Ruthenium nitrosyl complexes [RuNOL2(NO2)2OH] with ethyl isonicotinate and pyrazine: Synthesis, structure and formation of metastable linkage isomers

Abstract

New complexes of ruthenium nitrosyl with ethyl isonicotinate and pyrazine were prepared in the reaction of [RuNO(NO2)2(H2O)3]+ with corresponding ligands. With the ligand excess the reaction results in cis-[RuNOL2(NO2)2OH] with good yields (78% for I L = inicEt, 35% for II L = Pyz). The dimeric complex [(RuNO(Pyz)(NО2)(μ-NO2))2μ-O] (III) forms in a small yield when less than 2 molar equivalents of pyrazine are taken for the reaction. Crystal structures of all three complexes were determined by single crystal XRD. Upon blue light irradiation complexes I and II undergo isomerization from Ru–NO (ground state, GS) to Ru-ON (metastable state, MS1) group. Reverse thermal transformation MS1 – GS was studied by IR and DSC techniques, activation parameters of MS1 – GS transition are: I - Ea = 53.4(4.0) kJ mol−1, lg k0 = 10.6(4); II – Ea = 58.9(4.3) kJ mol−1, lg k0 = 13.5(0.4).