Hydrothermal Preparation, Crystal Structure, Photophysical Properties and Theoretical Calculation of a Cu(II) Complex

Article abstract of DOI:10.1007/s10870-020-00837-2

Abstract: A novel Cu(II) compound [CuL₂]·2H₂O was synthesized by hydrothermal methods, and its crystal structure was determined by single-crystal X-ray diffraction. The title compound crystallized in the monoclinic space group P2₁/c as an isolated monocyte structure. The strong π…π stacking and hydrogen bonding interactions produce one-dimensional (1D) chains. A series of properties of the title compound were tested by solid state photoluminescence, CIE analysis and solid-state diffuse reflectance. The results show that the compound is a blue light emitter, CIE (0.1291, 0.0783) and has an energy bandwidth of 1.65?eV. Time-dependent density functional theory (TDDFT) calculation results show that the emission of the compound can be attributed to charge transfer from metal to ligand and ligand to ligand (MLCT and LLCT). Graphic Abstract: A novel Cu (II) complex is synthesized via hydrothermal preparation, which is characteristic of an isolated structure, at the same time, it displays a narrow and intense photoluminescence emission band in the blue region and theoretical study reveals that the photoluminescence emission is originated from the metal-to-ligand and ligand-to-ligand charge transfer transition. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10870-020-00837-2

Journal of Chemical Crystallography
https://doi.org/10.1007/s10870-020-00837-2
ORIGINAL PAPER
Hydrothermal Preparation, Crystal Structure, Photophysical Properties
and Theoretical Calculation of a Cu(II) Complex
Yin‑Feng Wang1 · Xiu‑Guang Yi1 · Xiao‑Niu Fang1 · Jin Guo1 · Fei‑Ping Lai1 · Shi‑Kun Xie2
Received: 12 January 2020 / Accepted: 14 May 2020
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
A novel Cu(II) compound [CuL2]·2H2O was synthesized by hydrothermal methods, and its crystal structure was determined
by single-crystal X-ray difraction. The title compound crystallized in the monoclinic space group P21/c as an isolated
monocyte structure. The strong π…π stacking and hydrogen bonding interactions produce one-dimensional (1D) chains. A
series of properties of the title compound were tested by solid state photoluminescence, CIE analysis and solid-state difuse
refectance. The results show that the compound is a blue light emitter, CIE (0.1291, 0.0783) and has an energy bandwidth
of 1.65 eV. Time-dependent density functional theory (TDDFT) calculation results show that the emission of the compound
can be attributed to charge transfer from metal to ligand and ligand to ligand (MLCT and LLCT).
Graphic Abstract
A novel Cu (II) complex is synthesized via hydrothermal preparation, which is characteristic of an isolated structure, at the
same time, it displays a narrow and intense photoluminescence emission band in the blue region and theoretical study reveals
that the photoluminescence emission is originated from the metal-to-ligand and ligand-to-ligand charge transfer transition.
Keywords Hydrothermal preparation · Crystal structure · Properties · TDDFT
Introduction
Coordination compounds hold promise in various applica-
* Xiu-Guang Yi
tions including as fuorescent materials, magnetic materi-
jayxgggchem@163.com
als, in solar cells and in biomedicine [1–7]. However, in the
* Shi-Kun Xie
design of coordination compounds, the choice of the metal
xskun@163.com
ion is limited while the selection of ligands appears to be
1
School of Chemistry and Chemical Engineering,
infnite. In particular, nitrogen-containing carboxylic ligands
are very in part because their diverse coordination modes,
but also because of the rigidity of binding nitrogen [8, 9].
