Sudies on Structural Chemistry of Neptunyl Complexes by ^<237>Np Mossbauer spectroscopy.

2005 Fiscal Year Final Research Report Summary

• Project/Area Number: 15550056
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Inorganic chemistry
• Research Institution: Toho University
• Principal Investigator: TAKEDA Masuo Toho University, Faculty of Science, Professor, 理学部, 教授 (80011633)
• Co-Investigator(Kenkyū-buntansha): TAKAHASHI Masashi Toho University, Faculty of Science, Professor, 理学部, 教授 (30171523) ; KITAZAWA Takafumi Toho University, Faculty of Science, Associate Professor, 理学部, 助教授 (60246767) ; NAKADA Masami Japan Atomic Energy Agency, Nuclear Science and Engineering Directorate, Researcher, 原子力基礎工学研究部門, 研究員 (60370441)
• Project Period (FY): 2003 – 2005
• Keywords: ^<237>Np Mossbauer spectroscopy / neptunyl(VI) complex / chemical bonding / uranyl(VI) complex / nitrogen-ligating ligand / pyridine complex / Schiff base complex / macrocvclic complex

Research Abstract

The aim of this research is to obtain the information on the chemical bonding in the actinide compounds through the ^<237>Np Mossbauer spectroscopic study of neptunyl(VI) complexes containing nitrogen-containing ligands. Mossbauer parameters of the pyridine complex [NpO_2(acac)_2py] and the oxalate NpC_2O_4・3H_2O, both having the pentagonal bipyramidal structure, are compared. The value of isomer shift of [NpO_2(acac)_2py] having a nitrogen donor atom is larger than that of NpC_2O_4・3H_2O, suggesting that the nitrogen atom donates more electrons to the Np 5f orbitals than the oxygen atoms do. The isomer shift of [NpO_2(NO_3)_2(2,2'-bpy)] is larger than that of [NpO_2(acac)_2py], indicating that the increase in the coordination number from 7 (the latter) to 8 (the former) causes the decrease in the contribution of 7s electron. These results show that the electrons from the coordinating nitrogen atom are donated to 5f orbitals rather than 7s one, being in good contrast to the lanthanide complexes where the electrons are directly accommodated in 6s orbital.
Synthetic investigations are also carried out to develop the nitrogen-ligating actinyl(VI) complexes using uranyl(VI) in order to strengthen the Mossbauer spectroscopic data. Several [UO_2(acac)py] derivatives, [UO_2(acac)(4-R-py)] (R=Me,Et,'Bu,CN,Cl,NMe_2) are prepared and their structures are determined. A good correlation between U-N and U=O distances are observed. Six macrocyclic N_6-coordinating Schiff base UO_2 complexes derived from pyrroledicarboaldehyde and diamines are prepared and two of the structurally characterized. Four acyclic Schiff base UO_2 complexes including a heterobinuclear Cu^<2+>-UO_2 complex are also obtained and their structures are determined.