Page 1 of 25
European Journal of Applied Sciences – Vol. 11, No. 4
Publication Date: August 25, 2023
DOI:10.14738/aivp.114.15168
Titah, J. T., Yang, L., Sheets, T., Fan, H. J., McLoud, J. D., Karime, C. W., & Stewart, T. (2023). Design of New N-Salicylidene Alanine
Transition Metal Schiff-Base Complexes with Zn (II), Mn (II), Fe (II), and Fe (III): Synthesis, Characterization, Toxicity, and
Computational Studies of the Potential Metal-Ligand Binding Sites. European Journal of Applied Sciences, Vol - 11(4). 78-102.
Services for Science and Education – United Kingdom
Design of New N-Salicylidene Alanine Transition Metal Schiff- Base Complexes with Zn (II), Mn (II), Fe (II), and Fe (III):
Synthesis, Characterization, Toxicity, and Computational
Studies of the Potential Metal-Ligand Binding Sites
James Tembei Titah
Department of Chemistry, Science and
Mathematics, Tabor College, Hillsboro, KS, USA
Liang Yang
College of Chemical Engineering, Sichuan University
of Science and Engineering, Zigong, PR China
Tara Sheets
Department of Chemistry, Science and
Mathematics, Tabor College, Hillsboro, KS, USA
Hua Jun Fan
College of Chemical Engineering, Sichuan University
of Science and Engineering, Zigong, PR China
Josh Daniel McLoud
Department of Biology and Kinesiology,
LeTourneau University,Longview, TX, USA
Coulibaly Wacothon Karime
Department of Mathematics, Physics and Chemistry,
University of Peleforo Gon Coulibaly, Korhogo, Ivory Coast
Tobias Stewart
Department of Chemistry,Science and Mathematics,
Tabor College, Hillsboro, KS, USA
ABSTRACT
We have proposed the structures and potential metal-ligand binding sites of four N- Salicylidene alanine transition metal Schiff-base complexes with Zn (II), Mn (II),
Fe(II) and Fe(III) using both experimental and computational methods. Different
models of the structures were fully optimized and analyzed using density functional
theory (DFT) B3LYP method and the binding modes revealed that models 4a, 5c, 6c,
and 7f correspond to complexes I, II, III, and IV respectively. The geometry adopted
are tetrahedral, trigonal bipyramidal, octahedral, and octahedral respectively for
complexes I, II, III, and IV. Characterization of the complexes were done using
Page 2 of 25
79
Titah, J. T., Yang, L., Sheets, T., Fan, H. J., McLoud, J. D., Karime, C. W., & Stewart, T. (2023). Design of New N-Salicylidene Alanine Transition Metal
Schiff-Base Complexes with Zn (II), Mn (II), Fe (II), and Fe (III): Synthesis, Characterization, Toxicity, and Computational Studies of the Potential
Metal-Ligand Binding Sites. European Journal of Applied Sciences, Vol - 11(4). 78-102.
URL: http://dx.doi.org/10.14738/aivp.114.15168
melting point/decomposition temperatures, solubility test, FT-IR and UV-visible
spectroscopy. All the complexes were seen to have a different melting point from
the amino acid; alanine, which was used in the synthesis. The complexes were
soluble in water and most polar solvents, which is important for intended use in
biological systems as drugs. In addition, the experimental and calculated IR spectra
of the complexes revealed prominent stretching frequencies including the -C=N- imine group that are similar within 5-10 % margin to the most stable structures 4a,
5c, 6c, and 7f. Furthermore, the UV-visible studies of complex I showed three
prominent electronic transitions, two prominent transitions for complex II, three
prominent transitions for complex III and three prominent transitions for complex
IV in both the experimental and computational model structures. These electronic
transitions were assigned to the π →π* and HOMO-1→ LUMO+2, HOMO-4→LUMO,
HOMO→ LUMO for complex I, π→ π* and HOMO-5→LUMO-5, HOMO →LUMO+1 form
complex II, 2T2g → 2Eg, π → π* and HOMO-2 →LUMO+1, and HOMO→LUMO+1 for
complex III, π→π* and HOMO-3→ LUMO+1, HOMO-3→LUMO for complex IV. The
complexes were non-toxic towards prokaryotic gram positive (Staphylococcus
aureus, Staphylococcus epidermis, Streptococcus mutants) and gram negative
(Aquaspirillum serpens Escherichia coli) bacterial and eukaryotic (Saccharomyces
cerevisiae) bacterial.
