Akinobu Sasane

Mechanism of the fractionation of 7Li ions into aqueous solutions: ion-exchange with the six-membered oxygen ring of zeolite-A

Lithium-isotope fractionation by ion exchange was investigated using an aqueous solution (LiOH+HNO3) fed to an NH4+-zeolite-A column at 293 K. The Li+ ion concentration [Li] and isotopic ratio [7Li]/[6Li] of the feed solution and the effluent fractions were measured, and from their differences, the accumulation of Li+ ions and the isotopic ratio ([7Li]/[6Li])zl in the zeolite were determined. The accumulation rate changed significantly at 60% Li filling. The accumulation below 60% Li filling was attributed to the Li+ ion adsorption on the six-membered oxygen rings of zeolite-A. The isotopic ratio ([7Li]/[6Li])ef for the effluent passing through the six-membered oxygen rings showed a wide plateau as a function of the effluent volume. The observed ratio ([7Li]/[6Li])ef/([7Li]/[6Li])feed=1.03, corresponded to three stages of separation. A single-stage factor of 1.01 was evaluated from the ratio ([7Li]/[6Li])feed/([7Li]/[6Li])zl. The basis of the wide plateau ([7Li]/[6Li])ef was attributable to the thermodynamic coexistence of the two solid-phases of zeolite. The fractionation mechanism of 7Li is discussed using ab initio molecular orbital calculations. The excess of 7Li in the Li+ tetrahydrate and the deficit of 7Li in the six-membered oxygen rings were theoretically deduced. The calculations proved that the small number of Li oscillatory modes, where the O atoms are almost at rest, served for 7Li enrichment. The mode frequencies accounted for the magnitude of the separation factor.

1H NMR STUDIES ON THE MOTION OF WATER MOLECULES IN MAGNESIUM HEXACHLOROSTANNATE(IV) AND HEXACHLOROTELLURATE(IV) HEXAHYDRATES

Abstract The temperature dependence of the 1 H NMR spin-lattice relaxation time T 1 and the second moment M 2 have been measured for [Mg(H 2 O) 6 ]SnCl 6 (magnesium hexachlorostannate(IV) hexahydrate) and [Mg(H 2 O) 6 ]TeCl 6 (magnesium hexachlorotellurate(IV) hexahydrate). The same length of a T 1 minimum, with 215 ms at the Larmor frequency of 18 MHz, was observed at 195 K for the Sn(IV) complex and at 153 K for the Te(IV) complex. The T 1 minimum has been explained by the 180° flips of water molecules about their C 2 axes. Activation energies associated with the motion were evaluated as 21 kJ mol −1 for the Sn(IV) complex and 15 kJ mol −1 for the Te(IV) complex. Steep drops of T 1 observed for both complexes above room temperatures were assigned to the uniaxial rotation of the hydrated cations. From the slope of the drops, activation energies of 83 kJ mol −1 and 76 kJ mol −1 were estimated for the Sn(IV) and Te(IV) complexes, respectively. The differences in the activation energy between the two complexes have been interpreted in terms of the hydrogen bonds in the crystals.

A 1H NMR study of molecular motions in chloropentamethylbenzene

Abstract The temperature dependence of the 1H NMR spin-lattice relaxation time T1 has been measured for solid chloropentamethylbenzene in the range 90–380 K. A single T1 minimum of 36.5 ms was observed around 278 K at the Larmor frequency of 18 MHz and has been assigned to in-plane molecular reorientation about the pseudohexad C′6 axis over the nonequivalent potential wells. With the aid of the reported X-ray analyses, the results have been analyzed by employing the method developed by Anderson. The activation energy has been evaluated as 27 kJ mol−1 which amounts to nearly the same value as hexamethylbenzene. A gradual decrease of T1 below 150 K was attributed to the methyl groups rotation about their C3 axes over the barriers of 3.0 kJ mol−1.

A Temperature Dependence Study of 35Cl Nuclear Quadrupole Resonance Frequencies in Some Hexachloroplatinate(IV) Hexahydrates

The temperature dependence of 35Cl NQR frequencies was investigated in various hexachloroplatinate( IV) hexahydrates containing the following divalent ions as counter cations: Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Ba(II). All of the compounds except the Cu(II) and Ba(II) salts yield a single 35Cl NQR line at all temperatures studied. For the Mn(II), Cu(II), and Ba(II) salts, the NQR frequencies are considerably shifted by deuteration. For the deuterated Mn(II) salt, two 35Cl NQR lines were observed whose relative peak-height intensities vary in dependence on the history of the thermal treatment of the sample. The very broad higher frequency line could be observed for a sample which had been at 77 K or below. It could not be observed for a sample which was cooled slowly to room temperature after it had been heated up to ca. 420 K. A structural phase transition was located at 135.6 and 129.4 K for the Cu(II) salt and its deuterated analog, respectively. The frequency shift by deuteration is discussed in relation to the strength of O - H ... CI type hydrogen bonds.

35Cl Quadrupole Relaxation Study on Cs2[Au(I)Cl2][Au(III)Cl4] and Cs2[Ag(I)Cl2][Au(III)Cl4]

Two 35ClNQR spin echo signals, VQ1 = 17.28MHz (Au(I)-Cl) and VQ2 = 27.10MHz (Au(III)-Cl), have been observed at 77 K from two samples of Cs2[Au(I)Cl2][Au(III)Cl4] prepared differently. The resonances resulted at the same frequencies but with different line widths. Cs2[Ag(I)Cl2]- [Au(III)Cl4] yielded a singlet, VQ2 = 27.96 MHz, at 77 K. The three samples gave rise to ESR signals indicating the presence of paramagnetic Au(II) or Ag(II) sites with low concentration. 35ClNQR spin-lattice relaxation time T1Q measurements revealed that only the reorientational motions of the anions [Au(III)Cl4]− are exited at high temperatures.

