Incommensurate crystal-instability and a role of internal degrees of freedom in bis (4-chlorophenyl) sulfone molecules

Negative‐to‐Positive Thermal Conductivity Temperature Coefficient Transition Induced by Dynamic Fluctuations of the Alkyl Chains in the Layered Complex (C4H9NH3)2CuCl4

“…As described above, these atoms are the “soft” points that connect the “hard” octagons in the CuCl 4 2− layers. It is also noteworthy that the existence of a modulated intermediate phase is a characteristic feature of such displacive transitions even in other molecular systems …”

“…[36][37][38] In the literature, rotationalm otions of MX 6 octahedra have been designated as soft modes.T he existence of "soft" points is clearly revealed in the crystal structure of the g phase of the C4CuCl4 crystal,i nw hich the bridging angle of the corner-shared Cl atoms varies greatlyw ith the structure modulation ( Figure S5 gi nt he Supporting Information).A sd escribed above,t hese atoms are the "soft" points that connect the "hard" octagons in the CuCl 4 2À layers.I ti sa lso noteworthy that the existence of am odulated intermediate phase is a characteristic feature of such displacive transitions eveni n other molecular systems. [39] Thus, the excitation of dynamic fluctuationsi nr esponse to the VDW repulsions in the C 4 H 9 NH 3 + layers presumably cooperates with the displacive transitions in the 2D perovskite CuCl 4 2À layers.T he fluctuationsl ower the hardness of the C 4 H 9 NH 3 + layers, which could allow the excitation of lowenergyv ibration modes in the CuCl 4 2À layers,r esulting in the cooperative sequential phase transition involving an intermediate incommensurate structure, in addition to the negative-topositive transition of the temperature coefficient of thermal conductivity.T hisa ssumption is quite qualitative, and further discussion of C4CuCl4 may require quantitative analyses, such as analysis of the group velocities of phonons in the inorganic and organic layers, interlayer electrostatic interactions, VDW interactions betweent he C 4 H 9 NH 3 + chains, and others. Phonon band calculations and molecular dynamics simulations may revealt he phase transition mechanisms and thermal conductance properties in detail.…”

Polarization reversal by intramolecular disordering in organic ferroelectrics: trichloroacetamide

“…4,10 In this sense, the TCAA is a rare example of compounds showing an order-disorder transition deeply related to intramolecular motional degrees of freedom, together with p-polyphenyls (p-terphenyl [26][27][28] and p-quaterphenyl [29][30][31] ). As crystals undergoing displacive phase transitions, biphenyl [32][33][34][35][36] and bis(4-chlorophenyl)sulfone [37][38][39][40] are to be noted. Also we can mention crystalline trans-stilbene and trans-azobenzene, which undergo glass transitions due to freezing of intramolecular crankshaft motions (also noted as pedal motions).…”

Study of tetraphenyltin dynamics by Raman and infrared spectroscopy

“…That is why we expected to obtain some interesting results for tetraphenyltin and we have undertaken a study of nuclear magnetic relaxation 5 and neutron scattering in this compound. 6 Further, this class of substances has not hitherto been extensively studied.…”