Studies on Tetramethylammonium Selenate(VI) and Chromate(VI)

Abstract

[N(CH3)4]2SeO4 and [N(CH3)4]2CrO4 have been investigated by Infrared and Raman spectroscopy, coupled thermogravimetric and differential thermal analysis combined with mass spectroscopy of the evolved gases and temperature dependent X-ray diffraction. The crystal structure of [N(CH3)4]2SeO4 has been determined from single crystal data (cubic, Fm3̄m. a -11.1077(7) Å, Z = 4) and reveals [N(CH3)4]+ cations and SeO42- anions to be arranged in a Li2O -type of structure. While the cation framework of regular tetrahedra is orientationally fixed, the selenate anions are disordered. Powder diffraction data show [N(CH3)4]2CrO4 to be isostructural (cubic, Fm3̄m, a = 11,039(1) Å, Z = 4).

Study of molecular reorientation and quantum rotational tunneling in tetramethylammonium selenate by 1H NMR

“…Further, in contrast to Sato et al, they have not reported any phase change in the temperature range 130-300 K. IR and Raman studies by the same authors [4] [4]. Thus, these studies led to a controversy regarding the structure of this compound [4,5]. In the present study, we have made an attempt to resolve this.…”

“…Cylindrical crystals formed upon slow evaporation of the solvent, over a few months, are dried under vacuum before using them for further studies because of their hygroscopic nature. The powder XRD measurements are carried out at room temperature using the Panalytical diffractometer and our XRD pattern compares well with that of Malchus and Jansen [4]. The compound is finely powdered and vacuum-sealed into glass ampoules of 5 mm diameter in helium atmosphere for NMR studies.…”

“…Malchus and Jansen [4] also have synthesized the same compound by adopting a different preparation method and carried out the temperature-dependent single-crystal XRD measurements and they found a disagreement with that of Sato et al According to the XRD analysis of Malchus and Jansen, the compound crystallizes in cubic lattice (Fm3m) with a ¼ 11.12 Å and the complex ions are packed in an Li 2 O 2 -type arrangement. Further, in contrast to Sato et al, they have not reported any phase change in the temperature range 130-300 K. IR and Raman studies by the same authors [4] [4]. Thus, these studies led to a controversy regarding the structure of this compound [4,5].…”

“…Substitution of the CH 3 leads to additional symmetry elements and hence increased reorientation motions [3]. Tetramethylammonium (TMA) metal salts are known to exhibit phase transitions, hindered reorientational motion of the symmetry groups like CH 3 as well as whole cation (CH 3 ) 4 N and quantum rotational tunneling of the CH 3 groups. Moreover, TMA salts are of general interest in preparative chemistry.…”

“…Moreover, TMA salts are of general interest in preparative chemistry. Their enhanced solubility in aprotic solvents in comparison to the corresponding alkali metal salts as well as their increased reactivity, which is due to a lower degree of solvation of their anions in solutions of non-polar solvents, make them powerful and versatile synthetic reagents [4]. Among them, tetramethylammonium selenate (TMA-Selenate) is particularly interesting to study, not only for its interesting molecular reorientational dynamics but also for its use in preparative chemistry [4].…”