Bonding study on trivalent europium complexes by combining Mssbauer isomer shifts with density functional calculations

メスバウアー異性体シフトと密度汎関数計算の組合せによる三価ユウロピウム錯体の結合状態研究

金子 政志   ; 渡邉 雅之   ; 宮下 直*; 中島 覚*

Kaneko, Masashi; Watanabe, Masayuki; Miyashita, Sunao*; Nakashima, Satoru*

Eu錯体の配位結合におけるf電子の役割を理解することを目的として、相対論密度汎関数計算をEu(III)錯体に適用した。既報のEuメスバウアー異性体シフト実験値とEu原子核位置での電子密度計算値の線形性を比較することによって、B2PLYP理論がメスバウアー異性体シフトを最もよく再現することが分かった。また、分子軌道に基づく電子密度の解析によって、d及びf電子が配位結合に大きく関与していることを明らかにした。

Scalar-relativistic density functional calculations applied to some trivalent europium complexes. Five Eu(III) complexes whose Eu Mssbauer isomer shifts vary from -1.8 to 0.5 mm/s are referred by previously reported results. Geometrical optimizations of their complexes reproduces the experimental coordination structures. Single-point calculations are applied to their optimized geometries at three density functionals, namely, BP86, B3LYP, and B2PLYP, to obtain their electron densities at Eu nucleus. A comparison of the linearity between the electron densities and the corresponding Eu Mssbauer isomer shifts reveals that B2PLYP functional shows the best linearity. Electron population and bond analyses indicate that d- and f-orbital electrons of Eu ion in the complexes are found to be correlated to the experimental Eu Mssbauer isomer shifts. This indicates that the d- and f-orbital electrons are involved in the covalent interaction of the coordination bond between the Eu ion and the ligands.