Jinggangshan University, Ji’an 343009, Jiangxi, China
2
School of Mechanical and Electrical Engineering,
Jinggangshan University, Ji’an 343009, Jiangxi, China
Vol.:(0123456789)
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Journal of Chemical Crystallography
Quinoline carboxylic acid possess two kinds of coordinating
atoms and a number of coordination sites. It can form dif-
ferent kinds of anions by adjusting the pH, thereby allowing
for tuning of the coordination modes [10, 11]. We focused
on the derivatization of the quinoline carboxylic acid, in
particular the introduction of a hydroxyl group to investi-
gate new coordination modes and obtain complexes with
better performance. Here we report on the synthesis of the
ligand 3-hydroxy-2-methylquinoline-4-carboxylic acid and
its Cu(II) complex as well as their characterization, includ-
ing their crystal structure, solid-state fuorescence and dif-
fuse refectance spectra.
temperature. dilute H2SO4 (10%, 250 mL) was added and
the mixture was stirred at 43 °C for 1.5 h. Subsequently, the
mixture was diluted with twice its volume of distilled water,
and the precipitate was fltered of, dissolved in a 10% NaOH
solution, fltered again, acidifed with 10% HCl to pH 7 and
refltered. The intermediate product insatin was obtained.
Yield: 116 g (90%); m.p. 210 °C; HRMS m/z (ESI) calcd for
C8H5NO2 [M+H]+ 147.0320, found 147.0826.
Isatin (73.5 g, 0.5 mol) and NaOH (20 g, 0.5 mol) were
dissolved into a sufcient amount of distilled water and fl-
tered. The fltrate and NaOH (20 g, 0.5 mol) were added into
chloroacetone (92 g, 1.0 mol), and hydrochloric acid was
added dropwise to adjust to a pH of 7. The fltered prod-
uct yielded the ligand HL. Yield: 96 g (95%); m.p. 225 °C;
HRMS m/z (ESI) calcd for C11H9NO3 [M+H] + 203.0582,
found 203.0548. 1H NMR (400 MHz, DMSO) δ 9.15(s, 1H),
7.93(d, J=8.0 Hz 1H), 7.64(t, J=8.0 Hz, 1H), 7.60–7.52(m,
2H), 2.70(s, 3H).
Experimental
Materials and Physical Measurements
All reagents and chemicals were commercially available and
of analytical reagent grade and used without further purifca-
tion. The infrared spectra were recorded as KBr pellets on a
Perkin Elmer Spectrum One Fourier transform infrared spec-
trometer. Elemental analyses of carbon, hydrogen and nitro-
gen were performed on a Vario EL elemental analyzer. 1H
NMR spectra were measured on Bruker Avance 400 MHz
instrument. Solid state photoluminescence was measured on
a Hinotek F97XP Spectrophotometer, and solid state UV/Vis
refectance spectroscopy was carried out with a TU-1901
UV/Vis-spectrophotometer from Beijing Purkinje General
Instrument Co equipped with an integrating sphere.. TDDFT
investigations were performed using the Gaussian 09 suite
of program packages [12–14].
Synthesis of [CuL2]·2H2O
HL (203 mg, 1 mmol), CuCl (49.5 mg, 0.5 mmol),
CH3CH2OH (9 mL), H2O (1 mL), and NaOH (to adjust to a
pH value of 10) were added to a 20 mL Tefon-lined stain-
less steel autoclave. The autoclave was heated to 100 °C
and kept 7 days in a baking box, and then left to cool to
room temperature. Brownish yellow rod-shaped crystals for
the single-crystal X-ray data collection were isolated. The
yield was 69% based on CuCl. IR (KBr, cm−1): 3450(vs),
2555(m), 2048(m), 1568(m), 1522(m), 1444(vs), 1240(vs),
987(s), 864(s),732(m),698(w) and 469(m).
X‑ray Crystallographic Determination
Synthesis
The single crystal data for the title compound were col-
lected on a SuperNova difractometer (Agilent) equipped
with a CCD detector at 292(2) K. The structure was solved
with intrinsic methods [16] and refned by full-matrix least-
squares techniques [17] employing the SHELX software
in Olex2 [18]. Subsequent Fourier diference maps com-
pleted the structure model, and all non-hydrogen atoms
were refned anisotropically. Hydrogen atoms were placed
in calculated positions and refned using a riding model.
