Online ISSN: 1884-4111 Print ISSN: 0033-8303
Radioisotopes 66(8): 289-300 (2017)


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Bonding Study on Trivalent Europium Complexes by Combining Mössbauer Isomer Shifts with Density Functional Calculations

1日本原子力研究開発機構原子力基礎工学研究センターNuclear Science and Engineering Center, Japan Atomic Energy Agency ◇ 319–1195 茨城県那珂郡東海村白方2–4 ◇ 2–4 Shirakata, Tokai-mura, Naka-gun, Ibaraki Pref. 319–1195, Japan

2広島大学大学院理学研究科Graduate School of Science, Hiroshima University ◇ 739–8526 広島県東広島市鏡山1–3–1 ◇ 1–3–1 Kagamiyama, Higashi-Hiroshima, Hiroshima Pref. 739–8526, Japan

3広島大学自然科学研究支援開発センターNatural Science Center for Basic Research and Development, Hiroshima University ◇ 739–8526 広島県東広島市鏡山1–4–2 ◇ 1–4–2 Kagamiyama, Higashi-Hiroshima, Hiroshima Pref. 739–8526, Japan

受付日:2017年2月21日Received: February 21, 2017
受理日:2017年4月19日Accepted: April 19, 2017
発行日:2017年8月15日Published: August 15, 2017

相対論密度汎関数計算を−1.77から0.57 mm s−1151Euメスバウアー異性体シフトを示す5つの三価Eu錯体に適用した。BP86による構造最適化の後,3種類の理論(BP86, B3LYP, B2PLYP)による一点計算に基づくEu位置の電子密度とメスバウアー異性体シフトの相関を議論した結果,B2PLYPがメスバウアー異性体シフトをよく再現した。Mulliken密度解析の結果,Euのd, f電子密度がメスバウアー異性体シフトと相関し,d, f電子がEu錯体の共有結合性に関与することが示唆された。

Scalar-relativistic density functional calculations were applied to some trivalent europium complexes to discuss the covalent interactions in their coordination bonds. Five Eu (III) complexes whose 151Eu Mössbauer isomer shifts vary from −1.77 to 0.57 mm s−1 were modeled by referring previously reported Mössbauer experiments. Geometrical optimizations of their complexes using BP86 functional reproduced the experimental coordination structures. Single-point calculations were applied to their optimized geometries at three different 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 151Eu Mössbauer isomer shifts revealed that the B2PLYP functional shows the best linearity. We also performed electron population and bond analyses of the molecular orbitals in their complexes obtained by single-point calculations using Mulliken’s procedure. As a result, the electron densities of both d- and f-orbital electrons of Eu ion in the complexes were found to be correlated to the experimental 151Eu Mössbauer isomer shifts. This result indicated that the d- and f-orbital electrons in the Eu ion are involved in the covalent interaction of the coordination bond between the Eu ion and the ligands.

Key words: density functional theory; Mössbauer isomer shift; f-block complex; coordination bond; electron population analysis; trivalent europium complexes

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