Jinsai Hidaka

COORDINATION OF 8-QUINOLINOL-5-SULFONIC ACID TO ALUMINIUM(III) COMPLEXES OF 8-HYDROXY-7- [(6 ' -SULFO-2 ' -NAPHTHYL)AZO]-QUINOLINE-5-SULFONATE. EVIDENCE FOR MIXED LIGAND COMPLEX FORMATION

Abstract Studies have been made on the coordination behaviour of the aluminium(III) 8-quinolinol-5-sulfonate (hqs)1 and aluminium(III) nqs1 complexes2 with hqs in 0.1 mol dm−2 aqueous sodium chloride solution at 25°. Mixed-ligand complex formation was evidenced by electronic absorption spectral and other spectrophotometric equilibrium studies. Stopped-flow kinetic studies revealed that mixed-ligand complex formation with a mono-nqs complex proceeds via its reaction with Hhqs− and hqs2- whereas formation of the tris-hqs complex proceeds via the reaction of [Al(H2O)6]3+ with Hhqs− and hqs2- and also of [Al(OH)(H2O)5]2+ with H2 hqs and Hhqs−. Coordination mechanisms and structures for the mixed-ligand and the tris-hqs complexes are also discussed.

Rotatory Dispersion of Metallic Co-ordination Compounds. II. Absorption Spectra and Rotatory Dispersion of Cobalt(III) Complexes of EDTA

The rotatory dispersion measurements have been made for D-Na2[Co(edta)NO2]·3H2O, D-K[Co(edta)]·3H2O, D-K2[Co(edta)Cl]·3H2O and D-cis-[Co en2(NO2)2] I. On the basis of these measurements, the relation of the splitting of the first absorption band with the so-called anomalous rotatory dispersion has been discussed. In the anomalous rotatory dispersion of D-[Co(edta)NO2]2−, there appear two inver-sive dispersions due to the component absorption, Ia and Ib, of the split first absorption band. Similarly considered, it has been shown that the first absorption band of [Co(edta)]− or [Co(edta)Cl]2− may have two component absorptions in accordance with the behavior of its rotatory dispersion curve.

Preparation and some properties of cobalt(III) complexes with a dipeptide containing L-methionine residue

Abstract Cobalt(III) complexes with a dipeptide containing L -methionine residue, [Co(dipeptidato- N,N,O ) 2 ] − , [Co(dipeptidato)(diamine)] + and cis -[Co(dipeptidato)(NH 3 ) 2 ] + , have been prepared, where dipeptidate is L -methionyl-glycinate, glycyl- L -methioninate, L -methionyl- L -alaninate or L -alanyl- L -methioninate, and diamine is 1,2-ethanediamine or 1,3-propanediamine. All the complexes were characterized by electronic absorption, 1 H NMR and 13 C NMR and circular dichroism (CD) spectra. In the diamine and diammine complexes, the dipeptide coordinates to the cobalt(III) ion as the quadridentate through the nitrogen atoms of NH 2 and peptide N, the oxygen atom of COO − and the sulfur atom of SCH 3 . The 500 MHz 1 H NMR spectra indicate that the NS chelate rings of the L -met residue take the chair conformation and the S-methyl groups take the S ( S ) configuration for the C-terminal L -met., The CD spectra of the complexes were discussed with respect to their configurations.

Molecular structure and stereoselective isomerization of (-)CD504-mer-bis(ethylenediamine-N-acetato)cobalt(III) bromide

Abstract The crystal structure of the (-) CD 504 - mer -[Co(edma) 2 ]Br isomer (edma=ethylenediamine- N -acetate) has been determined by a single crystal X-ray diffraction technique. The crystal was orthorhombic with space group P 2 1 2 1 2 1 , a =8.507(1), b =18.363(2), c =8.499(1) A, V =1327.6(3) A 3 , and Z =4. The cobalt atom is surrounded octahedrally by cis two oxygen and four nitrogen atoms of the two edma ligands, which coordinate to the cobalt ion in the meridional form. The (-) CD 504 isomer has an S ( C 2 ) configuration and both of the asymmetric nitrogen donor atoms in the two edma ligands take an S configuration. The (+) CD 504 - mer -[Co(edma) 2 ] + isomer isomerized to the (+) CD 543 - C 2 - trans (O) and C 1 - trans (O) isomers in a basic aqueous solution (pH 10.35) at 40 °C, and the formation ratio of these two isomers was c . 1:1. The isomerization mechanism of the (+) CD 504 - mer isomer was discussed in relation to its absolute configuration.

