Abstract
The electronic, structural and optical properties (including Spin–Orbit Coupling) of metal nitrosyl complexes [M(CN)5(NO)]2− (M = Fe, Ru or Os) are investigated by means of Density Functional Theory, TD-DFT and MS-CASPT2 based on an RASSCF wavefunction. The energy profiles connecting the N-bound (η1-N), O-bound (η1-O) and side-on (η2-NO) conformations have been computed at DFT level for the closed shell singlet electronic state. For each structure, the lowest singlet and triplet states have been optimized in order to gain insight into the energy profiles describing the conformational isomerism in excited states. The energetics of the three complexes are similar—with the N-bound structure being the most stable—with one exception, namely the triplet ground state of the O-bound isomer for the iron complex. The conformation isomerism is highly unfavorable in the S0 electronic state with the occurrence of two energy barriers higher than 2 eV. The lowest bands of the spectra are assigned to MLCTNO/LLCTNO transitions, with an increasing MLCT character going from iron to osmium. Two low-lying triplet states, T1 (MLCTNO/LLCTNO) and T2 (MLCTNO/ILNO), seem to control the lowest energy profile of the excited-state conformational isomerism.
Highlights
Metal-Nitrosyl coordination compounds are of great interest because they exhibit two essential photo-induced primary reactions, namely NO/ON linkage isomerism and NO release (Scheme 1), which are of crucial importance in cardiovascular treatments and cancer therapies [1].Molecules 2019, 24, x FOR PEER REVIEW1
Linkage isomerism, NO release and CN dissociation, have been evidenced within the first 500 fs after 400 nm pump irradiation using transient IR spectroscopy [11]. These experiments indicate that population of the absorbing states detected at 393 nm and 520 nm at room temperature in methanol, most probably corresponding to LLCTNO /MLCTNO /MC excited states, opens the route to both ligand dissociation and Fe-NO linkage isomerism
Energy profiles and critical geometries characterizing the conformational isomerism in the three molecules are investigated for the S0 electronic ground states, as well as for the low-lying excited states, in order to gain some insight on the mechanisms of inter-conversion
Summary
Metal-Nitrosyl coordination compounds are of great interest because they exhibit two essential photo-induced primary reactions, namely NO/ON linkage isomerism and NO release (Scheme 1), which are of crucial importance in cardiovascular treatments and cancer therapies [1]
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