Vol.3, No.8, 683-688 (2011) Natural Science
http://dx.doi.org/10.4236/ns.2011.38091
Density functional theory studies on the
structure, vibrational spectra of three new
tetrahalogenoferrate (III) complexes
Shahriare Ghammamy1,2*, Kheyrollah Mehrani1, Somayyeh Rostamzadehmansor1,
Hajar Sahebalzamani1
1Departments of Chemistry, Faculty of Science, Ardabil Branch, Islamic Azad University, Ardabil, Iran;
*Corresponding Author:
2Department of Chemistry, Faculty of Science, Imam Khomeini International University,Ghazvin, Iran.
Received 9 January 2011; revised 2 March 2011; accepted 12 March 2011.
ABSTRACT
Three new tetrahalogenoferrate (III) complexes
with the general formula (R)4N[FeCl3X]– in that
(X = F−, Cl−, Br−) synthesized by the reaction of
FeCl3 with (C2H5)4NF, (CH3)4NCl and (C4H9)4NBr
salts in anhydrous CH3CN. These were charac-
terized by elemental analysis, IR, UV/Visible and
81Br-NMR spectroscopy. The optimized geome-
tries and frequencies of the stationary point are
calculated at the B3LYP/LANL2DZ level of theory.
Harmonic vibrational frequencies and infrared
intensities for FeCl3F−, FeC4 l and FeCl3Br− are
studied by means of theoretical and experi-
mental methods. The calculated frequencies are
in reasonable agreement with the experiment
values.
Keywords: Tetrahalogenoferrate(III); Theoretical
Study; Br-NMR; Density Functional Calculations
1. INTRODUCTION
Recently, the interesting history and development of
the chemistry of iron halides was reviewed [1]. A new
interest steeply increasing in the last decade is caused by
possibility of ferrate use as a strong oxidizing agent for
environmental uses [2-5] and as a high capacity source
of cathodic charge [6-8]. Furthermore it was found that
some iron (III) complexes provide a useful structural and
electronic model for the similarly coordinated iron (III)
sites found in the heme iron enzymes [9]. The tetrahalo-
genoferrates (III) have been utilized in bioinorganic
chemistry as reagents for synthesizing some model
compounds, such as [Fe2S2Cl4]2– [10,11]. The investiga-
tion of the structures and properties of these compounds
and their similarities are interested. In this work, we re-
port on the synthesis and characterisation of new com-
plexes of type (R)4N[FeCl3X]– (X = F–, Cl–, Br–) Ob-
tained directly from FeCl3 and tetraalkylammonium salts.
During this study we report the optimized geometries
and infrared spectral measurements, assignments and
electronic structure calculations for compounds. The str-
uctures of compounds have been optimized by the den-
sity functional theory (DFT) based method at B3LYP/
LANL2DZ levels of theory, using the Gaussian 03
package of programs [12-14]. The comparison between
theory and experiment is made.
2. EXPERIMENTAL SECTION
2.1. General
The density functional and abinitio calculation have
been performed with the Gaussian program and the basis
sets implemented therein [13,15-17].
Acetonitrile (Fluka, P.A.) was distilled several times
from phosphorus pentaoxide before use, thereby reduc-
ing its water content to < 4 ppm. FeCl3 (Merck, p.a.)
were used without further purification. Anhydrous
Et4N+F– and Me4N+F were obtained by a drying proce-
dure of the tetrahydrate in high vacuum (d, 130˚C) [18].
Infrared spectra were recorded as KBr disks on a Shi-
madzu model 420 spectrophotometer. The UV/Visible
measurements were made on an Uvicon model 922
spectrometer. 81Br-NMR were recorded on a Bruker
AVA NCEDRX 500 spectrometer. The percent compo-
sitions of elements were obtained from the Microana-
lytical Laboratories, Department of Chemistry, OIRC,
Tehran.

