (mg, %)
Molecular formula (Mw)
C
H
N
Bi
1
6.94, 79.4
C28H26BiN9O11 (873.54)
38.50(38.54)
3.00(3.06)
14.43(14.48)
23.92(23.97)
2
9.24, 78.6
C28H22Bi2Cl8N6O2 (1176.08)
28.59(28.65)
1.89(1.94)
7.15(7.19)
35.54(35.59)
2.3 | Synthesis of Bi(III) complexes
Bismuth(III) nitrate pentahydrate (0.01 mmol, 4.85 mg)
in 2 ml methanol was added to 3 ml ethyl acetate
(EA) solution of the ligand L (0.02 mmol, 4.79 mg). The
reaction mixture was stirred for about 2 h and then
allowed to evaporate slowly. The solvent was volatilized
at room temperature for 2 weeks to obtain several light
yellow crystals suitable for X-ray single-crystal diffraction. The synthesis method of complex 2 was similar to
complex 1, except that bismuth(III) nitrate pentahydrate
was replaced with bismuth(III) chloride (0.01 mmol,
3.15 mg). The data of molecular formula and elemental
analyses of both complexes were compared in Table 1.
2.4 | Computational method
The Gaussian 09 and GaussView 5.0 packages were
applied to perform quantum calculations and visualizations of both complexes.[20] In the gaseous, the geometrical optimizations and the corresponding molecular
orbital energies of two complexes were calculated by DFT
using Becke-3-Lee-Yang-Parr (B3LYP) functional with
6-31G(d) basis set.[21,22] LANL2DZ basis set for bismuth
atom was treated.[23,24] The most stable structure was
determined through frequency calculation, and there was
no virtual frequency in the optimized structure. UV–
visible (UV–Vis) spectra and electronic transitions were
calculated using the same basis set at the B3LYP level
through the TD-DFT method, and the effects of solvents
were simulated using a conductor-like polarized continuum model (CPCM).[25,26] The fractional contributions of
the ligand to Bi(III) complexes were calculated by
Multiwfn program.[27]
2.5 | X-ray crystallography
X-ray diffraction data for complexes 1 and 2 were collected on a SuperNova Dual with graphite monochromatized Mo-Ka/Cu-Ka radiation (λ = 0.71073/1.54184 Å),
and OLEX2 was used for data reduction.[28] The structures were solved by the Fourier difference method and
refined by the full-matrix least squares method on F2 data
using the SHELXL-2018 program.[29] Anisotropy parameters can be used to refine all non-hydrogen atoms, the
hydrogen atoms were refined into rigid groups and
assigned to ideal geometric positions. The crystallographic data and details for structural analyses were
given in Table 2.
3 | RESULTS A ND DISCUSSION
As shown in Scheme 1, the ligand L was complexed with
Bi(III) nitrate pentahydrate and Bi(III) chloride to obtain
complexes 1 and 2. The complexes existed stably at room
temperature and were soluble in common organic
solvents, such as methanol, trichloromethane, EA, and
N,N-dimethylformamide (DMF), but insoluble in n-hexane, petroleum ether, and diethyl ether.
3.1 | Description of crystal structures
3.1.1 |
X-ray crystal structure of 1
The crystal structure and coordination configuration of
[Bi(L)2(NO3)2]NO3 were illustrated in Figure 1. Some
significant optimized parameters and experimental
values were collected in Table 3. Crystallographic analysis revealed that octa-coordinated complex 1 formed a 2:1
ligand-to-metal ratio and belonged to the orthorhombic
lattice with Pbcn space group. In the asymmetric units,
there were independent one Bi(III), two L units, and
three nitrate anions, of which two nitrate ions participated in coordination and the other nitrate ion was free.
The five atoms N(3), N(3), O(1), O(2), and O(3) defined
the equatorial plane, and the distance from Bi(III) to
this plane was 0.558 Å (plane equation: 0.5357
(13) x + 0.8163 (8) y 0.2161(13) z = 5.6856 (236)).[30]
The bond length distance of Bi1–N3 was 2.539(6) Å,
whereas the bond length distances of Bi–O were in the
range 2.334(5)–2.669(6) Å; thus, these bond lengths were
in the appropriate ranges.[31]
Intermolecular C–HN, C–HO, and C–Hπ
(Ph) interactions (Figure 2 and Tables S1 and S2)
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CHAI ET AL.
