Masahiko Suhara

Crystal structure and dynamic behavior of CaSnCl66H2O

Abstract In order to investigate the origin of the anomalous temperature dependence of Cl NQR frequency in CaSnCl66H2O, we carried out the determination of crystal structure by X-ray diffraction and NQR Zeeman effect measurements. The crystal is trigonal with a space group of R3, a=10.750, c=11.474 A and Z=3 at room temperature. The complex ions, Ca(H2O)2+6 and SnCl2−6 , form a rhombohedrally distorted CsCl type structure through hydrogen bonds. The asymmetry parameter is 0.035 and the x and y axes of EFG tensor direct to the hydrogen bonding between the chlorine atom and the water molecule. The precise measurement of the temperature variation of NQR frequency showed one minimum (at 230 K) and one maximum (at 370 K) values in the temperature range of 77 to 390 K, and the signal faded out at 390 K. The temperature dependence of proton NMR and Mn2+ -doped ESR spectral line shapes indicates that the anomaly in the NQR data is due to the thermal motion associated with the hydrogen bond among the complex ions in crystal. Several successive phase transitions were also found by X-ray diffraction, DTA and ESR measurements. The transition temperatures are 360, 401, and 413 K.

Analysis of XPS and XES of diamond and graphite by DFT calculations using model molecules

X‐ray photoelectron and emission spectra (XPS and XES) of diamond and graphite have been analyzed by deMon density‐functional theory (DFT) calculations using the model adamantane derivative (C10H12(CH3)4) and pyrene (C16H10) molecules, respectively. The theoretical valence photoelectron and C Kα X‐ray emission spectra for the allotrope are in good accordance with the experimental ones. The combined analysis of the valence XPS and C Kα XES enables us to divide the valence electronic distribution into the individual contributions for pσ‐, and pπ‐bonding MOs of the diamond and graphite, respectively.

Theoretical X-ray photoelectron and emission spectra of Si- and S-containing polymers by density-functional theory calculations using model molecules

Abstract The X-ray photoelectron and emission spectra (XPS and XES) of Si- and S-containing polymers [(–Si{–CH 2 –} 3 ) n (PCS), (–Si(CH 3 )(OH)–O–) n (PMHSO), (–Si(C 6 H 5 )(OH)–O–) n (PTES), (–Si(C 6 H 5 )(OH)–O–Si(CH 3 )(OH)–O–) n (PPMHSO), (–C 6 H 4 –O–C 6 H 4 –SO 2 –) n (PES)] were simulated by the deMon density-functional theory (DFT) calculations using the model molecules. The theoretical valence photoelectron and C Kα X-ray emission spectra showed good accordance with some experimental ones. The combined analysis of the valence XPS and C and O Kα XES enables us to divide the observed valence electronic distribution into the individual contributions for pσ-, pπ- and non-bonding MOs of the polymers.

Dynamical structure of paramagnetic [M(H2O)6][SiF6] (M = Fe2+,Ni2+) crystal studied by means of 2H nuclear magnetic resonance

The temperature dependences of the 2H nuclear magnetic resonance (NMR) spectra and the spin-lattice relaxation time T1 were measured for [Ni(H2O)6][SiF6] and [Fe(H2O)6][SiF6]. The motional modes for both compounds were discussed on the basis of the spectral simulation. The temperature variations of the 2H NMR spectra at high temperatures could be explained by three-site jumps of [Ni(H2O)6]2+ about the C3 axis for [Ni(H2O)6][SiF6]. For [Fe(H2O)6][SiF6], however, six-site jumps of [Fe(H2O)6]2+ about the C3 axis were found to be most probable form of motion at high temperatures. At low temperatures, the 2H NMR spectra of both compounds could be explained by 180° flips of the water molecule. The 2H NMR T1 was dominated by the fluctuations of the electric field gradient caused by the molecular motion and of the magnetic interaction between the 2H nucleus and the unpaired electron spin in the metal ion. T1 was analysed in terms of the motional modes predicted from the spectral simulation. The activation energies, the jumping rates at infinite temperature for each form of motion and the quadrupole interaction parameters (e2Qq/h,η) were obtained from the 2H NMR spectra and T1. The conclusions from the spectral simulation are in good agreement with the results for T1. These results suggest that [Fe(H2O)6][SiF6] possesses dynamic disorder structure in the high-temperature phase.

Structural analysis of AgxCu1−xI (0≤x≤0.5) by solid 63Cu NMR and X-ray diffraction methods

Abstract 63 Cu NMR and X-ray diffraction methods have been used to investigate the temperature dependence of the nuclear chemical shifts and the diffraction patterns, respectively, for mixed crystal Ag x Cu 1− x I (0 x T d CuI 4 3− and O h CuI 6 5− species, as obtained by the finite perturbation theory in an ab initio Gaussian 94 program using double-ζ basis set for Cu and I atoms. In the case of the nonlinear temperature dependence of the shift, we introduce the shift model as proposed by Negita and coworkers: The shift is also due to the cation which moves to the qausi-stable interstitial octahedral sites.

