| Research Abstract |
There are two factors the stabilization of oxidation state of metal elements ; i. e., l) electronic state of ligand coordinated to the metal, and 2) coordination structure. The purpose of the present study is to stabilize metal oxidation states which are usually unstable by choosing suitable ligands to stabilize such oxidation states.
Donor atoms with high electron density generally tends to stabilize a high oxidation state of the central metal. As a suitable ligand of our purpose N-2-hydroxyphenyl) salicylamide and its homologues were adopted in this study. By employing this ligand we have obtained several manganese (IV) and (V) complexes as pure crystals. Further, we have confirmed the formation of copper (III) and cobalt (IV) complexes in solution. Varying the substituents on the ligand, we could see the effect of electron density of the donor atoms on the oxidation states of central metal.
It is well-known that cobalt (II) ammine and amine complexes are readily oxidized to cobalt (III) complexes. However, we have found that the oxidation of cobalt (II) complexes with 1, 4, 8, 11-tetrakis (2-aminoethyl)-1, 4, 8, 11-tetraazacyclo-tetradecane (abbreviated as taec) are difficult. This fact has been explained as that in such complexes, because of the steric hindrance of the ligand, cobalt could not take 6-coordination which is the spacifically favored coordination number of cobalt (III). Based on this view, we have synthesized air-stable chromium (II) complexes. Further, this view has been verified by the ready oxidation of Co (II) in the case of Co_2CO_3 (taec) (ClO_4)_2 in which the cobalt is 6-coordinated.
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