The authors' publications on M2(RCS2)4I are summarized with some additional discussion. Because of the nature of heat capacity calorimetry at relatively high temperatures, emphases are put not on the properties of respective ground state of Q1D electron systems on MMX main chain but on dynamical nature of ligands and its coupling to the electron systems.
(Curr. Inorg. Chem., 4, 74 (2014); account)
Heat capacity of a mixed-valence complex having a one-dimensional chain structure, [{Ni2(n-BuCS2)4}I] (n-Bu = butyl group), was measured between 10 and 325 K by adiabatic calorimetry. Anomalies due to phase transitions were detected around 135 K and 260 K. The anomaly around 260 K was of multiple-peaks. The excess entropy acquired below the phase transition around 260 K is much smaller than the simple estimate based on the structural disorder found in the crystal structure, implying the presence of motional correlation in dynamics of n-BuCS2 ligands. Through the comparison with the corresponding Pt complex, [{Pt2(n-BuCS2)4}I], the phase transition around 135 K is also discussed in relation to the absence in the present complex of a spin-Peierls transition observed in other members of Ni complexes with similar chain structures.
(Bull. Chem. Soc. Jpn., 83, 261 (2010))
Long is different! The title compound newly synthesized shows a quite different physical properties from similar compounds having shorter alkyl chains in alkyl dithiocarboxylato ligands. This finding demonstrates an important role of ligands and their dynamics in designing physical properties of inorganic complexes.
(Chem. Lett., 38, 1190 (2009))
Heat capacities of halogen-bridged one-dimensional binuclear metal complexes (so-called MMX chain) having alkyl groups, Ni2(RCS2)4I (R = Et and n-Pr), were measured by adiabatic and relaxation calorimetry. For each complex, a small broad thermal anomaly due to a spin-Peierls transition was observed around 40 K. For Ni2(n-PrCS2)4I, a first-order phase transition was observed at 205.6 K. The enthalpy and entropy of transition were estimated to be about 4.05 kJ mol-1 and 19.7 J K-1 mol-1, respectively. The magnitude of thermal anomaly shows that the effect of molecular dynamics of ligand on the electronic state in one-dimensional chain is small for Ni complexes having localized electrons in comparison with Pt complexes.
(J. Phys. Soc. Jpn., 78, 094704 (2009))
Heat capacity of halogen-bridged one-dimensional binuclear metal complex (so-called MMX chain) having four n-pentyl groups, Pt2(n-PenCS2)4I, was measured by adiabatic calorimetry. A first-order phase transition was observed at 207.4 K when measurement was made after cooling from room temperature. The enthalpy and entropy of transition were determined to be 10.19 kJ mol -1 and 49.1 J K-1 mol -1, respectively. A monotropic phase transition was observed at 324 K on heating, and the entropy of transition was essentially null. The sample once heated above 324 K never returned to the initial phase at room temperature, and underwent a higher-order phase transition at 173 K and a first order phase transition at 220.5 K. The enthalpy and entropy of the first-order phase transition were estimated to be 11.6 kJ mol -1 and 52.4 J K-1 mol -1, respectively. The magnitude of the entropy gain at the phase transition from the initial room-temperature phase to the high-temperature phase at 324 K shows that in Pt2(n-PenCS2)4I a large amount of entropy reserved in alkyl chain is transferred to dithiocarboxylato groups upon the phase transition, as in the cases of Pt2(n-PrCS2)4I and Pt2(n-BuCS2)4I.
(J. Phys. Chem. B, 109, 2956 (2005))
Heat capacity of a halogen-bridged quasi-one-dimensional (Q1D) mixed-valence binuclear metal complex (the so-called MMX chain), Pt2(n-PrCS2)4I,
was measured by adiabatic calorimetry. A higher-order phase transition
due to structural disorder was observed at 209 K. Another first order
phase transition having a large tail on the low-temperature side was
detected at 358.8 K. Their enthalpy and entropy of transition
were determined and analyzed. As evidenced by the magnitude of the
entropy of transition, similar structural disorder occurs at the
corresponding phase transition in Pt2(n-BuCS2)4I
and Pt2(n-BuCS2)4I, but
the shape of thermal anomaly is largely different between the two. The
magnitude of the entropy of transition shows that the change of both
structural disorder and electronic states occurs simultaneously in
gradual manner on the low-temperature tail of the thermal anomaly at
358.8 K. The change in entropy assignable to the Q1D electron system
was estimated as about 2.3 J K-1 mol -1.
(J. Phys. Chem. B, 108, 387 (2004))
Heat capacity of a halogen-bridged quasi-one-dimensional mixed-valence binuclear metal complex (the so-called MMX chain), Pt2(n -BuCS 2)4I, 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 -1 and 20.09 J K-1 mol -1, respectively. Those of the latter were 2.41 kJ mol-1 and 7.46 J K-1 mol -1, 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 Pt2(n-BuCS 2)4I are changed from an ordered 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.
(Phys. Rev. B, 66, 115110 (2002))
Heat Capacity of the halogen-bridged mixed-valence complex Pt2(dta)4I
has been measured in the temperature region between 6 and 386 K.
The complex exhibited a phase transition of order-disorder type
at 373. 4 K, from being arranged in an ordered helical form of four dta
ligand planes around the central Pt-Pt axis to dynamically jumping
between two orientations. Neither latent heat nor distinct
thermal hysteresis was observed for
the phase transition, suggesting that the phase transition is of
higher-order rather than of the first-order. The enthalpy and
entropy of transition wee determined to be (1.91 +- 0.02) kJ mol-1
and (5.25 +- 0.07) J K-1 mol-1, respectively.
The entropy of transition close to Rln2 (= 5.76 J K-1
mol -1), where R is the gas constant, implies that
the twisting motion of the four dta ligands takes place in a
synchronized way. No thermal anomaly was detected around 300 and
90 K, where a Mott transition from the one-dimensional metallic phase
to the semiconducting phase and a spin-Peierls like transition have
been expected. The reason for the absence of these transitions in
calorimetry is discussed briefly.
(J. Phys. Chem. B, 106, 197 (2002))