Sumio Ichiba

Kinetics and mechanism of the thermal dehydration of calcium oxalate monohydrate

Abstract The kinetics and mechanism of the thermal dehydration of CaC 2 O 4 · H 2 O were studied by means of thermogravimetry, both at constant temperature and linearly increasing temperature. The dehydration mechanism was determined as a random nucleation and subsequent growth mechanism, an Avrami—Erofeyev law with m ≅ 2. The mechanistic equation could be expressed as [−ln(1 −α)] 1 1.904 = kt where α is the fraction dehydrated at time t and k is the rate constant. The plausibility of the Avrami—Erofeyev mechanism in the thermal dehydration of CaC 2 O 4 · H 2 O is discussed.

Mössbauer effect of 129I in n–σ and π–σ charge‐transfer complexes of iodine in the frozen solution

The Mossbauer effect of 129I was applied to investigate charge‐transfer complexes of the n–σ and π–σ types in the carbon disulfide frozen solution at 16 K. In the case of n–σ type complexes such as triethylamine–iodine and pyridine–iodine, two chemical species of iodine, which correspond to the bridging and terminal iodines, were observed in the Mossbauer spectra. It is elucidated that a charge‐transfer bond is described as a mixture of a four‐electron three‐center bond and a covalent bond involving dσpσ hybrid orbitals in the bridging iodine. On the other hand, for the π–σ type complexes such as benzene–iodine and methylated benzene–iodine the Mossbauer spectra show only one chemical species of iodine. The acceptor orbital of iodine is thought to be described by an spd hybrid orbital. That is, a small amount of s and d characters contributes to the formation of the charge‐transfer bond. From the Mossbauer parameters the charge densities and the charge distributions of iodine in these complexes were obtained.

129I Mössbauer Effect in Several Charge‐Transfer Complexes of Iodine

The Mossbauer effect of the 27.8‐keV transition in 129I has been studied in the iodine complexes I2·phenazine, I2·acridine, and I2·hexamethylenetetramine. The Mossbauer spectrum of the I2·phenazine complex has shown only one chemical species of iodine, whereas those of the other complexes have shown the existence of two species of bridging and terminal iodine. From the Mossbauer parameters such as the isomer shift, quadrupole coupling constant, and asymmetry parameter, the electron distribution on the iodine atoms in the complexes was calculated. In the I2·phenazine complex, 0.09e− is transferred to the iodine atom from the phenazine molecule. In the I2·acridine and I2·hexamethylenetetramine complexes, the charges on the bridging iodine atoms are decreased and those on the terminal atoms are increased. In the later complex, a net charge of 0.08e− is transferred to the iodine molecule through the nitrogen atom from the hexamethylenetetramine molecule.

The kinetic deuterium isotope effect in the thermal dehydration of boric acid

Abstract The kinetic deuterium isotope effect in the thermal dehydration process from H 3 BO 3 to HBO 2 (III) was determined using simultaneous TG and DSC. The rate constant ratio of H 3 BO 3 to D 3 BO 3 obtained by the analysis of isothermal TG and DSC curves was found to be smaller than unity. Both activation energy, E , and frequency factor, A , for the dehydration of H 3 BO 3 proved to be larger than those of D 3 BO 3 , using non-isothermal TG and DSC. The origin of the deuterium kinetic isotope effect in the thermal dehydration of boric acid is also briefly discussed.

127I-NQR, 119 Sn Mössbauer Effect, and Electrical Conductivity of MSnI3 (M = K, NH4 , Rb, Cs, and CH3NH3 )

Abstract In a series of MSnI3 compounds (M = K, NH4 , Rb, Cs, CH3NH3) two types of coordination around the central Sn(II) were found by 127I-NQR and powder X-ray diffraction techniques. They are square pyramidal (for M = NH4 , Rb) and octahedral (for M = CH3NH3). CsSnI3 , on the other hand, showed a drastic structural change of the anion at 425 K from a square pyramid to a regular octahedron. Associated with this phase transition, the electrical conductivity increased from 4 x 10-3 S cm-1 to about 102 S cm-1 . This metallic modification was characterized by 127I-NQR and 119Sn Mössbauer spectroscopy.

Deuterium isotope effects in the thermal dehydration of boric acid

Abstract The thermal dehydration of boric Acid, H3BO3, was studied systematically by means of TG and DSC. Deuterium isotope effects in enthalpy change and dehydration temperature in the thermal dehydration stages of H3BO3 were examined by means of DSC. The enthalpy change of D3BO3 was found to be appreciably larger than that of H3BO3, whereas the thermal stability was little affected by deuteration. The isotopic difference in enthalpy change calculated from vibrational frequency shifts upon deuteration of H3BO3 was compared with the experimental value.

Nuclear Quadrupole Resonance in Chloro- and Bromoantimonate(III) Complexes

C1, 3581Br, and 121Sb N Q R spectra were observed in com plexes o f the type RxSbyX z with anionstoichiometries SbCl4 , SbClg- , SbBr4 , SbBr^~, SbBr^- , and Sb2Br^~. Several complexes showwidely spaced halogen resonance lines and unusual temperature dependences o f the NQ Rfrequencies. These findings are accounted for 35Cl, 81Br, and 121Sb NQR spectra were observed in complexes of the type RxSbyXz with anion stoichiometries SbCl4- , SbCl63- , SbBr4- , SbBr52-, SbBr63- , and Sb2Br93-. Several complexes show widely spaced halogen resonance lines and unusual temperature dependences of the NQR frequencies. These findings are accounted for in terms of a three-center four-electron bond of the X-Sb-X group and cation-anion interaction.

Mössbauer effect of 119Sn in thiostannates, selenostannates and selenothiostannates

The thiostannates, selenostannates and selenothiostannates of the alkali metals and alkaline earth metals were prepared. From the Mossbauer studies on these compounds, it seems likely that discrete dimeric S2S64−, tetrahedral SnS44−, dimeric Sn2S76− and related seleno-ions exist in the solids.

Mössbauer effect of 129I in the bridged and isolated forms of mercury (II) iodide

Abstract The Mossbauer effect of the 27.8 keV transition in 129 I was observed to investigate the electronic structure of mercury (II) iodide in the bridged and isolated forms. From Mossbauer parameters such as the isomer shift, the quadrupole coupling constant, and the asymmetry parameter, the electronic configurations of iodine were derived to be 5s 1.97 5p 5.27 and 5s 2 5p 5.52 for the bridged and isolated forms, respectively. The s-character in the iodine bond was found to be 4% and the quadrupole coupling constant was positive for the bridged form. On the other hand, the quadrupole coupling constant was negative and its absolute value was larger for the isolated form. Based on these results, the bond character of iodine in mercury (II) iodide was discussed.

Structural study of anilinium chloroantimonate(III) complexes [C6H5NH3]nSbCl3+n(n=1,2,3) by means of NQR

Abstract NQR spectra were observed for [C 6 H 5 NH 3 ] n SbCl 3+ n ( n =1,2,3) at various temperatures. A good correlation was found between the 121 Sb quadrupole coupling constant and charge on the SbCl n − 3+ n anion. Temperature dependences of 35 Cl NQR frequencies for the compounds with n =2 and 3 showed characteristic patterns of three-center, four-electron bonds.