Crystal and electronic structure of poly-halogenated lanthanide Schiff base complex: Insights into halogen bond from structural and theoretical analysis

Article abstract of DOI:10.1016/j.molstruc.2020.129054

With the aim to explore the electronic structure and the influence of halogen bonds to the supramolecular networks of lanthanide Schiff base complexes, halogenated salen-type Schiff-base and cerium nitrate were chosen as starting materials and isolated a new salen-type cerium(IV) complex [Ce^IV(3,5Br-salpn)₂] (1) where 3,5Br-salpn = N,N’-bis(3,5?bromo salicylidene)-1,3-diaminopropane. The complex was investigated in the solid state by single-crystal X-ray diffraction. Structural analysis reveal the substitutional halogen atoms play an important role in tuning the molecule structure and supramolecular networks. The electronic structure of halogen bonds was confirmed by theoretical calculation, which uncovered an interesting phenomenon that the σ-hole of bromine atoms of different substituents present quite different molecular electrostatic surface potential (5-Br: V_max = 6.8 kcal/mol and 3-Br: V_max = 13.2 kcal/mol). Hirshfeld surface analysis showed that bromine atoms involved intermolecular contacts donate 56.6percent contribution of all the interactions, indicating the significant role of bromine atoms in crystal structures. Additionally, fluorescence experiments proved that the halogenated ligand has an important influence on the fluorescence behavior of the complex.

Full text of DOI:10.1016/j.molstruc.2020.129054

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Crystal and electronic Structure of poly-halogenated lanthanide Schiff
base Complex: Insights into Halogen Bond from Structural and
Theoretical Analysis
Qiong Wu , Meifen Huang , Tianyu Li , Liang Jiao , Yujiao Tu ,
Xindi Xu , Xun Ma , Hui Tian , Yongfeng Qiao
PII:
S0022-2860(20)31377-6
DOI:
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https://doi.org/10.1016/j.molstruc.2020.129054
MOLSTR 129054
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9 August 2020
Please cite this article as: Qiong Wu , Meifen Huang , Tianyu Li , Liang Jiao , Yujiao Tu , Xindi Xu ,
Xun Ma , Hui Tian , Yongfeng Qiao , Crystal and electronic Structure of poly-halogenated lanthanide
Schiff base Complex: Insights into Halogen Bond from Structural and Theoretical Analysis, Journal of
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Crystal and electronic Structure of poly-halogenated lanthanide Schiff
base Complex: Insights into Halogen Bond from Structural and
Theoretical Analysis
Qiong Wua,b*, Meifen Huanga, Tianyu Li,a Liang Jiao,a Yujiao Tu,a Xindi Xu,a Xun Ma,a
Hui Tian,a Yongfeng Qiaoa*
aDepartment of Chemical Science and Technology, Kunming University, Yunnan, Kunming
65200, P. R. China
bYunnan Engineering Technology Research Center for Plastic Films, Kunming
email：wuqiongkm@163.com
Abstract: With the aim to explore the electronic structure and the influence of halogen bonds
to the supramolecular networks of lanthanide Schiff base complexes, halogenated salen-type
Schiff-base and cerium nitrate were chosen as starting materials and were isolated a new
salen-type cerium(IV) complex [CeIV(3,5Br-salpn)2] (1) where 3,5Br-salpn
=
N,N’-bis(3,5-bromo salicylidene)-1,3-diaminopropane. The complex was investigated in the
solid state by single-crystal X-ray diffraction. Structural analysis reveal the substitutional
halogen atoms play an important role in tuning the molecule structure and supramolecular
networks.
The electronic structure of halogen bonds was confirmed by theoretical calculation, which
uncovered an interesting phenomenon that the σ-hole of bromine atoms of different
substituents present quite different molecular electrostatic surface potential ( 5-Br: Vmax = 6.8
kcal/mol and 3-Br: Vmax = 13.2 kcal/mol ). Hirshfeld surface analysis showed that bromine
atoms involved intermolecular contacts donate 56.6% contribution of all the interactions,
indicating the significant role of bromine atoms in crystal structures. Additionally,
fluorescence experiments proved that the halogenated ligand has an important influence on
the fluorescence behavior of the complex.
1