Synthesis of 3‑hydroxy‑2‑methylquinoline‑4‑carboxylic
acid (HL)
The preparation follows published procedures (Scheme 1)
[15]. Firstly, indigo is oxidized by K2CrO7 to form the inter-
mediate product isatin. Indigo (131 g, 0.5 mol), K2Cr2O7
(74 g, 1.0 mol) and distilled water (200 mL) were added
into a three-neck fask and stirred. After cooling to room
Scheme 1 Preparation of HL
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Journal of Chemical Crystallography
Table 1 Crystallographic data and refnement results
and refnement results. Table 2 lists selected bond lengths
and of the title compound.
Empirical formula
C22H20CuN2O8
CCDC deposition number
Formula weight
1,975,850
503.94
Results and Discussion
Temperature/K
293(2)
Crystal system
Space group
monoclinic
P21/c
Infrared Spectrum
In the IR spectrum the strong broad band at 3450 cm−1
indicates the presence of water. The absorption bands at
2555 cm−1 and 2048 cm−1 are assigned to the O–H stretch-
ing vibration. The absorption at 1568 cm−1 is assigned to
the C=N stretching vibration. The absorption at 1444 cm−1
belongs to the methyl stretching vibration and the absorp-
tions at 1522 cm−1 indicate the presence of monodentate
carboyxlate in the title complex.
a/Å
b/Å
c/Å
α/°
14.043(2)
4.7971(4)
15.1256(13)
90
96.814(10)
90
1011.78(19)
2
β/°
γ/°
V/Å3
Z
ρcalc g/cm3
1.654
1.136
518.0
μ/mm−1
Crystal Structure
F(000)
S
1.164
[CuL2]·2H2O crystallizes in the monoclinic space group
P21/c. The asymmetric unit contains half of the formula
unit, the copper complex and two lattice water molecules,
as shown in Fig. 1. The copper (II) ion resides on a crystal-
lographic inversion center and is coordinated in a square-
planar fashion by four oxygen atoms of two quinoline car-
boxylic acids. To the best of our knowledge, this is the frst
report of a Cu complex with quinolincarboxylic acid ligand
Final R indexes [I> =2σ (I)]
Final R indexes [all data]
Largest dif. peak/hole / e Å−3
R1=0.0823, wR2=0.1554
R1=0.1156, wR2=0.1703
0.90/−0.61
Tables 1 provides a summary of the crystallographic data
Table 2 Selected bond lengths (Å) and bond angles (°) for the title complex
Bond
Dist
Bond
Dist
Cu(1)–O(1)
Angle
1.897(3)
(°)
Cu(1)–O(2)
Angle
1.901 (4)
(°)
O(1)–Cu(1)–O(1)i
O(1)–Cu(1)–O(2)i
180.0
88.83 (14)
O(1)–Cu(1)–O(2)
91.17 (14)
Fig. 1 ORTEP drawing of the
title complex; ellipsoids are
shown at the 50% probability
level
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Journal of Chemical Crystallography
Table 3 Hydrogen bond lengths (Å) and bond angles (°)
forming a square planar structure; more common are octahe-
dral and pyramidal coordination environments [19–21]. The
bond distances of Cu–O(1) and Cu–O(2) are 1.897(3) Å and
1.901(4) Å, respectively. The N atom of the quinoline ring
is protonated and involved in hydrogen bonding. Geometric
parameters are comparable with those reported in the litera-
ture for similar or related compounds [19–21].
D-H⋯A
D-H (Å) H…A (Å) D…A (Å) D-H…A (°)
N1–H⋯O3v
O4–H4A···O3 0.85
C7–H7⋯O3 0.93
0.86
1.87
2.05
2.32
2.732 (4)
2.874 (6)
2.861 (6)
176
164
117
In the packing of the title compound, strong π…π
stacking interactions between Cg1···Cg2′ (symmetry
code, +x,−1+y,+z), with Cg1 being the centroid of ring
(C6–C11) and Cg2 the centroid of ring (N1, C2–C6, C11)
are observed. The Cg1···Cg2′ distance is 3.556 Å, the shift
distance is 1.171 Å, and the twist angle between the planes is
2.391°. These π···π stacking and Van der Waals interactions
result in a one-dimensional chains along the crystallographic
b axis (Fig. 2).
the wavelength range of 300–500 nm. Excitation maxima
occur at 452 and 483 nm, while the corresponding emission
spectrum has maxima at 533 and 564 (Fig. 4).
