Calorimetric Study of MMX Chain Complexes Having Alkyl Groups, Ni2(EtCS2)4I and Ni2(n-PrCS2)4I

Heat capacities of halogen-bridged one-dimensional binuclear metal complexes (so-called MMX chain) having alkyl groups, Ni-2(RCS2)(4)I (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 Ni-2(n-PrCS2)(4)I, It first-order phase transition was observed at 205.6 K. The enthalpy and entropy of transition were estimated to be about 4.05 kJmol(-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.