TABLE 2
Crystallographic data and structure refinements for 1 and 2
Empirical formula
C28H26BiN9O11
C28H22Bi2Cl8N6O2
Formula weight
873.54
1176.08
Temperature (K)
293 (2)
293.05(10)
Wavelength (Å)
0.71073
1.54184
Crystal system
Orthorhombic
Monoclinic
Space group
Pbcn
P 21/c
a
21.7625(14)
8.9575(10)
b
9.4788(6)
15.7510(2)
c
15.2895(10)
14.2489(2)
α
90
90
β
90
93.8130(10)
90
90
Unit cell dimensions (Å, )
γ
3
Volume (Å ), Z
3154.0(4), 4
2005.92(4), 4
Calculated density (Mg/m )
1.835
1.947
Absorption coefficient (mm1)
5.665
22.204
F(000)
1704
1,100
3
Crystal size (mm )
0.18 0.15 0.12
0.15 0.11 0.09
θ Range for data collection ( )
3.537 26.021
4.948–66.596
Index ranges
26 ≤ h ≤ 25
8 ≤ h ≤ 10
5 ≤ k ≤ 11
18 ≤ k ≤ 15
16 ≤ l ≤ 18
16 ≤ l ≤ 15
3
Reflections collected
7795
7035
Independent reflections
2067 [R (int) = 0.0505]
4068 [R (int) = 0.0486]
Completeness to θ = 26.32(%)/66.97(%)
99.56
99.92
Data/restraints/parameters
Goodness-of-fit on F
2
Final R indices [I > 2σ(I)]
R indices (all data)
3
Largest difference peak and hole(e Å )
3102/0/224
3539/0/209
1.016
1.068
R1 = 0.0480, wR2 = 0.1136a
R1 = 0.0530, wR2 = 0.1344b
R1 = 0.0726, wR2 = 0.1298
R1 = 0.0548, wR2 = 0.1371
2.821 and 3.740
4.123 and 4.956
w = 1/[σ (Fo2) + (0.0663P)2].
b
w = 1/[σ 2(Fo2) + (0.0969P)2], where P = (Fo2 + 2Fc2)/3.
a
2
F I G U R E 1 Crystal structure,
intermolecular hydrogen bonds, and
coordination configuration of 1.
(Hydrogen atoms are omitted for clarity
except those forming hydrogen bonds.)
CHAI ET AL.
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T A B L E 3 Selected bond lengths
(Å) and angles ( ) from single-crystal Xray diffraction data and DFT
optimization data in calc. column of 1
FIGURE 2
plane of 1
Bond lengths
X-ray (Å)
Calc. (Å)
Bond lengths
X-ray (Å)
Calc. (Å)
Bi1–O3
2.580(5)
2.5735
Bi1–O1
2.334(5)
2.2753
Bi1–O2
2.669(6)
2.5393
Bi1–N3
2.539(6)
2.5712
Bond angles
Bond angles
X-ray ( )
Calc. ( )
X-ray ( )
Calc. ( )
O3–Bi1–O3
140.50(3)
143.6211
O1–Bi1–O1
78.00(2)
82.0053
O2–Bi1–O2
O3–Bi1–O2
146.20(3)
144.7846
N3–Bi1–N3
154.00(2)
156.9214
117.50(16)
116.4918
O3–Bi1–O2
48.83(15)
50.5337
N3–Bi1–O3
117.51(17)
121.1203
N3–Bi1–O3
71.95(16)
74.5920
O1–Bi1–O3
141.97(18)
146.8638
O1–Bi1–O3
74.79(17)
77.7724
N3–Bi1–O2
118.93(17)
120.3217
N3–Bi1–O2
69.35(17)
72.1133
O1–Bi1–O2
140.90(19)
143.7050
O1–Bi1–O2
71.12(19)
74.9687
O1–Bi1–N3
78.27(16)
75.4026
O1–Bi1–N3
81.57(16)
80.2756
O2–Bi1–O2
146.2(3)
143.7846
An infinite 1-D chain, intermolecular hydrogen bonds, C–Hπ (Ph) interaction, and 2-D layered structure along the ab-
connected molecules of [Bi(L)2(NO3)2]NO3, where
stacking interaction distance for C(4)–H(4)Cg
(2) was 2.952 Å. There were three pairs of C(9)–H(9)
O(1), C(8)–H(8C)O(1), and C(11)–H(11)N(1) intramolecular hydrogen bonds on the ligand molecules
involved in the coordination, forming a six-membered
ring and two five-membered rings. Simultaneously, two
adjacent molecules were connected by two pairs of C
(9)–H(9)O(5) and C(14)–H(14)O(6) intermolecular
hydrogen bonds to form an infinite 1-D chain-like
structures. These intermolecular interactions were critical to the stability of the Bi(III) complex.[32,33] Owing
to intermolecular interactions, 1 directed self-assembly
2-D symmetrical funnel-shaped structure along the abplane, especially an infinite 3-D ladder-shaped layer
supramolecular framework and 3-D perspective structure along the ac-plane (Figures 2 and 3).