Keywords: Design, Synthesis, N-Salicylidene Alanine, Density functional Theory, Toxicity
INTRODUCTION
The recent study and development of new therapeutic schiff-base complexes in the field of bio- inorganic chemistry, biochemistry and medicinal chemistry has been in an exponential growth
over the years. This is because most of these schiff-base complexes play an important role in
biological systems owing to the presence of the imine or azomethine group and the recognition
that many of these complexes can be used as models that could mimic and/or interact with
biologically important molecules for the mitigation, control and/or cure of many diseases.
Previous research has shown that schiff-bases derived from amino acids contain bidentate or
multidentate binding sites to transition metals and biomolecules with application in drug
design and development. These metal complexes can be synthesized through the reaction
between the Schiff-base ligands derived from amino acids and a metal precursor in a suitable
solvent and under different experimental conditions. Many Schiff-base complexes show
excellent catalytic and biological activity in various reactions such as polymerization reactions,
reduction of thionyl chloride, oxidation of organic compounds, reduction of ketones, aldol
reactions, Henry reaction, epoxidation etc, which gives us the need and motivation to expand
the synthesis of schiff-base ligands derived from amino acids and their subsequent binding to
transition metals. In addition, schiff-base complexes have been used industrially and exhibit a
wide range of biological activities and/or properties such as anti-fungal, anti-malarial, anti- bacterial, anti-diabetic, anti-cancer, anti-proliferative, anti-tumor, antimicrobial, antioxidant,
etc agents including their use as dyes and insecticides. Schiff-bases and their complexes also
have the ability to interact with DNA to mitigate or control different diseases [1-13]. The
discovery of cisplatin, auranofin, and other chemotherapeutic drugs in the early 1990s, the
exploration of the binding between schiff-bases and metals as potential drug candidates has
continued to motivate scientists in the process of drug development, design and discovery [14-
17]. In this paper, we will present routes towards the development and design of new
Page 3 of 25
Services for Science and Education – United Kingdom 80
European Journal of Applied Sciences (EJAS) Vol. 11, Issue 4, August-2023
compounds synthesized between Schiff-bases derived from salicylaldehyde, alanine and their
binding to transition metals. The transition metals used in this research are Zn (II), Mn(II),
Fe(II), and Fe(III). In addition, we will determine the toxicity of these compounds and the
potential binding modes between the Schiff-bases and the metals using computational B3LYP
density functional theory (DFT) method. The characterization of the complexes will include
melting/decomposition temperatures, solubility in different solvents, Fourier Transform Infra- red spectroscopy (FT-IR), ultra violet-visible spectroscopy (UV-Vis), etc. The computational
DFT studies will compare the results with the experimental results and predict the possible
binding sites in the complexes.
EXPERIMENTATION
All the chemicals and solvents mentioned in this paper were used as purchased without any
modification and all the complexes were synthesized in-situ.
Synthesis of N-Salicylidene Alanine Zn (II) Complex [N-S-ala-Zn (II)]-I
Sodium hydroxide (NaOH; 0.0112 mols) and alanine (C3H7NO2; 0.0112 mols) were completely
dissolved in a 250 mL beaker containing 30.0 mL of water with the help of a magnetic stirrer at
room temperature. An equimolar amount of salicylaldehyde (0.0112 mols) was added drop
wise to the resulting mixture while stirring continuously for 45 minutes. A 30.0 mL aqueous
solution of zinc (II) chloride heptahydrate (ZnCl2.7H2O; 0.0056 mols) was slowly added onto
the resulting solution and allowed to react for an additional 45 minutes in the fume hood. The
resulting mixture was concentrated to about 60 % of the original volume to initiate
crystallization. The mixture was allowed in the fume hood for three days and the resulting
yellow powder was filtered through suction, air dried and stored in a vial for subsequent
characterization. The percentage yield was 80 %.
