Raman spectra and structures of the high‐ and low‐temperature phases in the two‐dimensional layer‐type compound (CH₃CH₂NH₃)₂SnCl₆

Abstract

Polarized Raman spectra of oriented single crystals of (CH,CH,NH,),SnCl, measured over the temperature range 15-300 K have been used to investigate the mechanism of the structural transition at 125 K. A detailed study of some of the external modes and of the internal modes of both the SnClk and CH3CH2NH: ions in the high-and low-temperature phases has enabled the structure of the disordered high-temperature phase to be confirmed and suggestions for the structure of the low-temperature phase to be proposed.

Raman scattering study of temperature induced phase transition in [C8H10NO]2 [ZnCl4]

“…The understanding of phase transitions of these hybrid structures is quite important from materials point of view. In addition, these compounds exhibit numerous structural phase transitions related to reorientation motion in the organic part, [3][4][5][6][7] and so are classified to be of "order-disorder". Raman scattering investigations as a function of temperature present great interest since this indirectly brings information regarding molecular conformation and how the cations contribute to the mechanism of the phase transitions.…”

Distinct critical fluctuations and molecular motions manifest in a model biomembrane

“…in the kHz range [21], the highfrequency critical fluctuation observed in the 200 MHz NMR spin-lattice relaxation is believed to be the collective flip-flops of the NH 3 polar head. Because the NH 3 polar head is known to spend its time between two favorable sites in the disordered phase [3,28,29], we have employed the kinetic Ising model in order to check the conjecture, satisfactorily describing the experimental results [4,27].…”

“…In our previous 1 H NMR studies of the CnSn systems, two typical successive phase transitions were observed [4][5][6][7]: (a) order-disorder transition of the rigid alkyl chains accompanied by a uniaxial reorientation about their long axes along with the flipping of the polar groups, such as NH 3 , between the potential wells, and (b) conformational transition leading to a partial melting of the alkyl chain part. In the low temperature (LT) phase below the order-disorder transition temperature, the alkyl chains are rigid and adopt an all-trans conformation.…”

“…The SnCl 6 2K octahedra do not form a 2D macroanion but exist separately [1][2][3]. The NH 3 group of alkylammonium ion links the three closest octahedra through equivalent hydrogen bonds of the N-H/Cl type, forming an inorganic layer.…”

“…The distance between the ammonium groups or between the tin atoms in CnSn is great enough (7.3-7.5 Å , depending on the chain length) to accommodate a monolayer of interdigitated alkyl chains. The alkylammonium groups are statically disordered around the three fold-axes at (1/3, 2/3, z) and (2/3, 1/3, z), with the alkyl chains alternately pointing upwards and downwards [3].…”