3.1.2 |
X-ray crystal structure of 2
The crystal structure and coordination configuration of
[Bi2(L)2Cl8] were shown in Figure 4. Some significant
parameters obtained from the experiment and DFT
6 of 17
CHAI ET AL.
FIGURE 3
View of 3-D supramolecular frameworks and 3-D perspective structure along the ac-plane of 1
F I G U R E 4 Crystal structure, intramolecular hydrogen bond, and coordination configuration of 2. (Only the hydrogen atom that form
hydrogen bond was retained for clarity.)
TABLE 4
Selected bond lengths (Å) and angles ( ) from single-crystal X-ray diffraction data and DFT optimization data of 2
Bond lengths
Experimental
Calculated
Bond lengths
Experimental
Calculated
Bi(1)–Cl(2)
2.574(2)
2.5752
Bi(1)–Cl(4)
2.871(18)
2.8951
Bi(1)–Cl(4)
2.901(19)
2.9558
Bi(1)–Cl(3)
2.602(2)
2.5645
Bi(1)–Cl(1)
2.572(18)
2.5449
Bi(1)–O(1)
2.482(5)
2.4485
Bond angles
Experimental
Calculated
Bond angles
Experimental
Calculated
Cl(2)–Bi(1)–Cl(4)
174.67(7)
171.0320
Cl(2)–Bi(1)–Cl(4)
91.13(7)
91.1710
Cl(2)–Bi(1)–Cl(3)
97.95(7)
96.2046
Cl(4)–Bi(1)–Cl(4)
89.89(5)
87.3344
Cl(3)–Bi(1)–Cl(4)
87.32(6)
91.8161
Cl(3)–Bi(1)–Cl(4)
87.34(6)
84.3263
Cl(1)–Bi(1)–Cl(2)
91.60(7)
88.9401
Cl(1)–Bi(1)–Cl(4)
176.57(6)
174.8363
Cl(1)–Bi(1)–Cl(4)
87.58(6)
91.7570
Cl(1)–Bi(1)–Cl(3)
90.22(7)
91.4583
O(1)–Bi(1)–Cl(2)
95.69(14)
93.6050
O(1)–Bi(1)–Cl(4)
79.02(13)
77.0544
O(1)–Bi(1)–Cl(4)
94.19(12)
92.1762
O(1)–Bi(1)–Cl(3)
166.25(13)
169.4885
O(1)–Bi(1)–Cl(1)
87.61(12)
83.8249
theoretical calculation were collected in Table 4. X-ray
single-crystal analysis revealed that 2 crystallized in the
monoclinic system with P21/c space group and consisted
of two Bi(III), two L units, and eight-coordinated chloride anions. In contrast to 1, 2 was binuclear structure in
which L and Bi(III) were bound at a ratio of 1:1. The
CHAI ET AL.
7 of 17
coordination environments of two central metal atoms
were consistent, and both of them displayed slightly
twisted octahedral geometric configuration. Two Bi(III)
centers were connected to each other through two bridging halide ligands (Cl4) to form [Bi2(L)2Cl8]. The Bi(III)
was situated on the center of the plane formed by the
O1Cl3 (O1, Cl2, Cl3, and Cl4) donor group (plane equation: 0.1403 (5) x 0.9758 (2) y 0.1679 (9) z = 0.5727
(59)). The distance from Bi(III) to the plane was 0.027 Å.
