The influence of the trans-ligand to NO on the thermal stability of the photoinduced side-bond coordinated linkage isomer

Abstract

The influence of the trans-to-NO ligand (X) on the thermal stability of the transient side-on coordinated nitrosyl linkage isomer (MS2) is investigated in a series of trans-[RuNOPy₄X](PF₆)₂ (X = F⁻(RuF), Cl⁻(RuCl), Br⁻(RuBr) and OH⁻(RuOH)) compounds. Based on differential scanning calorimetry (DSC) and IR-spectroscopy investigations, activation energies (E_a) and frequency factors (k₀) are determined for MS1 → GS and MS2 → GS reactions. Calculated decay temperatures (T_d) of both processes correlate with Mulliken electronegativities of X and Hirshfeld charges of the (RuNO) unit, and the increase in the electronegativity of X or in the positive charge on the (RuNO) group leads to an increase in the thermal stability of the MS2 isomer with almost linear dependence. Since the MS2 isomer is a transient state in MS1 isomer formation or the NO release reaction, the obtained correlation can be used for the design of compounds with higher quantum yields of these processes.