Keywords: halogen bond; lanthanide Schiff-base complex; DFT studies; electrostatic potential;
fluorescent property ;
1. Introduction
Electron disperse from dense to sparse area is one a common interact way in molecular
contacts [1-3]. Similar scenario occurs in the case of noncovalent intermolecular interactions
such as hydrogen bonds, π-π stacking, cation-π, electrostatic interactions, hydrophobic
interactions as well as van der Waals interactions [4-6]. Although its strength is much weaker
than that of covalent or ionic bonds, its position in the fields of chemistry, material and life
science is very important [7-9]. Recent studies reveal that weak intermolecular interactions
are not only related to almost of chemical reactions but also have impact on the
physicochemical property of materials, such as catalysis, ferroelectricity, and conductibility in
material science [10-12].
Theoretical calculation uncovered the intrinsically anisotropic electron density
distribution of halogens and commonly termed the partial positively charged region (covalent
bond direction) as sigma-hole (σ-hole) and named the negative potential ring as π -region
[13-15]. Compared with the isotropical hydrogen bond, halogen bond (XB) are featured by
their high directionality, strong hydrophobicity, and tunable strength [16-18]. These charming
characteristics attracted researchers to exploit it to establish various crystalline materials with
specific structures and properties [19-21]. However, probably because limited computational
resources and lack of ideal experimental models, only a few works have specially concerned
the roles and potential impact of halogen bonds in metal complexes, related research is still at
an early stage and mainly focuses on the transition metal complexes [22-25].
As an important member of coordination complexes, Schiff base complexes have
attracted extensive attention due to their special structural diversity and potential applications
in ion exchange, nonlinear optics, molecular recognition and luminescent materials. Design
and synthesis of new Schiff base metal complexes and extend their applications are of great
significance to the development of Schiff base chemistry [26-29]. However, in a long period,
the enrichment of Schiff based complexes library has mainly relied on the modification of
ligand skeletons with different organic groups [30-32]. In contrast, the development made on
2

(of) halogenated Schiff based ligand only proceeded a comparatively slow step, although
some recent advances have uncovered the special regulation effect of XB to the structures and
properties of early transition metal Schiff based complexes [33-35], to the best of our
knowledge, studies on the electronic structure and the regulation effect of halogen bonds in
rare-earth Schiff base complexes remains largely unexplored.
With the aim to better understand the influence of halogen bond in rare-earth Schiff
based complex and make a electronic structure comparison between different substitutions of
halogens, in this work we reported a new poly-halogenated sandwich-type cerium complex
[CeIV(3,5Br-salpn)2] (1) , the electrostatic potential, orbital contributions and spatial
distributions analyses have been carried out by theoretical calculations. Hirshfeld surface and
finger print plots have been introduced to quantitatively analysis the halogens involved
intermolecular interactions. In addition, luminescence measurement indicated that compound
(1) exhibit strong fluorescence intensity which is 12 times higher than that of the ligand.
2. Experimental
2.1. material and physical measurements
All chemicals were also commercially available and used without further purification.
Elemental analyses (C, H and N) were carried out on a Perkin-Elmer 240C instrument.
UV-vis absorption spectrum was recorded using 752 PC UV-vis spectrophotometer in 1 cm
path length quartz cell in dichloromethane and sample concentration of 0.01 mM in the
spectra range of 200-700 nm. Fluorescence emission spectrum was recorded using a
Edinburghinstruments FS5 fluorescence spectrophotometer in 1 cm path length quartz cell
with MeOH/H2O (1/2, v/v) as solvent and sample concentration of 0.01 mM in the spectral
range of 200-700 nm. Fluorescence measurements have been performed using 2 nm x 2 nm
slit width.
Since the stability of salen-type complexes are susceptible to the pH environment, the
stable pH range of compound 1 was probed in this work. By mixed 1 in different pH media,
the fluorescence intensities and the peak positions were recorded and compared. Fig. S7 and
S8 (ESI) shows the remarkable change of emission peaks from pH 1.0-14.0, which clearly
indicates the stable environment for 1 is from pH 5 to 7 and all the tests are conducted within
this scope.
3

2.2. Quantum yield measurement
The quantum yield (QY) was determined according to the compar-ative method. The QY of
quinine sulfate dissolved in H2SO4 (0.1 M) was54% at excited wavelength 368 nm, and
assigned as a reference [36]. The following equation was applied:
Qob  Qref (Iob / Iref )(A / A )(o2b /r2ef )
ref
ob
Where the subscript overall refers the test object and ref refers to reference; Qoverall refers to
QY of the reported compound, I is theintegrated emission intensity, is the solvent

