Isomerism, molecular structure, and vibrational assignment of tris(triflouroacetylacetonato)iron(III): An experimental and theoretical study

Article abstract of DOI:10.1016/j.molstruc.2021.131347

The isomerism, optimized molecular structure, UV spectrum, metal-ligand bond strength, and vibrational assignment of tris(triflouroacetylacetonato)iron(III), Fe(TFAA)₃, were investigated by the aid of theoretical calculations (using DFT and Atoms-in-Molecules (AIM) at the B3LYP/6-311++G(d,p) level) and experimental methods (vibrational and UV spectroscopy). To explore the effect of the CF₃ substituent in the β-position on the properties of complex, the above theoretical and experimental results of the titled complex compared with the corresponding data for tris(acetylacetonato) iron(III), Fe(AA)₃. Both theoretical and experimental results confirmed that there is no significant difference in the strength of the Fe?O bond in these complexes. The effect of the CF₃ group on the experimental vibrational bands of the chelated ring agrees with the calculated results. Comparing the observed and calculated vibrational spectra suggests that vibrational spectroscopy cannot be used to determine the type of isomer in the sample. However, due to the small difference of energy between the fac and mer isomers in the Fe(TFAA)₃, the presence of both isomers in the sample is possible. The computed quantum chemical descriptors of Fe(TFAA)₃ and Fe(AA)₃ were also compared.

Full text of DOI:10.1016/j.molstruc.2021.131347

Journal of Molecular Structure 1248 (2022) 131347
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Isomerism, molecular structure, and vibrational assignment of
tris(triflouroacetylacetonato)iron(III): An experimental and theoretical
study
Farzad Gandomi, Mohammad Vakili∗, Reza Takjoo, Sayyed Faramarz Tayyari
Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The isomerism, optimized molecular structure, UV spectrum, metal-ligand bond strength, and vibrational
assignment of tris(triflouroacetylacetonato)iron(III), Fe(TFAA)3, were investigated by the aid of theoret-
ical calculations (using DFT and Atoms-in-Molecules (AIM) at the B3LYP/6-311++G(d,p) level) and ex-
perimental methods (vibrational and UV spectroscopy). To explore the effect of the CF3 substituent in
the β-position on the properties of complex, the above theoretical and experimental results of the ti-
tled complex compared with the corresponding data for tris(acetylacetonato) iron(III), Fe(AA)3. Both the-
oretical and experimental results confirmed that there is no significant difference in the strength of the
Fe−O bond in these complexes. The effect of the CF3 group on the experimental vibrational bands of the
chelated ring agrees with the calculated results. Comparing the observed and calculated vibrational spec-
tra suggests that vibrational spectroscopy cannot be used to determine the type of isomer in the sam-
ple. However, due to the small difference of energy between the fac and mer isomers in the Fe(TFAA)3,
the presence of both isomers in the sample is possible. The computed quantum chemical descriptors of
Fe(TFAA)3 and Fe(AA)3 were also compared.
Received 23 May 2021
Revised 2 August 2021
Accepted 19 August 2021
Available online 23 August 2021
Keywords:
Vibrational spectroscopy
DFT
UV spectra
Tris(triflouroacetylacetonato)iron(III)
Tris(acetylacetonate) iron(III)
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
1-(2-furyl)-1,3-butanedione (TTFU) by DFT, elemental analyses, FT-
IR, and UV-Vis techniques [14,15]. Conradie and Tachikawa et al.
The β-diketones (1,3-diketones) bear two carbonyl groups sep-
arated by one carbon atom (α-carbon) [1]. The substituents on the
carbonyl functional can be an alkyl, a fluorinated alkyl, an aro-
matic, or a heteroaromatic group [2–4]. The simplest β-diketone
is acetylacetone (AA), where the substituents on both carbonyl
groups are methyl groups. All other β-diketones can be considered
as derived from acetylacetone by substitution of the CH3 groups by
other groups. The enolic hydrogen atom can be replaced by metal
cation under appropriate conditions. Triflouroacetylacetone (TFAA),
one of the ligands studied in this work, was used in the extraction
of several metals such as Cu, Ni, Co, and Fe [5,6].
studied iron (III) complexes with the mentioned ligands by DFT
calculations and experimental cyclic voltammetry measurements
[16,17]. Metal acetylacetonates, as nontoxic precursors, were used
for the synthesis of transition metal oxide nanoparticles [18].
The structure, isomerism, vibrational spectra, and metal-ligand
strength of numerous metal β-diketonate complexes have been
studied [19–32]. Despite general studies, there are a few reported
works about the vibrational analysis of β-substituted trivalent
complexes [3–7,14–16,33–38]. The DFT methods showed an agree-
ment with the experiment results, tris(β-diketonato)iron(III) com-
plexes are stable molecules with the metal in a high spin state
1
1
1
1
The experimental structures for some trivalent metals with
acetylacetone and triflouroacetylacetone ligands were recognized
[7–12]. Kato and Gohda have investigated the magnetic circu-
lar dichroism (MCD) of M(AA)3and M(AA)2, that M = Cu, Fe,
and Co [13]. Conradie et al. characterized complexes of iron
with 2,4-pentanedione (AA), 1-phenyl-1,3-butanedione (BA), 4,4,4-
trifluoro-1-(2-thienyl)-1,3-butanedione (HTTA), and 4,4,4-Trifluoro-
(dz2 dxy dyz dxz dx2-y21, S = 5/2) [14,34–36,39].
Diaz-Acosta et al. [40,41] reported the IR spectra for Fe(AA)3
and its deuterated analogous. Jayasooriya et al. [42] reported the
vibrational spectra of Fe(AA)3, using IR, Raman, and nuclear in-
elastic spectroscopy. The crystal structure of ferric acetylacetonate
has been determined [10,43,44]. The structure, isomerism, vibra-
tional assignment, and metal-ligand strength of the title molecule,
tris(triflouroacetylacetonato)iron(III), Fe(TFAA)3, were not reported
previously. Therefore, the study of this molecule and comparing it
with Fe(AA)3, could be valuable materials from the scientific point
of view.
∗
Corresponding author.
E-mail address: Vakili-m@um.ac.ir (M. Vakili).
https://doi.org/10.1016/j.molstruc.2021.131347
0022-2860/© 2021 Elsevier B.V. All rights reserved.

