The heat capacity of [Hdamel]2[CuII(tdpd)2].2THF was measured from 6 to 250 K by adiabatic calorimetry. There are four heat anomalies around 150 K associated with disordering in the orientation of the uncoordinated THF molecules and in the conformation of the out-of-plane allyl groups of [Hdamel]+ units. The total entropy of transition was determined to be 19.8 J K-1 mol-1, less than the 4Rln 2 (R: gas constant) expected from the crystal structure at room temperature. The smallness of the total entropy change on phase transitions proves the presence of the strong motional correlation between the adjacent allyl groups. The calorimetric conclusion agreed with the crystal structure at 200 K re-examined in this study.
(J. Phys. Chem. A, 112, 4465 (2008))
Heat capacity of Cs2(18-crown-6)3[Ni(dmit)2]2 was measured by adiabatic calorimetry. A broad thermal anomaly was observed around 225 K. The entropy gain (about 52 J K-1 mol-1) is much larger than that expected for two-fold disordering of 18-crown-6 assumed in the previous structure analysis. The shape of thermal anomaly was qualitatively explained by a linear Ising model developed for cooperative disordering in polymers. 18-crown-6 molecules forming one-dimensional chain in the crystal are orientationally disordered with moderate cooperativity.
(J. Chem. Phys., 123, 044514 (2005))
Nanoscale molecular rotors that can be driven in the solid state have been realized in Cs2(-crown-6)3[Ni(dmit)2]2 crystals. To provide interactions between the molecular motion of the rotor and the electronic system, [Ni(dmit)2]- ions, which bear one S =1/2 spin on each molecule, were introduced into the crystal. Rotation of the crown-6 molecules within a Cs2(crown-6)3 supramolecule above 220 K was confirmed using X-ray diffraction, NMR, and specific heat measurements. Strong correlations were observed between the magnetic behavior of the [Ni(dmit)2]- ions and molecular rotation. Furthermore, braking of the molecular rotation within the crystal was achieved by the application of hydrostatic pressure.
(J. Am. Chem. Soc., 127, 4397 (2005))
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