An experimental and theoretical investigation of lanthanide complexes [Ln = Nd, Yb, Eu, Dy and tb] with 4-((2-hydroxy-naphthalen-1-yl)methylene amino)benzenesulfonamide ligand

Article abstract of DOI:10.1016/j.ica.2020.119955

Reaction of lanthanide(III) salts with N, O donors 4-((2-hydroxynaphthalen-1-yl) methyleneamino)benzenesulfonamide (L) Schiff base ligand afforded five new mononuclear lanthanide complexes of type [Ln(NO₃)₂(L)(H₂O)₂

Full text of DOI:10.1016/j.ica.2020.119955

InorganicaChimicaActa513(2020)119955
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
An experimental and theoretical investigation of lanthanide complexes
[Ln = Nd, Yb, Eu, Dy and tb] with 4-((2-hydroxy-naphthalen-1-yl)
methylene amino)benzenesulfonamide ligand
Sikandar Paswana, Nitesh Jaiswalb, Vishnu Kumar Modanawala, Manoj Kumar Patela,
⁎
Rana Krishna Pal Singha,
a Synthetic Inorganic and Metallo-Organic Research Laboratory, Department of Chemistry, University of Allahabad, Prayagraj 211002, Uttar Pradesh, India
b Department of Chemistry, Prof. Rajendra Singh (Rajju Bhaiya) Institute of Physical Sciences for Study and Research, Veer Bahadur Singh Purvanchal University, Jaunpur
222003, Uttar Pradesh, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
Reaction of lanthanide(III) salts with N, O donors 4-((2-hydroxynaphthalen-1-yl) methyleneamino)benzene-
sulfonamide (L) Schiff base ligand afforded five new mononuclear lanthanide complexes of type [Ln(NO3)2(L)
(H2O)2](H2O)x {where Ln = Nd (1), x = 2, Yb (2), x = 1, Eu (3), x = 2, Dy (4), x = 1, Tb (5), x = 2}. These
newly synthesized complexes were characterized by elemental analysis, molar conductance, FT-IR, UV–Vis
spectroscopy and mass spectrometry. The thermal behavior of complexes was studied by TGA technique. The
computational calculations using density functional theory (DFT) of ligand and their lanthanide complexes were
performed to obtain optimized molecular geometry, the highest occupied molecular orbital (HOMO), the lowest
unoccupied molecular orbital (LUMO) and other parameters. The fluorescence studies reveal that emission
spectra of lanthanide complexes show the characteristic luminescence due to lanthanide ions which indicates
that Schiff base ligand can sensitize the Ln(III) ions. The Schiff base and their lanthanide complexes were
screened for their in vitro antibacterial studies against Escherichia coli (ATCC 25922), Staphylococcus aureus
(ATCC 29213), Klebsiella pneumoniae (BAA 1705), Acinetobacterr baumannii (BAA 1605) and Pseudomonas aer-
uginosa (ATCC 27853). The results exhibit that the antibacterial activity of Ln(III) complexes was greater than
the free Schiff base ligand.
Lanthanide complexes
Schiff base
DFT
Fluorescence studies
Antibacterial studies
1. Introduction
therapeutic agents against different diseases [11–14]. Sulfur donor
Schiff base ligands play an important role in metal coordination
The growing demand of luminescent materials for different societal
applications has been witnessed in recent times. The luminescence and
magnetic features of lanthanide complexes motivated the researcher for
its exploration. The design and synthesis of lanthanide complexes with
organic ligands including Schiff bases emerged as an important research
area in recent times [1–4]. The existence of long-lived excited states of
trivalent lanthanide ions (Ln3+) produces the luminescence properties
in lanthanide complexes. These photophysical properties of lanthanide
complexes could be tuned and enhanced with the help of rationally
designed ligands. The emerging interest of chemists towards research in
the lanthanide complexes is due to their interesting structures [5,6] and
a wide range of potential applications in biological sectors, catalysis,
luminescence and magnetic properties [7–10].
chemistry due to its important biological properties including anti-
bacterial, anti-toxicity, antifungal and antitumor properties [15,16].
The biological activities of metal complexes in several cases improved
significantly on the addition of sulfonamide derivative ligands to metal
salts rationally. The metal complexes of sulfonamide derivatives ligands
have shown significant potential against cancer cell lines and other
biological activities [17]. The interesting coordination chemistry of
lanthanide metals with N, O donor Schiff base ligands and their ap-
plications in different scientific areas including chemical, medical and
industrial sectors make enough for their importance and fascinate the
chemist for the synthesis of new complexes [18].
Due to the above promising facts and our continued interest [19], an
attempt was made to investigate the synthesis, characterization and
antimicrobial properties of lanthanide (III) Schiff base complexes. In
Sulfonamides were the first drugs used as preventive and
⁎ Corresponding author.
