Density functional theory study on the Ir Mssbauer spectroscopic parameters of Vaska's complexes and their oxidative adducts

Kaneko, Masashi; Nakashima, Satoru*

Inorganic Chemistry, 60(17), p.12740 - 12752, 2021/09

https://doi.org/10.1021/acs.inorgchem.1c00239

In the present study, density functional theory (DFT) calculation was applied to Vaska's complexes of formula -[IrCl(CO)(PPh)], and their oxidative adducts with small molecules (YZ) including H, i.e., -[IrCl(YZ)(CO))(PPh)], to successfully correlate the electronic states of the complexes with the corresponding Ir Mssbauer spectroscopic parameters. After confirming the reproducibility of the DFT methods for elucidating the equilibrium structures and Ir Mssbauer isomer shifts of the octahedral Ir complexes, the isomer shifts and quadrupole splitting values of Vaska's complexes and their oxidative adducts were calculated. A bond critical point analysis revealed that the tendency in the isomer shifts was correlated with the strength of the covalent interaction in the coordination bonds. In an electric field gradient (EFG) analysis of the oxidative adducts, the sign of the principal axis was found to be positive for the complex with YZ = Cl and negative for the complex with YZ = H. This reversal of the sign of the EFG principal axis was caused by the difference in the electron density distribution for the coordination bonds between Ir and YZ, according to a density of states analysis.

Complexation and bonding studies on [Ru(NO)(HO)] with nitrate ions by using density functional theory calculation

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

RSC Advances (Internet), 10(41), p.24434 - 24443, 2020/06

https://doi.org/10.1039/D0RA05042C

Complexation reactions of ruthenium-nitrosyl complexes in HNO solution were investigated by density functional theory (DFT) calculations in order to predict the stability of Ru species in high-level radioactive liquid waste (HLLW) solution. Equilibrium structure of [Ru(NO)(NO)(HO)] obtained by DFT calculations reproduced the experimental Ru-ligands bond lengths and IR frequencies reported previously. Comparison of the Gibbs energies among the geometrical isomers revealed that the complexation reactions of the ruthenium-nitrosyl complexes with NO proceed via the NO coordination to the equatorial plane toward the Ru-NO axis. We also estimated Gibbs energy differences on the stepwise complexation reactions to succeed in reproducing the fraction of Ru-NO species in 6 M HNO solution, such as in HLLW, by considering the association energy between the Ru-NO species and the substituting ligands. Electron density analyses of the complexes indicated that the strength of the Ru-ligands coordination bonds depends on the stability of the Ru species and the Ru complex without NO at the axial position is more stable than that wit NO, which might attribute to the difference in the trans influence between HO and NO. Finally, we demonstrated the complexation kinetics in the reactions . The present study is expected to enable us to model the precise complexation reactions of platinum-group metals in HNO solution.

Benchmark study of DFT with Eu and Np Mssbauer isomer shifts using second-order Douglas-Kroll-Hess Hamiltonian

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

Hyperfine Interactions, 239(1), p.20_1 - 20_10, 2018/12

BB2017-0056.pdf:0.5MB

https://doi.org/10.1007/s10751-018-1495-1

We optimized a mixing ratio of exchange energy between pure DFT and exact Hartree-Fock using TPSS exchange-correlation functional to estimate the accurate coordination bonds in f-block complexes by numerically benchmarking with the experimental data of Mssbauer isomer shifts for Eu and Np nuclides. Second-order Douglas-Kroll-Hess Hamiltonian with segmented all-electron relativistically contracted basis set was employed to calculate the electron densities at Eu and Np nuclei, i.e. contact densities, for each five complexes for Eu(III) and Np(IV) systems. We compared the root mean square deviation values of their isomer shifts between experiment and calculation by changing the mixing ratio of Hartree-Fock exchange parameter from 0 to 100 % at intervals of 10 %. As the result, it was indicated that the mixing ratio of 30 and 60 % for Eu and Np benchmark systems, respectively, gives the smallest deviation values. Mulliken's spin population analysis indicated that the covalency in the metal-ligand bonds for both Eu and Np complexes decreases with increasing the Hartree-Fock exchange admixture.

Computational chemical analysis of Eu(III) and Am(III) complexes with pnictogen-donor ligands using DFT calculations

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

Dalton Transactions (Internet), 47(42), p.14924 - 14931, 2018/11

https://doi.org/10.1039/C8DT01973H

We demonstrated density functional calculations of Eu(III) and Am(III) complexes with pnictogen-donor (X) ligands, CH)X-CH-CH-X(CH) (X = N, P, As and Sb). We investigated the optimized structures of the cmoplexes and the Gibbs energy differences in the complex formation reactions. Those results indicated that the N- and P-donor ligands have Am(III) ion selectivity over Eu(III) ion, especially, the P-donor ligand showed the highest selectivity. The tendency of the Am(III)/Eu(III) selectivity by the pnictogen-dono ligands was found to be comparable to that of soft acid classification in hard and soft acids and bases rule. Mulliken's spin population analysis indicated that the bonding property between the metal ion and the pnictogen atoms correlated with the Am(III)/Eu(III) selectivity. In particular, the participation of f-orbital electrons of the metal ion in the covalency was indicated to have an important role for the selectivity.

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

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

Radioisotopes, 66(8), p.289 - 300, 2017/08

https://doi.org/10.3769/radioisotopes.66.289

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.

A Spin-crossover phenomenon depending on the environment around an iron atom for the assembled coordination polymers

Nakashima, Satoru*; Kaneko, Masashi

Advances in Chemistry Research, Vol.36, p.171 - 195, 2017/01

Spin-crossover (SCO) phenomena of the assembled coordination polymers are introduced. When the bridging ligand is flexible like 1,2-bis(4-pyridyl)ethane, 1,3-bis(4-pyridyl)propane, a variety of assembled structure can be obtained, depending on the conformer of the ligand and the guest molecules. Guest-dependent SCO phenomena of the assembled iron complexes are shown. Density functional theory is applied to know the cause of guest-dependent SCO phenomena. The validity of an iron mono-nucleus model is evaluated for the coordination polymers. It is shown that SCO occurs or not depends on the local structure around iron ion.

Correlation between the bonding property of f-orbital electron and the separation behavior of minor-actinides

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

no journal, , 

To understand the separation mechanism of minor-actinides (MA) from lanthanides (Ln) is important for the development of partitioning and transmutation of high-level radioactive waste. We aim to discuss the bonding nature between MA/Ln ions and ligands with the separation behavior of MA from Ln, which leads to the elucidation of the selectivity of MA compared to Ln. In this study, we demonstrate the separation behavior of MA from Ln at molecular level by means of density functional calculations and discuss how the bonding properties of valence electrons contributes to the selectivity of MA.

Construction of chemical bonding database for development of separation prediction code of minor-actinides

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

no journal, , 

We aim to developt the prediction code for separation performance of minor-actinides from lanthanides. In this study, we constructed a chemical bonding database of Am and Eu with Group 15 and 16 element donor ligands. As the result of energy analysis using density functional theory calculations, the trend of separation behavior of Am from Eu with group 15 and 16 donor ligands correlated with the trend of soft acid classification of hard and soft acids and bases principle. As the result of bonding analysis, the donor ligands which strongly bond to Am were indicated to possess the high selectivity to Am.

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.