Density Functional Theory (DFT)-based bonding analysis correlates ligand field strength with Ru Mssbauer parameters of ruthenium-nitrosyl complexes

Kaneko, Masashi; Kato, Akane*; Nakashima, Satoru*; Kitatsuji, Yoshihiro

Inorganic Chemistry, 58(20), p.14024 - 14033, 2019/10

https://doi.org/10.1021/acs.inorgchem.9b02024

We applied density functional theory calculations to ruthenium-nitrosyl complexes, which are known to exist in high-level radioactive waste, to give a theoretical correlation between Ru Mssbauer spectroscopic parameters ( and ) and ligand field strength () for the first time. The structures of the series of complexes, [Ru(NO)L] (L = Br, Cl, NH, CN), were modeled based on the corresponding single-crystal X-ray coordinates. The comparisons of the geometries and total energies between the different spin states suggested that the singlet spin state of [Ru(II)(NO)L] complexes were the most stable. The calculated results of both the and values reproduced the experimental results by reported previously and increased in the order of L = Br, Cl, NH, CN. Finally, we estimated the ligand field strength () based on molecular orbitals, assuming C symmetry and showed the increase of values in that order, being consistent with well-known spectrochemical series of ligands. The increase attributes to the strengthening of the abilities of -donor and -acceptor of the L-ligands to the Ru atom, resulting in the increase of the values.

Identification of structures of the deep levels in 4H-SiC

Nakane, Hiroki*; Kato, Masashi*; Ichimura, Masaya*; Oshima, Takeshi

Materials Science Forum, 778-780, p.277 - 280, 2014/02

Deep levels in electron irradiated semi-insulating 4H-SiC; Electronic, optical and structural observation

Nakane, Hiroki*; Kato, Masashi*; Ichimura, Masaya*; Oshima, Takeshi; Ivanov, I. G.*; Trinh, X. T.*; Son, N. T.*; Janzn, E.*

no journal, , 

Ligand field analysis of ruthenium nitrosyl complexes using DFT calculation combined with Ru Mssbauer isomer shift

Kaneko, Masashi; Kato, Akane*; Nakashima, Satoru*; Kitatsuji, Yoshihiro

no journal, , 

A linear relationship between Mssbauer isomer shift values and electron densities at nucleus position assures the quantitative evaluation of the covalent interaction between a Mssbauer element and its surroundings. The use of this linear relationship makes us to predict a covalency in unknown compounds by electron density analysis based on quantum chemical calculations. As the first step to elucidate stability of ruthenium, which is known to be one of obstructive factors for separation process of high-level radioactive waste, in this study, we performed a fundamental investigation to predict the chemical bonding properties of nitrosylruthenium complexes. We modeled several nitrosylruthenium complexes with basic ligands, such chloride ion and ammonia, namely, [Ru(NO)L] (L = Br, Cl, NH, CN), by density functional calculation and estimated Ru Mssbauer isomer shifts by electron density analysis. The calculated results reproduced the experimental metal-ligand bond lengths and Mssbauer isomer shifts within the error of 0.1 mm/s. We also calculated the orbital splitting values of Ru d-electron. The value increased in the order of L = Br, Cl, NH, CN and correlated to that of Mssbauer isomer shift values. This indicated that the covalent interation between metal and ligand originates in the d-electron contribution of ruthenium to the coordination bonds.

Structure of ruthenium complex in nitric acid solution estimated using DFT calculation

Kato, Akane*; Kaneko, Masashi; Nakashima, Satoru*

no journal, , 

Aiming to predict ruthenium spices in high-level radioactive liquid waste, we demonstrated to simulate the complexation reaction between nitrosylruthenium and nitrate ions. When comparing the thermodynamic stability of the twelve geometrical isomers of the nitrosylruthenium nitrate complexes, the complexes with nitrate ions at the equatrial position toward the Ru-NO axis were confirmed to be the most stable isomers. Moreover, the Gibbs free energies analysis of the stepwise complexation reactions indicated that the Gibbs energy difference was improved the dependency of the fraction of the ruthenium species on the nitrate ions concentration by considering the association energy between the complex and the substituting ligands.

The Effort for the nuclear material recovery from the reprocessing process and relevant MC&A in the TRP Decommissioning Project

Kato, Akane; Shimizu, Yasuyuki; Kitao, Takahiko; Nakamura, Hironobu

no journal, , 

Tokai Reprocessing Plant (TRP) had reprocessed 1,140 tons spent fuel (SF) since 1977 to 2007, and the Post-Fukushima safety regulations triggered TRP to decide to shut the plant and shifted to decommissioning phase from 2018. The estimated entire duration of TRP decommissioning is expected to be 70 years. The early stage of the TRP decommissioning includes the recovery of remaining nuclear material in the process and transferring those nuclear material between multiple facilities ("Flush-out"), vitrification activity of remaining high active liquid waste and transferring collected nuclear material to the storage facility, and the management of radioactive waste. The Flush-out is as the first step of TRP decommissioning and it is in progress since July 2022 for two years prior to the start of serious decommissioning activities such as the decontamination, dismantling/removing the process. Since these decommissioning activities are unexperienced challenges and they are not related to "SF reprocessing", therefore ensuring appropriate nuclear material control and accountancy (MC&A) and the transparency in terms of safeguards verification implemented by IAEA are important role as the operator. In this paper, we report about the residual nuclear material recovery process and relevant MC&A and safeguards measures in the Flush-out as the first stage of TRP decommissioning project.