E-mail address: rkp.singh@rediffmail.com (R.K.P. Singh).
https://doi.org/10.1016/j.ica.2020.119955
Received 26 July 2020; Received in revised form 16 August 2020; Accepted 16 August 2020
Availableonline20August2020
0020-1693/©2020ElsevierB.V.Allrightsreserved.

S. Paswan, et al.
InorganicaChimicaActa513(2020)119955
our investigation, we have utilized the sulfanilamide and 2-hydroxy-1-
naphthaldehyde derive Schiff base ligand (L), to prepare a series of
mononuclear lanthanide derivatives (1–5) [Ln(III)(L)(NO3)2(H2O)2]
(Ln = Nd, Dy, Eu, Yb, Tb; L = 4-((2-hydroxynaphthalen-1-yl) methy-
leneamino)benzenesulfonamide). These complexes were investigated
by elemental analysis, molar conductance, FT-IR and UV–Vis spectro-
scopy, mass spectrometry and thermal technique. Theoretical in-
vestigation using the DFT method was performed to get validation of
experimental data. The fluorescence activity and biological properties
of these complexes were also investigated.
2. Experimental
2.1. Materials and reagent
Nd(NO3)3·6H2O, Dy(NO3)3·5H2O, Yb(NO3)3·5H2O, Eu(NO3)3·5H2O,
Tb(NO3)3·xH2O, sulfanilamide, 2-hydroxy-1-naphthaldehyde were
bought from Sigma Aldrich and utilized without any further purifica-
tion. AR grade solvents were utilized for the production and re-
crystallization of compounds.
2.2. Physical measurements
The fundamental (C, H and N) analyses have been performed on
CHN-932 Perkin- Elmer 7300 DV elemental analyzer. In KBr pellets and
on a Perkin-Elmer 1000 FT-IR spectrophotometer the FT-IR spectrum
has been performed from 4000 to 400 cm−1 region. The mass spectra
(HRMS) were taken in ESI mode on Xevo G2-S Q Tof. Under the inert N2
atmosphere, on STA 6000 Perkin Elmer instrument the thermogravi-
metric analyses (TGA) and differential thermal analyses (DTA) of
complexes have been recorded. UV–Vis spectra were measured within
the DMSO solution at temperature and λmax was taken in (nm) by UV-
1800 Shimadzu UV spectrophotometer. The fluorescence analysis was
carried out by the Perkin Elmer LS-55 fluorescence spectrophotometer
with a spectral resolution of ~0.5 nm, slit widths ~9 mm, quartz cell
1 cm.
Scheme 1. Synthetic route for the preparation of ligand and Ln(III) complexes.
2.3. Synthesis of Schiff base ligand
2.4.1. [Nd(L)(NO3)2(H2O)2](H2O)2 (1)
Yield: 69%, yellow solid, m.p. 260–65 °C, Elem. Anal. for
The ligand 4-((2-hydroxynaphthalen-1-yl) methyleneamino) benzene
sulfonamide [20,21] (L) has been synthesized by the reaction of sulfa-
nilamide and 2-hydroxy-1-naphthaldehuyde in 1:1 M ratio(s). The
5.22 mmol each of Sulfanilamide and 2-hydroxy-1-naphthaldehuyde
were mixed in ~35 cm3 methanol solvent and refluxed for ~5 h. The
resulting yellow product washed with cold methanol and dried at room
temperature. Finally recrystallization of this compound with hot me-
thanol gives analytically pure powdered yellow product.
C
17H17N4O11SNd, Calcd. C, 32.43; H, 2.72; N, 8.90 Found: C, 32.37; H,
2.66; N, 8.82%. TOF-MS: Calcd. 626.87, Found: 625.42. IR (KBr,
cm−1): 3445 ʋ(H2O); 3291 ʋ(NH2); 1594 ʋ(C]N); 1437 ʋ(AreO);
1494, 1135, 820, 1287 ʋ(NO3); 1365, 1150 ʋ(SO2); 963 ʋ(SeN); 830 ʋ
(CeS); 547 ʋ(Nd-O); 468 ʋ(Nd-N); UV–Vis (DMSO, λmax): 384 (π →
π*), 438, 462 (n
102 Ω−1 cm2 mol−1
→ π*) nm. Molar conductance (DMF, Ʌm):
.