Cl1 and Cl4 were located at the axial position, and the
distances to the equatorial plane were 2.543 and 2.893 Å,
respectively. The Bi–O bond length was equal to 2.482
(5) Å, and the bond length of Bi–Cl was varied in the
range of 2.572(18)–2.901(19) Å. These distances were all
within the appropriate range.[34]
Molecules of 2 were connected by hydrogen bond
(Figure 4 and Table S3) and π (Ph)π (Ph) weak interactions (Figure 5 and Table S4), which play principal roles
in making [Bi2(L)2Cl8] more stable.[35] C(11)–H(11)N
(1) hydrogen bond formed a five-membered ring. The distances of Cg(3)Cg(4) and Cg(4)Cg(3) were 3.758
(5) and 3.759(5) Å, respectively. Most strikingly, 2 formed
2-D layered framework, 3-D meter-shaped multilayer
supramolecular, and 3-D butterfly-shaped perspective
structure along the bc-plane through π (Ph)π
(Ph) interactions (Figures 5 and 6).[36]
3.2 | FT-IR spectra
The main FT-IR absorptions of the ligands L and Bi(III)
complexes in the wavelength range of 400–4000 cm1
were shown in Figure S1. L found two bands at 1611 and
1490 cm1, respectively, which were the C=N stretching
vibrations of azomethine and pyridine ring.[37,38] The
same characteristic absorption peaks in the spectra of
FIGURE 5
π (Ph)π (Ph) and 2-D layered structure along the bc-plane of 2
FIGURE 6
View of 3-D supramolecular frameworks (left) and 3-D perspective structure (right) of 2
8 of 17
complexes 1 and 2 appeared at 1607, 1577 and 1483,
1485 cm1, respectively. The bands in the metal complexes shifted to lower frequencies, which manifested the
imine nitrogen atoms participated in the coordination.
The peak of the ν(N ! O) stretching frequency in L were
lying in 1193 cm1 and was shifted to lower frequency
region of 1168 and 1177 cm1 for complexes 1 and 2. The
appreciable shifts for two complexes indicate the coordination between the oxygen atom and Bi(III) ion.[39] The
band originating from the stretching vibration of N–H
was discovered at 3156 cm1 in L, whereas this peak in
the spectra of the metal complexes were observed at 3117
and 3160 cm1, respectively.[40] Some new ν(Bi–N) and
ν(Bi–O) stretching vibration bands have been found in
the far-infrared region. In complexes 1 and 2, they
appeared at 640, 628 and 463, 493 cm1, respectively.[41]
The above data were consistent with the result obtained
by X-ray crystallography.
3.3 | UV–Vis absorption spectra and
TD-DFT calculations
The UV–Vis absorption spectra of the methanol solution
(2 105 mol L1) of freshly prepared the ligand and
Bi(III) complexes were measured at room temperature.
CHAI ET AL.
As shown in Figure 7, the spectrum of L demonstrated
three intense absorption bands below the region 450 nm.
The two lower wavelength bands at 235 and 259 nm
(ε = 18, 420, 49, 785 mol1 L cm1) were assigned to
intra-ring π ! π* transitions of phenyl rings.[42,43] They
were observed at 239 nm (ε = 12 745 mol1 L cm1) for
complex 1, whereas 225 nm (ε = 40, 975 mol1 L cm1)
for complex 2. The shifts of characteristic absorption
peaks were the consequence of the chemical modification
of the ligand after the coordination with Bi(III).
The absorption peak at 381 nm (ε = 7,250 mol1 L cm1)
was
discovered
in
1,
whereas
at
366 nm
(ε = 4,750 mol1 L cm1) in 2, these bands belonged to
π ! π* transitions accompanied with the charge transition (L ! M).[44] The absorption edge (λedge) of Bi(III)
complexes 1 and 2 were 452 and 471 nm, respectively,
and the corresponding optical band gaps (Egopt) were
2.743 and 2.633 eV.[18]
TD-DFT simulated UV–Vis spectra of both complexes
were represented in Figure 7. According to Table 5, calculated vertical electronic excitation energy (eV), oscillator strength (f), and tentative nature of the transition
with the help of the TD-DFT level were listed. The
absorption peaks observed at 381 and 239 nm in complex
1 were belonged to ligand-to-metal (LMCT) and
ligand-to-ligand (LLCT) charge transfers, respectively.
