Reversible photoswitching between nitrito-N and nitrito-O isomers in trans-[Ru(py)4(NO2)2]

Abstract

Nitro-nitrito photoisomerisation is investigated in solid samples and solutions of trans-[Ru(py)(4)(NO(2))(2)]. Using light of wavelength 325 nm 50% of the N-bound Ru-NO(2) ligands can be switched to the O-bound Ru-ONO configuration (nitrito-N to nitrito-O isomerisation) at temperatures below T = 250 K in solids. The population of the isomeric configurations is determined with infrared spectroscopy from the decrease of the area of the nu(NO) stretching and delta(NO) deformation modes. In a frozen methanol-ethanol solution nearly 100% can be converted to the nitrito-O configuration. Upon heating above T = 250 K the Ru-NO(2) configuration is restored. The nitrito-O Ru-ONO configuration can be partially transferred back to the nitrito-N configuration by irradiation with light in the spectral range 405-442 nm. Using absorption spectroscopy on a frozen methanol-ethanol solution, two new bands at 447 and 380 nm are observed in the nitrito-O configuration compared to one at 334 nm of the nitrito-N ground state configuration. The photoconversion is initiated by the metal-to ligand charge transfer transition Ru(d) -->pi*(NO(2),py) as shown by the calculated partial density of states using Density Functional Theory. The calculations yield also the structure of the nitrito-N and nitrito-O isomer as well as the corresponding vibrational densities. The experimental structure of the ground state is determined using powder diffraction.

Photocrystallographic, Spectroscopic, and Calorimetric Analysis of Light‐Induced Linkage NO Isomers in [RuNO(NO2)2­(pyridine)2OH]

“…To identify potential linkage isomers of the NO 2 ligand, we need to inspect the spectral range $\tilde {\nu}$ = 1200–1500 cm –1 (see Figure 4), in which the corresponding vibrations are situated 17. The light‐induced structural changes in the [RuNO(NO 2 ) 2 Py 2 OH] molecule are visible in the asymmetric ν as (NO 2 ) as well as the symmetric ν s (NO 2 ) mode.…”

Solid‐State Interconversions: Unique 100 % Reversible Transformations between the Ground and Metastable States in Single‐Crystals of a Series of Nickel(II) Nitro Complexes

“…A rare exception is the 92 % single-crystal conversion of [Ru(py) 4 Cl(NO)][PF 6 ] 2 ⋅ 0.5 H 2 O from a η 1 -N O nitrosyl to a metastable η 1 -O N nitrosyl upon irradiation reported by Woike,[7n] however, excitation levels around 50 % are typical. If metastable linkage isomers are to find applications in devices[9] then reversible 100 % interconversion between isomers is essential. Various explanations have been put forward to justify why complete interconversion between isomeric forms is difficult to achieve.…”

Electronic excitations in molecular solids: bridging theory and experiment

“…Firstly, although the isomers themselves have been characterised, understanding the reaction paths which connect them is a work in progress. [53][54][55] Numerical modelling has allowed mechanisms to be proposed for some systems, 39,40 although explicit study of the excited-state potential energy surfaces, and establishing the photochemical-isomerisation pathways, remains an important undertaking. A second key challenge is to understand the role that the crystalline environment plays in controlling the kinetics and energetics of the process, which would, in principle, provide valuable input to crystal-engineering approaches for tuning the properties of different systems for specic applications.…”