Photo-induced linkage NO isomers in the dinitrosyl complex [Ru(NO)2(PCy3)2Cl](BF4) identified by photocrystallography and IR-spectroscopy

Abstract

Photoinduced metastable linkage NO isomers have been known for a long time in mono-nitrosyl ruthenium or iron transition metal complexes [ML_xL_y(NO)]ⁿ for which appropriate temperature and excitation conditions allow a controlled generation of different metastable states. Dinitrosyl complexes offer attractive possibilities owing to the potential switching of the two nitrosyl ligands, possibly in a selective manner, leading to a complicated and intricated population of metastable states. [Ru(NO)₂(PCy₃)₂Cl]BF₄ belongs to a complete series of bis-phosphane complex salts of general formula [Ru(NO)₂(PR₃)₂X](BF₄) (X = Cl, Br, I). It presents a square pyramidal geometry with both a linear and a bent NO ligand, and an Ru(d⁶) electron configuration. Multiple light-induced reversible metastable NO linkage isomers (PLIs) are detected by a combination of photocrystallographic and infrared (IR) analysis. The IR signature of three PLI states has been clearly identified. The structural configuration of the major component (PLI-1) has been derived by X-ray photocrystallography. After irradiation with 405 nm, the orientation of the bent nitrosyl is changed by rotation towards the Cl ligand, opposite to the linear NO. The minor second metastable state (PLI-2) is proposed to result from a side-bonded (similar to MS2 in mono-nitrosyl complexes) state of the linear nitrosyl.