S. Ghammamy et al. / Natural Science 3 (2011) 683-688 684
2.2. Synthesis of Tetraethylammonium
Fluorotrichloroferrate (III),
[(C2H5)4N][FeCl3F] (1)
To a solution of FeCl3 (0.26 g, 1.6 mmol) in MeCN
the solid powder tetraethtylammonium fluoride(0.26 g,
1.74mmol) was added under stirring at room temperature
until yellow solid precipitate was formed. After 2 h stir-
ring, the mixture was filtered, washed ether, and dried at
room temperature. m.p. 229 - 231˚C. Anal. Calc. for
C8H20NFeCl3F: C, 25.78; H, 5.37; N, 3.76. Found: C,
26.45; H, 5.89; N, 4.32%. IR (KBr) (cm–1): 3438, 3225,
3028, 2987, 2946, 2780, 2655, 2358, 1850, 1462, 1401,
1307, 1021, 792, 499, 483, 428. UV-Vis in CH3CN,
λ/cm–1: 41493, 36496, 31847, 27548.
2.3. Synthesis of Tetramethylammonium
Tetrachloroferrate (III),
[(CH3)4N][FeCl4] (2)
Solid powder tetrametylammonium chloride (0.22 g, 2
mmol) was added to a solution of FeCl3 (0.29 g, 1.78
mmol) in MeCN under stirring at room temperature until
yellow solid precipitate was formed. Stirring was con-
tinued for 3 h. the mixture was filtered, washed with
ether, and dried at room temperature. m.p. 299 - 300˚C.
Anal. Calc. for C4H12NFeCl4: C, 17.65; H, 4.41; N, 5.15.
Found: C, 17.96; H, 4.96; N, 5.52%. IR (KBr) (cm–1):
3421, 3225, 3017, 2980, 2960, 2780, 2655, 2477, 1850,
1484, 1411, 1283, 948, 499, 416. UV–Vis in CH3CN,
λ/cm–1: 41666, 36630, 31948, 27624.
2.4. Synthesis of Tetrabuthylammonium
Bromotrichloroferrate (III),
[(C4H9)4N][FeCl3Br] (3)
To a solution of FeCl3 (0.167 g, 1.02 mmol) in MeCN
the solid powder tetrabuthtylammonium bromide (0.365
g, 1.13 mmol) was added under stirring at room tem-
perature until dark red solid precipitate was formed. Af-
ter 2 h stirring, the mixture was filtered, washed ether,
and dried at room temperature. m.p. 69 - 70˚C. Anal.
Calc. for C16H36NFeCl3Br: C, 39.46; H, 7.43; N, 2.89.
Found: C, 40.01; H, 8.21; N, 3.59%. IR(KBr) (cm–1):
3431, 3315, 3225, 3010, 2961, 2875, 2765, 2398, 1950,
1466, 1382, 1169, 1042, 531, 463, 453. UV–Vis in
CH3CN, λ/cm–1: 42016, 36764, 31645, 27624.
2.5. Computational Methods
Density functional theory (DFT) calculations were
carried out at B3LYP/LANL2DZ levels of theory with
the Gaussian 03 package of programs [13,19] which
combines the exact Hartree-Fock exchange with Becke,s
and uses the Lee-Yang-Parr correlation function in order
to include the most important correlation effects. The
structures of the molecules were completely optimized
without any symmetry in all the levels. The optimized
structural parameters were used in the vibrational fre-
quency calculations at the HF and DFT levels to charac-
terize all stationary points as minima [20]. Harmonic
vibrational frequencies in cm–1 and infrared intensities
(int) in Kilometer per mole of all compounds were per-
formed at the same level on the respective fully opti-
mized geometries. These compounds and their data are
in accordance with recent works on the formation of four
coordinate intermediates.
3. RESULTS AND DISCUSSION
The (C2H5)4N[FeCl3F] complex was obtained by the
reaction of (C2H5)4NF with FeCl3 in the acetonitrile sol-
vent (reaction (1)). The reaction of FeCl3 with (CH3)4NCl
in acetonitrile solvent gave (CH3)4N[FeCl4] (reaction
(2)). (C4H9)4N[FeCl3Br] synthesized by the reaction of
FeCl3 with (C4H9)4NBr in acetonitrile (reaction (3)).
(C2H5)4NF + FeCl3 → (C2H5)4N[FeCl3F] (1)
(CH3)4NCl + FeCl3 → (CH3)4N[FeCl4] (2)
(C4H9)4NBr + FeCl3 → (C4H9)4N[FeCl3Br] (3)
The structures of complexes 1, 2 and 3 are shown in
Figure 1 Geometry optimization shows that symmetry
for compounds 1 and 3 is C3V. Geometry optimization
shows that symmetry for compound 2 is D4h. Selected
bond distances and angles are reported in Table 1. We
Table 1. Geometrical parameters optimized of compounds1-3,
bond length (Å) and angle (◦).
B3LYP/LANL2DZ
[FeCl3F]– [FeCl4]– [FeCl3Br]–
Bond lengths (Å )
Fe1-Cl2 2.298 2.289 2.286
Fe1-Cl3 2.298 2.289 2.287
Fe1-Cl4 2.298 2.289 2.286
Fe1-X5 1.817 2.289 2.458
Bond angles (◦)
Cl2-Fe1-Cl3 109.829 109.462 109.971
Cl2-Fe1-Cl4 109.755 109.437 109.809
Cl2-Fe1-X5 109.129 109.46 109.075
Cl3-Fe1-Cl4 109.831 109.474 109.971
Cl3-Fe1-X5 108.152 109.501 109.918
Cl4-Fe1-X5 109.125 109.493 109.072