Ligand substitution reaction of (carbonato) bis(ethylenediamine) cobalt (III) complex with ethylenediamine

Abstract Substitution reaction of coordinated carbonate ligand in [Co(CO3)(en)2]+ in alkaline aqueous solution of 1.0 mol dm−3 chloride at 55 °C under the pesudo-first-order kinetic condition with respect to ethylenediamine has been studied, by employing the electronic absorption and circular dichroism spectral methods for the racemate and the optically active isomers. The reaction proceeded stepwise with two rate-determining steps. Δ-(−)589-[Co(CO3)(en)2]+ changed via two parallel pathways principally with racemization to [Co(OCO2)(OH)(en)2], which subsequently changed to [Co(en)3]3+ through [Co(OCO2)(en-N)(en)2]+; were OCO22− and en-N denote unidentate carbonate and ethylenediamine, respectively. Some stereoselectivity was noticed in the first base-catalyzed hydrolysis step. A substitution reaction mechanism was discussed.

Ligand substitution reactions of (bidentato-O,O and −O,N) bis(ethylenediamine)cobalt(III) complexes with ethylenediamine catalyzed by photoexcited tris(2,2′-bipyridine)ruthenium(II) complex: The role of circularly polarized light in photoirradiation

Abstract The substitution reactions with ethylenediamine of the bidentato-O,O ligand of (bidentato-O,O)bis(ethylenediamine)cobalt(III) complex have been studied in a weakly alkaline aqueous solution in the presence of tris(2,2′-bipyridine)ruthenium(II) complex under photoirradiation. The reaction was catalyzed by the photoexcited ruthenium(II) complex. Enhanced generation of the photoexcited ruthenium(II) complex and acceleration of the reaction of the bidentato-O,N ligand of (bidentato-O,N)bis(ethylenediamine)cobalt(III) complex were noticed when the optically active isomer of the ruthenium(II) complex was irradiated by the corresponding circularly polarized light.

Kinetics and mechanism of substitution reaction with ethylenediamine of coordinated glycinate ligand in bis(ethylenediamine) glycinatocobalt(III) complex

The substitution reaction with ethylenediamine of the coordinated glycinate ligand of bis(ethylenediamine)glycinatocobalt(III) complex has been studied at 60–70°C in a weakly alkaline aqueous solution (buffered around pH 12) of 1.0 mol dm−3 chloride concentration. The reaction was studied under the pseudo-first-order kinetic conditions with respect to ethylenediamine and followed by means of electronic absorption spectra for the racemate and by circular dichroism spectra for the optically active isomers. The reaction proceeds stepwise with three rate-determining steps: the first step is dependent neither on ethylenediamine nor on hydroxide ion concentration but in accompanied by loss of optical activity, while the second one is dependent both on ethylenediamine and on hydroxide ion concentrations. Mechanisms of the ligand substitution reaction are discussed.

Coordination reaction of iron(III) with 8-hydroxy-7[(2-hydroxy-5-carboxyphenyl)Azo]-5- acid: Evidence for kinetic linkage isomerism

Abstract Coordination reaction kof kinetics of a bifunctional multidentate ligand 8-hydroxy7-(2-hydroxy-5-carboxyphenyl)-azo]-5-quinolinesulphonic acid (H4hcqs), to iron(III) has been investigated in an aqueous 0.10 mol dm−3 sodium perchlorate solution at 22°C. This ligand initially coordinates to the metal ion to form an intermediate complex with its bidentate quinolinolato (NO) moiety, Fe (H2hcqs-N, O)+, which then transforms to a complex with its terdentate dihydroxyazo(ONO) moiety, Fe(H2hcqs-O,N,O)+, with the stability constant (β11) of log β11 (mol−1 dm3) of 18.32±0.11, thus showing a kinetic linkage isomerism. The first step proceeds through the parallel pathways of Fe3+ + H2hcqs2− (k32) and FeOH2+ + H4hcqs (k20) with the composite rate constant of k32+k20Ka(qyNH), KOH (mol−1 dm3 s−1) of 1.92±0.35 × 103 showing the greater importance of the pathway of k20 as compared with that of k32, where K(qyNH) and KOH are the protonation constant of the quinolinol nitrogen of H4hcqs and the hydrolysis constant of Fe3+, respectively; the second step of the linkage isomerization from Fe(H2hcqs-N,O)+ to Fe(H2hcqs-O,N,O)+ has the rate constant (kisom of 1.3±0.1 × 10−1 s−1. Thermodynamic and kinetic characteristics of these sequential reactions and those for the related ligands to the metal ion are described in detail.