4-((2-hydroxynaphthalen-1-yl) methyleneamino) benzene sulfonamide
(L) Yield: 82%, yellow powder, m.p. 281–83 °C, Elem. Anal. for
2.4.2. [Yb(L)(NO3)2(H2O)2](H2O) (2)
Yield: 72%, brown solid, m.p. 258–62 °C, Elem. Anal. for
C17H17N4O11SYb, Calcd. C, 31.01; H, 2.60; N, 8.51 Found: C, 30.91; H,
2.51; N, 8.46%. TOF-MS: Calcd. 659.00, Found: 658.11. IR (KBr,
cm−1): 3390 ʋ(H2O); 3290 ʋ(NH2); 1594 ʋ(C]N); 1444 ʋ(AreO);
1502, 1050, 827, 1180 ʋ(NO3); 1358, 1157 ʋ(SO2); 971 ʋ(SeN); 835 ʋ
(CeS); 540 ʋ(Yb-O); 461 ʋ(Yb-N); UV–Vis (DMSO, λmax): 386 (π → π*),
C
17H14N2O3S, Calcd. C, 62.56; H, 4.32; N, 8.58 Found: C, 62.48; H,
4.26; N, 8.51%. TOF-MS: Calcd. 326.07, Found: 327.42. IR (KBr,
cm−1): 3320 ʋ(eOH); 3294 ʋ(eNH2); 1630 ʋ(C]N); 1465 ʋ(AreO);
1360, 1157 ʋ(SO2); 971 ʋ(SeN); 835 ʋ(CeS). UV–Vis (DMSO, λmax):
380 (π → π*), 435, 457 (n → π*) nm.
440, 463 (n
→
π*) nm. Molar conductance (DMF, Ʌm):
2.4. General procedure for the synthesis of lanthanide complexes
101 Ω−1 cm2 mol−1
.
The preparation of all Ln(III) complexes [Ln(L)(NO3)2(H2O)2]
(H2O)x (1–5) have been done by the following procedure.
The Schiff base (0.537 g, 1.64 mmol) was dissolved in ethanol
(20 mL) and subsequently an ideal ethanolic solution of Nd(NO3)3·6H2O
(0.722 g, 1.64 mmol) was added to this solution. After few minutes,
KOH in ethanol was added to the resulting solution and stirring for 24 h
at 40 °C. A deep yellow color solution was obtained. The complex was
dried by vacuum rotavapor to give yellow solid which is purified by
ethanol solution (Scheme 1).
2.4.3. [Eu(L)(NO3)2(H2O)2](H2O)2 (3)
Yield: 66%, dark brown, m.p. 261–62 °C, Elem. Anal. for
C
17H17N4O11SEu, Calcd. C, 32.04; H, 2.69; N, 8.79 Found: C, 31.98; H,
2.60; N, 8.71%. TOF-MS: Calcd. 637.98, Found: 636.73. IR (KBr,
cm−1): 3505 ʋ(H2O); 3291 ʋ(NH2); 1602 ʋ(C]N); 1447 ʋ(AreO);
1502, 1043, 827, 1287 ʋ(NO3); 1355, 1150 ʋ(SO2); 978 ʋ(SeN); 831 ʋ
(CeS); 540 ʋ(EueO); 460 ʋ(EueN); UV–Vis (DMSO, λmax): 356 (π →
π*), 425, 464 (n
→ π*) nm. Molar conductance (DMF, Ʌm):
2

S. Paswan, et al.
InorganicaChimicaActa513(2020)119955
{where Ln = Nd (1), x = 2, Yb (2), x = 1, Eu (3), x = 2, Dy (4), x = 1,
Tb (5), x = 2} synthesized by Ln(NO3)3·nH2O and ligand (L) in a 1:1 M
ratio in ethanol. All the reported compounds are very stable at room
temperature, non-hygroscopic. These complexes are insoluble in me-
thanol, chloroform, benzene and soluble in DMSO, DMF and THF.
94 Ω−1 cm2 mol−1
.
2.4.4. [Dy(L)(NO3)2(H2O)2](H2O) (4)
Yield: 71%, black solid, m.p. 270–74 °C, Elem. Anal. for
C
17H17N4O11SDy, Calcd. C, 31.51; H, 2.64; N, 8.65 Found: C, 31.44; H,
2.55; N, 8.58%. TOF-MS: Calcd. 648.99, Found: 648.23. IR (KBr,
cm−1): 3530 ʋ(H2O); 3290 ʋ(NH2); 1602 ʋ(C]N); 1447 ʋ(AreO);
1494, 1035, 820, 1275 ʋ(NO3); 1355, 1157 ʋ(SO2); 963 ʋ(SeN); 835 ʋ
(CeS); 535 ʋ(DyeO); 460 ʋ(DyeN); UV–Vis (DMSO, λmax): 363 (π →
3.1. Infrared spectra
The infrared vibrations are very important in the structure -
elucidation of complexes. The representative IR spectra of Schiff base
ligand and their Nd(III) (1) complex have been presented in (Fig.