S. Ghammamy et al. / Natural Science 3 (2011) 683-688
685685
(a)
(b)
(c)
Figure 1. Optimized geometries of (a) [(C2H5)4N][FeCl3F]–, (b) [(CH3)4N][FeCl4]–, (c)
[(C4H9)4N][FeCl3Br]– at B3LYP/LANL2DZ level of theory.
could not compare the calculation results given in Table
1 with the experimental data. Because the crystal struc-
ture of the title compound is not available till now. The
calculations shown that the structures of these three tri-
chlorohaloferrate salts, are not formed dimer, trimer, or
more multi nuclear structures in solid states. B3LYP/
LANL2DZ results showed that the Fe-X (X = F, Cl, Br)
bond length values for the [FeCl3X]– in compounds 1 - 3
are 1.817, 2.289 and 2.458 Å, respectively. Also, the
Fe-Cl2 bond lengths values in [FeCl3X]– are 2.298,
2.2893 and 2.286 Å, respectively. These results reveal
that the bond order for Fe-X bonds decrease from com-
pounds 1 to 3, while for Fe-Cl2 bonds, the bond orders
increase. It can be concluded that the decrease of Fe-X
bonds lengths and the increase of Fe-Cl2 bond lengths in
compounds 1 - 3 result from the increase of the hyper-
conjugation from compounds 1 - 3 Besides, the θCl2-Fe1-X5
bond angle values in compounds 1 - 3 are 109.129,
109.46 and 109.075, respectively (see Table 1). The
decrease of θCl2-Fe1-X5 bond angle values from com-
pounds 1 to 3, could again, be explained by the increase
of the hyperconjugation from compounds 1 to 3. The
calculated infrared spectra of three ferrate complexes are
presented in Figure 2. The solid-state IR spectrum for

S. Ghammamy et al. / Natural Science 3 (2011) 683-688 686
the complexes 1, 2 and 3 shows Fe-Cl stretching reso-
nances (300 - 400 cm−1). The harmonic vibrational fre-
quencies of all the stationary points at the B3LYP/
LANL2DZ level along with the available experimental
data [21-23] presented in Table 2. The compounds
structure shows the presence of Fe-Cl stretching vibra-
tions in the region 350 - 400 cm−1 which is the charac-
teristic region for the ready identification of the Fe-Cl
stretching vibrations. In general the compounds Fe-Cl
vibrations calculated theoretically are in good agreement
with the experimentally reported values.
Zero-point energies (ZPE) and several calculated
thermodynamic parameters of compounds 1 - 3, are given
in Table 3. The total energies of compounds [FeCl3F]−,
[FeCl4]− and [FeCl3Br]− at 298 temperature at B3LYP/
LANL2DZ methods are also presented.
Figure 2. Calculated infrared spectra of FeCl3F−, 4 FeCl

and FeCl3Br− (top to bottom, fre-
quencies in cm−1, intensities in arbitrary units).

S. Ghammamy et al. / Natural Science 3 (2011) 683-688
687687
Table 2. Calculated and experimental frequencies of com-
pounds 1 - 3 (cm–1).
Compound B3LYP/LANL2DZ Exptl
[FeCl3F]– 125, 165, 309, 362, 630 792,483
[FeCl4]– 119, 362 378
[FeCl3Br]– 110, 235, 325, 362 376
Table 3. Theoretically computed energies, zero-point vibra-
tional energies and Gibs free energy for compounds 1 - 3.
B3LYP/LANL2DZ
Parameters [FeCl3F]– [FeCl4]– [FeCl3Br]–
HF energy –268.437381–183.540346 –181.756907
Zero-point energy 0.0050809990.004219585 0.003912898
Total energy –268.4323003–183.536126 –181.7529941
Gibs Free energy –268.468259–183.5732334 –181.7912501
4. CONCLUSIONS
Three tetraalkylammonium salts of FeCl3 were synthe-
sized in one step and characterized by elemental analysis,
IR, UV/Visible, and 81Br-NMR techniques. Production
of these compounds show the ability of tetraalkylammo-
nium salts in halide addition to transition metal and main
group elements compounds and the optimized geometry
parameters calculated at B3LYP/LANL2DZ level. The
optimized structures are in good agreement with the
available experimental results. In the present article, the
infrared spectra of the ferrate halide complexes were
studied using the theoretical and experimental methods.
Our theoretical infrared spectrum of compounds 1 - 3 are
in very good agreement compared to our experimental
spectrum.
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