F. Gandomi, M. Vakili, R. Takjoo et al.
Journal of Molecular Structure 1248 (2022) 131347
This work aims to compare the structure and vibrational assign-
ment of Fe(TFAA)3 with those for Fe(AA)3. This comparison is per-
formed with the aid of DFT calculations and IR, Raman, and UV-Vis
spectroscopy. By comparing the Fe−O bond strength of Fe(TFAA)3
and Fe(AA)3 it is possible to explore the effect of the CF3 substi-
tution on the metal-O bond strength of the complex. For better
accuracy of vibrational assignments, the vibrational spectra of both
complexes are compared with those of aluminum trifluoroacety-
lacetonate, Al(TFAA)3, and Cr(AA)3 [3,33].
with a DTGS/polyethylene detector and a solid substrate beam
splitter with the use of polyethylene disks. The spectra were col-
lected with a resolution of 4 cm−1 by signal averaging the results
of 32 scans.
For Fe(TFAA)3, Raman measurements were performed by Horiba
XploRA Raman spectrometer equipped with a confocal microscope.
The laser excitation of 785 nm with grating 1800 grooves/mm was
employed in a spectral range of 1700–300 cm−1
.
The UV spectra were examined in the range of 200–400 nm
at 298 K using a Perkin Elmer Lambda 25 spectrophotometer. The
complexes were dissolved in C2H5OH as the solvent.
2. Methodology
The mass analysis was achieved on a Varian Mat CH-7 at 70 eV.
2.1. Method of analysis
3. Results and discussion
All the calculations are performed using Gaussian 09W soft-
ware [45]. The geometry optimization, vibrational frequencies of
Fe(TFAA)3 and Fe(AA)3 obtained at the B3LYP [46–48] level, us-
ing 6-311++G(d,p) basis set. Raman activities of the mentioned
complexes were computed at the same level of calculation, using
standard procedures (Freq = Raman). Vibrational assignments have
been achieved based on the comparison of calculated and observed
Raman and IR spectra and their intensities. The assignments of ob-
served wavenumbers are aided by the animation of GaussView 6.0
visualization [49]. The zero-point vibrational energy, ZPE, was ob-
tained by using the results of frequency calculations. The topolog-
ical parameters such as the electron density and Laplacian of elec-
tron density at the critical points of Fe−O bonds are evaluated us-
ing the AIM 2000 [50] software. The HOMO and LUMO were ob-
tained at the same level of calculations.
3.1. Structure and isomerism
In the reported works, the most stable electronic spin for
Fe(AA)3 is considered as 5/2, so its multiplicity is 6 [14,41]. Accord-
ing to the results of the calculations at the B3LYP/6-311++G(d,p)
level, we also confirmed the value of 6 for multiplicity as the
most stable multiplicity for the understudy complexes, see Table
S1 (supplementary material). In Fe(TFAA)3 the relative energies for
other multiplicities, 2 and 4, are 9.9–14.7 kcal/mol more than that
of multiplicity 6. According to the calculation results, the symme-
try of Fe(AA)3 and Fe(TFAA)3 complexes is D3 and C1 (C3), re-
spectively, with sextet multiplicity. This symmetry and multiplic-
ity agree with the reported work by Diaz-Acosta et al. studies for
Fe(AA)3 [41]. The C1 and C3 point groups are due to mer and fac
isomers, respectively.
The Potential Energy Distribution (PED) of all normal modes
calculated by VEDA 4.0 program via optimization method [51]. Ac-
cording to reported work by Jamróz and Darugar et al., the opti-
mization method improved the PED contributions [52,53].
The optimized structure of Fe(AA)3 and Fe(TFAA)3 and their
numbering are shown in Fig. 1. Theoretically, two isomers sug-
gested for Fe(TFAA)3 complex, as fac and mer isomers, see Fig. 1.
The calculation results in the gas phase show that the relative en-
ergy of fac isomer of Fe(TFAA)3 is 0.54 kcal/mol more than the mer
isomer, and ZPE correction does not affect this energy difference.
Therefore, the coexistence of both isomers can be considered in
the gas phase. The calculated energy difference was obtained for
the multiplicity of 6.
2.2. Experimental
Synthesis of the iron (III) β-diketone complexes with trifluo-
roacetylacetone and acetylacetone ligands.
1,1,1-trifluoro-2,4-pentanedione and 2,4-pentanedioneas ligands
and the other compounds including iron (III) chloride hexahy-
drate, sodium acetate, and ammonia for synthesis were purchased
from Alfa Aesar and Merck companies. The Fe(TFAA)3 and Fe(AA)3
complexes are prepared according to the similar procedures de-
scribed by Fay and Chaudhuri et al. [54,55]. For this purpose, an
aqueous solution (10 ml) containing iron (III) chloride hexahydrate
(10 mmol, 2.70 g) and sodium acetate (0.5 g) was shaken with
1,1,1-trifluoro-2,4-pentanedione (30 mmol, 3.60 ml) in 20 ml of
ethanol. After passing about 30 min, red crystalline solids which
had precipitated, washed with distillated water then were filtered
and dried under vacuum. The Fe(AA)3 complex was synthesized ac-
cording to the mentioned method too. The melting points of the
light and dark red solids of Fe(AA)3 and Fe(TFAA)3 are 178 and
108 °C, respectively. These melting points are near to those re-
ported in the literature, 179 °C for Fe(TFAA)3 and 111 °C for Fe(AA)3
[56,57]. Calculated m/z = 515.09 for C15H12F9FeO6 [Fe(TFAA)3]+;
founded: m/z = 514.0, see Fig. S1, Supplementary materials.
The optimized parameters along with their experimental struc-
ture of Fe(AA)3 [10,41,58] and the calculation results of Fe(TFAA)3
isomers, along with their averaged values, are compared in Table 1.
According to this table, the calculated structure of Fe(AA)3 is sim-
ilar to that by Diaz-Acosta et al. [41]. Also, the gas-phase electron
diffraction (GED) results [58] are in agreement with the calculated
structure.
As Table 1 shows, the averaged Fe−O bond length in both fac
and mer isomers of Fe(TFAA)3 is slightly shorter than those in
Fe(AA)3. This small difference in Fe−O bond strength is also con-
firmed with the other bond lengths of the chelated ring and AIM
calculation results too, see Table 1. So, the comparison of these av-
eraged values with the calculated Fe−O bond length indicates that
there is no significant difference in Fe−O bond strength. This result
is also confirmed by the experimental UV results.
