Theoretical and Vibrationnal Study of Tetraethylammonium Hexafluorosilicate of [(C₂H₅)₄N]₂Sif₆

Theoretical and Vibrationnal Study of Tetraethylammonium Hexafluorosilicate of [(C₂H₅)₄N]₂Sif₆

O. Berradi1, M. S. Elyoubi2

Laboratory of Materials, Electrochemistry and Environment Department of Chemistry, Faculty of Sciences, University Ibn Tofail

Kenitra -morocco

R. Ghailane3, K. Marrakchi4

1. Laboratory of organic synthesis, organometallic and theoretical, Faculty of Sciences, Ibn Tofail University, Kenitra, Morocco

2. Laboratory of Theoretical Chemistry and Modeling University Mohammed Agdal, Faculty of Sciences

   Rabat, Morocco.

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   Abstract Systematically study of crystal structures and molecules of compounds R2MX6 type of the general formula R2MX6 or R: cation substitute Ammonium, M: tetravalent metal and X:Halogène have a big importance for interpretation of certain number of basic physical propriety of crystals of this family [1].In this study we determined in advance the structure of compounds tetraethyl ammonium hexafluorosilicate of formula [(C2H5)4N]2SiF6 by using the technique of diffraction RX in powder which is calculated in normal temperature and after resolution of principal peak, we have seen that this compound is crystallized in monoclinic system with a space group P21[2].Theoretical analysis of cation [(C4H5)4N]+ displays that the outnumbering of vibration in the molecular group D2d, we have 177 modes of internal vibrations and 6 modes of vibration for anion SiF 2-[2].

   compounds, the observation of reflections not indexed in the Fm3m symmetry (Z=4) shows that the symmetry is exactly Fd3c [6, 5]. Maximum when the symmetry of the cation does not reach Td, the crystal is much lower than Fm3m, SnCl 2- anions can suffer distortions and rotational movements around the central atom Sn. such a situation is observed for hexachlorostannate of CH3NH3+ and (CH3)3NH+ trigonal symmetry [4].

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   The IR spectroscopy of [(C2H5)4N]2SiF6 was performed on the basis of a C1 symmetry for cations and anions [7] it was concluded that these groups are located on general positions compatible with the group space P21. Our objective is to study quantum compound of formula [(C H ) N] SiF aim to make an identification with the

   2 5 4 2 6

   Experimentally results [2] are comparable with those obtained theoretically by the HF method with STO-3G basis [7].

   Keywordstetraethylammonium;hexafluorosilicate;Crystal; Theoretical analysis; IR spectra.

   1. INTRODUCTION

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      The IR vibrational spectra of hexachlorostanate alkylamm- onium compounds of the general formula where is R2MX6: ammonium cation substituted, M: tetravalent metal (M = Re, Te, Sn, U, Sb, Si, Pt, Zr, Pd) and X: halogen (X = Cl, F, I, and Br) has been widely reported in the literature have been classified into various structural types. Their classification depends mainly: methods of synthesis, nature and size of the organic groups 1.In terms of crystal symmetry, the compounds of this type generally have a kinship with anti- fluorite structure of the compound (NH4)2SnCl6[1], in these compounds the symmetry of tetrahedral site occupied by the cation is the same as cation of free Td (43m), the vertices and centres of faces of the mesh cube are occupied by anion MX -2 with orientation compatible with the symmetry Fm3m. Generally, the compounds of the types [(R4N)2N]2MCl6 antifluorines keep their network, they sometimes suffer distortions and become a different symmetry in certain

      experimental results [2].

      Characterization of [(C2H5)4N]2SiF6 by X-ray diffraction powder has enabled us to provide a better structure for this compound.

      The study vibrational spectroscopic IR is developed to achieve additional information from those determined by X-ray diffraction for this compound. This study is supported by calculations of vibrational spectra from the theoretical optimized geometry obtained by calculating HF/STO-3G [8], allowing us to achieve a more rigorous assignment of the bands observed in the experimental IR spectrum.

   2. EXPERIMENTAL

      The single crystals of formula [(C2H5)4N]2SiF6 is obtained by slow evaporation, at room temperature, of a hydrofluoride acid solution containing stoichiometric amounts of tetraethylamm-onium (C2H5)4N+, (acidified with (HF) and SiCl4.

