Structure analysis of the high-temperature phases of [NH₃(C₃H₇)]₂CuCl₄. II. The modulated phase

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

“…As noted above, crystals of the C n MX4 family are known to show sequential transitions. The phase transition mechanism of the C n MX4 family into commensurate structures has been described based on van der Waals (VDW) interactions between the alkyl chains . Actually, in the γ phase of C4CuCl4 , the C 4 H 9 NH 3 + chains are aligned in such a way that the VDW energies are minimized.…”

“…The interlayer distances were roughly estimated from the XRD data, and are shown in Figure S10 (in the Supporting Information). Note that some of these compounds have been already reported in detail, especially n =1–3 . For reference, selected C n CuCl4 crystal structures are included in the Supporting Information (Table S3 and the CIF).…”

“…In the g phase, the pattern showedg radual changes, as shown in Figure S3 (in the Supporting Information),s uggesting the high temperature dependenceo ft he structuralm odulations. [18][19][20][21][22][23][24] Note that ap air of very small reversible peaks at around 350 Kh ave been neglected, and only the four phases below 300 Kw ere considered in this work because of the limitations of our instruments.…”

“…The phase transition mechanism of the CnMX4 familyi nto commensurate structures has been described based on van der Waals (VDW) interactions between the alkyl chains. [19,33] Actually,i nt he g phase of C4CuCl4,t he C 4 H 9 NH 3 + chains are alignedi ns uch aw ay that the VDW energies are minimized. We also confirmed the criticala lkyl chain length dependence of the phase transition behaviori nt he CnCuCl4 family by using DSC measurements (n = 2-14, 16, and 18) and XRD diffraction (n = 2-8) in the range 100-400 K, as shown in Figures S9 and S11( in the Supporting Information).…”

“…[17] Incommensurate crystal structures are also found in the family of organic-inorganic 2D layered compounds with the structure (C n H 2n + 1 NH 3 ) 2 MX 4 (CnMX4,M 2 + = Cu 2 + ,M n 2 + ,Z n 2 + , etc.,X À = Cl À ,B r À ). [18][19][20][21][22][23][24] These compounds show sequential temperature-dependent structural phase transitions, with some phases exhibitingi ncommensurate structures. In addi-tion, crystalso ft he Cu 2 + salts (CnCuCl4)s how ferromagnetism below 8K.…”