F I G U R E 7 UV–Vis absorption spectra: L, complexes 1 (a) and 2 (b) in CH3OH (2 105 mol L1). Theoretical simulation of UV–Vis
absorption spectra: complex 1 (c) and complex 2 (d) and the oscillator strength of main excited states (strength >0.02) shown in the red
color. (color online)
CHAI ET AL.
TABLE 5
9 of 17
Electronic excitations of 1 and 2 in methanol calculated by TD-DFT
Excitation (eV)
λexcitation (nm)
Osc. strength (f)
375.52
0.0010
Key transitions
Character
λexpt
Complex 1
3.3016
(53%) β-HOMO 18 ! β-LUMO
L (π) ! BiL (π*)
381
(37%) β-HOMO 12 ! β-LUMO
L (π) ! BiL (π*)
–
242.61
0.0032
(30%) α-HOMO 7 ! α-LUMO + 1
L (π) ! L (π*)
239
3.3488
370.23
0.0030
(56%) HOMO 1 ! LUMO + 1
L (π) ! BiL (π*)
366
4.1646
227.71
0.0459
(50%) HOMO 38 ! LUMO + 1
L (π) ! BiL (π*)
225
(17%) HOMO 7 ! LUMO + 3
L (π) ! L (π*)
–
4.0689
Complex 2
These excitation states were contributed to the (53%)
β-HOMO 18/(37%) β-HOMO 12 ! β-LUMO and
(30%) α-HOMO 7 ! α-LUMO + 1 transitions, respectively, as well as the corresponding peaks theoretically
obtained at 375.52 and 242.61 nm.[19] Complex 2 had two
main electron transitions at 225 and 366 nm in TD-DFT
analysis. The simulated broad peak was located at
370.23 nm, and experimental peak at 366 nm was originated at π (L) ! π* (BiL) electronic transition; it could be
interpreted as LMCT charge transfer, which contributed
to (56%) HOMO 1 ! LUMO + 1. In addition, theoretical peak at 227.71 nm, whereas experimental peak at
225 nm was assigned to π (L) ! π* (BiL) and π (L) ! π*
(L) electronic transitions, which were construed to LMCT
and
LLCT
types,
corresponding
to
(50%)
HOMO 38 ! LUMO + 1
and
(17%)
HOMO 7 ! LUMO + 3. These observations were
good agreement with the theoretical simulation.
3.4 | Fluorescence spectra
Luminescence behaviors of L and Bi(III) complexes in
2 105 mol L1 CH3OH were studied at room temperature. As can be seen in Figure 8, when the ligand
L excited at 401 nm, the maximum emission peak
appeared at 496 nm, which was the result of the intraligand π–π* transition.[45] The emission peaks were
located at 505 and 530 nm in 1 and 2, whereas both complexes exhibited redshift relative to the ligand, which
may be caused by the coordination to Bi(III) ion.[46] On
the other hand, the Stokes shift between the emission
and the excitation wavelengths manifested that the Jahn–
Teller distortion has occurred in the sp excited state. The
highest emission wavelength was observed in complex 2,
which probably due to hydrogen bonding interaction.[47]
In order to study the influence of disparate solvents
on emission spectra of Bi(III) complexes, the fluorescence
properties for both complexes were surveyed in different
F I G U R E 8 Emission spectra of L, complex 1, and complex 2 in
CH3OH (c = 2 105 mol L1)
solvents. Measurement results were shown in Figure 9;
the right side was the normalized fluorescence spectra.
The polarity of solvent had an impact on emission wavelength and intensity of Bi(III) complexes. The maximum
emission wavelengths of complex 1 in DMF, DMSO
(dimethyl sulfoxide), DCM (dichloromethane), TCM
(chloroform), EA (ethyl acetate), and CAN (acetonitrile)
were at 418, 435, 398, 396, 399, and 401 nm, whereas the
maximum emission wavelengths of complex 2 in these
solvents were at 419, 434, 401, 399, 400, and 402 nm,
respectively. In polar aprotic solvents CAN, DMF, and
DMSO, complexes 1 and 2 showed significant redshifts in
DMF and DMSO relative to the CAN with the lowest
polarity, which was caused by the charge transfer in the
emitting state.[48] Both complexes displayed blueshifts in
DCM, TCM, and EA compared with CAN. Bi(III) ion in
complexes was a comparatively hard cation, which can
coordinate with the oxygen atoms in DMF and DMSO.