Also, Table 1 shows that the C−CMet bond lengths of Fe(TFAA)3
are higher than those in Fe(AA)3, which is consistent with Zahedi-
Tabrizi and Tayyari et al. works [59,60]. In addition, due to the
electron-withdrawing effect of the CF3 group, the C−CF3 bond
length of Fe(TFAA)3 is longer than that of Fe(AA)3. This elonga-
2.3. Instruments analyses
The infrared spectra in the 4000–500 cm−1 region were
recorded on a Bomem MB-154 Fourier transform spectrophotome-
ter using KBr pellets and CCl4 solution. The spectra were collected
with a resolution of 4 cm−1 by signal averaging the results of 15
scans.
tion could be explained by the electron-withdrawing effect of the
δ−
CF3 group. In this view, the attractive interaction in Cδ+−C
of
C−CH3 becomes repulsive (Cδ+−C +), if the hydrogen atoms of the
methyl group replaced by the fluorine atoms. On the other hand,
the C −CCF bond length in Fe(TFAA)3 is shorter than the corre-
δ
α
3
The Far-IR spectra in the region 700–250 cm−1 were obtained
sponding value in Fe(AA)3. This shortening is also caused by the
same effect the carbon atom attached to the CF3 group is more
using a Thermo Nicolet NEXUS 870 FT-IR spectrometer equipped
2

F. Gandomi, M. Vakili, R. Takjoo et al.
Journal of Molecular Structure 1248 (2022) 131347
Fig. 1. The optimized structure of Fe(AA)3 and Fe(TFAA)3, mer and fac, complexes and their numbering of the atoms.
Table 1
Some selected theoretical and experimental geometrical parameters of Fe(AA)3 and Fe(TFAA)3 (fac and mer) calculated
˚
at B3LYP/6-311++G(d,p) level of theory (bond lengths and bond angles are in A and °, respectively.
Fe(TFAA)3
Fe(AA)3
Parameters
Theoretical
Theoretical
Exp.♣
[58]
Exp.
[41]
Exp.
[10]
Configuration
Symmetry
mer
(C1)
fac
(This
work)
Ref.
[41]
Avg.
(C3)
Avg.
(D3)
(C1)
Bond angles
Fe−O2
2.021
2.027
2.019
2.029
2.027
2.022
1.265
1.267
1.387
1.414
1.543
1.506
2.743
2.741
2.737
1.079
—
2.024
2.024
2.025
1.266
1.401
1.525
2.74
2.025
2.023
2.025
2.023
2.025
2.023
1.265
1.267
1.388
1.414
1.543
1.506
2.743
2.743
2.743
1.079
—-
2.024 2.026
2.024
2.011
2.018
1.992
2.004
1.993
1.983
1.976
1.998
2.000
Fe−O7
Fe−O5
Fe−O6
Fe−O3
2.024
Fe−O4
O=CCF3
1.266
O=CCH3
C−CCF3
1.271
1.275
1.405
1.512
—-
1.268
1.399
1.262
1.382
1.262∗
1.382∗
1.401
C−CMet
1.404
C−CF3
1.525
C−CH3
1.511
1.507
1.504
1.504∗
2.753∗
O2…O7
2.743 2.749
—
-
—
-
O5…O6
O3…O4
C−Hα
1.081
—-
—-
—-
1.070
—-
—-
0.947∗
0.9949
R2
0.9999
Bond angles
O2FeO7
85.2
85.2
85.3
85.3
85.4
87.1
87.4
87.4
87.8
86.6
87.9
O5FeO6
85.3
85.3
O3FeO4
85.1
85.3
O6/O5CβCF3
O5/O6CβCH3
O3Cβ8Cα15
O4Cβ9Cα15
FeO7Cβ12
FeO4Cβ9
Cβ12Cα14Cβ13
Cβ10Cα16Cβ11
Cβ8Cα15Cβ9
113
113
116.3
127.8
123.7
129
116.3
127.7
123.8
129.1
132.1
121.8
121.8
121.8
115.6
124.6
131.0
—-
115.9
—-
—-
115.3∗
124.5∗
124.9
124.5
132.2
121.9
121.8
121.7
129.8
123.5
129.0
123.2
129.1
124.8
129.1∗
124.8∗
121.8
121.8 123.4
a
AIM
ρBCP
2
0.0779
-0.0980
—
0.0774
-0.0971
—-
0.0774
-0.0976
—-
—-
—-
—-
—
—
-
—
∇
-
-
R2
0.9990
—-
0.9937
a
2
The units of AIM results are: the density of critical point, ρ, (e.au−3), the Laplacian of critical point, ∇ ρ, (e.au−5).
∗
Due to the complex asymmetry, these values are different in each ligand and their averages are presented in the
table.
♣
Experimental results reported from GED analysis.
3

F. Gandomi, M. Vakili, R. Takjoo et al.
Journal of Molecular Structure 1248 (2022) 131347
Fig. 2. The correlation between theoretical and reported experimental GED structure of Fe(AA)3.
Table 2
positive while the C atom is negative, which causes shortening of
α
Quantum chemical descriptor parameters for Fe(AA)3 and Fe(TFAA)3 isomers.
C −C bond length.
α
According to the AIM results in Table 1, the average of density
Property
Fe(AA)3
mer-Fe(TFAA)3
fac-Fe(TFAA)3
2
(ρ) and its Laplacian (∇ ) at metal-oxygen bond critical point in
ρ
EHOMO (eV)
-6.33
-1.32
5.01
-2.5
2.5
-7.38
-2.56
4.82
-2.41
2.41
4.97
1.16
0.21
3.92
-7.40
-2.56
4.84
-2.42
2.42
4.98
1.21
0.21
3.93
Fe(TFAA)3 are 0.0776 and 0.0976, respectively. The mentioned val-
ues do not important change in comparison to Fe(AA)3. These val-
ues indicate that the effect of CF3 subgroup is negligible and has
no significant effect on the metal-ligand bond strength, which is
in agreement with other results including UV and vibrational ana-
lyzes.
ELUMO (eV)
Energy gap (eV)
Electronegativity (χ)
Global hardness (η)
Chemical potential (μ)
Global electrophilicity (ω)
3.83
2.93
0.20
4.67
Chemical softness S (eV−1
)
Dipole moment (Debye)
The most stable form of Fe(AA)3, with six multiplicity, has been
used to compare with the experimental reported structure [13].
The regression coefficient parameter (R2) between theoretical bond
lengths and bond angles with the reported experimental, GED and
X-ray, for Fe(AA)3 are given in Figs. 2 and S2, supplementary ma-
terials. The regression coefficients of Fe(AA)3 with GED are 0.9999
and 0.9990 for bond lengths and bond angles, respectively. Also,
the mentioned R2 values with X-ray were obtained as 0.9949 and
0.9937. The higher R square values of GED correlation respect to
X-ray can be related to intermolecular interactions existent within
crystal which are absent in the theoretical gas-phase geometry and
experimental gas electron diffraction structure [61].
χ = - [E(LUMO)- E(HOMO)]/2; μ = [E(LUMO) + E(HOMO)]/2; η = [E(LUMO) -
E(HOMO)]/2;S = ½ η; ω = μ2/2 η.
any significant difference in water respect to the ethanol. Hence it
seems that the solvent has not effect on the transitions.