TDDFT Calculations
We used the geometrical parameters obtained from the
single crystal X-ray difraction data of the title compound
and performed a time-dependent density functional theory
(TDDFT) calculations. The TDDFT is calculated by B3LYP
function, Cu is calculated using the SDD basis set and C,
H, O, N are calculated using the 6–31G* basis set in the
Gaussian09 program [12, 13, 22]. The electron-density dis-
tributions of the HOMO and LUMO of the title complex
are shown in Fig. 5. The HOMO is located on the Cu(II)
atom and part of the HL ligand molecule with an energy
of−5.16 eV. However, the electron density distribution of
the LUMO is situated at the π-orbital of the HL ligand with
an energy of − 2.31 eV. The energy diference (2.85 eV)
between HOMO and LUMO is small enough to allow for
charge transfer between HOMO and LUMO. We conclude
that the photoluminescence of the title complex can be
attributed to metal-to-ligand and ligand-to-ligand charge
transfer (MLCT and LLCT).
Further, strong classical intermolecular hydrogen bonds
N1–H···O3v and O4-H4A···O3) are observed between N–H
and the carboxylate group and the solvent water and the car-
boxylate group, respectively (Table 3). Additionally, a week
non-classical hydrogen bond can be found between the car-
boxyl oxygen atom O3 and ring carbon atom C7 (Table 3).
Thus, the chains generated through π…π stacking are fur-
ther linked via hydrogen bonds into layers along (1 0 0), as
shown in Fig. 3.
Solid‑State Photoluminescence Spectra
In order to investigate the photoluminescence characteris-
tics of the title compound at room temperature, the pho-
toluminescence spectra of the solid state samples were
measured. The title complex absorbs UV–visible light in
Fig. 2 The packing of the title complex, π…π stacking shown as dashed lines
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Journal of Chemical Crystallography
Fig. 3 Hydrogen bonding. All hydrogen atoms not involved in hydrogen bonding are omitted for clarity
Solid‑State Difuse Refectance Spectrum
We explored the semiconductor properties of the title com-
plex. The UV–Vis refectance spectra of the title solid-state
complex were measured at room temperature, using barium
sulfate as the reference material with 100% refectance, We
processed that data using the Kubelka–Munk formula [14]:
α/S=(1-R)2/2R (Fig. 6). The title complex shows a narrow
optical energy band gap of 1.65 eV, which is obviously larger
than those of GaAs (1.4 eV), CdTe (1.5 eV), and CuInS2
(1.55 eV) [23, 24], which are band gap of efcient photo-
voltaic materials. We believe that the title complex may be
a candidate material for narrow band gap semiconductors.
Fig. 4 Emission spectrum in blue line and excitation spectrum in red
line; Inset: solid-state photoluminescence spectrum of HL
Fig. 5 HOMO and LUMO of the title complex with an isosurface of 0.02 au
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Journal of Chemical Crystallography
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In summary, a novel copper complex with quinoline carbox-
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complex packs for form a layer structure including weak
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Based on TDDFT calculations, we attribute the photolu-
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Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
Acknowledgements This work was supported by the National Natural
Science of Foundation of China (51363009), Natural Science Foun-
dation of Jiangxi Province of China (20181BAB206028), Science
and Technology Research Project & Higher Education and Teach-
ing Reform of Jiangxi Education Committee of China(GJJ160732,
GJJ190550, JXJG-17–9-14), Doctoral Research Startup Foun-
dation and Natural Science Foundation Project of Jinggangshan
University(JZB1905, JZ1901).
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