Tsutomu Ishioka

Vibrational spectra and structures of zinc carboxylates I. Zinc acetate dihydrate

Abstract The crystal structure of zinc acetate dihydrate was re-refined by X-ray diffraction analysis of the single crystal. The monoclinic cell dimensions were revised as a=14.394 (3), b=5.330 (2), c=10.962 (3) A and β=99.8 (2)° with Z=4. The bond distances and bond angles were also refined. Based on the structure, a normal mode analysis was made and the valence force constants were determined. Precise spectral assignments were made. Based on the assignments and the structure, the relation between the coordination forms and the vibrational frequencies of the carboxylate antisymmetric stretch and the symmetric stretch were discussed. In order to identify the coordination form of the carboxylate group from the vibrational frequencies, we propose the importance of other carboxylate modes other than the stretches.

Infrared and XAFS study on structure and transition behavior of zinc stearate

Structure and transition behavior of zinc(II) stearate crystal were investigated by infrared and XAFS spectroscopies. Structure of zinc stearate at room temperature was estimated as follows. From XAFS analysis, the coordination number of the carboxylate groups around the zinc atom was evaluated as 4 and the Zn-O distance as 1.95 A. Based on the infrared spectrum and a normal mode analysis, the conformation of the alkyl chain was confirmed as all-trans and the sub-cell packing was considered as parallel type, and also the coordination form of the carboxylate groups was determined as bridging bidentate type. As increasing temperature, zinc stearate has a solid liquid phase transition at 130 degrees C. At the transition, the alkyl chains goes into liquid like state as reported by Mesubi but the coordination structure was confirmed to be maintained.

Vibrational spectra and structures of zinc carboxylates II. Anhydrous zinc acetate and zinc stearate

Abstract A normal mode analysis was carried out for a monoclinic anhydrous zinc acetate crystal in which the acetate groups had bridging bidentate coordination forms, and spectral assignments were made. Based on the assignments, a relation between the coordination structure of the carboxylate groups around the zinc atom and the vibrational frequencies of the carboxylate rocking mode was found. This relation was applied to zinc stearate to determine its coordination form, and we found that zinc stearate had a bridging bidentate form.

Zinc(II) acetate dihydrate

The Zn atom in bis(acetato-O,O′)diaquazinc(II), [Zn(CH3COO)2(H2O)2], adopts a distorted octahedral structure coordinated by two water O atoms and four acetate O atoms.

Normal mode analyses of methyl palmitate all-trans and disordered forms in wagging progressive region

Normal mode analyses are made for methyl palmitate molecule having all-trans or conformational disorders around the ester head group, in order to explain characteristic observed frequency shifts in the wagging progressive region between all-trans and disorder chains in triglyceride molecules. It was found that one gauche conformation at C(alpha)-C(beta) position and 90 degrees rotation of the ester head group in an alkyl chain produce frequency shifts for twisting mode as observed. For wagging modes, contamination of the disorders around the head group makes assignments change and apparent frequency shifts occur.

MOLECULAR DYNAMICS SIMULATION OF INFRARED SPECTRA FOR POTASSIUM PALMITATE B-FORM CRYSTAL

The intra‐ and intermolecular potentials of potassium palmitate B‐form crystal were estimated by a normal mode analysis and a molecular dynamics simulation. Based on these potentials, we calculated the time history of the dipolemoment in the nine unit cells (3a×3b) containing 18 molecules and obtained the polarized infrared spectra by a Fourier transformation. The frequencies and the intensities of the intense bands agreed well with the observed ones, and were consistent with the crystal structure.The intra‐ and intermolecular potentials of potassium palmitate B‐form crystal were estimated by a normal mode analysis and a molecular dynamics simulation. Based on these potentials, we calculated the time history of the dipolemoment in the nine unit cells (3a×3b) containing 18 molecules and obtained the polarized infrared spectra by a Fourier transformation. The frequencies and the intensities of the intense bands agreed well with the observed ones, and were consistent with the crystal structure.

Normal mode analysis of syndiotactic polypropylene (T2G2T6G2) form

Abstract Syndiotactic polypropylene of all-trans form is transformed to (T2G2T6G2) form (new form) on exposing to xylene vapor under tension. This new form was characterized by infrared spectra and normal mode analysis. By increasing the gauche component from the all-trans to the new form, the infrared intensities of some bands increase. The potential energy distributions (PED) and L vectors for six monomers, which compose the repeating unit, were investigated. As a result, the PED and L vectors of the conformation-sensitive bands were found to be localized at the gauche position.

Vibrational spectra and structural transitions of potassium caprate A-form crystal

Anhydrous potassium soaps with even-numbered carbon atoms take on two different crystal structures at room temperature, depending on the chain lengths. One is A-form of the monocnnic space group for the carbon numbers from 4 to 12.1 Another is B-form of the triclinic space group from 12 to 18.2 In this study, potassium caprate CH3(CH2)8CO2K having 99% purity was synthesized. Normal mode analysis was made for the crystalline phase (A-form) at room temperature, and vibrational assignments were made. Thermal structural transition behavior was investigated by vibrational spectra.

Vibrational study on structural transitions of potassium pelargonate CH3(CH2)7CO2K

Anhydrous potassium pelargonate (KC9) undergoes four thermal transitions from room temperature to 450 degrees C. A normal mode analysis was made for the molecule in phase I at room temperature and the molecule was considered to have an all-trains conformation. With increasing temperature, partial melting of the alkyl chains occurred in phase II and complete melting was observed in phase III, as confirmed by vibrational spectra. In addition, orientational disorder of the carboxylate groups was suggested in phase II. This transition behavior of potassium pelargonate was compared with the behavior of nonane and pelargonic acid.

Vibrational spectra and structure of zinc stearate

Zinc stearate Zn(CH3(CH2)16CO2)2 is one of metal soaps, but its molecular structure (the conformation of the alkyl chain and the coordination structure) is not fully clarified yet. In this study, we made a normal mode analysis of the compound and estimate its molecular conformation, and also we investigated the coordination structure of the carboxylate groups to zinc atom by the vibrational spectra. Zinc stearate has one phase transition at 133°C from room temperature to 400°C. From temperature dependence of the vibrational spectra, we discussed the structural transition behavior of the soap.