Correlation of Crystal Parameter with Vibrational Data of New Three Tetramethylammonium Salts

Examination of the solid state infrared spectra of the tetramethylammoniumcation in salts shows correlation of infrared spectral properties with C–H···X hydrogen bonding and crystal habits in these tetramethylammonium salts. The IR predicted crystal habits are comprised by experimental and theoretical data. A good relation between three data has been found. The C–H stretching region characteristic hydrogen bonding shifts in the above salts. In this research three complexes of tetramethylammoniumcation have been synthesized and the structures of them have been analyzed by correlation of vibrational data with crystal structures. These correlation shows that crystal symmetry (Tetrahedral), cation distortion (undistorted), site symmetry (D2d), unite cell symmetry (D4h 7) for (CH3)4NPF6 and crystal symmetry (Tetrahedral), cation distortion (distorted), site symmetry (D2d), unite cell symmetry (D4h 7) for (CH3)4NOH and crystal symmetry (Tetrahedral), cation distortion (undistorted), site symmetry (D2d), unite cell symmetry (D4h 7) for (CH3)4NF.


INTRODUCTION
Tetramethylammonium compounds have many applications in science and biology.It is extremely difficult, if not impossible, to prepare single crystals of tetramethylammonium salts suitable for diffraction studies; the available methods of preparation give microcrystalline powders that are not suitable for X-ray single crystal diffraction.Scientists' effort to find and use simple substituted methods for studying crystal habits of tetramethylammonium salts.One of the suggested methods is the use of infrared spectra and assigning of it by symmetry.The vibrational spectrum of the tetramethylammonium (Me 4 N + ) ion has been the subject of several publications during the last four decade [1][2][3] .Many studies had been done on the vibrational spectra of tetramethylammonium salts and ahowed that it possible to correlate of infrared spectral properties with C-H…X hydrogen bonding and crystal habit in tetramethylammonium salts fluoride,(CH 3 ) 4 NFwas synthesized by reported method 7 .
The substrates and the solvents were used after drying and purifying by distillation by usual procedures.The middle fractions were collected after rejecting the head and the tail portions.The IR spectra were recorded on a Shimadzu model 420 spectrophotometer.The UV/ Visible measurements were made on a Shimadzu model 2100 spectrometer.Proton, 13 C, 19 F NMR were carried out on a Bruker AVANCE DRX 500 spectrometer at 500, 125, 470.66 MHz.All the chemical shifts are quoted in ppm using the highfrequency positive convention; 1 H and 13 C NMR spectra were referenced to external SiMe 4 and 19 F NMR spectra to external CFCl 3 .This salt was estimated iodometrically after oxidizing the compound with acidic persulphate solution.Fluoride content was determined gravimetrically as PbClF [8][9] .The percentage compositions of carbon, hydrogen and nitrogen were obtained from the microanalytical Laboratories, Department of Chemistry, OIRC, Tehran.

Synthesis of tetramethylammonium compounds
(CH 3 ) 4 NPF 6 was prepared inside a glove box purged with argon.PF 5 was dissolved in dry acetonitrile (25 ml) in a polyethylene beaker and a stoichiometric amount of tetramethylammoniumfluoride was added with stirring at room temperature.Within 5 minutes a solution formed which upon refrigerating, gave solid (CH 3 ) 4 NPF 6 , which was isolated by filtration.The solid was washed with dry isopropanol and diethyl ether, and dried under vacuum for 1 hour.UV/Visible, 19 F-NMR, 13 C-NMR and 1 H-NMR were used for characterization of these compoundsformula.
For (CH 3 ) 4 NPF 6 green microcrystalline was obtained.The compound was finally dried in vacuum over phosphorous penfluoride.The yield of (CH 3 ) 4 N[MoCl 5 F] was ca 98%.Satisfactory elemental analysis was obtained.For (CH 3 ) 4 NPF 6 , IR data and spectrum for cation and anions have been assigned to different modes, respectively.(Fig. 1, Table 1) For (CH 3 ) 4 NOH,IRdata and spectrum for cation and anion have been assigned to different modes, respectively.(Fig.2, Table 2) For (CH 3 ) 4 NF,IR data and spectrum for cation and anion have been assigned to different modes, respectively.(Fig.3, Table 3)

Structure solution and refinement
The structure of crystallized compounds have been solved by direct methods and refined by full-matrix-least squares techniques on F 2 .All non-hydrogen atoms were refined anisotropically.The position of hydrogen atom was assigned an isotropic thermal parameter.Corrections for the LP as well as the empirical correction for absorption using the SADABS programs were applied.All structural calculations were carried out by using the SHELXTL V. 5.10 structure determination software.The intensity data were collected on a SIMENS SMART CCD diffractometer with graphitemonochromated Mo Ká radiation.The crystal structure was solved by directed methods 9 .

