Two new Fluoro complexes: Tetramethylammonium trifluoroplumbate (TMATriFP)
and Tripropylammonium tetrafluoroantimonate(TriPATFA)

Zahra Javanshir^a, Shahriare Ghammami ^a,b*, Kheyrollah Mehrani ^a

^aDepartments of Chemistry, Faculty of Science, Islamic Azad University, Ardebil Branch, Ardabil, Iran

^bDepartment of Chemistry, Faculty of Science, Imam Khomeini International University, Ghazvin, Iran,

E-mail: shghamami@ikiu.ac.ir or shghamamy@yahoo.com

Abstract

Two new complexes synthesized by tetralkylammonium fluoride salts. Tetramethylammonium trifluoroplumbate and tripropylammonium tetrafluoroantimonate have been prepared from N(CH₃)₄F and PbF₂or N(C₃H₇)₃, HF and SbF₃using either CH₃CN, or excess PbF₂or SbF₃ as a solvents. The structure of the PbF₃^-and SbF₄^- anion was studied by ¹⁹F NMR spectroscopy, IR, UV/Visible spectroscopy.

Introduction

The number of Antimony (III) and Lead (II) fluorocomplexes are still scarce, and very few studies on their reactivity have been reported. Particularly the fluorides have been subject of an intense scientific discussion since the first synthesis of such a compound [1, 2].This is because of the important prerequisites for a fluorinating agents to be useful which are theirs mildness, versatility, selectivity and operational simplicity. The subject of this investigation is obtaining of inorganic fluorides and complexes [3]. Lead and Antimony fluorocomplexes have more attraction because these compounds could be prepared by reaction of fluorinating agents such as CsF, NaF, HF with a complexes.

For this purpose we used a new and strong fluorinating agent that is tetramethylammonium fluoride produced at 1990 in anhydrous form [4].

Many fluorocompounds of main group elements were produced using this reagent, namely: PF₄^- [5], SeF₅^-, TeF₅^-, [6] IF₈^-[7], and in few amounts row of transition metals fluorocomplexes like (CH₃)₄NMoO₃F [8],(CH₃)₄NCrO₃F [9], MoF₇^-, WF₇^-, ReOF₆^- [10], MoO₃F^- [11].

There were two primary incentives for selection of (CH₃)₄N⁺and(C₃H₇)₃NH with HFas the counter ion. Firstly, quaternary ions such as tetramethylammonium and tripropylammonium are often used as phase transfer catalysts. Secondly, quaternary ions such as tetramethylammonium and tripropylammonium are used as crystal growing agents. In this article a direct, simple one-step method has been used to obtaining these compounds.

Another reason that encouraged researchers for synthesizing this range of fluorinated compounds is the fewer and rare amounts of the spectroscopic data of this compounds, especially ¹⁹ F-NMR data. Some of data were reported in [12-15].

Tetramethylammonium fluoride is an ionic compound and many efforts have been made for preparation of its anhydrous form. It produces by reaction of tetramethylammonium hydroxide with hydrofluoric acid as follow:

Reagent grade PbF₃ was used. Anhydrous tetramethylammonium fluoride (CH₃)₄NF was prepared by the method reported by Christe. [20]

(CH₃)₄N[PbF₃] was prepared by the reaction of (CH₃)₄NF and PbF₃ in a 1:1 ratio in MeCN solvent as follows:

PbF₂ + (CH₃)₄NF (CH₃)₄N[PbF₃]

The reactant solution color was bright green, and the product color was light green, The typical absorption lines in IR spectra at 469 (s) cm^-1 have been attributed to Pb-F. Absorption lines at 1472(ms), 3095(sh), 499(w, br) cm^-1, have been attributed to₁₅ N-C,_CH3C-H and₁₉ N-C of (CH₃)₄N⁺ counter ion respectively (Table 1).

There are two absorption lines in the compound electronic spectra. Electronic spectra of TMATriFPb shows two shifts for Lead 232 nm ( = 280 mol.^-1lit. cm^-1) and 259 nm (= 145 mol.^-1lit.cm^-1) and that belongs to EE and EA₁ shifts (Table 3). These shifts are expected in mono substituted Plumbate ions, because of Lead position making of strong crystalline field complexes.

The expected signals were found in the ¹H-NMR and ¹³C-NMR.