This coordination can cause resonance in the excited
state and increase the Stokes shift.[44] In addition, the
polarity of the solvent will affect the aggregation–
10 of 17
CHAI ET AL.
F I G U R E 9 The fluorescence spectra of complexes 1 (a) and 2 (b) (2.0 10–5 mol L1) in different solvents; the normalized spectra are
shown on the right.
F I G U R E 1 0 The diameter of inhibition zones of L and both complexes on Escherichia coli (left) and Staphylococcus aureus (right) in
different concentrations
disaggregation process of the supramolecular structures
of complexes 1 and 2.
3.5 | Antimicrobial activity
The antibacterial properties of L and Bi(III) complexes
against E. coli (Gram-negative bacterium) and S. aureus
(Gram-positive bacterium) at different concentrations
(0.625, 1.25 and 2.5 mg/ml) were studied by disk diffusion method. The Sabouraud dextrose agar was poured
into the petri dish; bacterial strains were brought into the
surface of the agar and cultured at 37 C for 24 h. Antibacterial performances of samples against two kinds of
bacteria were determined by observing the size of the
inhibition zone.[49] In the experiment, kanamycin was
selected as the standard drug, and blank petri dishes were
CHAI ET AL.
11 of 17
wetted with DMF and different concentrations of test
samples.
As shown in Figure 10, the ligand L, bismuth nitrate,
and bismuth chloride all had relatively weak antibacterial activities under the same experimental condition
(1.25 mg/ml); especially, complexes 1 and 2 were significantly stronger than the ligand. Most strikingly, both
complexes demonstrated only moderate antimicrobial
effects relative to the standard drug kanamycin. The bactericidal performances of complex 1 against E. coli and S.
aureus strains were obviously better than complex 2. The
experimental results manifested that Bi(III) complexes
had certain antibacterial performances against microorganisms and antibacterial activities enhanced with the
increase in concentration.[50] The resistance of complexes
to the strain may be caused by the enhanced cell
FIGURE 11
membrane. This phenomenon was interpreted by the
chelation theory. During the chelation process, a certain
degree of overlap of the ligand orbital brought about significant decrease in the polarity of the metal ion. On the
other hand, the orbital overlap delocalized π electrons on
the entire chelating ring and increased the lipophilicity of
complexes, thereby destroying the cell permeability barrier and hindering the normal cell transportation process.
Blank experiment revealed that using DMF solution as
blank test had no effect on the results.[51]
3.6 | Theoretical investigations
Gaussian 09 software with B3LYP functional was used
to conduct geometric structure optimization of
Frontier molecular orbitals of the α (a) and β (b) spin of 1
12 of 17
CHAI ET AL.
complexes 1 and 2. The calculated optimal bond length
and bond angle data around the metal ion were given
in Tables 2 and 3. The optimized values of both complexes by theoretical calculation were not much different
from
the
experimental
data
of
X-ray
crystallography. Subtle differences did not affect our
comparison and conclusion.[52]
The fully optimized geometric structures of Bi(III)
complexes were shown in Figure S2. The highest occupied molecular orbitals (HOMOs) and lowest unoccupied
molecular orbitals (LUMOs) of two complexes were presented in Figures 11 and 12, mainly from LUMO+2 to
HOMO2. Frontier molecular orbitals were very significant for investigating chemical stability of molecule.[53]
As shown in Table S5, molecular orbital energies of
α/β-LUMO and α/β-HOMO for complex 1 were 1.812/
1.748 eV and 5.341/4.019 eV, whereas the energy
level of the LUMO for complex 2 was 4.955 eV and the
HOMO was 8.386 eV. The surface plots manifested that
the α-spin HOMOs of 1 were mainly resided on the integrated quinazoline fragment and Bi(III) orbital, the
LUMOs were concentrated on the integrated quinazoline
fragment, and the β-spin was opposite of the α-spin. On
the other hand, the HOMOs and LUMOs of 2 were
mainly distributed on quinazoline fragment, chloride
anions, and Bi(III) orbital. The HOMO–LUMO energy
gap (ΔE = ELUMO EHOMO) of 1 was 3.529 eV for
α-orbital and 2.271 eV for β-orbital, whereas the ΔEH–L
of 2 was 3.431 eV. The large energy gap between HOMO