From the DFT calculations, different descriptors such as EHOMO
,
ELUMO, energy gap, global hardness (η), softness (S), electrophilic-
ity index (ω), were considered to compare the structure-activity
relationship (SAR) of the mentioned complexes [64,65]. The com-
puted quantum chemical descriptors established upon DFT results
are listed in Table 2. EHOMO measures the electron-donating role
of a complex, whilst ELUMO measures its electron-accepting role.
Therefore, the bigger the EHOMO corresponds to the larger electron-
donating ability, and the smaller the ELUMO is related to the lower
the resistance to accept electrons. The more softness indicates the
more chemical activity. The electrophilicity index has lately been
recognized as a factor of biological activity. According to Table
2, the electrophilicity (ω) of Fe(AA)3 (2.93) is more than that of
Fe(TFAA)3 (about 1.20). So, the Fe(AA)3 complex shows more elec-
trophilicity attack strength. Besides, the chemical potentials (μ)
of Fe(TFAA)3 about 5.0 is larger than that 3.83 value for Fe(AA)3.
Hence, the reactivity property of Fe(TFAA)3 is more than that
Fe(AA)3.
3.2. Experimental sections
3.2.1. UV spectra and frontier molecular orbital analyzes
In the present work, we have calculated the HOMO (the high-
est occupied molecular orbital) and LUMO (the lowest unoccu-
pied molecular orbital) energies [62,63] for optimized structures
of Fe(AA)3 and both isomers of Fe(TFAA)3. The 3D plots of fron-
tier molecular orbital of the under studied metal complexes are
shown in Fig. 3. The difference of HOMO-LUMO energy gap of
Fe(AA)3 is a little more than that of fac and mer. Accordingly, the
HOMO→LUMO transition implies an electron density transfer for
Fe(AA)3 and fac of Fe(TFAA)3 from π-conjugated of all three chelat-
ing rings to the metal-ligand regions of LUMO orbital, while tran-
sition for mer of Fe(TFAA)3 is from two chelating rings of HOMO
orbital to LUMO orbital, see Fig. 3.
3.2.2. Vibrational analysis
The shortened and full assignment along to PEDs of Fe(TFAA)3
complex are given in Tables 3 and S2 (supplementary materials),
respectively. To increase the assignment accuracy, the vibrational
spectra and their assignment of the title complex compared with
those of Fe(AA)3 complex, see Tables 4 and S3 (supplementary ma-
terials) for vibrational assignment of Fe(AA)3. The internal coordi-
nates achieved from VEDA (.dd2 files) of the both complexes are
given in Tables S4–6, supplementary materials.
The experimental UV spectra of both complexes are shown in
Fig.4. The recorded UV spectrum of the Fe(AA)3 complex shows a
maximum absorption peak at 270 nm, but this band in Fe(TFAA)3
is shown at 285 nm, which its red shift is in agreement with in-
creasing of π conjugation transition and lowering band gap of this
complex, in comparison to Fe(AA)3. Additionally, the UV spectra of
both complexes indicate the presence of a low-intensity band at
210 nm, which is due to Fe to oxygen charge transfer. The sim-
ilarity of the wavelengths of this peak for both complexes is in
agreement with the small difference of metal-ligand strength that
is obtained by molecular structure. Also, the recording UV spectra
are repeated in water solvent and the wavelengths do not show
Fig. 5 shows the solid IR spectra of Fe(AA)3 and Fe(TFAA)3 in
the 1800–500 cm−1 along with 3100–2800 cm−1 regions. The ex-
perimental Raman spectra of Fe(AA)3 and Fe(TFAA)3 and theoret-
ical Raman of fac-mer isomers of Fe(TFAA)3 are shown in Figs. 6
and S3 (supplementary material), respectively. The recorded and
4

F. Gandomi, M. Vakili, R. Takjoo et al.
Journal of Molecular Structure 1248 (2022) 131347
Table 3
Shorted vibrational assignments, experimental and calculated wavenumbers along to VEDA’s PEDs (in cm−1 and %) of Fe(TFAA)3.
a
b
Fe(TFAA)3 M = 6
Assignment
Sym
Theoretical
Experimental
IR(Solid)
GaussView animation
Fac (C3)
Mer (C1)c
VEDA’s PEDs ≥10%
Fs
IIR
1
AR
Fs
IIR
AR
IR(CCl4)
R(Solid)
A
A
A
E
E
E
E
A
A
A
A
E
E
E
E
A
E
A
A
A
E
E
E
E
A
A
A
E
E
E
E
A
A
A
E
E
A
A
E
E
E
A
A
E
A
E
E
E
A
A
E
E
A
A
A
A
3111
229
3112
3013
1
112
71
3091(1)
3004(3)
3004
3089(1)
3001(2)
3001
νCH
νCH (99)
α
α
11
νaCH3
νaCH3(86)
νaCH3(99)
νaCH3(80)
νaCH3(94)
νaCH3(98)
νaCH3(89)
νaCH3(88)
νsCH3(99)
νsC-O(61)
νsC-O(50)
νsC-C-C(53)
νsC-O(62)
νsC-O(71)
νsC-C-C(45)
3012
3012
0
81
67
νaCH3
3013
3012
16
16
74
74
3004
3001