refractive index, and A refers to the absorbance value at the excitation wavelength.
2.3. Synthesis of of [CeIV(3,5Br-salpn)2] (1)
The title compound was synthesized with the following procedure.
3,5-dibromosalicylaldehyde 0.026 g (0.094 mmol) and 0.0040 mL 1,3-diaminopropane (0.047
mmol) were stirred in a mixture of 20 mL ethanol and 10 mL DMF at room temperature for
20 min. Then, 0.10 g cerium(III) nitrate was added to the above solution and the resulting red
mixture was further stirred for another 30 min and filtered. The blocked-shaped dark red
crystals of the title compound were obtained after 3 days by slow evaporation. The 35% yield
is obtained by filtration, then washed with methanol, and dried in air. Elemental analysis for
C34H24Br8CeN4O4 (Mr = 1331.97), (%): Calcd. C, 30.66; H, 1.82; N, 4.20. Found: C, 30.93; H,
1.86; N, 4.21. FT-IR (cm-1) (Fig. S2, ESI): 3430.76 (O-H), 1623.78 (C=N), 1430.93 (-CH2-).
UV–vis. (Fig. S9, ESI): λ in MeOH/ H2O (3/1,v/v) , 358 nm (0.12 ), 296 nm (0.28), 244 (0.80)
and 214 (3.2). The intense bands at 214 nm (3.2) and 244 (0.80) are assigned to π-π* electron
transition while that of 296 nm (0.28) band is ascribed to low energy n- π* electron transition
from non-bonding terminal imine N center. The band at 358 nm (0.12 ) is due to the LMCT
process. The emission spectrum of the complex is presented in Fig. S3 (ESI).
2.4. Characterization
Best quality single-crystal sample of 1 was collected for X-ray diffraction measurement.
The crystal sample was selected by microscope and mounted on a glass fiber. The data set of
reflections were collected at 273.15 K on a Xcalibur Eos automated diffractometer with
MoKα radiation (λ = 0.71073 Å). CrysAlisPro software was used for the integration of
intensities and correction for Lorentz and polarization effects [37]. The central cerium atom
4

was located by direct methods, and successive Fourier syntheses revealed the remaining
atoms. Refinements were carried out by the full-matrix method on F2 using the Olex2
software package [38]. In the final refinement, all the non-H atoms were anisotropically
refined. All the hydrogen atoms were theoretically placed onto the ligand and refined using
the riding model approximation. For the -CH2- groups, C-H bonds length were fixed at 0.97
Å, the Uiso values of the hydrogen atoms was set to 1.5 Ueq(C) and the Uiso values of all other
hydrogen atoms were set to 1.2 Ueq(C), with aromatic C-H distances of 0.93 Å. All
inter/intramolecular interactions based on crystal structures were calculated using the
PLATON program. The detailed crystal data and structure refinement for 1 was given in
Table 1. Selective bond lengths and angles of 1 were listed in Table S1.
Table 1. Crystallographic data and structure refinement for compounds 1
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a / Å
C34H24Br8CeN4O4
1331.97
273.15
monoclinic
P21/n
17.2808(6)
9.0066(3)
24.6116(11)
95.424(2)
3813.4(3)
4
b / Å
c / Å
β / °
Volume/ Å3
Z
ρ calc g/cm3
μ/mm-1
2.320
9.620
F(000)
2504.0
Crystal size/mm3
Radiation
0.16 × 0.16 × 0.12
MoKα (λ = 0.71073)
5.72 to 52.82
Theta range for data collection/°
5

-21 ≤ h ≤ 21, -11 ≤ k ≤ 11, -30
≤ l ≤ 30
Limiting indices
Reflections collected
44413
44413 / 7809 [Rint = 0.0525,
Rsigma = 0.0342]
7809/6/460
Reflections collected / unique
Data/restraints/parameters
Goodness-of-fit on F2
1.028
Final R indices [I>2sigma(I)]
R1 = 0.0246, wR2 = 0.0465
R1 = 0.0387, wR2 = 0.0504
0.99/-0.88
R indices (all data)
Largest diff. peak and hole,e.Å-3
2. 5. Theoretical calculation
DFT calculations for the title compound have been performed by the Gaussian 09 set of
programs and the Gauss-view visualization program [39]. The molecular structure
optimization of the molecule was calculated using the SDD basis functions for Ce and
6-31G(d) basis set for Br, C, N, O, and H. Hirshfeld surfaces computational analyses were
carried out using the Crystal Explorer 17.5 software [38] and TONTO system.
Crystallographic data (excluding structure factors) for the structure in this paper have
been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road,
Cambridge CB21EZ, UK.Copies of the data can be obtained free of charge on quoting the
depository
number
CCDC-1995166
(Fax:
+44-1223-336-033;
E-Mail:deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk). The potential hydrogen bonds
and short inter-molecular contacts were calculated via PLATON software [35] and were listed
in Table 2 and 3.
Table 2. Inter-molecular hydrogen bonding geometries
D-H···A
D-H, Å
1.893
H···A, Å
3.03
D-H···A, deg
C(2)-Br(2)···H(30)i
C(21)-Br(4)···H(32)ii
146
130
1.898
3.12
6