S1). The free ligand revealed a significant band at 1630 cm−1 that
corresponds to azomethine (eC]N) moiety [32]. This band indicates a
lower wavenumber shift and appears at 1597 cm−1 in complex because
of the manipulation of the nitrogen atom with metal center [33,34].
This observation was also supported by the appearance of a new
medium intensity group at 468 cm−1 because of Nd ← N extending
vibration [35].
π*), 434, 463 (n
105 Ω−1 cm2 mol−1
→ π*) nm. Molar conductance (DMF, Ʌm):
.
2.4.5. [Tb(L)(NO3)2(H2O)2](H2O)2 (5)
Yield: 67%, dark brown, m.p. 240–46 °C, Elem. Anal. for
C
17H17N4O11STb, Calcd. C, 31.69; H, 2.66; N, 8.70 Found: C, 31.59; H,
2.57; N, 8.61%. TOF-MS: Calcd. 634.99, Found: 633.09. IR (KBr,
cm−1): 3510 ʋ(H2O); 3290 ʋ(NH2); 1597 ʋ(C]N); 1440 ʋ(AreO);
1498, 1040, 821, 1285 ʋ(NO3); 1356, 1155 ʋ(SO2); 970 ʋ(SeN); 830 ʋ
(CeS); 541 ʋ(TbeO); 462 ʋ(TbeN); UV–Vis (DMSO, λmax): 385 (π →
A wide absorption band observed at 3320 cm−1 on account of
the phenolic (eOH) group in ligand was found absent in the Ln(III)
complexes. The disappearance of the OH group in Ln(III) complex -
suggests deprotonation of phenolic hydrogen and coordination of
oxygen with Nd(III). This coordination was further substantiated by the
appearance of the phenolic (CeO) group at lower wavenumber
1437 cm−1 in complex compared to the ligand and appearance of the
band at 547 cm−1 due to Nd ← O in the Nd(III) complex [36]. The
stretching vibration frequencies of coordinated water [37] appeared in
the region 3390–3530 cm−1 in complexes. The band at 3294 cm−1 was
ascribed to (eNH) in ligand and this band remained unchanged in the
spectrum of Nd(III) complex, which indicates the no participation of
(eNH) group in the complexation [20]. The bands in the ligand due to
ʋas(SO2) and ʋs(SO2) appeared at 1360 and 1157 cm−1, respectively
[38] remain unchanged in the complexes indicative that this group is
not coordinating with a metal center. This is further supported by the
unchanged absorption band of ʋ(SeN) and ʋ(CeS) groups appear at
971 and 835 cm−1 in the ligand, respectively [39,40]. The wavenumber
of coordinated nitrates in Nd(III) complex was observed at 1494 (ʋ1),
1035 (ʋ2), 820 (ʋ3) and 1287 (ʋ4). Besides, the frequency gap between
the two highest frequencies band (ʋ1-ʋ4) approximately appears at
207 cm−1 consistent with the value reported in the literature that the
coordinated NO3− ion in the complex is a bidentate ligand [41]. The IR
spectra of the other complexes are almost similar to those of Nd(III)
complex. This indicates that all Ln(III) complexes have similar struc-
tures where ligand coordinated to metal center in a bidentate N O donor
capacity.
π*), 438, 463 (n
→ π*) nm. Molar conductance (DMF, Ʌm):
97 Ω−1 cm2 mol−1
.
2.5. Computational method
Gaussian 09 program [22] was used to perform the computational
investigation of newly synthesized complexes. The optimized geometry
of the lanthanide complexes was obtained using density functional
theory (DFT) methods at B3LYP level [23] with SDD (d, f) basic set
[24]. The B3LYP/SDD employs three-parameter Becke exchange func-
tional, B3 [25], the Lee-Yang-Parr nonlocal correctional functional LYP
and the polarized SDD basis set [26–28].
2.6. In vitro antibacterial study
The ligand (L) and their Ln(III) complexes were screened for in vitro
antibacterial testing against different pathogens Escherichia coli (ATCC
25922), Pseudomonas aeruginosa (ATCC 27853), Acinetobacterr bau-
mannii (BAA 1605), Klebsiella pneumoniae (BAA 1705) characterized
into gram negative and Staphylococcus aureus (ATCC 29213) character-
ized into gram positive by using micro broth dilution assay. These pa-
thogens were regularly cultivated on Mueller-Hinton broth Agar
(MHA). Before the experiment, a single colony was picked from the
MHA plate, inoculated in Mueller-Hinton cation supplemented broth II
(CA-MHB) and incubated overnight at 37 °C. The stock solution
(1 mg mL−1) of the drug samples was prepared in the DMSO solution
which was diluted to 100 µg mL−1 with sterilized distilled water. The
Minimum Inhibitory Concentration (MIC) was determined as per the
Clinical Laboratory Standards Institute (CLSI) guidelines [29,30]. MIC
is defined as the minimum amount of compounds at which observable
bacterial growth is repressed. The optical density (OD600) of the cul-
tures was measured, followed by dilution for 1 × 106 CFU/mL. This
inoculum was added into a series of test wells in a microtitre plate that
contained various concentrations of the compound under test ranging
from 64 to 0.03 mg/mL. The controls i.e., cells alone and media alone
(without compound þ cells) and levofloxacin used as a reference stan-
dard. The plates were incubated at 37 °C for 24 h followed by ob-
servation of MIC were made. MIC determinations were performed in-
dependently using duplicate samples each time [31].