νaCH3
21
3004
3001
νaCH3
3004
3001
νaCH3
3012
2978
2921
21
4
67
3004
3001
νaCH3
123
641
2978
2921
1634
3
72
2977(3)
2926(4)
1635(3)
1635
2975(2)
2925(1)
1629(9)
1629
νaCH3
3
2
252
365
νsCH3
17
1625(58)
1625
νsC-O, νsC-C-C
νsC-O, νsC-C-C
νsC-O, νsC-C-C
νsC-O, νsC-C-C
νsC-O, νsC-C-C
νsC-O, νsC-C-C
1634
48
347
1610
965
30
1610(94)
1610
1610(85)
1610
1610
1610
863
863
35
35
1610
1610
1610
1538
1537
1466
1450
1436
1426
811
191
302
73
28
8
1610
1610
1539
1538
1466
1451
1435
417
76
5
7
9
4
2
1578(25)
1526(75)
1452(35)
1420(11)
1364(52)
1364
1576(38)
1526(51)
1444(23)
1564(51)
1529(49)
1439(61)
νaC-C-C, δCH
δCH (31), νaC-C-C(11)
α
α
5
νaC-C-C, δCH
νaC-C-C(15), δCH (34)
α
α
60
7
νaC-O, δaCH3
δaCH3(64)
1
6
7
δaCH3
δaCH3(85)
220
222
18
1
1363(37)
1363
1368(59)
1368
δaCH3
δaCH3(52)
6
δaCH3, νaC-C-C, νaC-O
δaCH3, νaC-C-C, νaC-O
δaCH3, νaC-C-C, νaC-O
δaCH3, νaC-C-C, νaC-O
δsCH3
νaC-C-C(22), νaC-O(13)
νaC-O(49)
1425
1425
76
76
2
2
1364
1363
1368
1364
1363
1368
νaC-C-C(16), νaC-O(14)
νaC-O(54)
1425
1375
125
42
10
12
1364
1363
1368
1375
1291
73
17
67
1351(18)
1288(100)
1288
δsCH3(82)
752
1299(100)
1299
1283(49)
1283
νC-CF3, νsC-C-C, νC-CH3
νC-CF3, νsC-C-C, νC-CH3
νsCF , δCH
νsC-C-C(14), νC-CF3(10)
νsC-C-C(33)
νsCF3(46)
1290
1286
756
153
10
14
1227
1223
1226
α
α
α
α
α
α
α
α
α
3
1287
1287
162
162
10
10
1227
1223
1226
νsCF , δCH
νsCF3(29)
3
1227
1223
νsCF , δCH
νsCF3(27)
3
1286
1220
1154
176
19
21
12
3
1227
1223
νsCF , δCH
νsCF3(41)
3
1221
45
3
1195(53)
1145(86)
1145
1199(46)
1158(46)
1158
1194(32)
νsCF , δCH
δCH (38)
α
3
98
δaCF , δCH
δaCF3(47)
3
1155
1152
47
4
1
δaCF , δCH
δaCF3(60)
3
400
1145
1158
δaCF , δCH
δaCF3(58)
3
1151
1136
390
182
1
5
1145
1158
δaCF , δCH
δaCF3(44)
3
1145
1158
δsCF , δCH
δsCF3(16)
α
α
α
α
3
1143
1134
436
84
5
8
1145
1158
δsCF , δCH
δCH (42), δsCF (11)
α
3
3
1145
1158
δsCF , δCH
δsCF (50), δCH (10)
α
3
3
1130
1128
1033
958
42
265
3
12
4
1145
1158
δsCF , δCH
δsCF3(25)
3
1124
1033
958
957
851
802
755
313
1
9
2
3
3
2
1
3
1138(86)
1024(17)
949(18)
929(10)
864(24)
791(26)
753(5)
753
1138(43)
1024(6)
952(4)
929(4)
862(10)
1138(39)
1021(34)
949(30)
δaCF , δCH
δaCF3(58)
πCH3(89)
α
3
0
πCH3
2
1
8
δC-C-C, ρCH3, δaCF3
δC-C-C, ρCH3, δaCF3
νC-CH3, νC-CF3
δC-C-C(13), ρCH3(13)
δC-C-C(27)
1
957
1
1
48
33
2
850
30
33
1
861(27)
789(26)
νC-CF3(24), νC-CH3(10)
802
1
γ CH
γ CH (78)
α
α
ꢀ
ꢀ(86)
755
1
1
ꢀ
ꢀ(56)
716
30
20
730(31)
730
732(41)
732
δsCF3, νsO-Fe-O
δsCF3, νsO-Fe-O
δsCF3, νaO-Fe-O
γ C-CH3
δsCF3(35)
716
714
608
583
579
506
9
15
4
νsO-Fe-O(16)
νaO-Fe-O(34), δsCF3(16)
γ C-CH3(60)
δaCF3(18)
714
608
583
579
506
483
26
1
5
36
3
670(8) #
609(9)
581(48)
551(11)
500(10)
451(10)
451
673(32)
2
1
0
8
1
1
596(48)
νaO-Fe-O, δaCF3, δOCCH3
νaO-Fe-O, δC-C-O, δC-CH3, δaCF3
δaCF3
63
2
6
27
3
5
νaO-Fe-O(33), δC-C-O(15)
δaCF3(67)
1
1
496(59)
451(95)
451
5
10
δaCF3, νaO-Fe-O
δaCF3, νaO-Fe-O
νsO-Fe-O, δC-C-CH3, δC-C-CF3
νsO-Fe-O, δC-C-CH3, δC-C-CF3
δO-Fe-O, δC-CH3, δC-CF3
δO-Fe-O, δC-CH3, δC-CF3
ꢀ
νaO-Fe-O(25)
δaCF3(41)
480
421
420
325
305
294
18
29
17
12
32
1
2
A
E
E
A
E
E
E
E
E
422
418
324
300
294
281
14
46
9
34
2
16
8
425(33)
425
δC-C-CH3(34)
νsO-Fe-O(39)
δC-CF3(58), δO-Fe-O(29)
δC-CH3(19)
2
4
311(9)
299 (14)
287(16)
276(12)
276
342(25)
0
18
3
4
300 (70)
1
6
ꢀ(39)
34
5
νaO-Fe-O, ꢁ
νaO-Fe-O(17)
νaO-Fe-O(29)
νaO-Fe-O(13)
νaO-Fe-O(25)
283
279
55
19
6
7
νaO-Fe-O, ꢁ
276
νaO-Fe-O, ꢁ
281
34
5
276
νaO-Fe-O, ꢁ
(a) Fs, the scaled theoretical frequencies calculated at the B3LYP/6-311++G∗∗ level. IIR, IR intensity (in kM/mol); and AR, Relative calculated Raman intensity (obtained
at same level); the relative observed intensities are given in parentheses; ν, stretching; δ, in-plane bending; γ , out-of-plane bending; ꢁ, in-plane ring deformation; ꢀ,
out-of-plane ring deformation; τ, torsion; ρ, in-plane rocking; π, out-of-plane rocking; # below 700 cm−1 recorded with different instrument.
(b) Multiplicity
(c) All symmetry species of mer isomer are A.
5

F. Gandomi, M. Vakili, R. Takjoo et al.
Journal of Molecular Structure 1248 (2022) 131347
Fig. 3. The calculated HOMO-LUMO energy gaps for the Fe(AA)3, mer and fac of Fe(TFAA)3 complexes.
Fig. 4. The experimental UV spectra of Fe(AA)3 and Fe(TFAA)3 complexes in ethanol as solvent.
simulated Far-IR spectra of the Fe(AA)3 along with fac-mer isomers
of Fe(TFAA)3 are shown in Fig. 7a and b. In addition, IR spectra of
Fe(TFAA)3 in the solid phase and CCl4 solution are compared in Fig.
