Density Functional Theory (DFT)-Based Bonding Analysis Correlates Ligand Field Strength with 99Ru Mössbauer Parameters of Ruthenium–Nitrosyl Complexes

We applied density functional theory calculations to ruthenium–nitrosyl complexes, which are known to exist in high-level radioactive waste generating during reprocessing of spent nuclear fuel, to give a theoretical correlation between 99Ru Mossbauer spectroscopic parameters and ligand field strength for the first time. The structures of the series of complexes, [Ru(NO)L5] (L = Br–, Cl–, NH3, 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+)L5] complexes were the most stable. This result was supported by the benchmark calculations of the 99Ru Mossbauer isomer shift (δ) and quadrupole splitting (ΔEQ) values. The calculated results of both the δ and ΔEQ values reproduced the experimental results by reported previously and increased in the order of L = Br–, Cl–, NH3, CN–. Finally, we estimated the ligand field strength (Δo) based on molecul...