Synthesis of N-Salicylidene Alanine Mn (II) Complex [N-S-ala-Mn (II)]-II
Similarly, (NaOH; 0.0112 mols) and alanine (C3H7NO2; 0.0112 mols) were completely dissolved
in 40.0 mL of water in a 250 mL beaker with the help of a magnetic stirrer at room temperature.
An equimolar amount of salicylaldehyde (0.0112 mols) was added drop wise to the mixture
allowed to for 40 minutes. A 20.0 mL aqueous solution of anhydrous manganese (II) chloride
(MnCl2; 0.0056 mols) was slowly added onto the resulting mixture and allowed to react for an
additional 1 hour in the fume hood. The mixture was allowed in the fume hood for four days
and the resulting yellow powder was filtered via suction, recrystallized in ethanol-water
mixture (50/50), air dried and stored in a vial for subsequent characterization. The percentage
yield was 85 %.
Synthesis of N-Salicylidene Alanine Fe (II) Complex [N-S-ala-Fe (II)]-III
Sodium hydroxide (NaOH; 0.0112 mols) and alanine (C3H7NO2; 0.0112 mols) were completely
dissolved in 40.0 mL of water in a 250 mL beaker with the help of a magnetic stirrer at room
temperature. An equimolar amount of salicylaldehyde (0.0112 mols) was then added drop wise
to the resulting mixture allowed to react for 50 minutes. A 30.0 mL aqueous solution of Iron (II)
chloride monohydrate (FeCl2.H2O; 0.0056 mols) was slowly added onto the above mixture and
allowed to react for an additional 1 hour in the fume hood. The mixture was concentrated to
about 55 % of its original volume and allowed in the fume hood for five days. The resulting light
Page 4 of 25
81
Titah, J. T., Yang, L., Sheets, T., Fan, H. J., McLoud, J. D., Karime, C. W., & Stewart, T. (2023). Design of New N-Salicylidene Alanine Transition Metal
Schiff-Base Complexes with Zn (II), Mn (II), Fe (II), and Fe (III): Synthesis, Characterization, Toxicity, and Computational Studies of the Potential
Metal-Ligand Binding Sites. European Journal of Applied Sciences, Vol - 11(4). 78-102.
URL: http://dx.doi.org/10.14738/aivp.114.15168
red powder was filtered via suction, recrystallized in ethanol-water mixture (60/40), air dried
and stored in a vial for subsequent characterization. The percentage yield was 87 %.
Synthesis of N-Salicylidene Alanine Fe (III) Complex [N-S-ala-Fe (III)]-I
Sodium hydroxide (0.0112 mols) and alanine (0.0112 mols) were dissolved in a 250 mL beaker
containing 40.0 mL of water while stirring continuously with the help of a magnetic stirrer at
room temperature. An equimolar amount of salicylaldehyde (0.0112 mols) was added drop
wise to the resulting mixture while stirring. The reaction was allowed to go on for 45 mins and
a 30.0 mL aqueous solution of Iron (III) chloride pentahydrate (FeCl3.5H2O; 0.0056 mols) was
slowly added onto the resulting solution and allowed to react for an additional 45 minutes in
the fume hood. The resulting mixture was concentrated to 60 % of the original volume to initiate
crystallization. After four days, a dark purple powder was filtered through suction,
recrystallized in ethanol-water mixture (50/50), air dried and stored in a vial for subsequent
characterization. The percentage yield was 90 %.
Toxicity Test of the Complexes
The Kirby-Bauer assay was used to test the toxicity of the complexes for bacterial growth
against the following gram-positive and gram-negative bacterial species: Aquaspirillum serpens,
Escherichia coli strain K12, Saccharomyces cerevisiae strain Alpha 1, Staphylococcus aureus,
Staphylococcus epidermis, and Streptococcus mutants. The Kirby-Bauer assay is one of the most
sensitive tests used for bacterial growth against prokaryotes and eukaryotes in microbiology
[18-19].