C(16)-Br(5)···H(24)iii
C(18)···C(9)-H(9A)vi
C(19)···C(9)-H(9A)vi
C(20)···C(9)-H(9A)vi
C(8)-H(8B)···C(13)vi
C(9)-H(9A)···C(18)v
C(9)-H(9A)···C(19)v
C(9)-H(9A)···C(20) v
C(10)-H(10B) ···C(2) iv
C(13)-H(13)···C(8)v
C(24)-H(24)···C(13)vii
C(25)-H(25B) ···C(12)vii
C(25)-H(25B) ···C(13)vii
1.900
0.970
0.970
0.970
0.971
0.970
0.970
0.970
0.970
0.93
3.1
137
116
104
109
127
166
161
134
130
133
119
141
143
2.99
2.71
2.82
2.49
2.99
2.71
2.82
2.98
2.49
2.95
2.87
2.9
0.929
0.970
0.970
Symmetrycode: (i) -1/2-x,-1/2+y,1/2-z; (ii) -1/2+x,1/2-y,1/2+z; (iii) -x,-y,-z; (iv) x,1+y,z; (v)
1/2-x,1/2+y,1/2-z; (vi) 1/2-x,-1/2+y,1/2-z; (vii) x,-1+y,z; (viii) -1/2-x,1/2+y,1/2-z
Table 3. Halogen bond geometries
D-X···A
D-X, Å
1.893
1.893
1.893
1.898
X···A, Å
3.135(2)
3.600(3)
3.159(3)
3.4972(6)
D-X···A, deg
146.53
C(31)-Br(7)···O(2)i
C(2)-Br(2)···C(29)i
C(2)-Br(2)···C(30)i
C(21)-Br(4)···Br(8)x
133.26
153.23
169.51
Symmetry codes: (i)-1/2-x,-1/2+y,1/2-z; (vii) x,-1+y,z; (x) 1/2+x,1/2-y,-1/2+z.
3. Results and Discussion
3.1 Crystal Structure
7

Fig. 1. The molecular structures of compounds 1, showing the selected atom labelling. Displacement
ellipsoids are drawn at the 30% probability level.
Compound 1 crystallizes in Monoclinic space group P21/c, as is shown in Fig.1, there is
one ceric(IV) center and two 3,5Br-salpn salen-type ligand in the asymmetric unit. Two
poly-halogenated Schiff-base ligands 3,5Br-salpn adopt crossover coordination mode to
chelate the Ce(IV) atom. The Ce(IV) atom sited in the center of the complex,
octa-coordinated with four oxygen atoms and four nitrogen atoms and overall presenting a
distorted prismatic geometry. The bond lengths of Ce-O(N) are in the range of 2.224(2) ~
2.597(3) Å, the average bond length of Ce-N [2.592(3) Å] is longer than Ce-O [2.236(2) Å].
It should be noted that albeit only small differences between halogenated and
non-halogenated salen-type ligands (with a ratio of ligand to Ce(IV) 2 : 1), a close survey of
literature indicate that all the complexes with halogenated ligands are ‘X’ type distortion [40,
41], while the non-halogenated ones are exhibiting either ‘V + Λ’ (sandwich type) [41-45] or
‘Vertical’ type geometry (Fig. 2) [42, 43], although there is no good explanation for this
phenomenon, from a statistical point of view, this observation at least implies the regulatory
effect of halogens to salen-type lanthanide complexes. Moreover, the bond lengths in 1 are
obviously shorter than that of non-halogenated Schiff base complexes [44, 45, 47], which not
only indicate stronger metal-ligand covalency in 1 but also prove the high oxidation state for
Ce center. We deduce these shortened distances may be caused by the better overlap between
the special crossover ligand systems and vacant f° orbitals of Ce4+ ion.
8

Fig. 2. Diffferences between the distorted structures of salen-type Ce complexes. ‘ X ’ type distortion
of halogenated Schiff base ligand (left) and ‘V + Λ’ as well as ‘Vertical’ type (right) distortion of
non-halogenated Schiff base ligand geometries around each Ce ion.
Since all the N and O atoms coordinate to the central cerium(IV), in the packing
arrangement, atoms with high electronegativity atoms are almost entirely surrounded by outer
carbon and hydrogen atoms, therefore, there is no typical intermolecular hydrogen bond exist
in the supermolecular networks. Platon software analysis result show that halogen atoms
involved hydrogen bonds and halogen bonds constitute the most important factor in
stabilizing the three-dimensional supramolecular networks. As is shown in Figure 2 (a and b),
L-geometry XB linked adjacent molecules forms one-dimensional chain structure
(Br(4)···Br(8)x = 3.4972(6) Å, θ1= 99.88°, θ2 = 169.51°, Symmetry code: x =
1/2+x,1/2-y,-1/2+z ),
9

Fig. 3. Partial packing view of 1-D chain structure of 1. a) Selected bond parameters are labeled for
viewing clarity; b) more complete 1-D chain structure of 1.
Further, the adjacent chains are connected by a multiple intermolecular C-Br...H and O...Br
interactions, generated a two-dimensional layers along ac plane (Fig. 4(a)), further,(重复)
these 2D layered structure are held together via the C-H...H and C-Br...H contacts to form the
3D-supramolecular network (Fig. 4(b)), detailed inter-molecular hydrogen bonding and
halogen bond geometries geometries are listed in Table 2 and 3, respectively.
Fig. 4. Partial view of H-bonding and XB interactions among supramolecular network in 1. C-Br...H and
O...Br contact formed 2D layer structure, and C-H...H and C-Br...H contact formed 3D network.
Crystal structure analysis can provide qualitative results of intermolecular contacts,
however, the information it can give about quantitative results are very limited. In order to
obtain detailed and comparison result of all the contacts, in this work we introduced Hirshfeld
surface analysis to conduct quantitative calculation, detailed results are given in the following
discussion.
3.2 Optimized Structure and Frontier molecular orbitals (HOMO-LUMO)
10