      The characterization by X-ray diffraction of tetraethyl ammonium hexachlorossilicate was performed using a diffractometer system "XPERT-PRO" menu of a Goniometry "PW3050/60" to counter, anticathode copper (Cu) lengths wave K-Alpha 1.54 Ã… [2].

      Infrared spectra is recorded at room temperature in the 4004000 cm-1 spectral range with 8 cm-1, resolution with Bruker Tensor 27 FTIR spectrometer and the application of the KBr pellet technique [2].

   3. RESULTS AND DISCUSSIONS

1. Crystallography

   The x-ray crystallographic data obtained at ambient temperature [(C2H5)4N]2SiF6 indicated that it belongs to the monoclinic system with the space group P21 shows that this compound crystallizes in the monoclinic system with its setting: a = 13.430Å,b =13.825 Å, c =12.940 Å, = 90.942°

   Cell volume: V = 2402.24 and space group P21[2].

2. Quantum Calculations

   The quantum calculations have allowed us to optimize the geometry of this compound [8] and to establish the infrared spectra of a vibrational frequency calculation [8]. This was achieved using HF method and STO-3G basis (HF/STO-3G).

   1. optimized geometry

      Optimized geometry of the complex of formula [(C2H5)4N] 2SiF6 is obtained by the method HF/STO-3G using the program GAUSSIAN 07 (Figure 1) [8].

      Figure 1: The optimized Geometry of complex [(C2H5)4N]2SiF6 method HF/STO-3G

   2. Geometric theoretical and experimental parameters of [(C2H5) 4N]2SiF6

      The theoretical geometric parameters are comparable with those obtained experimental in the case of compounds same family (Table 1) [1, 2,3].

      Parameters	Theoretical values	experimental values
      Si-F	1.6484- 1.6873	2.680 – 2.668
      N-C	1.5309- 1.5639	1.528 – 1.548
      C-C	1.5362- 1.5411	1.513 – 1.561
      CNC	107.65- 112.535	107.0 – 113.5
      NCC	114.75- 116.35	112.5 – 114.3

      Table1: Interatomic distances (A°) in angstroms and bond angles in degrees (°) of [(C2H5)4N]2SiF6

      Geometrical parameters of the angles that which we no have experimental values for the family compound [(C2H5)4N]2SiF6 are grouped in the table below (Table 2).

      Values of the compound geometric dihedral of compound [(C2H5)4N]2SiF6 confirms the XRD results leave theoretical analysis and can also be made by the interpretation made the CH3 and CH2 groups are distorted and rotational displacements

      around the central atom if those who will lead a lowering of symmetry crystalline compound (Table 3).

      Tableau 2: Angles in degrees of connection the complex [(C2H5) 4N]2SiF6

      A	V/U(Degré)	A	V/U(Degré)
      C-C-H	112.25-114.24	F-F-F	108.5
      Si-F-H	<>69.10-138.75	F-F-C	63.84-116.86
      F-Si-H	70.35-114.22	Si-F-C	123.59
      H-Si-H	20.64-67.50	F-H-H	57.03
      F-Si-C	94.1134	F-H-C	154.90-177.7
      C-F-H	44.74-64.47	F-C-N	108.4907
      F-C-H	164.0229	N-H-F	61.3245
      H-F-H	49.94-60.34	N-H-C	114.3288
      F-Si-F	87.80-91.68	N-C-H	104.60-109.70
      H-C-H	107.27-112.08	Si-H-H	120.309
      		F-F-C	63.83-116.86