and LUMO revealed favorable chemical stability and
large chemical hardness. The energy difference (ΔEH–sL)
of the β-orbital for 1 was lower than 2, demonstrating
that 1 had stronger potential, which meant molecule was
more active.[54] According to the ΔEH–L, antibacterial
FIGURE 12
Surface plots of HOMO and LUMO of 2
performances of Bi(III) complexes should be 1 > 2. In
addition, frontier orbitals occupied by complexes 1 and
2 were both negative, which proved both complexes had
certain chemical stability.[55]
3.7 | Molecular electrostatic potential
Both complexes' Mulliken atomic charges were calculated at the level of B3LYP/6-31+G** theory in order to
investigate the distribution of electric charge in molecules. According to Figure 13, the highest positive charge
was attributed to bismuth atom and nitrogen atoms from
nitrate anions in complex 1, although it was only derived
from the bismuth atoms in complex 2. Meanwhile, the
largest negative charge in 1 came from the carbon atoms
on benzene rings and the oxygen atoms from nitrate
anions, whereas in 2 it ascribed to the carbon atoms on
the benzene ring and coordinated chloride ions. The
dipole moments of complexes 1 and 2 were 5.6733 and
3.6708 D, respectively. In addition, all hydrogen atoms
had a small amount of positive charge.[56]
Molecular electrostatic potential (MEP) diagrams
were widely used to predict reaction sites of electrophilic
and nucleophilic attacks, as well as to study biological
identification and hydrogen bond interactions. It could
be displayed the charge distribution of molecules in three
dimensions and give us visual view of the variable
charged regions of molecules.[57] Based on partial atomic
charge distribution, MEP energy map was drawn using
grid point technology applied by GaussView 5.0 program
and were shown in Figure 13b,d. Each MEP surface had
a color scale; red represented the negative domain, which
showed the smallest electrostatic potential and as
CHAI ET AL.
13 of 17
F I G U R E 1 3 Atomic charge
distribution for 1 and 2 (a,c) and
molecular electrostatic potential map for
1 and 2 (b,d)
F I G U R E 1 4 Hirshfeld surfaces
mapped with dnorm (left), shape index
(middle), and curvedness (right) for
complexes 1 (a) and 2 (b)
electrophilic attack sites. Blue represented the positive
domain, which indicated the maximum electrostatic
potential and defined as nucleophilic attack sites.[58] In
metal complexes, the most positive region was concentrated on N-atoms on the pyridine ring (complex 1) and
C-atoms on the aromatic ring (complex 2). Meanwhile,
hydrogen atoms on the benzene ring in 1, and the coordination chloride ions in 2 were located in the highest negative region, which showed the largest and most negative
MEP values. MEP surface diagrams demonstrated that
both complexes had possible site for electrophilic attack
(red region on H and Cl) and site for nucleophilic attack
(blue region on N and C).[59] These theoretical results
were basically consistent with the experimental results
obtained by X-ray single-crystal diffraction.
3.8 | HSA
The Hirshfeld surface represented the region of molecules interact and was a powerful tool to describe the
surface properties of complexes. Therefore, HSA gave us
deeper understanding of the intermolecular interactions
in the crystalline state. The HSA and fingerprint plots
introduced here were carried out with CrystalExplorer17
based on the X-ray structure.[60] The surface with dnorm,
shape index, and curvedness were shown in Figure 14. In
HSA, red was defined as the contact distance between
atoms was less than the sum of van der Waals radii,
whereas white and blue were, respectively, defined as the
contact distance between atoms was equal to and greater
than the sum of van der Waals radius.[61] As shown in
Figure 15, the proportions of OH/HO (ClH/HCl)
interactions contributed the most to complexes 1 and 2,
accounting for 33.7% and 43.9% of the Hirshfeld surface
of each molecule in complexes. The HH interactions
accounted for 28.6% in 1, whereas 21.8% of the entire surface in 2. Simultaneously, CH/HC interactions consisted for 23.0 and 7.3%, respectively. In addition, NH/
HN (ClN/NCl) interactions covered 4.1% in 1,
whereas 6.9% in 2, respectively. These weak interactions
made the metal complexes more stable.[62]
14 of 17
FIGURE 15
CHAI ET AL.
