Density functional theory studies on the structure, vibrational spectra of three new tetrahalogenoferrate (III) complexes

doi:10.4236/ns.2011.38091

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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: [email protected]

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

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(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

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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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