3.2. UV–Vis spectra
The UV–Vis spectra of ligand (L) and their lanthanide complexes
(1–5) were measured in the concentration of 10−4 mol/L using a DMSO
solvent at room temperature (Fig. 1). The ligand shows mainly three
absorption bands at 380, 435 and 457 nm [42]. The band at 380 nm is
due to π → π* transition within the aromatic ring. The absorption band
at 440 and 462 nm of ligand, are assigned to n → π* transition between
lone pair electron of azomethine (eC]N) group and a conjugated π
bond of the aromatic unit [43,44]. The absorption spectra of complexes
are similar to each other which concern resemblance in the structures of
complexes. The absorption bands at the presence of Ln(III) ions had
slight change and variable decrease in the intensity as compared to the
free ligand which indicates that the ligand has been the energy donor in
addition to the luminescence sensitizer of Ln(III) ions [45]. Lanthanide
ions do not lead to the absorption spectra of the complexes [46], con-
sidering that f-f transition is Laporte forbidden. They are supposed to be
weak due to the low molar absorption coefficient in the UV–Visible
region.
3. Results and discussion
In the existing investigation, five new Ln(III) complexes of synthe-
sized ligand (L) were prepared and characterized by different spectro-
scopic techniques. The synthesis of ligand was done by the one-step
condensation of sulfanilamide and 2-hydroxy-1-naphthaldehyde. The
lanthanide complexes formulated as [Ln(NO3)2(L)(H2O)2](H2O)x
3

S. Paswan, et al.
InorganicaChimicaActa513(2020)119955
Fig. 1. UV–Vis absorption spectra of Schiff base ligand (L) and their Ln(III)
complexes.
3.3. Molar conductance
The Ʌm values of the Ln(III) complexes in DMF solution at 25 °C
were estimated. The conductance of prepared complexes is in the range
reported for 1:1 electrolytes reveals that two nitrate ions occupy the
inner coordination sphere [47]. This is further supported by the results
obtained from IR and TGA analysis.
3.4. Mass spectrometry
The TOF-MS ES + spectral data of ligand (L) and its lanthanide -
compounds (1–5) were recorded and fragmentation patterns with m/
z have been indicated. The mass spectra of ligand (L) and their Ln(III)
complexes were displayed in (Fig. S2). The group of peaks observed in
the spectra of complexes is due to isotopes of metals. In the spectra of
complexes, the molecular ion peaks were observed at m/z 327.42
(calcd. 326.07), 625.42 (calcd. 626.87), 658.11 (calcd. 659.00), 636.73
(calcd. 637.98), 648.23 (calcd. 648.99), and 633.09 (calcd. 634.99) due
to [C17H14N2O3S] (L), [C17H17N4O11SNd] (1), [C17H17N4O11SYb] (2),
[C17H17N4O11SEu] (3), [C17H17N4O11SDy] (4) and [C17H17N4O11STb]
(5), respectively. In the spectra of Ln(III) complexes the base peak ob-
served due to fragments (C17H17NdN2O5S)+. at m/z 500.89 (calcd.
502.99) (1), (C17H17YbN2O5S)+. at m/z 533.86 (calcd. 535.02) (2),
Scheme 2. Fragmentation pattern of Eu(III) (3) derived from the TOF-MS
spectrum.
3.5. Computational studies
Several attempts have been made to acquire a single crystal for X-
rays studies but unfortunately, we did not get an appropriate crystal. In
the absence of a suitable single crystal for crystallographic studies, the
computation calculation became significant. The computational in-
vestigation helps in the authentication of experimental observation
with theoretical data. The molecular geometry suggested by different
experimental analysis was compared with the ground state optimized
geometry. The optimized ground state geometry was calculated by
using the DFT/B3LYP-SDD (d, f) method was illustrated in (Fig. 2). The
dipole moment, optimized energy and energy bandgap values are
summarized in Table 1. The molecular structure of ligand and their
neodymium, ytterbium complexes with the atom labeling scheme was
shown in (Fig. S3) and selected bond length and bond angle were
summarized in Table 2. Theoretically calculated values of important
bond lengths (LneO, Ln ← N, eC]N) and bond angles were compared
with X-ray crystallographic data of the similar type of lanthanide
complexes and it was found in a very close agreement [48] The stability
of complexes concerning ligand can also be predicted by observing the
energy gap of HOMO and LUMO. The HOMO (highest occupied mole-
cular orbital) energy reflects the capability to contribute an electron
while the LUMO (lowest unoccupied molecular orbital) as an electron
acceptor signifies the capability to get an electron. The HOMO and
LUMO of ligand and their Nd(III) (1) and Yb(III) (2) complexes are
(C17H17EuN2O5S)+
at
m/z
511.25
(calcd.
