Masato Oshima

Aluminum-stabilized low-spin iron(II) hydrido complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane.

We investigated herein the reactions of (Me3tacn)FeCln (1a: n = 3, 1b: n = 2) with common aluminum hydride reagents and a bulky dihydridoaluminate {Li(ether)2}{Al(OC6H3-2,6-(t)Bu2)}(μ-H)2, which yielded the diamagnetic hydrido complexes 2-4 containing Fe(II) and Al(III). In particular, the use of divalent 1b afforded excellent isolated yields. The structures of 2-4 were determined using spectroscopic and crystallographic analyses. The crystal structures showed distorted octahedral Fe centers and fairly short Fe-Al distances [2.19-2.24 Å]. The structures of cation moiety 2 and neutral complex 4 were further probed using DFT calculations, which indicated a stable low-spin Fe(II) state and strongly electron-donating nature of the (Me3tacn)FeH3 fragment toward the Al(III) center.

Chirality and Molecular Dynamics of Smectic Compound Studied by 13C-NMR Spin-Lattice Relaxation Time Observation

The temperature dependence of the spin-lattice relaxation time T 1 is investigated in the racemic mixture of a smectic liquid crystal, 4-(1-methylhexyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate ((±)-MH(6)POBC) by means of solid-state 13 C-NMR spectroscopy. T 1 of almost all of aromatic carbons has a minimum at the smectic C (SmC) temperature region, because the frequency of the molecular rotational motion corresponds to the Larmor frequency of 100 MHz in the present measurements. In addition, analysis of the temperature dependence of T 1 reveals that the activation energy of the molecular rotation in the SmC phase is higher than that in the SmA phase.

Molecular Dynamics in Smectic and Crystalline Phases Studied by 13C-NMR Spin Lattice Relaxation Time Observation

The temperature dependence of the spin-lattice relaxation time T1 is investigated in the chiral smectic liquid crystal (S)-4-(1-methylhexyloxycarbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate (S-MH(6)POBC) by solid-state 13C-NMR spectroscopy. The T1 of an aromatic carbon belonging to the core part of the liquid-crystalline molecule decreases from 1 s to 0.2 s with decreasing temperature in smectic phases, where the frequency of the molecular rotation around its long axis is higher than the Larmor frequency of 100 MHz in the present study. Because the molecular rotation freezes during the phase transformation from the smectic phase to the crystalline phase, T1 rapidly increases from 0.2 s to 16 s.

Phase Transformation of Swollen Thermotropic Liquid Crystals Studied by X-Ray and 2H-NMR Measurements

Molecular realignments during the successive phase transformations of a binary mixture of smectogenic and aliphatic compounds have been studied. The layer spacing, which is about 38.5 A in the crystal phase, abruptly increases up to 54 A during the transformation to the smectic phase, because aliphatic molecules are taken into the smectic liquid crystals during the transformation. A myelinic texture is observed in the smectic phase in which the liquid crystals are swollen with the aliphatic molecules. In addition, the quadrupolar splitting is observed in the 2H-NMR spectra of the sample swollen with d8 -octane, because the aliphatic molecules are averagely oriented parallel to the director of the smectogens in the swollen smectic liquid crystals.