Cationic motions and phase transitions in [(CH3)4N]2SO4·4H2O, [(CH3)4N]2SO4, and [(CH3)4N]2SeO4 as studied by 1H NMR, differential thermal analysis, and X-ray powder diffraction techniques

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

“…Therefore, both our NMR and powder XRD results support the argument of Malchus and Jansen. Hence, we can conclude that the compound used in the present study is in the cubic space group in agreement with that of Malchus and Jansen [4] and not the hydrated TMASelenate as reported by Sato et al [5].…”

“…The observed activation energies for both CH 3 and (CH 3 ) 4 ions obtained from the present study are, respectively, lesser than that of Sato et al [5] SeO 4 because of larger radius of the selenium atom and its increased cell volume [5].…”

“…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.…”

“…TMA-Selenate is synthesized by mixing TMA hydroxide (Aldrich, 33,163-5) and selenic acid (Aldrich, 30,843-9) in stoichiometric proportions [5]. 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.…”

“…Sato et al [5] have claimed that they have prepared the title compound TMA-Selenate and reported it as a tetragonal lattice system with a ¼ 13.95 Å and c ¼ 12.90 Å from the powdered XRD pattern. They have also observed three heat anomalies at 127, 279 and 290 K through DTA.…”