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

Abstract

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 Mössbauer 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 Mössbauer isomer shift (δ) and quadrupole splitting (ΔE Q) values. The calculated results of both the δ and ΔE Q 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 molecular orbitals, assuming C 4v symmetry and showed the increase of Δo values in that order, being consistent with well-known spectrochemical series of ligands. The increase attributes to the strengthening of the abilities of σ-donor and π-acceptor of the L-ligands to the Ru atom, resulting in the increase of the δ values. Furthermore, the increase of the σ-type donation into Ru d x 2–y 2 orbital and the π-type back-donation from Ru d xz , d yz orbitals in that order caused the decrease of the electron density along the Ru-NO axis, resulting in the increase of the ΔE Q values. This study is expected to contribute to the ligand design for the ruthenium–nitrosyl complexes, leading to the drug design for NO carrier and the decontamination of radioactive ruthenium from the ecological system, as well as the recovery of platinum-group metals from high-level radioactive waste.

Solution and solid-state light-induced transformations in heterometallic vanadium-ruthenium nitrosyl complex

“…After the light excitation, the excited singlet state of MLCT nature tends to undergo inter-system crossing (ISC) to the triplet MLCT of the same nature [98,99]. The triplet as well as first excited singlet states are known to have bended Ru-N-O fragment [100]. The relaxation of triplet state ends up in a point on the ground state potential energy surface, which is far from equilibrium linear geometry.…”

Complexation and bonding studies on [Ru(NO)(H2O)5]3+ with nitrate ions by using density functional theory calculation

“…(L ¼ Br À , Cl À , NH 3 ). 21 The contribution of BODOS between the Ru d-orbitals and the nitrogen atom of NO + to the sum of PDOS was 13.3 and 11.9% for the complexes a and f, respectively. This indicates that the Ru-NO + bond has positive bond overlap (bonding-type) interaction and the bond overlap of the complex a is larger than that of the complex f. Fig.…”

“…We focused on the difference in the Ru-NO bond strength between the complexes a and f. Partial density of states, PDOS, of Ru d-orbitals and bond overlap density of states, BODOS, between Ru d-orbitals and the donor atoms of the ligands were estimated by using our previous method, 21 which was based on Mulliken population analysis, 47 and the analytical procedure and numerical data are shown in ESI. † The Ru d-orbitals for both the complexes a and f in the valence orbitals region were…”

“…singlet state (t 6 2g ), because our pervious DFT results for several ruthenium-nitrosyl complexes, [Ru(NO)L 5 ] (L ¼ Br À , Cl À , NH 3 , and CN À ), of the singlet state reproduced the experimental data, such as the metal-ligand bond lengths, bond angles, IR frequencies, and 99 Ru Mössbauer spectroscopic parameters. 21 The DFT methods for geometry optimizations and single-point energy calculations and the electron density analyses were carried out based on the condition previously reported. 21 Segmented all-electron relativistically contracted (SARC) Gaussian-type basis set 29 optimized for the corresponding relativistic correction was assigned to all atoms to perform all-electron scalar-relativistic DFT calculations.…”

“…21 The DFT methods for geometry optimizations and single-point energy calculations and the electron density analyses were carried out based on the condition previously reported. 21 Segmented all-electron relativistically contracted (SARC) Gaussian-type basis set 29 optimized for the corresponding relativistic correction was assigned to all atoms to perform all-electron scalar-relativistic DFT calculations. SARC basis set was used as the recontracted version implemented in ORCA: the exponents are cited in ref.…”