The inner mobility of fluorine ions and electrophysical characteristics of complex fluorides NaSbF₄, KSbF₄, RbSbF4, CsSbF₄ and SbF₃ are studied by means of ¹⁹F NMR method and impedance spectroscopy. Types of ion motions in the fluorine subsystem of these compounds in the range of temperatures 180 - 510K are determined.Discrete mononuclear units have been characterized in the form of the matrix-isolated SbF₃ molecule and of the anion SbF₄^–, identified for the first time, in association with appropriately bulky cations in the solid phase and in organic solvents solution; the vibrational spectra of the SbF₄^– anion imply C₂symmetry. (C₃H₇)₃NH[SbF₄] was prepared by the reaction of (C₃H₇)₃N and SbF₃ and HF in a 1:1:1 ratio in MeCN solvent as follows:

SbF₃ + (C₃H₇)₃N + HF(C₃H₇)₃NH[SbF₄]

The method for the reaction of (C₃H₇)₃N with SbF₃ and HF is as for to (CH₃)₄NF and its analytical and spectroscopic data are: The reactant solution color was pale white, and the product color was white, IR spectrum at 520 (W, br) cm^-1 have been attributed to Sb-F and absorptions at 1443(m), 3065(sh), 1100(w) cm^-1, have been attributed to₁₅ N-C,_CH2C-H and_CNof (C₃H₇)₃N⁺ counter ion respectively (Table 2). There are one absorption bands in this compound electronic spectrum Electronic spectrum of TriPATFA shows one transitions for Antimony at 271nm ( = 244 mol.^-1lit.cm^-1) that belongs to B₁A₁ shift (Table 4). The expected signals were found in the¹⁹F-NMR, ¹H-NMR and ¹³C-NMR.

Acetonitrile (Fluka, P.A.) was distilled and dried by phosphorus pentaoxide before using, thereby reducing its water content to <4 ppm. Tetramethylammonium fluoride or Tripropylammonium and fluoric acid were bought from Merck. PbF₂and SbF₃ (Merck, p.a.) were used without further purification. Solvents were purified by standard methods. Infrared spectra were recorded as KBr disks on a Shimadzu model 420 spectrophotometer. The UV/Visible measurements were made on an Uvicon model 922 spectrometer. ¹H and ¹³C-NMR were recorded on a Bruker AVANCE DRX 500 spectrometer at 500 and 125 MHz, respectively. All the chemical shifts are quoted in ppm using the high-frequency positive convention; ¹H and ¹³C-nmr spectra were referenced to external SiMe₄. Antimony and Lead were estimated iodometrically. The percent compositions of elements were obtained from the Microanalytical Laboratories, Department of Chemistry, OIRC, Tehran.

Synthesis of Tetramethylammonium trifluoroplumbate (II),[(CH₃)₄N][PbF₃]

Tetramethylammonium trifluoroplumbate (II), [(CH₃)₄N][PbF₃] was prepared by dissolving PbF₂ (07.1 mg, 2.9 mmol) in MeCN and adding this solution to a solution of tetramethylammonium fluoride (0.29 g, 3.1 mmol) in MeCN under stirring at room temperature until a white precipitate was formed. After 2 hours stirring, the mixture was filtered, washed with ether and dried at room temperature. The tetraethylammonium salts are some what hygroscopic, and it was better to be stored under a layer of hexane, whereas all of the salts are photosensitive and moisture-sensitive, both in solution and solids. Mp: 196^oC. C₄H₁₂F₃NPb: Cacl. %C, 14.19; %H, 3.54; %N, 4.13. Found: %C, 15.30; %H, 3.56; %N, 4.15. UV/Visible, IR, ¹H-NMR and ¹³C-NMR were all consistent with the TMATriFPb structure.

Synthesis of Tripropylammonium tetrafluoroantimonate (III), (C₃H₇)₃NH[SbF₄]

Tripropylammonium tetrafluroantimonate (III), [(C₃H₇)₃NH][SbF₄] was prepared as follow: SbF₃ (8.9 mg, 5 mmol)was dissolved inMeCN in a beaker and tripropylamine (1.36 ml, 10 mmol) was added dropwise under stirring over a period of 0.5 h and the stirring was continued for 0.5 h at 0 °C. To the resultant clear white solution, hydrofluoric acid 40% (0.2 ml, 5 mmol) was added under stirring at 0 °C. The precipitated white solid was isolated by filtration, washed with hexane and dried under vacuum for 2 h at room temperature. Mp: 275°C. C₉H₂₂F₄NSb: Calc. %C, 31.60; %H, 6.43; %N, 4.09. Found: %C, 33.15; %H, 6.45; %N, 4.11. UV/Visible, IR, ¹H-NMR and ¹³C-NMR were all consistent with the TriPATFA structure.

Conclusion

Two tetramethylammonium fluoride and tripropylammonium fluoride salts of SbF₃were synthesized simply. (CH₃)₄N[PbF₃] was prepared by the reaction of (CH₃)₄NF and PbF₂ in a 1:1 ratio in MeCN solvent and (C₃H₇)₃NH[SbF₄] was prepared by the reaction of (C₃H₇)₃N, HF and SbF₃ in a 1:1:1 ratio in MeCN solvent. Electronic and vibrational spectra of these two new Fluoro-complexes were studied. These compounds were characterized by IR, UV/Visible, and ¹³C-NMR and ¹H-NMR techniques. Production of these compounds shows the ability of tetramethylammonium fluoride and tripropylammonium With fluoric acid in fluoride addition to main group elements compounds.

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Table 4. Transitions specifications of TriPATFA