Phase Transition in 4-(CH₃)C₆H₄NH^⊕ ₃X^⊖ (X = Br, I)

Abstract

Bv 79-81 Br apd ,27I NQR spectroscopy 4-(CH3)C6H4NHf Xe , X = Br and I, and 4-(CH3)C6H4ND f 19 were studied in the temperature range' 77 S 7VK ^ 340. The three compounds experience phase transitions, most likely of higher order. Two reversible transitions are observed for the para-toluidinium iodide. 7~i-n being in the temperature range 247 ^ T/K ^ 258. Tn^m in the range 174 § 77K $ 179. The deuterated compound shows slight shift of the transition temperatures compared to the protonated one. whereas the l27I-NQR resonance frequencies are considerably lowered as is the nuclear quadrupole coupling constant. The asymmetry parameter tj, however, increases through deuteration of the NH3 group. The room temperature phase of the iodide crystallizes with an orthorhombic space group (Pmmn or Pmn2,.Z = 2). Temperature dependence of the 7vBrNQR spectrum of p-toluidinium bromide indicates a phase transition near t = 281 K. P h a s e T r a n s itio n in 4 -( C H 3) C 6H 4N H | X 9 (X = B r , I) Introduction © The ammonium ion. N H 4 , plays an important role in solid state phase transitions. It behaves like an alkali ion by its electronegativity and its radius, but due to its nonspherical symmetry and the ability to form hydrogen bonds, various packings and co ordinations are possible which promote phase transitions. Replacement of one hydrogen atom of the ion by a group R lowers the symmetry of the ion but the possibility of hydrogen bonding to the anions in the crystal lattice and the ease of rotation of the group -N H 3 around the bond R -NH 3 offers a variety of phases in the solid state which differ only little in lattice energy.In recent years we have studied several crystalline halides RNH?Xe (X = Br, CI) where R is the benzene ring or a substituted benzene ring. In case of R=C6Hs a ferroelastic phase transition occurs for both the anilinium bromide and the anilinium iodide and this transition was followed up by 9 slBr and 12 I nuclear quadrupole resonance (NQR) [1]. The crystal structures of both the high and low temperature phases of C6H5N H 3X (X = Br, I) were studied by X-ray and neutron diffraction In order to study the isotope effect, 4-(CH3)-C6H4N H 3I was dissolved in D20 and the solu tion was concentrated over P2Os in a dessicator.0340-4811 / 84 / 0400-380 S 01.3 0/0. -Please order a reprint rather than making your own copy.

Distinct phase transitions and dielectric anomalies in two 4-methylanilinium salts

“…Both compounds belong to a family of organic-inorganic hybrid compounds synthesized from bases and acids, such as aniline and its derivatives with various inorganic acids [12][13][14][15][16][17][18][19][20][21][22]. Differential scanning calorimetry (DSC), temperature-dependent single-crystal X-ray diffraction and dielectric studies reveal interesting structural phase transitions and dielectric anomalies in the two compounds.…”