Michihiko Kishita

Molecular Motions and Phase Transitions in Solid CH3NH3PbX3 (X = C1, Br, I) as Studied by NMR and NQR

Abstract The temperature dependence of 35C1, 81Br, and 127I NQR frequencies and 1Hspin-lattice relaxation times (T1) for CH3NH3PbX3 (X = Cl, Br, I) was measured through the successive phase transitions in these solids. The isotropic reorientation of the CH3NH3 ions takes place in the higher-temperature phases (tetragonal [I4/mcm] and cubic) of the three salts (Ea= 11 kJ mol -1). T1s in the lowest-temperature phases (orthorhombic) indicate that the cations undergo correlated C3-reorientation in the chloride (Ea = 5.45 kJ mol -1)and in the iodide (Ea = 5.80 kJ mol -1, whereas correlated (Ea = 2.40 kJ mol-1) and uncorrected (Ea = 7.50 kJ mol-1) C3- reorientations are excited in the bromide. It is also revealed that the rotational tunneling of the cations governs T1 at lowtemperature region in the orthorhombic phases of these salts

Organic ferromagnetism and antiferromagnetism of 4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl and 4-acryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl

The temperature dependence of the magnetic susceptibilities for 4-methacryloyloxy- and 4-acryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl (MOTMP and AOTMP, respectively) was measured. Intermolecular magnetic coupling in these radicals was changed from antiferromagnetic to ferromagnetic by substituting hydrogen at α-position with a methyl group. A magnetic phase transition for MOTMP was observed at 0.14 K in the measurement of the temperature dependence of heat capacity. The circumstantial evidences support that the ordered state is of ferromagnet.

Magnetic susceptibility and PMR spectrum of new basic copper(II) formates Cu3(HCOO)2(OH)4 and Cu(HCOO)(OH)

Abstract New basic copper(II) formates Cu 3 (HCOO) 2 (OH) 4 and Cu(HCOO)(OH) have been prepared and characterized by the magnetic susceptibility and PMR spectrum. The magnetic susceptibility of Cu 3 (HCOO) 2 (OH) 4 can be explained by the theoretical equation for linear trinuclear clusters. Cu(HCOO)(OH) shows a phase transition to an antiferromagnetic ordered state accompanied by a spin-flop phenomenon at 21.3 K. Each compound exhibits PMR spectrum consisting of two components each showing the Fermi contact shift. The coupling constants are determined as A CH = 1.8 G and A OH = −1.2 G for Cu 3 (HCOO) 2 (OH) 4 and as A CH = 3.9 G and A OH = −2.0 G for Cu(HCOO)(OH): the oxygen atoms in the hydroxy groups of each compound carry positive spin density and the carbon atoms of the formate groups negative spin density. The sign and magnitude of the spin exchange interaction depend markedly on the mechanism of spin delocalization onto the ligand molecules.

A unique mononuclear iron(III) complex with the binucleating ligand 2,6-bis[N-(2-pyridylethyl)iminomethyl]-4-methylphenol

In this paper, we report the synthesis, spectral and magnetic properties, and X-ray crystal structure of the unique mononuclear iron(III) complexe

Structure and properties of iron(III) 1,3-propanediaminetetraacetate complex in aqueous solutions

Abstract The structure of iron(III) 1,3-propanediaminetetraacetate (1,3-pdta) in aqueous solutions was studied on the basis of Raman spectroscopy, nuclear magnetic relaxation, and pH titration. It has been found that, in aqueous solution, Fe(1,3-pdta)− exists in a normal sexidentate hexacoordinate geometry. The six-membered chelate ring formed by the diamine moiety of the 1,3-pdta ligand does not adopt a skew-boat conformation having C2 symmetry (as found in sodium salt crystals) hut a twist-boat one having no C2 symmetry (as in the lithium salt crystals). Although edta complexes of iron(III) form a dimeric complex in slightly alkaline solutions, the 1,3-pdta complex of Fe(III) does not show such a tendency. The 1,3-pdta complex is stable only in the pH region of 2–7.5; the corresponding edta complex is stable even in a strongly acidic solution.

Phase Transition in trans-Azobenzene as Studied by 14N NQR

14 N NQR frequencies and T 1 s were measured between 54 and 150 K in crystalline trans -azobenzene which has two different molecular sites, orientationally ordered and disordered, at room temperature. The NQR parameters at 77 K were determined to be e 2 Q q / h =5.0150 MHz and η=0.4231 for the ordered site, and e 2 Q q / h =4.9619 MHz and η=0.4060 for the disordered site. The fine structure of each resonance line was observed by the Fourier transform method. It changes abruptly around 90 K, indicating the existence of a phase transition. The fine structures and their change at the phase transition can neither be attributed to the intramolecular dipole interaction between the two nitrogen nuclei, nor to crystallographic inequivalency of the molecules in the unit cell.

Phase Transitions in Bis(4-chlorophenyl)sulfone as Studied by 35Cl FT-NQR

Abstract The temperature dependence of 35Cl NQR frequencies in bis(4-chlorophenyl)sulfone was measured in the temperature range of 4.2-297 K. Below 115 K four NQR lines due to four inequivalent chlorines exist in the commensurate phase, contrary to the single NQR line reported by Corbero et al. It follows that the commensurate-incommensurate transition is of the first-order, and the incommensurate-normal transition at 150 K is quasi-continuous. It is also suggested that the successive phase transitions are triggered by the small angle rotation of the molecules about their C2-axes.

Synthetic atacamite, Cu2Cl(OH)3: A suspected spin glass behavior in low-temperature heat capacities

Abstract Heat capacities of synthetic atacamite, Cu 2 Cl(OH) 3 , were measured in an adiabatic calorimeter between 4 and 300 K with particular attention to the relaxation phenomenon below 8 K. A suspected spin glass behavior was observed, which was compatible with previous measurements of the magnetic susceptibility.

14N nuclear quadrupole resonance and relaxation in tetramethylpyrazine

Resonance frequencies and spin–lattice relaxation times (T1) of nitrogen-14 nuclei in solid tetramethylpyrazine from liquid-helium temperature to room temperature have been measured by the pulse method and the temperature dependence of the quadrupole resonance frequencies is compared with those in the low-temperature phase of pyrazine. Below 150 K, the relaxation times are governed by the reorientation of the methyl groups. The activation energy and the pre-exponential factor of the correlation time are found to be Ea= 6.0 kJ mol–1 and τ0= 2 × 10–13 s, respectively. Above 150 K the relaxation times depend on torsional lattice vibrations and are determined by the indirect two-phonon processes so that T–11∝T2.

Improvement of Bertaut's Method for Calculating Electric Field Gradient

Abstract Bertauts method for calculating the electric field and its gradient is analyzed. The formula for the electric field is always valid, whereas that for the electric field gradient holds only for an infinitely large unit cell. We present a practical method to use the formulae.