RESULTS AND DISCUSSION
The crystal and molecular structure of tetramethylammoniumcompounds, have been determined at 130(2) K by X-ray diffraction.X-ray data clearly demonstrate inequality between different bonds that is responsible for the higher reactivity of these compounds over similar agents in terms of the amount of solvent required, short reaction times and high yields.The reason for this inequality is due to the CH…N hydrogen bond that forms between the methyl hydrogen of the cation and hydroxide or halide atoms of the anion 10 .This type of hydrogen bonding in tetramethylammonium salts has been studied by Harmon et al.The IR spectrum and hydrogen bonding of these compounds is similar to the other tetramethylammoniumsalts that show the existence of hydrogen bonding.
Halo complexes of transition metals are also as general purpose, stoichiometric oxidant in synthetic organic chemistry,and a variety of reaction pathways including both atom-transfer and electron-transfer are involved 12 .
The results of chemical analyses of the(CH 3 ) 4 NPF 6 green product revealed the occurrence of C:H:N in the atomic ratio, while that of chemical determination of the different state of phosphorous by iodometry conspicuously showed the presence of phosphorous.It may be emphasized that the chemical estimation of oxidation state of a metal, capable of displaying variable oxidation numbers, is particularly important and crucial in assessing its actual oxidation state in a specific compound 11 .Also magnetic susceptibility measurements show that (CH 3 ) 4 NPF 6 has two odd electrons.Magnetic moment is 2.91BM that to confirm to amount mentioned in sources for phosphorous compound and d 2 electronic configuration of central metal.
The IR spectra of the (CH 3 ) 4 NPF 6 recorded both in KBr and in nujol media showed the characteristics of tetramethylammonium (CH 3 ) 4 N + ion, and this part of the spectrum is similar to that observed for (CH 3 ) 4 N + in the case of tetramethylammoniumsalt.The additional bands have been appeared and have been assigned respectively [11].Which owe their origins to the presence of coordintatedphosphorous and fluoride group at PF 6 -ion.Table 1 shows the assignment of (CH 3 ) 4 NPF 6 IR spectrum.Thus considering the results of elemental analyses, chemically estimated oxidation state phosphorous, electrochemical analyses and IR spectral studies it may be safely inferred that the brown reduced product is (CH 3 ) 4 NPF 6 with the metal occurring as phosphorous.
This again lends support to our notion that the phosphorous of(CH 3 ) 4 NPF 6 is reduced to a Molibden species in the oxidations of organic substrates studied herein.Calculation of structure of PF 6 -by DFT method shows the declined trigonal structure.
Infrared and Raman spectra of tetrahedral M(CH 3 ) 4 molecules have been discussed in considerable details.It is commonly assumed that tetramethylammonium ion on the average has T d symmetry, and an approximate tetrahedral C 4 N skeleton has been established for many (CH 3 ) 4 N + salts by means of X-ray crystallography.In this approximation, the 45 degrees of vibrational freedom of the ion are distributed on the symmetry species of point in this way by: Ã vib =3A 1 +1A 2 +4E+4T 1 +7 T 2 .The Me 4 N + ion has 19 normal vibrations which belong to the following irreducible representations of its symmetry group T d : 3A 1 +A 2 +4E+4T 1 .From group theoretical it follows that of all these vibrations only those with T 2 symmetry are infrared active, whereas in isotropic Raman scattering only the A 1 modes and in anisotropic scattering only the E and T 2 modes are allowed.Species of this type have seven infrared active T 2 bonds under T d symmetry, but formation of hydrogen bonding between tetramethylammonium and suitable anions can distort T d symmetry of this cation.At this state the infrared spectrum may be modified through the appearance of previously forbidden bands or the splitting of bands can arise from the coupling of the vibrations of molecules in the same unit cell.By examination of the solid state infrared spectrum of tetramethylammonium ion salt it is possible to predict the lattice, the approximate size of the anion, the closeness of approach of the cation to each other, the presence or absence of cation to anion hydrogen bonding and whether or not the cation is distorted from tetrahedral.The detail assignment of IR spectrum of tetramethyl ammonium compounds, show (Fig. 1, 2, 3).The IR