514.01)
(3),
(C17H17DyN2O5S)+ at m/z 521.89 (calcd. 525.01) (4) and
(C17H17TbN2O5S)+ at m/z 516.36 (calcd. 520.01) (5), respectively. All
the Ln(III) complexes contain different peaks observed at m/z 422.07
(calcd. 423.01) and 219.95 (calcd. 220.93) due to formation of different
fragments (C17H15NNdO3).+ and (CH5NdNO3).+ in (1), at m/z 453.34
(calcd. 455.04) and 231.06 (calcd. 234.96) due to formation of different
fragments (C17H15YbNO3).+ and (CH3YbNO2).+ in (2), at m/z 433.18
(calcd. 434.03) and 215.01 (calcd. 213.94) due to formation of different
fragments (C17H15EuNO3).+ and (CH3EuNO2).+ in (3), at m/z 443.88
(calcd. 454.03) and 221.45 (calcd. 224.95) due to formation of different
fragments (C17H15DyNO3).+ and (CH3DyNO2).+ in (4), whereas in
complex (5) these peaks observed at m/z 438.43 (calcd. 440.03) and
218.73 (calcd. 219.94) due to formation of different fragments
(C17H15TbNO3).+ and (CH3TbNO2).+. The different fragmentation
pattern of europium complexes (Fig. S2) has been suggested in Scheme
2.
4

S. Paswan, et al.
InorganicaChimicaActa513(2020)119955
Fig. 2. The optimized ground state geometry of the ligand (L) and their Ln(III) complexes at the B3LYP/SDD (d, f) level of theory.
shown in (Fig. 3). The reactivity and stability of the complexes are
related to the energy bandgap. The obtained energy gap (ΔE) values of
optimized Ln(III) complexes suggest that the ytterbium complex is less
stable than the neodymium complex.
3.6. Fluorescence study
The fluorescence properties of Ln(III) complexes (1.0 × 10−5 M in
DMSO) were analyzed at room temperature and spectra of the com-
plexes were obtained upon excitation at 300 nm. The fluorescence
Table 1
Computed electronic properties of Schiff base ligand (L) and their Ln(III) complexes.
S. No.
Compound
Total energy (eV)
Dipole moment (D)
HOMO (eV)
LUMO (eV)
HOMO-LUMO Energy gap (eV)
1.
2.
3.
L
−37,806.87
−72,434.51
−88,705.87
5.38
−6.25
−2.67
−3.58
−0.60
−0.52
Nd(III) (1)
Yb(III) (2)
25.20
26.38
−15.95
−16.03
−15.35
−15.51
5

S. Paswan, et al.
InorganicaChimicaActa513(2020)119955
Table 2
Table 3
Selected structural parameters for ligand (L), Nd(III) (1) and Yb(III) (2) at DFT/
Fluorescence spectral data of Ln(III) complexes in DMSO solution at room
temperature.
B3LYP level of theory.
Complexes
Bond length (Ǻ)
Bond angle (°)
S. No.
Compound
λex(nm)
ʋ(cm−1
33,333
33,333
33,333
33,333
)
λem(nm)
Assignment
(L)
19C = 21N
21N-22C
22C-24C
22C-23C
19C-11C
11C-4C
1.312
1.416
1.408
1.407
1.438
1.451
1.413
1.357
2.334
1.294
2.299
2.290
2.299
2.305
2.305
1.352
1.433
2.334
1.294
2.299
2.290
2.305
1.433
2.305
1.352
1.360
17O-14C-11C
17O-14C-15C
14C-11C-19C
4C-11C-19C
121.919
116.850
119.298
121.802
122.156
122.780
117.673
122.702
96.039
95.957
113.595
77.631
65.891
67.678
80.848
128.490
89.437
77.631
65.891
144.061
80.848
96.039
95.957
128.490
171.025
94.394
1.
Nd(III) (1)
490
550
695
440
545
695
482
545
695
490
545
593
691
π* → π
300
4G7/2
4G5/2
→
→
4I9/2
4I9/2
2.
3.
4.