In this paper, an aqueous solution of the complexes (N-Salicylidene alanine Zn (II)-I, N- Salicylidene alanine Mn (II)-II, N-Salicylidene alanine Fe (II)-III, and N-Salicylidene alanine Fe
(III)-IV were prepared with a slightly higher antibiotic concentration (1.0 μM) than those used
in the Kirby-Bauer assay (30.0 μg). The antimicrobial and antimicrobial-free discs used in this
research were purchased from Becton, Dickinson and Company located in New Jersey. The
antimicrobial-free discs were placed in a sterile 2.0 mL microcentrifuge tube containing the
aqueous solution of each compound to be tested and centrifuged for 5 minutes at 12,000 x g to
remove all air bubbles from the discs. The discs were stored over-night at room temperature
before being transferred onto the culture plates. Each compound in the disk was placed at
intervals of more than 24 mm apart, center to center, on the same 100 mm inoculated Mueller- Hinton culture plate. There were three culture plates of the same organism tested per sample,
these served as biological replicates in case there was inhibition of organism growth. The
incubated plates were observed in log phase of growth to prevent bacteria with slower growth
from skewing results [20].
Computational Method
The computational method used in this paper was the density functional theory (DFT)
technique B3LYP embedded in G09 with 6-31G(d,p) all electron basis set [21-25]. The structural
geometries were fully optimized and all elements were analyses using this basis set with the
exception of metals, which used the LANL2DZ basis set for the valence electrons with the
corresponding effective core potentials (ECPs). The lowest energy structure conformations
were confirmed by separate frequency calculations using the same method and basis set [26-
30]. The UV-Visible absorption spectra simulated using TD-DFT method and infrared (IR)
Page 5 of 25
Services for Science and Education – United Kingdom 82
European Journal of Applied Sciences (EJAS) Vol. 11, Issue 4, August-2023
spectra of the complexes were all modeled from the most stable conformation of the optimized
structures [31-, 35]. The calculated spectra of the different structural geometries would be
compared to the experiment results to determine the potential binding mode of the alanine
Schiff-base ligands to the transition metal centers. The geometric parameters (bond lengths and
bond angles) of the most stable optimized structures are shown in Table S1 of the supporting
materials.
RESULTS AND DISCUSSION
Melting Point/Decomposition Temperature and Reaction Time
The first characterization technique of a synthesized compound is to determine the
melting/decomposition and/or boiling point. The melting points/decomposition temperatures
of our compounds were determined using the digital melting point apparatus and this were
compared to the melting point/decomposition temperatures of the amino acid (alanine) from
which they were synthesized. The melting points/decomposition temperatures of all our
complexes were different from the melting point of the amino acid use, indicating that new
compounds were synthesized. The melting point of alanine was observed at a precise and sharp
temperature of 300 °C compared to N-Salicylidene alanine Zn(II) complex-I that melts at a
temperature below 250 °C while changing colour from white to yellow, N-Salicylidene alanine
Mn(II) complex-II melts below 350 °C and changes colour from yellow to orange, N-Salicylidene
alanine Fe(II)-III complex melts below 250 °C with colour changing from light red to dark red,
N-Salicylidene alanine Fe (III)-IV complex decompose at temperatures below 250 °C while
changing colour from dark purple to black. The results of melting point/decomposition
temperatures of the complexes are presented in Table 1
Table 1: Melting point/Decomposition Temperature and Reaction Times of the
complexes
Complex M.Pt/Decomp.T/°C Reaction Time /mins Yield (%) Colour
N-S-ala-Zn (II)-I 250 110 80 yellow
N-S-ala-Mn (II)-II 350 120 85 yellow
N-S-ala-Fe (II)-III 250 130 87 light red
N-S-ala-Fe (III)-IV 250 110 90 dark purple
Alanine 300 - - white
Solubility Test
Solubility of compounds is one of the fundamental requirements to ascertain the effectiveness
of a compound intended to be used as a drug. The solubility of our complexes was determined
in different solvents and the results will enable us to perform other techniques. This was done
manually by dissolving approximately 0.100 g sample of each complex in approximately 10.00
mL of solvent. The solubility results are presented in table 2. It is important to note that our
complexes were all soluble in water and other polar solvents and insoluble in non-polar
solvents with increased solubility of the complexes observed in a warmer solvent.
