Shigenobu Funahashi

Equilibrium and Structural Study of Chloro Complexes of Iron(III) Ion in Acidic Aqueous Solution by Means of X-Ray Absorption Spectroscopy

Using an extended X-ray absorption fine structure (EXAFS) technique, the formation constant of the pentaaquachloroiron(III) complex was determined to be 3.8 ± 0.4 mol-1 dm3 at 25.0 ± 0 .1 °C in a 1.00 mol dm-3 HCIO4 aqueous solution. The structures of [Fe(OH2)6]3+ and [FeCl(OH2)5]2+ were determined on the basis of the same EXAFS data. The Fe-O bond length (2.05 Å) in the latter is longer than that (2.01 Å) in the former due to the electron donation and charge neutralization by the coordinating chloride ion with the Fe-Cl bond length of 2.26 Å.

Newly devised spectrophotometric cell for measurements of solubility and slow reaction rate in supercritical carbon dioxide

Abstract A spectrophotometric cell for measurements of solubility and slow reaction rate in supercritical carbon dioxide (scCO 2 ) up to 30 MPa was developed. A free piston made of a Teflon-coated magnet in the cell is moved up and down in the cell cylinder by an outside magnet, which is automatically driven by a gas cylinder at an arbitrary time interval. There is a one-way path in the free piston, and solution flow in the opposite direction is prevented; thus, the solution is stirred by circulating scCO 2 in the looped pass. Using the developed cell, the solubilities of 5, 10, 15, 20-tetrakis(pentafluorophenyl)porphyrin (H 2 tpfpp) in scCO 2 were determined at various temperatures and pressures. The dynamic process of copper(II) ion incorporation into the porphyrin core for the reaction of H 2 tpfpp with Cu(hfac) 2 (hfac=1,1,1,5,5,5-hexafluoroacetylacetonate) was monitored by simultaneously dissolving both reagents in scCO 2 in order to evaluate the applicability of the developed spectrophotometric cell for rate measurements of slow chemical reactions in scCO 2 .

REACTION MECHANISM OF WATER EXCHANGE ON DI- AND TRIVALENT CATIONS OF THE FIRST TRANSITION SERIES AND STRUCTURAL STABILITY OF SEVEN-COORDINATE SPECIES

Abstract We studied the structural stability of heptahydrated trivalent cations of the first transition series from scandium to cobalt as model intermediary species in associative reaction pathways for the water exchange of the hexahydrated cations by ab initio molecular orbital methods. All the structures of heptacoordination are pentagonal bipyramidal with a distorted equatorial plane. The heptahydrated di- and trivalent cations with the same d-electron configuration are similar to each other for the structure and the structural stability which are strongly dependent on their d electron configurations. The associative mechanism is possible for the water-exchange reactions of the hexahydrated trivalent cations from scandium to cobalt, because the seven-coordinate species are located at the local minima or at the saddle points on the potential energy surface. The intrinsic reaction coordinates of the water-exchange reactions on the hexahydrated vanadium(II) and chromium(II) ions support the cis and trans attack of the associative mechanisms. The hexahydrated trivalent cations with d3 and d6 configurations [chromium(III) and cobalt(III)] prefer a cis attack, while manganese(III) with a d4 configuration prefers trans attack during the operative associative process of the water-exchange reaction.

Cobalt(II) phosphine complexes stable in aqueous solution: spectroscopic and kinetic evidence for low-spin Co(II)P6 and Co(II)P3S3 with tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane

Abstract Co(II) species produced by the controlled potential electrochemical reduction of Co(III)P 3 S 3 and Co(III)P 6 complexes with 1,4,7-trithiacyclononane and tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane in aqueous solution were characterized at ambient temperature by the EPR and spectrophotometric methods: the Co(II)P 6 and Co(II)P 3 S 3 species are in the low-spin t 2g 6 e g 1 state with large Jahn–Teller distortion. Kinetic studies of the redox reactions involving these Co(III)/(II) species revealed that the electron self-exchange reactions for the Co(III)/(II) couples are very fast ( k ex ∼10 4 dm 3 mol −1 s −1 ), which is consistent with the results for other low-spin/low-spin Co(III)/(II) couples. It was concluded that the nephelauxetic effect of the P donor atom stabilizes the low-spin state in Co(II).

Development of stopped-flow instrument with spectrophotometric detection for the study of fast reactions in supercritical carbon dioxide; kinetics of metalloporphyrin formation in supercritical carbon dioxide

Abstract A high-pressure stopped-flow instrument with spectrophotometric detection has been developed, which enables us to follow fast reactions with half-lives longer than 10 ms in supercritical carbon dioxide (scCO 2 ) at various temperatures up to 150xa0°C and pressures up to 30 MPa. The rate of the metalloporphyrin formation reaction in scCO 2 between 5,10,15,20- tetrakis (pentafluorophenyl)porphyrin and bis (1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)copper(II) (Cu(hfac) 2 ) was successfully measured under a variety of excess concentrations ( C Cu ) of Cu(hfac) 2 . Based on the dependence of the conditional first-order rate constants on C Cu , the metalation mechanism was evaluated in scCO 2 .

SOLVATION STRUCTURE OF SOLVATED CU(I) IONS IN NON-AQUEOUS SOLVENTS AS STUDIED BY EXAFS AND AB INITIO MOLECULAR ORBITAL METHODS

The structure parameters around the Cu(I) ion in pyridine (PY), 4-methylpyridine (4MPY), 2-methylpyridine (2MPY), 2,6-dimethylpyridine (26DMPY), and acetonitrile (AN) were determined by the extended X-ray absorption fine structure (EXAFS) method. The solvation structures of the Cu(I) ion in PY, 4MPY, and AN are 4-coordinate tetrahedral with Cu-N bond lengths of 205, 205, and 200 pm, respectively. In the case of 2MPY and 26DMPY, the Cu(I) ion has a 3-coordinate triangular structure with a Cu-N bond length of 201 pm. Such a decrease in the coordination number was interpreted in terms of the bulkiness of the solvent molecules. In order to clarify the most stable solvation structure of the Cu(I) ion, we carried out ab initio molecular orbital calculations for the solvation system of [Cu(NCH)n]+ (n = 1 - 6 ) where the steric effect is negligible. The Gibbs free energy of solvation was the smallest in the case of n = 4 and the 4-coordinate tetrahedral solvation of the Cu(I) ion was theoretically evaluated as most stable. The enthalpy of solvation monotonously decreases with increasing n, while the entropy of solvation proportionally increases. Although a larger gain of enthalpy is observed for the octahedral structure rather than the tetrahedral one, the entropic loss for the former overcomes the enthalpic gain.

An Investigation of the Photodegradation of Tetraphenyltin(IV) in THF

The decomposition process of triphenyltin radical produced by the irradiation of tetraphenyltin (IV) using 266 nm laser pulse (10 ns) was studied in tetrahydrofuran with and without the existence of water. NMR measurements were carried out to examine the decomposition products. The effect of water and propane-2-ol on the decay process of Ph3Sn z was also examined, which revealed that the primary process for the disappearance of the Ph3Snz radical was the recombination reaction with Phz when no appreciable amount of water and propane-2-ol exists in the reaction system. The second-order rate constant for the reaction of Ph3Snz with water was estimated as 4.4 x 106 dm3mol−1s−1 from the results obtained under the condition of [H2O]0, [propane-2-ol]0 z [Ph3Snz]0.