Eu(III) (3)
Dy(III) (4)
Tb(III) (5)
π* → π
11C-19C-21N
19C-21N-22C
21N-22C-23C
21N-22C-24C
300
5D0
→
→
7F1
5D0
7F2
11C-14C
π* → π
14C-17O
300
4F9/2
4F9/2
→
→
6H13/2
6H13/2
Nd(III) (1)
Yb(III) (2)
31Nd-19N
19N = 18C
31Nd-44O
31Nd-17O
31Nd-41O
31Nd-38O
31Nd-40O
38O-50N
31Nd-40O-50N
31Nd-38O-50N
40O-50N-51O
44O-31Nd-19N
44O-31Nd-17O
19N-31Nd-41O
19N-31Nd-17O
19N-31Nd-40O
19N-31Nd-39O
43O-51Yb-19N
43O-51Yb-17O
43O-51Yb-40N
17O-51Yb-19N
51Yb-39O-49N
51Yb-37O-49N
19N-51Yb-39O
19N-51Yb-37O
43O-51Yb-37O
π* → π
300
5D4
5D4
5D4
→
→
→
7F5
7F4
7F3
1C-17O
51Yb-19N
19N = 18C
51Yb-43O
51Yb-17O
51Yb-39O
17O-1C
51Yb-37O
37O-49N
49N-50O
emission bands of the Ln(III) complexes have been exemplified in
Table 3. A characteristic emission band was observed approximately at
490 nm in neodymium, ytterbium and approximately at 425 nm in
europium, dysprosium and terbium complexes, attributed to π* → π
electron transitions of the aromatic Schiff base ligand [49] (Fig. 4). The
luminescent properties of lanthanide complexes are due to the in-
tramolecular energy transfer from the lowest energy level of the triplet
state of the organic ligand to the resonance energy level of the lan-
thanide ions [50]. The augmentation of luminescence intensity is based
on the essence of the lanthanide ion that was in the order Eu(III) > Dy
(III) > Tb(III) > Yb(III) > Nd(III) [51]. Upon the excitation, Nd(III)
(1) complex exhibit three characteristic emission peaks in the region
490–700 nm corresponding to π* → π (490 nm), 4G7/2 → 4I9/2 (550 nm)
Fig. 4. Emission spectra of lanthanide complexes at λexc = 300 nm in DMSO
solution (1.0 × 10−5 M) at room temperature.
Fig. 3. Energy diagram of frontier molecular orbitals HOMO and LUMO of ligand (L), Nd(III) (1) and Yb(III) (2) complexes derived from DFT calculations using
B3LYP/SDD (d, f) level of theory.
6

S. Paswan, et al.
InorganicaChimicaActa513(2020)119955
4
and G5/2
→
4I9/2 (695 nm), transitions [45,52]. The Eu(III) (3) com-
and Tb(III) (5) complexes have been outlined in Table 4. The result
specifies that ligand shows moderate activity against S. aureus, K.
pneumoniae and P. aeruginosa with MIC 32 µg/mL and no activity
against E. Coli as well as A. baumanni (MIC > 64 µg/mL). The Dy(III)
and Tb(III) complexes showed high activity against S. aureus with MIC
16 µg/mL. Eu(III) complex showed less activity against S. aureus and no
activity against E. coli, K. pneumonia, A. baumanii and P. aeruginosa. The
Dy(III) complex demonstrated moderate activity against E. coli, A.
baumanii and P. aeruginosa with MIC 32 µg/mL and less activity against
K. pneumonia. The complex Tb(III) exhibits less activity against P. aer-
uginosa and no action against E. coli, K. pneumonia and A. baumanii. The
activity of these compounds was compared with standard antibiotic
levofloxacin, which shows that these complexes have less activity
compared to the standard drug. The larger activity of Ln(III) complexes
as compared to Schiff base ligand could be described on the basis of
Overtone’s concept [57] and Tweedy’s chelation theory [58]. This
theory concern delocalization of π-electrons in the whole chelate ring
because of this positive charge at metal ions reduces and the lipophi-
lic character of metal chelate rises, which favors its permeation over the
lipid layer of bacterial membranes [59].
plex displays three characteristic peaks in the region 440–708 nm.
These emission peaks are attributed to π* → π (440 nm), 5D0
→
7F1
(545 nm) and 5D0
→
7F2 (695 nm), transitions. In Dy(III) (4) complex
three narrow emission peaks are observed in the range of 482–700 nm
4
which is attributed to π* → π (482 nm), F9/2
→
6H13/2 (545 nm) and
4F9/2
→
6H11/2 (695 nm), transitions [53]. The Tb(III) (5) complex
exhibits four emission peaks in the range of 490–691 nm attributed to
π* → π (490 nm), 5D4 → 7F5 (545 nm), 5D4 → 7F4 (593 nm), 5D4 → 7F3
(691 nm), transitions [32]. Inspection of Nd(III), Yb(III), Eu(III), Dy(III)
and Tb(III) complexes exhibit the characteristic emission spectra of the
Ln(III) ions, respectively, which concern ligand act as good organic
chromophore that can be used to absorb and transfer energy to the Ln
(III) ions (Fig. S4).