Page 6 of 25
83
Titah, J. T., Yang, L., Sheets, T., Fan, H. J., McLoud, J. D., Karime, C. W., & Stewart, T. (2023). Design of New N-Salicylidene Alanine Transition Metal
Schiff-Base Complexes with Zn (II), Mn (II), Fe (II), and Fe (III): Synthesis, Characterization, Toxicity, and Computational Studies of the Potential
Metal-Ligand Binding Sites. European Journal of Applied Sciences, Vol - 11(4). 78-102.
URL: http://dx.doi.org/10.14738/aivp.114.15168
Table 2: Solubility of the Complexes
Complexes Water Ethanol methanol chloroform hexane D2O
N-S-ala-Zn (II)-I s S Ss I i s
N-S-ala-Mn (II)-II s S Ss I i s
N-S-ala-Fe (II)-III s S Ss I i s
N-S-ala-Fe (III)-IV s S Ss I i s
s = soluble; i = insoluble; ss = sparingly soluble
Fourier Transform Infra-red (FT-IR) Spectra of the Complexes
Fourier transform infrared (FT-IR) spectroscopy was used to determine the vibrations of the
atoms in the complexes. This will enable us to identify the different stretching frequencies of all
the functional groups and other atoms present in the complexes. This was done using a FLUKA
table top FT-IR instrument. The IR results of the prominent peaks measured in wavenumbers
(cm-1) are shown in table 3. The FT-IR spectra of the transition metal complexes reveal that the
different Schiff-base ligands bind to the metal centers in a multidentate form, in which the
coordinate bond takes through the nitrogen atom of the imine (C=N) group, deprotonated the
aromatic-O- (hydroxyl group), deprotonated Ac-O- (carboxylate group), water, and/or counter
anionic ligands to the transition metal ions. In all the complexes, a slight shift in the strong
azomethine (C=N) stretching frequencies is due to the distorted structures or geometries
adopted when the ligands bind to the metal centers. Generally, the weaker stretching
frequencies were observed for the deprotonated aromatic-O- (hydroxyl group), Ac-O-
(carboxylate group), water, and/or the counter anion.
The imine ν(C=N) stretching frequency was observed between 1646-1655 cm-1 in complex I,
1596-1631 cm-1 in complex II, 1560-1655 cm-1 in complex III, and 1541-1521 cm-1 in complex
IV. The aromatic and aliphatic ν(C-H) stretching vibrational bands were seen at 3062 cm-1 and
2900 cm-1 respectively in complex I, 3060 cm-1 and 2900 cm-1 respectively in complex II, 3054
cm-1 (aromatic) in complex III, 2977 cm-1 (aromatic) for complex IV. The symmetric or
asymmetric ν(O-H) vibrates at 3468 cm-1 in complex I, 3180-3367 cm-1 in complex II, 3240 cm- 1 in complex III, 3225 cm-1 in complex IV. The ν(C-O) group vibrates at a stretching frequency of
1465 cm-1 in complex I, 1442 cm-1 in complex II, 1442 cm-1 in complex III, 1466 cm-1 in complex
IV. The carbonyl ν(C=O) stretching frequency was seen at 2750 cm-1 for complex I, between
2250-2642 cm-1 in complex II, between 2345-2374 cm-1 in complex III, between 2281-2374 cm- 1 in complex IV. We observed a slight shift in the vibrational frequencies of all the functional
groups in all the complexes and this is due to the distorted structures after coordination to the
central metal ion when compared to literature values [1,5,11-13].
