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Complexation and bonding studies on [Ru(NO)(H$$_{2}$$O)$$_{5}$$]$$^{3+}$$ with nitrate ions by using density functional theory calculation

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

Complexation reactions of ruthenium-nitrosyl complexes in HNO$$_{3}$$ 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$$_{3}$$)$$_{3}$$(H$$_{2}$$O)$$_{2}$$] 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$$_{3}$$$$^{-}$$ proceed via the NO$$_{3}$$$$^{-}$$ 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$$_{3}$$ 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$$_{3}$$$$^{-}$$ at the axial position is more stable than that wit NO$$_{3}$$$$^{-}$$, which might attribute to the difference in the trans influence between H$$_{2}$$O and NO$$_{3}$$$$^{-}$$. Finally, we demonstrated the complexation kinetics in the reactions $$x = 1 rightarrow x = 2$$. The present study is expected to enable us to model the precise complexation reactions of platinum-group metals in HNO$$_{3}$$ solution.

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Category:Chemistry, Multidisciplinary

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