2-D fingerprint plots: decomposition into contributions from specific pair of atom types for complexes 1(left) and 2 (right)
Some complementary regions could be seen in the
fingerprint plots, de represented the distance from the
surface to the nearest atom outside the surface, and di
indicated the distance from the surface to the nearest
atom inside the surface. When de < di, the molecule
was defined as a donor. On the contrary, when de > di,
the molecule acted as an acceptor.[63] According to the
Figure 15, the lower spike (di = 1.29, de = 0.92 Å in 1,
and di = 1.62, de = 1.02 Å in 2) manifested OH/ClH
interaction, and the upper spike (di = 0.92, de = 1.29 Å
in 1, and di = 1.02, de = 1.62 Å in 2) indicated HO/
HCl interaction. Similarly, the CH interaction was
also acted by lower spike (di = 1.69, de = 1.15 Å in 1,
and di = 1.79, de = 1.42 Å in 2), and HC interaction
was acted by upper spike (di = 1.15, de = 1.69 Å in 1,
and di = 1.42, de = 1.79 Å in 2). The NH/ClN interaction was also represented by lower spike (di = 1.75,
de = 1.21 Å in 1, and di = 1.69, de = 1.58 Å in 2) and
HN/NCl interaction was represented by upper spike
(di = 1.21, de = 1.75 Å in 1 and di = 1.58, de = 1.69 Å
in 2).
4 | CONCLUSIONS
Two mono- and dinuclear complexes, [Bi(L)2(NO3)2]NO3
(1) and [Bi2(L)2Cl8] (2) (L = 2-(2-pyridyl)-4-methyl-1,2-dihydroquinazoline-N3-oxide), have been synthesized
and characterized structurally. The structures of both
complexes were determined by X-ray single-crystal diffraction method. X-ray crystallography revealed that the
ratio of ligand to metal was 2:1 in 1, whereas ligand-tometal ratio was 1:1 in 2. It was worth mention that in
eight-coordinated structures, 1 contained two coordinated nitrate ions and one non-coordinated nitrate ion.
Nevertheless, hexa-coordinated 2 had eight-coordinated
chloride anions in binuclear structures. Most strikingly,
1 had an infinite 1-D chain-like, 2-D funnel-shaped, and
even ladder-like 3-D supramolecular frameworks,
whereas symmetric adjacent molecules of 2 assembled
into 2-D layer and meter-shaped 3-D skeleton. Both complexes demonstrated different fluorescence behaviors in
disparate solvents. Fascinatingly, complexes 1 and
2 exhibited excellent antibacterial properties against E.
CHAI ET AL.
coli and S. aureus, and the antibacterial effect of both
complexes was higher significantly than the efficiency of
L, and 1 was greater than that of 2. Based on the optimization of DFT geometry, TD-DFT calculations were performed on both complexes to facilitate the recording of
specific electronic transitions in the UV–Vis spectra.
MEP predicted the electrophilic and nucleophilic attack
sites, and HSA quantified weak interactions and the percentage of hydrogen bond interactions.
A C K N O WL E D G M E N T S
This work is supported by the Fundamental Research
Funds of Gansu Province Universities (No. 214152) and
the Foundation of a Hundred Youth Talents Training
Program of Lanzhou Jiaotong University (No. 152022).
A U T H O R C ON T R I B U T I O NS
Lan-Qin Chai: Writing-review & editing; resources;
supervision. Yong-Mei Chai: Writing-Original draft;
investigation; validation. Xiao-Fang Zhang: Formal
analysis.
CONFLICT OF INTEREST
There are no conflicts to declare.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available in the Supporting Information of this article.
ORCID
Lan-Qin Chai https://orcid.org/0000-0003-4629-9653
Yong-Mei Chai https://orcid.org/0000-0003-2594-2988
Xiao-Fang Zhang https://orcid.org/0000-0002-67721481
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S UP PO RT ING IN FOR MAT ION
Additional supporting information can be found online
in the Supporting Information section at the end of this
article.
17 of 17
How to cite this article: L.-Q. Chai, Y.-M. Chai,
X.-F. Zhang, Appl Organomet Chem 2022, e6828.
https://doi.org/10.1002/aoc.6828
A PP E ND IX A : SUPPLEMENTARY DATA
CCDC 2099499 and 2099500 contain the supplementary
crystallographic data for complexes 1 and 2. These data
can be obtained free of charge via http://www.ccdc.cam.
ac.uk/data_request/cif., or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge, B2
1EZ, UK; fax +441223 336033; or e-mail: deposit@ccdc.
cam.ac.uk.