Hisao Negita

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.

Line Shape of 14N Pure Quadrupole Resonance by the Zeeman Modulation

The Zeeman patterns for 14N pure quadrupole resonances in powders have been deduced, calculating the relative intensities around the resonance frequencies. The shape of the resonance curve to be recorded can be found by the difference between the unperturbed and perturbed lines. When the asymmetry parameter η has a finite value, the recorded peak shifts from the unperturbed position. This effect is more evident for the weaker modulation field or the broader unperturbed line, and also for larger values of η. Furthermore, it is shown that the higher resonance line is much stronger than the lower, when η is large.

Zeeman effect on the nqr of the complex of copper(I) halide with triphenylphosphine

Abstract Nuclear quadrupole resonance (NQR) frequencies due to 63Cu were observed for Cu2X2(PPh3)3 (X=Cl, Br, and I). Each compound has two NQR lines in the separated frequency regions, 13-16 MHz and 27-30 MHz. The Zeeman effect on the higher lines was examined by using single crystals in order to deduce the asymmetry parameters of the electric field gradient tensor, which were found Co be 0.29, 0.31, and 0.33 for X=Cl, Br, and I, respectively. In the case of Cu2Br2(PPh3)3, two 81Br NQR lines were found at 47.52 and 49.53 MHz with large asymmetry parameters of 0.997 and 0.987, respectively.

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 deuterium isotope effect in enthalpy change on the thermal dehydration of calcium oxalate monohydrate

Abstract The enthalpy changes in the thermal dehydrations of calcium oxalate monohydrate and its deuterium analogue were determined as 15.21 ± 0.04 and 15.37 ± 0.05 kcal mole −1 , respectively by means of differential scanning calorimetry. The isotope effect calculated from measured vibrational frequency shifts on deuteration of the hydrate was found to be in good agreement with that observed. The origin of the deuterium isotope effect in the enthalpy change is briefly discussed.

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.

The structural investigation of SbBr3· (POBr3)2 BY 81Br and 121SbNQR

Abstract 81 Br and 121 Sb NQR have been observed for SbBr 3 ·(POBr 3 ) 2 , and the Zeeman effect on 81 Br NQR lines examined at 77 K. It is considered from these results that this complex consists of a dimer of two SbBr 3 ·(POBr 3 ) 2 molecules bridged by two Br atoms.

The bonding in the hexahalogenogallate(II) ions with an ethane-like structure studied by NQR

Abstract The nuclear quadrupole resonance (NQR) spectra due to 35Cl, 81Br and 69Ga have been recorded for L2Ga2X6 [L  (CH3)4N and (C2Hs)4N; X  Cl and Br]. The NQR frequencies of the halogen in these compounds are considerably lower than those in Ga(III) compounds. The 69Ga NQR signals at 77 K are observed in the range 22–24 MHz. The electron distributions on the Ga and halogen atoms have been calculated according to the Townes-Dailey theory. The results show that the charge on each atom in the hexahalogenogallate(II) anions is independent of the cation but depends on the halogen.

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.