S4 (supplementary material).
tween theoretical and experimental frequencies of both complexes
are shown in Fig. 8a and b. These figures clarified those R square
values, 0.9998 and 0.9991 from unscaled theoretical frequencies in-
creased to 0.9999 and 0.9993 in effect of scaled theoretical fre-
quencies for Fe(TFAA) and Fe(AA)3, respectively.
Since the theoretical wavenumbers are higher than the ex-
perimental ones, so the appropriate scales, 0.9609 for upper
2000 cm−1 and 0.9859 for below 2000 cm−1 regions, are used
to theoretical numbers [33]. For this purpose the correlation be-
3.2.2.1. 3000 cm−1 region. In this region, vibrational stretching of
CH and methyl groups can be observed. According to Table 3, in
α
6

F. Gandomi, M. Vakili, R. Takjoo et al.
Journal of Molecular Structure 1248 (2022) 131347
Table 4
Shorted vibrational assignments, experimental, and calculated wavenumbers along to VEDA’s PEDs (in cm−1 and %) of Fe(AA)3.
a
Fe(AA)3
Theoretical
Experimental
IR(Solid)
Assignment
Sym.
Fs
IIR
AR
R(Solid)
GaussView animation
VEDA’s PEDs≥10%
Ref [41].
Ref [66].
A1
E
3078
3078
3003
3003
3003
2974
2974
2917
2917
2917
1612
1584
1530
1458
1458
1452
1452
1407
1391
1376
1375
1276
1270
1270
1199
1197
1040
1040
1040
1029
1027
1026
1018
948
0
232
71
137
159
159
4
3085(7)
3085
νsCH
νsCH (97)
α
α
15
0
3081(3)
νaCH
νaCH (97)
ν(CH)
α
α
A1
E
3006(5)
3006
νaCH3
νaCH3(92)
νaCH3(87)
νaCH3(87)
νaCH3(92)
νaCH3(98)
νsCH3(78)
νsCH3(91)
νsCH3(90)
νsC-O(63)
νsC-O(70)
57
57
14
0
2998(6)
2998
νaCH3
E
3006
νaCH3
E
2961(5)
2960(8)
2960
νaCH3
A1
A1
E
248
1273
30
30
278
22
0
νaCH3
0
2928(32)
2928
νsCH3
7
2919(7)
2919
νsCH3
ν(CH3)
ν(CH3)
E
7
2928
νsCH3
A1
E
0
1608(7)
1579(100)
1525(70)
1442(15)
1442
1608(100)
1587(41)
νsC-O, νsC-C-C, δCH3
νsC-O, νsC-C-C, δCH3
νaC-C, νaC-CH , δCH
954
766
135
135
12
17
572
134
0
ν(C=O), ν(C=C)
ν(C=C), δ(C=CH)
ν(C=C)
A2
E
νaC-C(44), δCH (15)
ν(C=O)
α
α
3
8
δaCH3
δaCH3
δaCH3
δaCH3
δaCH3(85)
ν(C=O), δ(CH)
ν(C=O), δ(CH)
E
8
δaCH3(78)
A2
E
0
1421(18)
1421
δaCH3(89)
δ(CH3)
15
0
1428(8)
δaCH3(75)
δ(CH3)
A2
E
1390(34)
1371(33)
νaC-O, δaCH3, νaC-C-C,
νaC-C-C, νaC-O, δaCH3
δsCH3
νaC-C-C(52),
νaC-C-C(59), δaCH3(11)
δsCH3(82)
ν(C=O), ν(C=C)
ν(C=O), ν(C=C)
δ(CH3)
δaCH3
0
A1
E
32
11
31
7
1370(24)
1370
δsCH3
δsCH3
15
0
1358(45)
δsCH3
δsCH3(84)
δ(CH3)
A1
E
1278(32)
1278
νsC-C-C, νsC-CH3
νsC-CH3, νsC-C-C
νsC-C-C, νsC-CH3
νsC-C-C(50)
ν(C=C), ν(C-CH3)
ν(C=C), ν(C-CH3)
ν(C=C), ν(C-CH3)
δ(C=CH), ν(C=O)
δ(C=CH), ν(C=O)
127
127
35
3
1273(53)
1273
νsC-C-C(29),νsC-CH3(13)
νsC-C-C(50)
ν(C=C), ν(C-CH3)
ν(C=C), ν(C-CH3)
δsCH
E
7
1278
A2
E
0
1189(5)
1189
δsCH , νsC-O
δsCH (47), νsC-O(10)
α
α
18
2
1186(11)
1033(12)
δaCH , νsC-O
δaCH (57), νsC-O(13)
δsCH
α
α
A1
E
0
πCH3
πCH3(74)
0
0
πCH3
πCH3(80)
E
0
0
πCH3
πCH3(78)
A1
E
0
1
ρCH3, νsO-Fe-O
πCH3
ρCH3(25), νsO-Fe-O(12)
πCH3(82)
14
37
8
0
1024(26)
1018(17)
1009(20)
942(9)
1023(14)
ρr(CH3)
ρCH3
E
0
ρCH3, νsO-Fe-O
ρCH3, νsO-Fe-O
ρCH3, δC-C-C
νaC-CH3, ꢁ
Combination
ρCH3(45), νsO-Fe-O(27)
ρCH3(81)
ρr(CH3), ν(C=O), πring
A2
A1
A2
0
1010(9)
940(14)
0
13
0
ρCH3(19)
928
32
929(28)
801(10)
770(18)
666(25) #
νaC-CH3(82)
Combination
ν(C-CH3)
ν(C-CH3), νC-O
γ C-H
E
773
664
655
650
558
539
531
430
422
409
405
295
245
195
164
21
7
4
789(8)
γ CH
γ CH (91)
π(C-H)
α
α
E
0
γ C-CH3, ꢀ
γ C-CH3(58), ꢀ(12)
νsC-CH3(25), δC-C-O(18)
δC-C-O(37), νsO-Fe-O(33)
γ C-C-O(76)
πring, Mixed
ν(C-CH3),ν(Fe-O)
ν(C-CH3),ν(Fe-O)
πring, ν(M-O)
A1
E
0
12
6
669(14)
669
νsO-Fe-O,νsC-CH3, δC-C-O
νsO-Fe-O, νsC-CH3, δC-C-O
γ sC-CH3, γ C-C-O
νaO−Fe−O, δC-CH3
νaOFe-O, δC-C-O, δC-CH3
νsO-Fe-O, δC-C-C, δC-CH3
νsO-Fe-O, δC-C-C, δC-CH3
δC-CH3, δC-C-O
38
0
653(5)
δ(C-CH3), ν(M-O)
A1
A2
E
4
563(11)
38
13
0
0
559(9)
δC-CH3(67)
δ(O=C-CH3)
δ(O=C-CH3)
ν(Fe-O)
1
548(10)
541(7)
δC-C-O(63)
A1
E
74
3
446(64)
433(17)
δC-C-C(45), δC-CH3(10)
δC-C-C(51)
97
18
13
76
2
433(60)
414(14)
407(19)
298(28)
ν(M-O)
ꢀ
A2
E
0
δC-C-O(58)
δ(C=C-CH3, O=C=C)
δ(C=C-CH3, O=C=C)
ν(Fe-O), δ(O-Fe-O)
δ(C=O-Fe, CH3-C=C)
2
404(7)
δC-CH3, δC-C-O
δC-C-O(66), δC-CH3(10)
νaO-Fe-O(37), ꢁ(22)
ꢁ(57)
E
7
298(21)
253(12)
207(18)
170(11)
νaO-Fe-O, ꢁ
ν(M-O)
δC-CH3
Ring def
E
2
δO-Fe-O, ꢁ
ꢀ
E
3
1
205(16)
ꢀ(56)
A1
0
10
τCCOCH3
τCCOCH3(49)
a
See footnote Table 3.