The calculation of the temperature dependence of NQR frequencies in chlorine and α-nitrogen crystals

Abstract The temperature dependence of the NQR frequency was investigated in terms of the anharmonic libration of a molecule in a crystal. The statistical average value of the electric field gradient at the nuclear site was evaluated by using the eigenvalues and the eigenfunctions which were obtained by solving a spheroidal wave equation as an equation of motion of the molecular libration in a potential of V o sin 2 θ . The present theoretical treatments not only improve the conventional theory in harmonic approximation but also lead to a good agreement between the calculated results and the experimental ones in chlorine and α-nitrogen crystals.

Static and dynamic disordered states in VO2+-doped BaCl2·2H2O crystals

Abstract From the EPR investigation, two different crystalline states were found in the VO 2+ ion-doped BaCl 2 ·H 2 O crystal. One is a dynamic disordered state, where the trapped VO +2 ion exhibits hindered rotational motion in a wide temperature region. This state is transformed to a static disordered state even at ambient temperature. The orientation of the doped ion reveals random distribution in the lattice sites. Such polymorphism does not come from phase transition of the host crystal, but from the existence of the metastable state of the VO 2+ ion trapped in the lattice. The absence of the phase transition of pure BaCl 2 ·2H 2 O was confirmed by the measurement of 137 Ba NQR and by differential thermal analysis.

Phase transitions, hydrogen bond and crystal dynamics of p-methylbenzyl alcohol as studied by single crystal X-ray diffraction and 2H NMR

The title compound (pMBA) was found to undergo a first-order phase transition at 211 K (Tc1). Another transition with subtle enthalpy change appeared at 172 K (Tc2). Crystal structure determinations at various temperatures revealed that the transition at Tc1 was accompanied by remarkable changes in the molecular conformations around the CH2-C and O-CH2 bonds and a reversal of the direction of the O-H O hydrogen bond. Experiments of 2H NMR were carried out on pMBA-d where the hydroxyl hydrogen of pMBA was selectively deuterated. Analyses of the 2H NMR spectra and the temperature dependence of T1 of the 2H NMR indicated occurrence of jumping motions of 2H between asymmetric potential wells at temperatures lower than Tc1

Dynamical structure of AgxCu1−xI (x= 0.99–0.80) in ionic and superionic phases studied by solid 63Cu and 127I NMR spin–lattice relaxation time measurements

The temperature dependences of the 63Cu and 127I NMR spin–lattice relaxation time T1 and the 63Cu NMR spin–lattice relaxation time in a rotating frame T1ρ were measured for AgxCu1−xI (x = 0.99–0.80). In the γ phase, T1 and T1ρ were dominated by the lattice vibration at low temperatures. The minimum of T1ρ caused by the diffusion of the Cu ion was observed at ca. 360 K. The temperature dependence of T1ρ in the range 420–300 K can be explained in terms of a distribution of correlation times which arises from a distribution of activation energies for the ionic diffusion. The mean and the width of the distribution for the activation energies increased with increasing Cu concentration. The rapid T1 decrease observed above ca. 400 K can be attributed to the motion of the thermally generated defects. The enthalpy for the formation of the defect was estimated as 120 ± 10 kJ mol−1 from 63Cu NMR T1 and T1ρ values. In the α phase, the relaxation of the 63Cu nucleus was in the fast motion region and the activation energy of the ionic diffusion was determined as 7 ± 1 kJ mol−1 from the temperature dependence of 63Cu NMR T1.

35Cl NQR and 195Pt NMR spin-lattice relaxations in Zn1−xCuxPtCl6·6H2O

Abstract 35 Cl NQR spin-lattice relaxation time T 1 Q and 195 Pt NMR spin-lattice relaxation time T 1 of Zn 1− x Cu x PtCl 6 ·6H 2 O were determined in the temperature ranges 2.1–299K and 77–400K, respectively, to study the contribution of doped paramagnetic Cu 2+ ions to the relaxation of the resonant nuclei. For comparison, 35 Cl T 1 Q of ZnPtCl 6 ·6H 2 O and CuPtCl 6 ·6H 2 O, and 195 Pt T 1 of CuPtCl 6 ·6H 2 O were also measured in the temperature ranges 18–400K and 4.2–400K, and 77–400K, respectively. As for Zn 1− x Cu x PtCl 6 ·6H 2 O, the magnetization recoveries of the 35 Cl nucleus at low temperature and 195 Pt at observed temperatures followed the exp [−( τ T 1Q ) 1 2 ] or exp [−( τ T 1 ) 1 2 ] laws respectively as a function of time τ. These results suggest that nuclear relaxation is caused by direct dipolar interaction between the resonant nuclei and doped Cu 2+ ions. From T 1 Q and T 1 , the electron spin correlation time of Cu 2+ was estimated. The electron spin dynamics of Cu 2+ can be explained by the transition between the three distorted configurations, a result of the Jahn-Teller effect, and even at low temperature the transition can be considered to occur quite frequently. To confirm this fast transition, Cu 2+ ESR spectra of single crystals of Zn 1− x Cu x PtCl 6 ·6H 2 O were measured.