Fig. 5. A molecular fit of the experimental and optimized structures of 1 shown in black and red,
respectively. H atoms have been omitted for clarity.
Intermolecular interactions mainly occured in the frontier (FMOs) and neighbouring
orbitals. The highest occupied molecular orbital and the nearby occupied orbitals are
important in donating electrons, while the lowest occupied molecular orbital is vital for
accepting electrons. Therefore, the analysis of the FMOs is important in understanding
chemical reaction mechanisms and kinetic stabilities [48]. The experimental and optimized
structures of the title compound are illustrated in Fig. 5 and Fig. S4 (ESI), detailed Cartesian
coordinates of the DFT Optimized Structure of of 1 is given in table S1. The bond length and
angles of the optimized molecular structure are basically consistent with the experimental
structure, slightly differences is generally because the optimized geometry was obtained by
gas-phase DFT optimizations. Selected FMO 3D plots of 1 are shown in Fig. 4. The HOMO
(highest occupied molecular orbital) surfaces are mainly localized over benzene rings and the
coordination chlorine atom, while the LUMO (lowest unoccupied molecular orbital) are
shrinked to the metal center and -C=N- double bond showing an effective communication
from π-orbitals throughout the ligand. HOMO surfaces are spread over the Schiff-base plane
including substituted halogens and the LUMO has a congregation trend in the center. The
HOMO and LUMO energy values are -6.08 and -3.44 eV, respectively, the magnitude of the
energy separation between the HOMO and LUMO is ΔE = 2.64
4 eV. This result in accordance with previously reported salen-type non-halogenated
cerium(IV) Schiff-base complexes [46].
11

.
Fig. 6. Molecular orbital surfaces for the HOMO and LUMO of the compound computed at B3LYP/6-31G
(d, p) level.
Fig. 7. MEP surfaces of complex 1. MEP values in Kcal/mol are given in selected points of the surface.
12

Fig. 8. molecular electrostatic potential calculations of 1, (a) σ-hole of bromine atoms (b) σ-hole of
chlorine atom. MEP for the title compound is scaled from -20 kcal/mol to +20 kcal/mol
In order to rationalize the formation of supramolecular networks and chemical reactivity
of the title compound, molecular electrostatic potential (MEP) surface map of the compound
was investigated with theoretical calculations at the B3LYP/6-31G (d) level [49]. As is shown
in Fig.7, The MEP for the title compound is scaled from -20kcal/molto +20kcal/mol, and the
concentration of electrostatic potential electron is displayed in a descending order with color:
red indicates the negative region and blue indicates the positive region. As is shown in Fig.7
and Fig.S5, the most negative electrostatic potential appears at the region around oxygen
atoms that coordinated to the Ce(III) center (-17.7 kcal/mol). These value seem to suggest the
oxygen atoms can serve as electron donor in intermolecular contacts, whereas, because these
oxygen atoms embed in the center of the molecule and surrounded by outer carbon atoms,
there are no classical O...H hydrogen bonds exist in the three-dimensional structures. The
most positive potentials is observed in the region of hydrogen atoms on the amine group (19.0
kcal/mol), and the intermolecular contacts C-H...H (C(18)···C(9)-H(9A)vi) that link the 2D
sheets into 3D frameworks appear in this region. It is noteworthy that although salen type
complexes is an important member of the coordination compounds, up to the present, no
literature has specifically concerned magnitude of σ-hole for salen type complexes. In this
work, as shown in Fig.8, we found an interesting phenomenon that the σ-hole of bromine
atoms of different substituents present quite different molecular electrostatic surface potential
(Br1 (5-Br): Vmax = 6.8 kcal/mol and Br2 (5-Br): Vmax = 13.2 kcal/mol). It is known that the
strength and distance of halogen bonds can be modulated by σ-hole we can speculate that the
regulation of supramolecular structure can be achieved by tuning halogen atoms.
13

