Thermal Properties and Crystal Structures of Ionic Liquids from Ruthenium Sandwich Complexes with Trialkoxybenzene Ligands: Effects of Substituent Positions and Alkyl Chain Lengths

A series of ionic liquids containing [Ru­(C₅H₅)­(arene)]⁺, where the arene ligands are 1,2,3-C₆H₃(OC_<i>n</i>H_2<i>n</i>+1)₃ and 1,3,5-C₆H₃(OC_<i>n</i>H_2<i>n</i>+1)₃ (<i>n</i> = 6, 12, and 18), were synthesized. The counteranions were PF₆ and FSA (bis­(fluorosulfonyl)­amide). The melting points of the PF₆ and FSA salts were 33–93 °C and −18–62 °C, respectively. In the PF₆ salts, the melting points of the 1,3,5-derivatives were lower than those of the 1,2,3-derivatives by 28–55 °C, whereas no such tendency was observed in the FSA salts. X-ray crystallography showed the formation of lamellar structures in the PF₆ salts of the 1,2,3-derivatives in the solid state. In these crystals, cation–anion pairs via C_CpH···F H-bond-like interactions were commonly observed. Several 1,3,5-derivatives showed metastable phases with lower melting points than the stable phases. The salts of the 1,2,3-derivative (<i>n</i> = 2) were also synthesized and characterized

¹H NMR Study of Molecular Motion of Benzene and <i>n</i>-Decane Confined in the Nanocavities of Metal–Organic Frameworks

The molecular motion of benzene and <i>n</i>-decane confined in the nanocavities of [Zn₄O(O₂CC₆H₄CO₂)₃]<i>_n</i> (IRMOF-1) was investigated in terms of the temperature dependence of the proton spin–lattice relaxation time (¹H <i>T</i>₁). Both substances exhibited two components of <i>T</i>₁, below 216 K for benzene and 181 K for <i>n</i>-decane, indicating that the guest molecules are localized separately in large and small cavities. For <i>n</i>-decane below 181 K, methyl reorientation is excited although the rate of reorientation in large and small cavities differed, whereas the overall motion was frozen. A thermal anomaly accompanies the translational diffusion of <i>n</i>-decane and is associated with melting of the confined <i>n</i>-decane. For benzene, translational diffusion was also excited at the thermal anomaly at 216 K, indicating melting of benzene molecular assemblies in IRMOF-1. Below 216 K, the molecular motions in the large and small cavities differed. In the large cavities, benzene undergoes isotropic reorientation, which is unaffected by the thermal anomaly at 150 K, whereas in small cavities in-plane <i>C</i>₆ reorientation occurs, and the isotropic reorientation and the intracavity diffusion are successively excited as the temperature increases. In particular, the acceleration of the isotropic reorientation of benzene accompanies the thermal anomaly at 150 K, corresponding to the partial melting of molecular assemblies in the small cavities

Structure and Dynamic Behavior of the Na–Crown Ether Complex in the Graphite Layers Studied by DFT and ¹H NMR

Diffusion of alkali metals in graphite layers is significant for the chemical and electrochemical properties of graphite intercalation compounds (GICs). Crown ethers co-intercalate into graphite with alkali metal (Na and K) cations and form ternary GICs. The structures and molecular dynamics of 15-crown-5 and 18-crown-6 ether coordinating to Na⁺ or K⁺ in GICs were investigated by DFT calculations and ¹H solid state NMR analyses. DFT calculations suggest a stacked structure of crown ether–metal complex with some offset. ¹H NMR shows two kinds of molecular motions at room temperature: isotropic rotation with molecular diffusion and axial rotation with fluctuation of the axis. The structure and dynamics of crown ether molecules in GIC galleries are strongly affected by the geometry of the crown ether molecules and the strength of the interaction between alkali metal and ligand molecules