Page 11 of 25
Services for Science and Education – United Kingdom 88
European Journal of Applied Sciences (EJAS) Vol. 11, Issue 4, August-2023
example, Zn-O bond lengths in 4c and 4d has an elongation of 0.03 to 0.11 Å when compared
to 4a and 4b. Furthermore, the greatest structural changes in bond lengths were observed in
structure 4e. For example, the Zn-O and Zn-N bond lengths in 4e show an elongation of 0.14 to
0.24 Å when compared to 4a. This implies that bond lengths increase with coordination or
complexity of the complexes.
Generally, it was observed that the C-O-Zn bond angles were much larger than the O-Zn-N bond
angles. The presence of H2O and Clligands bonded to Zn (II) causes a decrease in the C-O-Zn
and O-Zn-N bond angles. For example, in structure 4a, the bond angle of C1-O1-Zn is 125.46°
while the bond angle of O1-Zn-N1 is 95.42°. Similarly, in structure 4c, the C1-O1-Zn bond angle
is 126.63° while the bond angle of O1-Zn-N1 is 93.37°. In the octahedral coordinated structure
4e, the C1-O1-Zn bond angle reaches a maximum value of 132.23° while the O1-Zn-N1 bond
angle reaches a minimum value of 81.83°.
The IR spectra of structures 4a – 4e were computed and the results are shown in Figure 5.
Comparing the experimental (Figure 2) and calculated IR spectra of N-S-ala-Zn (II) complex
(figure 4), we can see the profile of calculated IR spectra of 4a closely resembles the
experimental IR spectra of complex I. Similarly, the IR stretching frequency observed at 1797
cm-1 was assigned to the carbonyl ν(-C=O) group, the stretching frequency observed at 1692
cm-1 was assigned to the imine ν(-C=N-) functional group, and the peaks observed at 500 cm-1
and 717 cm-1 were assigned to the rocking vibration modes of water. Various peaks around
3500 - 3800 cm-1 were assigned to symmetric vibration of water. While the absolute values of
the calculated IR peaks differ slightly from the experimental values, the peak at 1797 cm-1 for
the imine ν(-C=N-) functional group and the O-H peaks at 500, 1700 and 3500 cm-1 regions
agree well with the experiment results [10-11].
Figure 5: The calculated IR spectra of model structures 4a – 4e.
Page 23 of 25
Services for Science and Education – United Kingdom 100
European Journal of Applied Sciences (EJAS) Vol. 11, Issue 4, August-2023
eukaryotic (Saccharomyces cerevisiae) bacterial. This is a very important consideration for the
design and development of a potential drug candidate.
ACKNOWLEDGEMENT
We are highly indebted to Tabor College for providing the laboratory space and chemicals used
in this research. We thank Dr. James Bann, Department of Chemistry at Wichita State University
for providing access in the IR, and UV-visible instruments used for the characterization of our
compounds. We also give thanks to the High-Performance Computing Center at the Sichuan
University of Science and Engineering for the computational resources used in this research.
Partial financial support comes from Science Foundation of Sichuan University of Science &
Engineering (2020RC06) and Sichuan Provincial Natural Science Foundation (SYZ202133 &
22RCYJ0029).
References
[1] Prakash, A.; Adhikari, D. Application of Schiff bases and their metal complexes-A Review. Int. J. ChemTech Res.
2011, 3, 1891−1896.
[2] Ahmed, M.; Abu-Dief and Mohamed, M. A. (2015), A Review on Versatile Applications of Transition Metal
Complexes Incorporating Schiff Bases. SUEF University Journal of Basic and Applied Sciences, (4): 119-133.
[3] Abdel-Rahman, L. H.; El-Khatib, R. M.; Nassr, L.A.E.; Abu-Dief, A.M.; Ismael, A. Abdou Seleem, 2014,
Spectrochim Acta, 117A (2014), p. 366
[4] Loehrer, P. J.; Einhorn, L. H. Cisplatin. Ann. Intern. Med. 1984, 100, 704−713.