3.7. Thermal behavior
The thermal study of ligand (L) and Eu(III) (3), Dy(III) (4) and Tb
(III) (5) complexes were performed under nitrogen atmosphere in the
temperature range from 30 to 700 °C (Fig. S5). TGA results showed that
ligand is thermally stable in the temperature range from 30 to 185 °C.
The decomposition start at 185 °C and completed at 700 °C with two
decomposition steps. A sharp endo peak observed in DTA curve around
272 °C may be due to loss of moisture and other two endo peaks around
315 °C and 505 °C due to loss of ligand [54,55]. The thermal behaviors
of all the complexes are almost same. The comparative TGA scans of
ligand and their lanthanide complexes were shown in (Fig. 5). The
coordinated water and lattice water molecules was decomposed below
100 °C with a good agreement between the calculated and found values
(11.30% calcd, 12.01% found for Eu(III); 11.11% calcd, 11.51% found
for Dy(III); 8.51% calcd, 9.77% found for Tb(III)). The coordinated
nitrate molecules decomposed around 300 °C with a weight loss of
(19.46% calcd, 19.81 found for Eu(III); 19.13% calcd, 20.23 found for
Dy(III); 19.55% calcd, 16.33% found for Tb(III)). A major level de-
composition occurred with temperature range from 300 to 700 °C due
to loss of organic moiety with the weight loss of about 25.86% for Eu
(III); 29.74% for Dy(III) and 36.80% for Tb(III) complexes. Finally,
these processes were followed by the last step, in which, oxidation of Ln
(III) complexes occurs to give the corresponding oxide as residue [56].
4. Conclusion
A sulfanilamide and naphthaldehyde derivative ligand was synthe-
sized and characterized. The bidentate N O donor Schiff base ligand was
used to synthesize five new lanthanide (III) complexes with Nd, Yb, Eu,
Dy and Tb. The structure of newly synthesize complexes were de-
termined by elemental analysis, molar conductance, FT-IR, UV–Vis
spectroscopy and mass spectrometry as well as TGA technique. The
experimental investigation supports mononuclear 1:1 metal to ligand
ratio with eight coordination central metal ion in lanthanide complexes.
The optimized ground state geometries of complexes by DFT calcula-
tions further validates the coordination of metal center. The anti-
bacterial studies reported in form of MIC value which show moderate to
low activity of lanthanide complex. The emission spectra of complexes
indicated the luminescence properties of all lanthanide complexes due
to lanthanide ions present at the center.
CRediT authorship contribution statement
3.8. Antibacterial activity
Sikandar Paswan: Methodology, Conceptualization, Investigation,
The result of antibacterial action of ligand (L), Eu(III) (3), Dy(III) (4)
Writing
- original draft, Funding acquisition, Resources. Nitesh
Jaiswal: Formal analysis, Writing - review & editing. Vishnu Kumar
Modanawal: Methodology, Visualization. Manoj Kumar Patel:
Methodology, Resources. Rana Krishna Pal Singh: Supervision,
Conceptualization.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgments
We gratefully acknowledge the Department of Chemistry,
University of Allahabad, Allahabad, for providing laboratory facilities.
The author (Sikandar Paswan) is very thankful to UGC, New Delhi for
financial support in the form of senior research fellowship (SRF). The
authors also acknowledge CDRI Lucknow for antibacterial screening,
MRC-MNIT Jaipur for IR, Mass, fluorescence analysis and BHU Varanasi
for TGA and UV-Vis analysis.
Fig. 5. The comparative TGA-DTA curve of ligand (L) and their Ln(III) com-
plexes.
7

S. Paswan, et al.
InorganicaChimicaActa513(2020)119955
Table 4
Minimum Inhibitory Concentration (MIC) of Schiff base ligand (L) and their Ln(III) complexes.
Sr. No.
Compound
MIC (µg/mL)
Gram −ve
E. Coli
Gram +ve
P.aeruginosa
K.pneumoniae
A.baumanni
S. aureus
1.
2.
3.
4.
5.
6.
DMSO
0.0
0.0
32
0.0
0.0
0.0
32
L
> 64
> 64
32
32
> 64
> 64
32
Eu(III) (3)
Dy(III) (4)
Tb(III) (5)
Levofloxacina
> 64
32
> 64
64
64
16
> 64
0.0156
64
> 64
64
> 64
8
16
1
0.25
a
standard drug.
Appendix A. Supplementary data
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