Regulation of Metal Complexes by Ligands

金属元素氧化态的稳定有两个因素：一是金属元素的氧化态稳定;例如，1）与金属配位的配体的电子态，和2）配位结构。本研究的目的是通过选择合适的配体来稳定通常不稳定的金属氧化态，具有高电子密度的供体原子通常倾向于稳定中心金属的高氧化态。本文选用N-（2-羟基苯基）水杨酰胺及其同系物作为配体。通过使用这种配体，我们已经获得了几个锰（IV）和（V）的配合物作为纯晶体。此外，我们已经证实了在溶液中形成铜（III）和钴（IV）络合物。通过改变配体上的取代基，我们可以看到给体原子的电子密度对中心金属氧化态的影响，钴（II）氨配合物和胺配合物很容易氧化成钴（III）配合物。然而，我们发现钴（II）与1，4，8，11-四（2-氨乙基）-1，4，8，11-四氮杂环十四烷（简称taec）的配合物的氧化是困难的。这一事实已被解释为，在这样的配合物中，由于配体的空间位阻，钴不能采取6-配位，这是钴（III）的空间上有利的配位数。基于这一观点，我们合成了空气稳定的铬（II）配合物。在Co_2CO_3（taec）（ClO_4）_2中，Co（II）的六配位氧化反应也证实了这一观点。

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.