Solid-State Photo-NMR Study on Light-Induced Nitrosyl Linkage Isomers Uncovers Their Structural, Electronic, and Diamagnetic Nature.

A light-induced linkage NO isomer (MS1) in trans -[Ru( 15 NO)(py) 4 19 F](ClO 4 ) 2 is detected and measured for the first time by solid-state MAS NMR. Chemical shift tensors of 15 N and 19 F, along with n J ( 15 N- 19 F) spin-spin couplings and T 1 relaxation times of MS1, are compared with the ground state (GS) at temperatures T < 250 K. Isotropic chemical shifts ( 15 N and 19 F) are well resolved for two crystallographically independent cations (A and B) [Ru( 15 NO)(py) 4 19 F] 2+ , allowing to define separately both populations of MS1 isomers and thermal decay rates for two structural sites. The relaxation times T 1 of 19 F in the case of GS (30/38.6 s for sites A/B) and MS1 (11.6/11.8 s for sites A/B) indicate that both isomers are diamagnetic, which is the first experimental evidence of diamagnetic properties of MS1 in ruthenium nitrosyl. After light irradiation (λ = 420 nm), the NO ligand rotates by nearly 180° from F-Ru-N-O to F-Ru-O-N, whereby the isotropic chemical shifts of δ iso ( 15 N) increase and those of δ iso ( 19 F) decrease. The n J ( 15 N- 19 F) couplings increase from 2 J ( 15 N-Ru- 19 F) GS = 71 Hz to 3 J ( 15 N-O-Ru- 19 F) MS1 = 105 Hz. These results are interpreted on the basis of DFT-CASTEP calculations including Bader-, Mulliken-, and Hirshfeld-charge density distributions of both states.