Search

Heat capacities of a molecular mixed-ligand complex [Zn(hfac)2(tmen)] were measured in the temperature range between 13 and 383 K with an adiabatic calorimeter and the proton magnetic spin–lattice relaxation times (T1, T1ρ and T1D) were measured in the range between 130 and 330 K, where hfac and tmen denote hexafluoroacetylacetonato and N,N,N′,N′-tetramethylethylenediamine, respectively. The orientationally disordered crystalline phase, designated as phase I, was found to appear only in the supercooled meta-stable state: The temperature, enthalpy and entropy of the fusion were Tfus=(370±1) K, ΔfusH=(2.2±0.1) kJ mol−1 and ΔfusS=(5.8±0.3) J K−1 mol−1, respectively. The small entropy was discussed in relation to the low globularity in the shape of the complex molecule. High- and low-temperature stable crystalline phases (II and III) were found: The temperature, enthalpy and entropy of the fusion from the phase II were Tfus=(375±1) K, ΔfusH=(24.32±0.02) kJ mol−1 and ΔfusS=(65.4±0.1) J K−1 mol−1, respectively. The temperature, enthalpy and entropy of the III-to-II phase transition were Ttrs=(293.8±0.1) K, ΔtrsH=(4.115±0.005) kJ mol−1 and ΔtrsS=(14.02±0.02) J K−1 mol−1, respectively. Glass transitions were found at Tg=(114±1) K in phase III and at Tg=(116±1) K in the supercooled metastable phase II, respectively, and interpreted as attributed to the freezing-in of the rearrangement motion between δ and λ conformations of tmen. The energy difference between the two conformations was less than 0.25 kJ mol−1, and the activation energy for the conformational change was Δea=(33±1) kJ mol−1. The activation energy for the C3 reorientation of methyl groups within the ligand tmen was Δea=(14±1) kJ mol−1.

An attempt at modifying the electronic conduction mechanism by guest-host charge transfer and thermally excited molecular motion is reported. Ethylenediamine was intercalated into a semiconducting layered material, titanium disulfide, and a significant increase in charge carriers was evidenced by metallic conductivity, Pauli paramagnetism, and conduction electron spin resonance. Rotational motion of the guest molecule was evidenced by the proton spin-lattice relaxation measurement. However, no anomalous behaviors were found on the electronic properties which are attributable to motion-induced modification of the electronic state.

An anionic motion in sodium thiocyanate was studied by the spin-lattice relaxation time measurements of 14 N nuclear quadrupole resonance. The relaxation time decreased rapidly obeying an Arrhenius equation above T = 375 K. This result suggests the onset of a head-tail reorientational motion of thiocyanate ion with an activation energy of ≈ 95 kJ mol −1 . The origin of an anomalous temperature dependence of the quadrupole coupling constant is reinvestigated in relation to the anionic motion. It is concluded that a gradual change in electronic state of the anions, not the anionic motion, in the crystal with varying temperature is responsible for the anomaly claimed previously. Intermolecular interaction between N and Na atoms is suggested to be the most important factor in the origin of the change in the electronic state of the anion.

Alkali metal-graphite intercalation compounds absorb hydrogen to form alkali metal hydride-graphite intercalation compounds. We investigate the electronic properties and the structures of potassium hydride-graphite intercalation compounds by means of proton nuclear magnetic resonance, Hall effect and UV photoelectron spectroscopy. Among the alkali metal hydride intercalation compounds, potassium hydride intercalation compounds, the structure of which consists of ionic K + H  K + sandwich triple atomic layers between graphitic sheets, were found to have novel two-dimensional metallic hydrogen sheets in the intercalate space.