and 2919 (2928) cm−1. The values in parentheses are Raman
bands.
IR spectra of Fe(TFAA)3 in the solid and CCl4, the very weak band
at about 3090 cm−1 is assigned to the CH stretching. The corre-
α
sponding band in Fe(AA)3, Cr(AA)3, and Al(TFAA)3 as trivalent com-
plexes, reported at 3081, 3083, and 3122 cm−1, respectively [3,33].
Diaz-Acosta et al. [41] also considered the band at 3088 cm−1 as
3.2.2.2. 1700–1000 cm−1 region. In addition to the CF3 stretching,
we expect to observe some bands due to the CH3 and CF3 de-
formations, C−CH3 and C−CF3 stretching, and CH in-plane bend-
ing vibrations in this region. The IR spectra of Fe(TFAA)3 in solid
and CCl4 solution show a very strong band at 1610 cm−1, that
according to our calculations assigned to the C−O coupled with
C−C−C symmetric stretching vibrations. VEDA’s PEDs shows that
for the mentioned mode the contributions of fac and mer of
Fe(TFAA)3 about 10% are changed. This Raman band appears as
a high-intensity band at 1625 cm−1. In the solid IR spectrum of
Fe(AA)3 this band appears at 1579 cm−1, that its experimental
and theoretical red shift can be due to coupling with CH3 bend-
CH stretching vibration of Fe(AA)3. This normal mode in the Ra-
α
man spectrum was observed at 3085 cm−1, see Table 4. The VEDA’s
PEDs of CHα str. are upper than 90%.
The IR spectrum of Fe(TFAA)3 shows three bands at 3004, 2977,
and 2926 cm−1, which according to theoretical results and com-
parison with the corresponding bands of Cr(AA)3 and Al(TFAA)3 as-
signed to the asymmetric and symmetric stretching of CH3 groups.
Although in asymmetric stretching of CH3 normal modes the PED
values for fac and mer of Fe(TFAA)3 have difference. The corre-
sponding bands for Fe(AA)3 observed at 2998 (3006), 2961 (2960),
7

F. Gandomi, M. Vakili, R. Takjoo et al.
Journal of Molecular Structure 1248 (2022) 131347
Fig. 5. The recorded infrared spectra of Fe(TFAA)3 (−) and Fe(AA)3 (…..) complexes in solid phase in the 1800–500 and 3100–2800 cm−1 region.
Fig. 6. The recorded Raman spectra of Fe(TFAA)3 (−) and Fe(AA)3 (…..) complexes in solid phase in the 1800–250 cm−1 region.
ing and electron-withdrawing effect of CF3. This band in Cr(AA)3
responding band in Al(TFAA)3 splitted as two bands, at 1490 and
1458 cm−1 [3]. In Fe(AA)3 the mentioned IR band observed at
1390 cm−1, as shoulder bands. Diaz-Acosta et al. also considered
this band as νC=O vibrations for Fe(AA)3 [41].
and Al(TFAA)3 were reported at 1575 and 1625 cm−1, respec-
tively [3,33]. The 1578 and 1526 cm−1 bands in the IR spectrum
of Fe(TFAA)3 were assigned to the asymmetric C−C−C stretching
which according to PEDs coupled to the in-plane bending mode,
The δaCH3 and δsCH3 vibrations, asymmetric and symmetric
deformation of the methyl group, in the IR spectrum of Fe(TFAA)3
appeared at 1420, 1364, and 1351 cm−1, respectively. These bands
in Fe(AA)3, Al(TFAA)3, and Cr(AA)3 complexes observed at 1421
(1358), 1419 (1368), and 1423 (1367), that the values in parenthe-
sis are δsCH3 of the mentioned molecules [3,33]. The correspond-
ing Raman bands of Fe(AA)3 for the mentioned asymmetric and
symmetric deformation are 1428 and 1370 cm−1, respectively.
The IR spectrum of Fe(TFAA)3 complex in the solid phase indi-
δCH . The corresponding Raman bands were observed at 1564 and
α
1529 cm−1, respectively. These bands were assigned to the C=O
and C=C stretching coupled to the CH in-plane bending by Diaz-
Acosta et al. [41], which is somewhat in agreement with our as-
signment.
According to the calculated results and comparing with the vi-
brational assignment of 1,1,1-trifluoro-2,4-pentanedione, TFAA [59],
the medium-intensity IR and Raman bands of Fe(TFAA)3 at 1452
and 1439 cm−1 assigned to the νaC−O coupled to δaCH3. The cor-
cates a strong-intensity band at 1288 cm−1 which is assigned to
,
8

F. Gandomi, M. Vakili, R. Takjoo et al.
Journal of Molecular Structure 1248 (2022) 131347
Fig. 7. (a) The recorded Far IR spectra of the Fe(TFAA)3 and Fe(AA)3 complexes in solid phase in the 700–250 cm−1 region. (b) Comparing of simulated Far IR spectra of
Fe(TFAA)3, fac and mer, and its experimental in the 700–200 cm−1 region.
Fig. 8. (a) The correlation between theoretical and experimental frequencies of Fe(TFAA)3 and for Fe(AA)3 in (b).
νC−CF3,νsC−C−C,νC−CH3 for fac isomer, while upon PED of mer
isomer there is not any coupling. This band in TFAA appeared at
1284 cm−1, with about the same intensity but with a broader band
width, which is due to coupling with δOH. The mentioned band
in Al(TFAA)3, Fe(AA)3, and Cr(AA)3 complexes observed at 1306,
1273, and 1278 cm−1 [3,33]. This vibrational frequency in the Ra-
man spectrum of Fe(AA)3 and Fe(TFAA)3 was observed at 1278 and
1283 cm−1, respectively.
animation of GaussView, the splitting in Fe(TFAA)3 maybe due to
coupling with δaCF3.