A 35Cl NQR Study on Cs2[AUICl2] [AuIIICl4]

Abstract A pair of 35Cl NQR spin echo signals has been observed for the mixed valence complex Cs2 [AuICl2] [AuIIICl4] between 77 and 243 K. At 77 K, two resonance lines with the half widths ΔvQ ~ 50 kHz were located at vQ1 = 17.28 MHz for the AuI-Cl chlorine and at vQ2 = 27.10 MHz for the AuIII -Cl chlorine in accordance with the crystal structure. The chlorine ionic characters of the AuI-Cl and AuIII-Cl bonds are estimated as 0.63 and 0.42, respectively. The central gold atom carries a fractional protonic charge of 0.26 in [AuICl2]- and 0.68 in [AuIIICl4]-. The charge distributions in the complex anions differ insignificantly from those in the isolated [AuCl2]- and [AuCl4]- for ordinary complexes, indicating that the charge transfer interactions between the anions are weak in the mixed valence complex. The observed linear temperature dependencies of VQ and log TlQ are well explained by the lattice vibration. When the temperature was increased from 77 K, the resonance lines became gradually weak without changing ΔvQ and immeasurable above 215 K. ESR spectra taken at various temperatures revealed the presence of paramagnetic sites of ca. 5 x 1020 mol- 1 arising from Au(II). The small but finite concentration of Au(II) or some other reason should be responsible for the fade out phenomenon and the large ΔvQ observed.

MOTION OF WATER MOLECULES AND HYDROGEN BONDS IN ZINC HEXACHLOROSTANNATE (IV) HEXAHYDRATE AS STUDIED BY 1H NMR AND 35CL NQR

Abstract The 1H NMR spin-lattice relaxation time T1, 35Cl NQR frequency νQ, and 35Cl NQR spin-lattice relaxation time T1Q of [Zn(H2O)6] [SnCl6] (zinc hexachlorostannate(IV) hexahydrate) have been measured at temperatures between 77 and 350 K. The NQR spin echo signal with νQ = 15.689 MHz at 77 K showed a positive temperature coefficient attributable to O-H-Cl type H-bonds in the crystal. νQ at 77 K is strongly correlated with the electronegativity χM of the metal M in the series of stannates [M(H2O)6] [SnCl6] (M = Mg, Ca, Mn, Co, Ni, Zn). A T1 minimum observed for the Zn salt is ascribed to 180° flips of water molecules with an activation energy of 20 kJ mol-1. The motion is influenced by repulsive forces among the water molecules within a cation rather than by attractive forces between the H-bonded H and CI atoms. T1Q proved to be mainly governed by lattice vibrations, weakly modulated by the fluctuating electric field gradient caused by the 180° flip motions.

81Br NQR for Uncoordinated Br ions in trans-[CoBr2(en)2][H5O2]Br2 and trans-[CoBr2(en)2] [D5O2]Br2

Abstract The temperature dependence of the 81Br NQR frequencies (vD) for uncoordinated Br- ions in trans-[CoBr2(en)2] [D5O2]Br2(D) has been determined by a continuous-wave spectrometer. vD amounted to 16.200 MHz at 273 K. This is lower by 418 kHz than the 81Br NQR frequency (vH) for trans-[CoBr2 (en2] [H5O2 ]Br2 (H). The frequency difference (Δv = vH -vD) remained almost constant in the temperature range studied. A shortening of the O-H bond length caused by deuteration could explain the magnitude and the sign of Av on the basis of a point charge model calculation. The compounds D and H yielded 81Br NQR lines in the range 110-320 K and 90-343 K, respectively. As to the 59Co NQR frequencies (7/2 - 5/2), the observed isotope frequency shifts (Δv1 = v1H - v1D) between D and H were smaller than 5 kHz. Below 160 K, 59Co resonances were only available by pulsed experiments. 59Co NQR spin-lattice relaxation times T1Q of 0.54 ms at 194 K and 4.8 s at 77 K for H have been observed.

Temperature Dependence Studies of 35Cl NQR Frequencies in Magnesium and Nickel Hexachlorotellurate(IV) Hexahydrates and Nickel Hexachloroiridate(IV) Hexahydrate

Abstract The 35Cl NQR frequencies in MgTeCl6 · 6H2O, NiTeCl6 · 6H2O, and NiIrCl6 · 6H2O have been determined at various temperatures. These compounds form rhombohedral crystals with the space group R3̄ ,showing a single resonance line. The 35Cl NQR frequencies of the Te(IV) complexes exhibit an unusual positive temperature coefficient. The deuterated analogs of the Te(IV) complexes show a small frequency shift at 77 K. These results are interpreted by the presene of O-H ··· CI type weak H-bonds. The resonance frequency of the Ir(IV) complex versus temperature curve shows a minimum and a maximum. This unusual temperature dependence is mainly explained by the same type of the H-bond as existing in the Te(IV) complexes. The π-bond formation between Ir and CI atoms is also partly responsible for the unusual temperature dependence.

Chlorine-35 NQR Studies on [(NH4)0.01K0.09]SnCl6 Mixed Crystals

The temperature dependence of 35Cl NQR frequencies was measured on the mixed crystal [(NH4)0.01K0.99]2SnCl6. Two phase transitions have been located at Tc1 = 259K and Tc2 = 252K , which are lower by 3 K than the corresponding transition temperatures of the pure K2SnCl6 crystal. The DSC experiments showed that the NH4+ concentration dependence of Tc2 almost parallels that of Tc1. The impurity effect resulting from the inclusion of a small amount of NH4⊕ ions in K2SnCl6 crystals is discussed in relation to the microscopic viewpoint of the phase transitions.