      A : Angles ; V : Valeurs ; U : unités

      Tableau 3: Deidre of connection the complex [(C2H5) 4N] 2SiF6

      D	V/U(Degré)	D	V/U(Degré)
      H-C-C-H	(-177 ,9)- (178,17)	H-F-H-C	(-27 ,89)-(49,90)
      C-C-H-F	(-158 ,8)-(178,5)	C-F-H-C	(-22 ,28)-(21,89)
      N-C-C-H	(-178 ,31)- (178,11)	Si-F-H-C	(-22 ,80)-(19,86)
      C-N-C -H	(-179 ,22)- (179,23)	F-Si-F-H	(-173,06)- (158,74)
      C-N-C -C	(-176 ,80)- (173,54)	H-F-H-F	(-176,70)- (107,91)
      F-C-C-H	(-176 ,11)- (65,11)	F-Si-F-C	(-122,05)- (149,56)
      N-CH-F	(-56 ,27)-(77,46)	C-F-F-H	(-170,68)- (156,58)
      H-F-C-C	(-15 ,11)- (146,25)

      A : Angles ; V : Valeurs ; U : unités

   3. Theoretical and Experimental vibrationnal spectra of

      [(C2H5)4N]2SiF6

      The infrared spectra experimental of [(C2H5)4N]2SiF6 (Figure II), the latter is mixed with 95% KBr, is recorded at T=25C°in the frequency range between 400 and 4000 cm-1, and with a spectral resolution of 8 cm-1 the different peaks observed and their assignment will be reported in (Table IV) [2].

      Theoretical and experimental Infrared Spectra of [(C2H5)4N]2SiF6 are similar to how they show (figure 2 and 3).

      Figure 2: Experimental Infrared Spectra of [(C2H5)4N]2SiF6

      Figure 3 : Theoretical Infrared Spectra of [(C2H5)4N]2SiF6

   4. Identification and interpretation the IR spectrum experimental and theoritical of [(C2H5)4N 2SiF6

      Experimental and Theoretical spectra of tetraethyl ammonium hexafluorosilicate studied are comparable, which we shared in the areas mentioned below:

      1. Domain in which these frequencies below 533 cm-1:

         These frequencies are assigned to the whole molecule of vibration and movement Roking CH3 and CH2 groups.

      2. Frequency range 533-1100 cm-1:

         These piks we attributed to the stretching of the Si-N bonds and F ( CN) / ( Si-F), and deformation of entities CH3 CH2 and torsion symmetrical DC link shown respectively to the frequencies 1083, 1060 and 1029 cm-1 asymmetrical deformation of the CH3 group CH2 and CN bond torsion asymmetric and CC are located about 1100 cm-1.

      3. Frequency range 1174-1396 cm-1:

         In this area we have allocated these frequencies to asymmetric deformation modes of CH2 and CH3 groups, Roking CH3 and torturers of liason CC.

      4. Frequency range 1450-1750 cm-1

         Frequencies that appear vers1450 cm-1 are attributed to deformation of the angles HCH and CNC groups CH3, CH2 and CH3 deformation, CH2 and CH3 group of Roking are located vers1620 cm-1 and finally twisting motion appears around 1750 cm -1.

      5. Frequency range 2750 -3250 cm-1.

The piks that appear in this area are attributed to CH stretching of liaison.

Tableau 4: Experimental and Theoretical Frequency of

[(C2H5)4N] 2SiF6

Exp: Experimental frequency ; th : Theoritical Frequency

IV-CONCLUSION

The interpretation of the IR spectrum of [(C2H5)4N] 2SiF6 was done satisfactorily on the basis of a C1 symmetry for cations and anions, it can be concluded that these groups are located on general positions consistent with space group P21. The calculation of vibrational frequencies by the method HF/STO-3G values provided in good agreement with the experimental values that allowed us to establish a detailed allocation of the IR spectrum. Frequencies of the entities constituting the crystal show no significant difference compared to their frequencies in the free state, thus reflecting

the ionic character of this compound and the individuality of the entities that constitute it.

REFERENCES

1-Ali uasri, laboratoire physico-chimie matériaux inorganique, Kenitra Maroc, (2003).

Kenitra Maroc, 2008

4-N .B. Col Thup, L. H. Daly and S. E. Wiberly, « Introduction to IR and Raman spectroscopy », 2nd edition, 1975.

5-R.W.Berg and I.Stofte, Acta.Chem.Scand.B,33(1979)157.

6-R.W. Berg,And K.Nielsen Acta.Chem.Scand.Ser.A33 (2) (1979) 157. [7]-M.S.Elyoubi, Thèse de specialité, Sfax, Tunisie, 1987