Calorimetric study of the halogen-bridged mixed-valence binuclear metal chain complexPt2(n−BuCS2

Abstract

Heat capacity of a halogen-bridged quasi-one-dimensional mixed-valence binuclear metal complex ͑the so-called M M X chain͒, Pt 2 (n-BuCS 2 ) 4 I, was measured by adiabatic calorimetry. First-order phase transitions were observed at 213.5 K and 323.5 K. For the former, the enthalpy and entropy of transition were 4.29 kJ mol Ϫ1 and 20.09 J K Ϫ1 mol Ϫ1 , respectively. Those of the latter were 2.41 kJ mol Ϫ1 and 7.46 J K Ϫ1 mol Ϫ1 , respectively. Another thermal anomaly probably due to a higher-order phase transition was detected at 114 K. The magnitude of the entropy of transition shows that, upon heating, the butyl chains in one-third complexes in crystalline Pt 2 (n-BuCS 2 ) 4 I are changed from an ordered state to a disordered state through the phase transition at 213.5 K, and resume the ordered state from this disordered state at 323.5 K. The transition at 213.5 K involves a ''spin-Peierls'' contribution beyond the structural one.

Calorimetric Study of a Halogen-Bridged MMX Chain Complex Having Alkyl Chains, Pt2(n-PrCS2)4I (n-Pr = Propyl Group)

“…20 In this work, the heat capacity of Pt 2 (n-PrCS 2 ) 4 I was measured with adiabatic calorimetry to characterize the phase transitions detected in the transport and the magnetic studies. The results are described in detail, and the validity of the analysis of Pt 2 -(n-BuCS 2 ) 4 I on structural disorder 22 is assessed. The comparison is made of the entropy involved and the shape of thermal anomaly in Pt 2 (n-PrCS 2 ) 4 I and Pt 2 (n-BuCS 2 ) 4 I to discuss the electron-lattice "coupling.…”

“…22 The first-order phase transitions involving disordering of the dithiocarboxylato group (CS 2 ) and the butyl chain occur at 213.5 and 323.5 K. The model of the structural disorder of each phase was established on the basis of the magnitude of the entropy of transition. From the analysis of entropy of transition due to structural disorder, the entropy contribution intrinsic to change between magnetic state and nonmagnetic state of the MT-RT phase transition at 213.5 K, where both changes in structural disorder and electronic state occur simultaneously, was estimated.…”

“…Representatives of the MMX chain compounds having been studied are A 4 [Pt 2 (pop) 4 X]‚nH 2 O (A ) Li, K, Cs, NH 4 ; pop ) H 2 P 2 O 5 2-, diphosphonato; X ) Cl, Br, I), [4][5][6][7][8] and M 2 (RCS 2 ) 4 I (M ) Pt, Ni; R) alkyl chain). [9][10][11][12][13][14][15][16][17][18][19][20][21][22] M 2 (RCS 2 ) 4 I has four alkyl chains (R) in ligands. Elongation of alkyl chains in ligands is considered to enhance the onedimensionality of the electronic system on the MMX chains because of weak van der Waals S-S contacts between neighboring chains.…”

Triple Hydrogen Bonds Direct Crystal Engineering of Metal‐Assembled Complexes: The Effect of a Novel Organic–Inorganic Module on Supramolecular Structure

“…If the THF molecules and the allyl groups are independently disordered in the type 1 unit and the motion of the THF molecules in the type 2 unit is synchronized, the contribution of the unit to entropy is 1/3 R ln(2 4 22 4 ) = 17.3 J mol À1 K À1 for the low-temperature phase. [24] The difference is 5.8 J mol À1 K…”

Nonlinear lattice relaxation of photoexcited diplatinum-halide chain compounds

“…The thus-fascinating MX family compounds have been gaining renewed interest in recent years due to their binuclear metal analogs, 26,27 abbreviated as MMX chains, which exhibit quantum, [28][29][30] thermal, [31][32][33] and pressureinduced [34][35][36][37] transitions between a wider variety of mixed-valent states. 38,39 The direct M (d z 2 )-M (d z 2 ) overlap effectively reduces the on-site Coulomb repulsion and therefore makes electrons more itinerant.…”