3.3 Hirshfeld surface analysis
The strengthen of intermolecular interactions is difficult to be revealed by traditional
methods, Hirshfeld surface analysis provides an effective method on the issue. It can help us
to quantitatively understand the strength of intermolecular interactions by their visualization
of appropriate color codes and shades on the surfaces [39]. The contacted atoms with distance
less than sum of the van der Waals radii are characterized by red spots showing negative dnorm
value on the surface, while contacts with distance equal to the van der Waals radii are lying in
zero dnorm value showing white color and contacts with longer than the sum of the van der
Waals radii are located in the positive dnorm value with blue color. As is shown in Fig. 9(a),
the C-Br...C bond are labelled as red spots (a), which is ascribed to the interactions formed by
bromine atom and adjacent carbon atom of benzene ring (C(2)-Br(2)...C(30)i i:
-1/2-x,-1/2+y,1/2-z ); the C-Br...O are labelled as red spots (b), which is assigned to the
interaction between bromine atom and phenolic group (C(21)-Br(7)··· Oi i:
-1/2-x,-1/2+y,1/2-z); the C-Br...Br bond are labelled as red spots (c), which is ascribed to
halogen bonding interactions between adjacent bromine atoms (C(21)-Br(4)··· Br(8)x x:
1/2+x,1/2-y,-1/2+z), these results also confirms that there is no classic hydrogen bond in the
title compound and bromine atoms related interactions are dominated overall crystal packing.
The shape index and curvedness are sensitive to very subtle changes in surface shape
(Fig. 9(c) and 9(c)), unlike the usually observed planar salen-type complexes, in the
compound 1 two halogenated Schiff base ligand adopt crossed coordination mode with the
central Ce atom, therefore, there is almost no large coplanar region and resulting in the
absence of π ··· π stack between adjacent aromatic rings.
The 2D fingerprint plots can give quantitatively summarize of all the intermolecular
contacts exist the crystal. As is shown in Fig.10, in compound 1 bromine atoms involved
contacts donate more than a half contribution which covers 56.6% Hirshfeld surfaces of all
the interactions, although there is no classic hydrogen bond in 1, we observed a sharp spike
attributed to Br...Br interactions in the 2D fingerprint map, which revealed a strong halogen
bonding interaction in the crystal structure.
14

Fig. 9. The orientation of molecule (a) as well as Hirshfeld surfaces mapped with dnorm (b), shape (c) and
curvedness (d) of compound 1.
Fig. 10. Two dimensional fingerprint plots of the title compound: resolved bromine involved contacts
showing the percentages of the weak contacts contributed to the total Hirshfeld Surface area of the title
compounds (left), columns highlight the relevant surface patches associated with the specific contacts in the
total Hirshfeld Surface area of the title compound (right).
15

Fig. 11. (a) The fluorescence spectra of the titration of halogenated Schiff-base ligand (H2L)) (10 μM) by
the addition of Ce4+ at room temperature and excited at 368 nm , [Ce4+] = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15,
20 μM); (b) Maximum fluorescence intensity versus concentration of (Ce4+/ H2L) .
3.4 Luminescent properties
Recently, the photoluminescence of salen-type Ce(IV) complexes has aroused great
research interest owing to their special fluorescence proprieties which can produce potential
applications for chemical sensor and photochemistry [46, 50-52]. However, by a careful
analysis of fluorescence behavior we found that, although many works literatured that after
ligand coordinated to metal center, the more rigid structure can both restrict the rotation and
vibration of ligands and fixed conjugate system in 3D supramolecular network, by which the
fluorescence intensity can be markedly enhanced, this kind of behavior is more apparent in
some salen type of rare earth complexes, but in this work, we observed totally different
fluorescence behavior. As is shown in Fig. 11(a), halogenated ligand shows a strong emission
peak at 538 nm (2.9×104), upon successive addition of Ce4+ (0-20 μM) the spectrum
undergoes a dramatically decrease and blue shift Fig. 11(b), when the stoichiometric ratio of
H2L and Ce4+ reach to 1:1, the intensity almost decrease to a minimum value (456nm,
2.4×103), further addition of Ce4+ ions did not affect the position and intensity of peaks. The
quantum yield (QY) of 1 and H2L were determined to be 0.10% and 0.64%, respectively (Fig.
S9 to S11 ), based on standard quinine sulfate (QY = 54%). Above results suggesting the
fluorescence properties of salen-type complex can be entirely governed by the halogenated
ligand.
16

4. Conclusion
With an aim to insights the electronic structure and topologies of halogen bond in
salen-type Schiff base compound, a new lanthanide poly-halogenated Schiff-base complex
was synthesized and determined by single crystal X-ray diffraction. Structural analysis shows
that bromine atoms involved contacts is the main driving force in stabilizing the
supramolecular networks. Theoretical calculation revealed that the σ-hole of Br atoms of
different substituents present quite different molecular electrostatic surface potential. Since
the supermolecular network of complexes could be regulated by different σ-hole of XB, it is
reasonable to speculate that the intermolecular forces as well as supermolecular network of
salen type complexes can be artificially adjusted by tuning the substitution of halogens. In
addition, we found that halogen atoms had important influence on the fluorescence properties
of ligands and complexes. These interesting differences will enlighten us to introduce other
types of halogenated ligands to construct more halogenated compounds and further explore
the influence of halogen atom to the structures and properties.
Acknowledgment
This work was supported by Fund for Less Developed Regions of the National Natural
Science Foundation of China (No. 31760257, 21761017); Joint Basic Research
Program (partial) of Yunnan Local Undergraduate Universities (2017FH001-002) ； The
reserve academic and technical leaders of Yunnan Province (2019HB098).
Credit author statement:
Methodology, Qiong Wu, Yujiao Tu, Yongfeng Qiao: Synthsis and Characterization: Meifen
Huang, Tianyu Li, Liang Jiao, Xindi Xu, Xun Ma, Hui Tian; Fluorescence properties: Meifen
Huang, Tianyu Li, Liang Jiao; Writing: Qiong Wu, Yujiao Tu, Yongfeng Qiao; Funding
acquisition: Qiong Wu.
Declaration of interest statement
We declare that we have no financial and personal relationships with other people or
organizations that can inappropriately influence our work, there is no professional or other
personal interest of any nature or kind in any product, service and/or company that could be
construed as influencing the position presented in, or the review of, the manuscript entitled.
17