[5] James, T. T.; Tara, S.; Liang, Y.; Hua, J.F.; Josh, D. M.; Lizhi, O.; Zoe, B. Comparative Analysis of the Experimental,
Computational, and Bacterial Growth Inhibition Studies on the Structure of N-Salicylidene Alanine Ni (II)
Complex. SJC-Advances in Materials. Vol. 10, No. 5, 2022, pp. 144-151
[6] Yousif, E.; Majeed, A.; Al-Sammrrae, K.; Salih, N.; Salimon, J.; Abdullah, B. Metal complexes of Schiff base:
preparation, characterization and antibacterial activity, Arabian J. Chem. 2017, 10, S1639-S1644
[7] Al Zoubi, W.; Al-Hamdani, A. A. S.; Ahmed, S. D.; Ko, Y. G. Synthesis, characterization, and biological activity of
Schiff base metal complexes. J. Phy. Org. Chem. 2018, 31, No. e3752
[8] Iftikhar, B.; Javed. K.; Khan, M. S. U.; Akhter, Z.; Mirza, B.; McKee, V. Synthesis, Characterization and biological
assay of Salicyaldehyde Schiff base Cu (II) complexes and their precursors. J. Mol. Struct. 2018, 1155, 337-348
[9] Malik, M. A.; Dar, O. A.; Gull, P.; Wani, M. Y.; Hashmi, A. A. Heterocyclic Schiff base transition metal complexes
in antimicrobial and anticancer chemotherapy. MedChemCom 2018, 9, 409-436
[10] Zhu, X.; Wang, C.; Dang, Y.; Zhou, H.; Wu, Z.; Liu, Z.; Ye, D.; Zhou, Q. The Schiff base Ni Salicylidene-O, S- dimethylthiophosphoryimine and its metal complexes, synthesis, characterization and insecticidal activity
studies. Synth. React. Inorg. Met. -Org. Chem. 2000, 30, 625-636, Bloino, J.; Biczysko, M.; Barone, V.
“Anharmonic Effects on Vibrational Spectra Intensities: Infrared, Raman, Vibrational Circular Dichroism and
Raman Optical Activity,” The Journal of Physical Chemistry A, 2015, 119, 11862–11874.
[11] Hassan, A; Said A. Importance of O-Vanillin Schiff Base Complexes. Adv. J. Chem., Sect. A 2020, 4, 87-103, J.
Bloino, M. Biczysko and V. Barone, “General perturbative approach for spectroscopy, thermodynamics and
kinetics: Methodological background and benchmark studies,” JCTC 8 (2012) 1015-1036.
Page 25 of 25
Services for Science and Education – United Kingdom 102
European Journal of Applied Sciences (EJAS) Vol. 11, Issue 4, August-2023
[28] De Castro, E.V. R.; and Jorge, F. E. “Accurate universal gaussian basis set for all atoms of the periodic table,”
1998, pp 5225-29.
[29] Zerner, M.C.; Lowe, G.H.; Kirchner, R.F.; and Mueller-Westerhoff, U.T. “An Intermediate Neglect of Differential
Overlap Technique for Spectroscopy of Transition-Metal Complexes. Ferrocene,” J. Am. Chem. Soc., 102 (1980)
589-99.
[30] Sosa, C.; Andzelm, J.; Elkin, B.C.; Wimmer, E.; Dobbs, K.; and Dixon, D. A. “A Local Density Functional Study of
the Structure and Vibrational Frequencies of Molecular Transition-Metal Compounds,” J. Phys. Chem., 96 (1992)
6630-36.
[31] Adamo C.; Le Bahers, T.; Savarese, M.; Wilbraham, L.; García, G.; Fukuda, R.; Ehara, M.; Rega, N.; and Ciofini, I.
“Exploring excited states using Time Dependent Density Functional Theory and density-based indexes,” 2015, pp
166–178.
[32] Adamo C.; and Jacquemin, D. “The calculations of excited-state properties with Time-Dependent Density
Functional Theory,” 2013, pp 845.
[33] Papousek, D.; and Aliev, M.R. in Molecular Vibrational Spectra, Ed. J. R. Durig (Elsevier, New York, 1982).
[34] Parr, R.G.; and Yang, W. Density-functional theory of atoms and molecules (Oxford Univ. Press, Oxford, 1989).