The medium intensity IR and Raman band in Fe(TFAA)3 at about
864 cm−1 assigned to the C−CF3 stretching mode coupled to the
C−CH3 stretching motion. This band was indicated in TFAA and
Al(TFAA)3 at 858 and 868 cm−1, respectively [3,59]. The CH out-
of-plane bending, γ CH , of the titled complex was observed at
α
791 cm−1 as a medium intensity IR band. The corresponding band
in Fe(AA)3 was observed at 770 cm−1, which agrees with the re-
ported assignment by Diaz-Acosta et al. [41]. This red shift agrees
with calculated wavenumbers too, see Tables 4 and S3.
Similar to Al(TFAA)3 [3], two strong intensity IR bands at
1227 and 1195 cm−1 of Fe(TFAA)3 complex assigned to the νsCF3
stretching vibration, which coupled to δCH . The contributions of
α
νsCF3 stretching mode in mer isomer about 15% more than that
fac isomer. The corresponding Raman bands appeared at 1226 and
1194 cm−1. The δCF3 movement for this complex coupled with
According to calculated results, the IR band at 753 cm−1 in
the titled complex assigned to the out-of-plane deformation of the
chelated ring, ꢀ. The contribution of the mentioned normal mode
for mer about 30% lower respect to the fac isomer. While the men-
tioned band in Al(TFAA)3 split as two, medium and weak intensity
bands, at 785 and 758 cm−1, respectively. This band in Fe(AA)3
and Cr(AA)3 shifted to about 666 cm−1, which is due to the cou-
pling with γ C−CH3 [3,33]. This shift agrees with the calculation
wavenumbers. Nakamoto et al. [66,67] assigned the 654 cm−1
band to the deformation vibration of Fe(AA)3.
Afzali et al. [3] assigned the IR band at 735 cm−1 of Al(TFAA)3
to symmetric CF3 bending coupled with symmetric Al−O stretch-
ing. This band in IR and Raman spectra of Fe(TFAA)3 complex
appeared as two bands at about 730 and 670 cm−1. Accord-
ing to GaussView visualization, they coupled with νsO−Fe−O and
δCH and observed at 1145 and 1138 cm−1 as strong intensity IR
α
bands. The IR weak intensity band of Fe(AA)3 at 1189 cm−1 as-
signed to δCH , νsC−O.
α
3.2.2.3. Below 1000 cm−1 region. We expect to observe Fe−O,
C−CF3, and C−CH3 stretching, in-plane bending of CF3 group, out-
of-plane bending of CH , and in- and out-of-plane deformations of
α
chelated ring movements in this region. Upon theoretical results
of Fe(TFAA)3, the IR weak intensity bands at 949 and 929 cm−1
assigned to the C−C−C in-plane bending coupled to the CH3 rock-
ing and δaCF3. This band in Fe(AA)3, Cr(AA)3, and Al(TFAA)3 com-
plexes reported at 942, 939, and 957 cm−1 [3,33]. According to the
9

F. Gandomi, M. Vakili, R. Takjoo et al.
Journal of Molecular Structure 1248 (2022) 131347
νaO−Fe−O movement, respectively, while upon VEDA’s PEDs the
first band is δsCF3 for fac and νsO−Fe−O for mer isomer. The men-
tioned band has not been observed in Fe(AA)3 and Cr(AA)3 com-
plexes.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
By increasing the metal-ligand, M−L, strength, the frequency of
the O−M stretching is expected to increases. The Fe−O asymmetri-
cal stretching band in Fe(AA)3 was observed as two medium inten-
sity bands at 559 and 548 cm−1 (average 554 cm−1). These vibra-
CRediT authorship contribution statement
tional band frequencies in Fe(TFAA)3 appear at 581 and 551 cm−1
,
Farzad Gandomi: Methodology, Formal analysis, Investigation,
Writing – original draft. Mohammad Vakili: Conceptualization, Su-
pervision, Writing – review & editing. Reza Takjoo: Writing – re-
view & editing. Sayyed Faramarz Tayyari: Supervision, Writing –
review & editing.
as a strong and a weak intensity band, respectively. The differ-
ence in their intensities is due to different contributions of cou-
pling with other vibrational modes. According to the animation
of GaussView, the contributions of δaCF3 and δC−C−O in the
high-intensity band are lower and higher than that in the low-
intensity band, respectively. Also, the symmetric Fe−O stretching,
νsFe−O, vibrational band in Fe(TFAA)3 and Fe(AA)3 are observed
at 425 and 433 cm−1, respectively. This band in Fe(AA)3 assigned
to νsFe−O, δCCC, δCCH3, while in Fe(TFAA)3 assign to νsFe−O,
δCCCH3, δCCCF3. In addition to M−L strength, the shifted of these
bands in Fe(TFAA)3 in comparison to Fe(AA)3 is due to their differ-
ent couplings.
Acknowledgments
The authors would like to express their sincere thanks and ap-
preciation to Ferdowsi University of Mashhad for the financial sup-
port during this research.
Funding
Nakamoto et al. [66,67] assigned the 298 cm−1 band to the
Fe−O stretching vibration of Fe(AA)3. According to our calculations,
this band is assigned to the asymmetric O−Fe−O stretching vibra-
tion coupled to the ring deformation. According to our calculation
results, in the Far-IR of Fe(TFAA)3, the medium intensity bands
in the 315–270 cm−1 region are assigned to the different vibra-
tional modes of the molecule, such as δO−Fe−O, δC-CH3, δC−CF3,
and out-of-plane and in-plane deformation of the chelated ring.
The νaFe−O vibration is coupled with in-plane deformation of the
chelated ring.
The authors did not receive support from any organization for
the submitted work.
Consent to participate
All authors agreed to participate in this research.
Supplementary materials
Additional supporting information can be found in Tables S1–6
and Figs. S1–4 in supplementary materials.
The theoretical and experimental Far-IR spectra of Fe(TFAA)3 in
the 700–250 cm−1 region are compared in Fig. 7a and b. For com-
parison and the best assignment, the recorded Far-IR spectrum of
Fe(AA)3 is also shown in Fig. 7a. According to Fig. 7b and Table
3, since there is no difference in the calculated frequencies and
their intensities of mer and fac isomers, so the vibrational spec-
troscopy cannot be used to determine the type of isomer in the
sample. Therefore, the possibility of two isomers in the sample is
reasonable, which agrees with their molecular structures and rela-
tive energies.
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.131347.
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