Reference
[1] L.N. Ignatieva, V.G. Kuryavyi, T.A. Kaidalova, V.M. Bouznik, A.I. Korchagin, J. Struct.
Chem., 46 (2005) 848-855.
[2] K. Wang, B. Xu, Physical Chemistry Chemical Physics Pccp, 18 (2016) 9569-9576.
[3] Y.D. Glinka, M. Jaroniec, Physical Review A, 56 (1997) 3056-3059.
[4] L. Voorhaar, R. Hoogenboom, Chem. Soc. Rev., 45 (2016) 4013-4031.
[5] F. Huang, E.V. Anslyn, Chem. Rev., 115 (2015) 6999.
[6] L.D. Muiznieks, F.W. Keeley, Biochimica et Biophysica Acta - Molecular Basis of
Disease, 1832 (2013) 866-875.
[7] B. Qin, Z. Yin, X. Tang, S. Zhang, Y. Wu, J.-F. Xu, X. Zhang, Prog. Polym. Sci., 100
(2020) 101167.
[8] P.K. Hashim, J. Bergueiro, E.W. Meijer, T. Aida, Prog. Polym. Sci., (2020) 101250.
[9] W. Ji, B. Xue, Z.A. Arnon, H. Yuan, S. Bera, Q. Li, D. Zaguri, N.P. Reynolds, H. Li, Y.
Chen, S. Gilead, S. Rencus-Lazar, J. Li, R. Yang, Y. Cao, E. Gazit, ACS Nano, 13 (2019)
14477-14485.
[10] G. Fukuhara, Journal of Photochemistry and Photobiology C: Photochemistry Reviews,
42 (2020) 100340.
[11] H.-Y. Zhang, Y.-Y. Tang, P.-P. Shi, R.-G. Xiong, Acc. Chem. Res., 52 (2019) 1928-1938.
[12] M.W. Shi, S.P. Thomas, G.A. Koutsantonis, M.A. Spackman, Crystal Growth & Design,
15 (2015) 5892-5900.
[13] P. Peluso, V. Mamane, R. Dallocchio, A. Dessì, R. Villano, D. Sanna, E. Aubert, P. Pale,
S. Cossu, J. Sep. Sci., 41 (2018) 1247-1256.
[14] H. Wang, W. Wang, W.J. Jin, Chem. Rev., 116 (2016) 5072-5104.
[15] A. Bauzá, A. Frontera, Coord. Chem. Rev., 404 (2020) 213112.
[16] J. Pancholi, P.D. Beer, Coord. Chem. Rev., (2020) 213281.
[17] M.S. Taylor, Coord. Chem. Rev., 413 (2020) 213270.
[18] M. Dong, T. Hu, Y. Wang, P. Pang, Y. Wang, X. Miao, B. Li, W. Deng, Appl. Surf. Sci.,
515 (2020) 145983.
[19] C.Z. Liu, H. Wang, D.W. Zhang, X. Zhao, Z.T. Li, Chinese Journal of Organic
Chemistry, 39 (2019) 28-37.
[20] R. Tepper, U.S. Schubert, Angewandte Chemie - International Edition, 57 (2018)
6004-6016.
[21] F.F. Awwadi, M.M. Turnbull, M.I. Alwahsh, S.F. Haddad, New J. Chem., 42 (2018)
10642-10650.
[22] A.V. Rozhkov, D.M. Ivanov, A.S. Novikov, I.V. Ananyev, N.A. Bokach, V.Y. Kukushkin,
CrystEngComm, 22 (2020) 554-563.
[23] J.A. Ridenour, M.H. Schofield, C.L. Cahill, Cryst. Growth Des., 20 (2020) 1311-1318.
[24] R.F. Mulagaleev, A.K. Starkov, Y.N. Zaitseva, G.A. Kozhuhovskay, N.I. Pavlenko, S.D.
Kirik, J. Mol. Struct., 1199 (2020).
[25] M. Joksch, H. Agarwala, M. Ferro, D. Michalik, A. Spannenberg, T. Beweries, Chemistry
18

