Multiple light-induced NO linkage isomers in the dinitrosyl complex [RuCl(NO)₂(PPh₃)₂]BF₄unravelled by photocrystallographic and IR analysis

Abstract

Photocrystallographic and IR analysis reveal light-induced reversible metastable NO linkage isomers in the dinitrosyl compound [RuCl(NO)2(PPh3)2]BF4.

Photocrystallography reveals new metastable nitrosyl linkage isomers in the solid state

“…This is dependent on the metal-to-ligand charge transfer processes, and these aspects have been reviewed by Schaniel & Woike (Schaniel & Woike, 2009 In the reported study of [RuCl(NO) 2 (PPh 3 ) 2 ]BF 4 the photcrystallographic investigation is augmented by a detailed infrared study (Casaretto et al, 2015) which confirms the presence of the major metastable linkage isomer as one with a bent N-bound nitrosyl. This infrared study provides clear evidence for the coordination mode overcoming any ambiguity from the crystallographic study where it is difficult to differentiate between nitrogen and oxygen atoms.…”

“…This can be achieved by engineering void space into the crystal structures through the use of bulky ligands. Thus, as has been illustrated by Casaretto et al (2015), for [RuCl(NO) 2 (PPh 3 ) 2 ]BF 4 only the bent NO group changes position by re-orientating in the grove formed by the phenyl rings of the two triphenylphosphine groups. Here, the bulk of the phosphines provides a cavity or 'reaction pocket' that affords sufficient space for the isomerization to occur without inducing unacceptable crystal strain.…”

“…Until the late 2000s there were no examples of high levels of conversion between the ground and metastable states, and the factors that would favour the conversion or the stability of the metastable state were not fully understood (Schaniel et al, 2007). The understanding of the factors that are important has been pioneered by Schaniel and Woike in a series of seminal papers of which Casaretto et al (2015) is the latest.Since the photocrystallographic studies of metastable linkage isomers involve singlecrystal to single-crystal transformations the unit-cell parameters do not change by more than 2%, as a maximum, otherwise the crystal strain induced would result in crystal deterioration. Thus a key factor in producing crystalline materials capable of undergoing solid-state linkage isomerism under photoactivation is the reduction of crystal stain.…”

“…In a complex that undergoes linkage isomerism, the compound contains one or more ligands that are capable of bonding to the metal centre in more than one way. For example, as elegantly illustrated by Casaretto et al (Casaretto et al, 2015) the nitrosyl ligand, NO, can coordinate to the metal through the nitrogen atom, through the oxygen atom or in an 2 -NO sideways bonding mode, and the mode of coordination may switch under photoirradiation in either the solid state or in solution.The timescale for the isomerization process is also of importance since this may alter with changes in the crystal environment. At low temperatures the excited photoactivated state may be metastable, lasting longer than the duration of the X-ray experiment, while at higher temperatures the timescale may be reduced to microseconds or even picoseconds.…”

In situlaser irradiation setup for a Bruker three-circle goniometer

“…When irradiation took place in a laboratory environment, it was usually performed in a stationary position and not simultaneously with data collection (see e.g. Casaretto et al, 2015).…”