分子構造と磁気共鳴スペクトロスコピによる,高度に歪んだ6座標の低スピン鉄 (III) ポルフィリナート複合体の調査
H Ogura1, L Yatsunyk, C J Medforth
1Department of Chemistry, University of Arizona, Tucson, AZ 85721-0041, USA.
Journal of the American Chemical Society
|July 6, 2001
まとめ
この研究は,軸性結合体を持つ新しい鉄 (III) ポーフィリン複合体を詳細に説明し,スペクトロスコピーを介して構造的洞察とダイナミックな行動を明らかにします. これらの発見は,ステリカルに阻害されたポルフィリン系に関する理解を深める.
科学分野:
- 協調化化学について
- 有機金属化学 有機金属化学
- マテリアルサイエンス 材料科学
背景:
- 鉄 (III) ポルフィリン複合体は,様々な触媒および生物学的プロセスにおいて極めて重要です.
- ポルフィリンマクロサイクルの形状と動態に対する軸性リガンドの影響を理解することが鍵となる.
- 軸性リガンドからのステリック障害は,複雑な構造と反応性を大幅に変化させることができます.
研究 の 目的:
- 新しい二軸結合鉄 (III) オクタエチルテトラフェニルポルフィリン (OETPP) Fe (III) 複合体を合成し,特徴づけること.
- これらの複合体の構造的,電子的,動的性質を,X線結晶学およびスペクトロスコーピーを用いて調査する.
- 軸性リンガンドのステリックバルクとポルフィリンマクロサイクルの構成と動態の関係を解明する.
主な方法:
- N-メチリミダゾール,4-ディメチラミノピリジン,2-メチリミダゾールを含む3つの二軸結合OETPPFe(III) 複合体の合成.
- 精密な分子および結晶構造を決定するためのX線結晶学.
- 電子パラマグネティック共振 (EPR) と核磁共振 (NMR) のスペクトロスコーピー (1Dと2D) で,電子的および動的特徴づけを行う.
主要な成果:
- 結晶構造は,固定されたマクロサイクルの形状を明らかにし,リガンドの方向性はステリック相互作用によって影響されます.
- 軸性Fe-N結合の長さは,bis-(2-メチリミダゾール) 複合体では,関連種と比較して長くなっています.
- スペクトロスコピカルデータは,温度依存の変動によるサドル逆転とリガンド回転を含む複雑なダイナミックな振る舞いを示しています.
結論:
- 軸性リガンドのステリック塊は,OETPPマクロサイクルの構成とリガンドの方向性に大きく影響する.
- 準備された複合体は,低温でもサドルの逆転とリガンドの回転が起こるような流動的行動を示します.
- この研究は,ステリカルに要求されるポルフィリン系における構造-動力学-特性関係に関する貴重な洞察を提供します.
関連する概念動画
02:34Structural Isomerism
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
03:02Colors and Magnetism
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
01:13¹H NMR: Complex Splitting
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
01:08NMR Spectroscopy: Spin–Spin Coupling
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
01:08Spin–Spin Coupling Constant: Overview
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...