- A European Journal, 26 (2020) 3571-3577.
[26] A.B. Canaj, S. Dey, E.R. Martí, C. Wilson, G. Rajaraman, M. Murrie, Angew. Chem. Int.
Ed., 58 (2019) 14146-14151.
[27] J.L. Segura, M.J. Mancheño, F. Zamora, Chem. Soc. Rev., 45 (2016).
[28] R. Ganguly, B. Sreenivasulu, J.J. Vittal, Coord. Chem. Rev., 252 (2008) 1027-1050.
[29] Q. Wu, W. Wu, Y. Wu, W. Li, Y. Qiao, Y. Wang, B. Wang, J. Mol. Struct., 1157 (2018)
616-620.
[30] S.K. Tadavi, A.A. Yadav, R.S. Bendre, J. Mol. Struct., 1152 (2018) 223-231.
[31] C. Kachi-Terajima, R. Ishii, Y. Tojo, M. Fukuda, Y. Kitagawa, M. Asaoka, H. Miyasaka,
The Journal of Physical Chemistry C, 121 (2017) 12454-12468.
[32] H. Miyasaka, A. Saitoh, S. Abe, Coord. Chem. Rev., 251 (2007) 2622-2664.
[33] V. Nemec, L. Fotović, T. Friščić, D. Cinčić, Cryst. Growth Des., 17 (2017) 6169-6173.
[34] M. Montazerozohori, S. Mojahedi Jahromi, A. Masoudiasl, P. McArdle, Spectrochimica
Acta - Part A: Molecular and Biomolecular Spectroscopy, 138 (2015) 517-528.
[35] Q. Wu, J.-C. Xiao, C. Zhou, J.-R. Sun, M.-F. Huang, X. Xu, T. Li, H. Tian, Crystals, 10
(2020) 334.
[36] X. Ji, X. Yuan, H. Nian, P. Song, Y. Xiang, Y. Wei, S. Wang, K. Qin, Q. Zhang, Y. Tu,
Dyes and Pigments, 182 (2020) 108621.
[36] v. Agilent Technologies: CrysAlisPRO Software system, Agilent Technologies UK Ltd,
Oxford, UK, (2015). in.
[37] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, J. Appl.
Crystallogr., 42 (2010) 339-341.
[38] M.A. Spackman, D. Jayatilaka, CrystEngComm, 11 (2009) 19-32.
[39] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P.
Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J.A.M. Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin,
V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S.
Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V.
Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R.
Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, Ö. Farkas, J.B. Foresman, J.V. Ortiz,
J. Cioslowski, D.J. Fox, Wallingford CT, (2009).
[40] E. Szłyk, A. Wojtczak, L. Dobrzańska, M. Barwiołek, Polyhedron, 27 (2008) 765-776.
[41] K. Kubono, N. Hirayama, H. Kokusen, K. Yokoi, Anal. Sci., 17 (2001) 193-197.
[42] E.E. Hardy, K.M. Wyss, J.D. Gorden, I.R. Ariyarathna, E. Miliordos, A.E.V. Gorden,
Chem. Commun., 53 (2017) 11984-11987.
[43] A. Terzis, D. Mentzafos, H.A. Tajmir-Riahi, Inorg. Chim. Acta, 84 (1984) 187-193.
[44] C. Chen, H. Chen, P. Yan, G. Hou, G. Li, Inorg. Chim. Acta, 405 (2013) 182-187.
[45] B.E. Klamm, C.J. Windorff, M.L. Marsh, D.S. Meeker, T.E. Albrecht-Schmitt, Chem.
Commun., 54 (2018) 8634-8636.
[46] M. Ghosh, S. Ta, M. Banerjee, M. Mahiuddin, S. Khanra, S. Kumar Hira, P. Pratim
Manna, D. Das, Journal of Photochemistry and Photobiology A: Chemistry, 367 (2018) 32-38.
19

[47] J.A. Bogart, A.J. Lewis, S.A. Medling, N.A. Piro, P.J. Carroll, C.H. Booth, E.J. Schelter,
Inorg. Chem., 52 (2013) 11600-11607.
[48] C.G. Zhan, J.A. Nichols, D.A. Dixon, J. Phys. Chem. A, 107 (2003) 4184-4195.
[49] M.P. Andersson, P. Uvdal, The Journal of Physical Chemistry A, 109 (2005) 2937-2941.
[50] L. Jin, W. Wang, Z. Shen, J. Xu, Q. Wang, C. Zhao, J. Mol. Struct., 1197 (2019) 73-79.
[51] J. Xu, X. Xia, G. Zhang, H. Wu, Y. Qu, L. Xia, X. Han, Inorg. Chim. Acta, 512 (2020)
119918.
[52] D. Majumdar, D. Das, S.S. Sreejith, S. Das, J. Kumar Biswas, M. Mondal, D. Ghosh, K.
Bankura, D. Mishra, Inorg. Chim. Acta, 489 (2019) 244-254.
GRAPHICAL ABSTRACT
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