Isomerization Mechanisms of a Labile Co(II) Octahedral Complex

The labile cobalt (II) complex [Co(TUF)2(Pic)2] with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (TUF) bidentate and 4-methylpyridine (Pic) monodentate ligands was studied by variable temperature (VT) 19F NMR from 184 to 312 K. In contrast to the solid state, all the isomers are present in a CD2Cl2 solution. Thermodynamic parameters (?H° and ?S°) of each isomer with reference to the trans(N)-trans(CF3)-trans isomer were obtained from the fitting of experimental mole fraction values. A kinetics investigation of the isomerization processes was performed by lineshape analysis of the spectra using the Kubo-Sack formalism. The suggested bidentate bond-rupture mechanism involves the breaking of the weakest Co–O bond (closest to the CF3 withdrawing group) with the TUF ligand