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 temp. (VT) 19F NMR from 184 to 312 K. In contrast to the solid state, all the isomers are present in a CD2Cl2 soln. Thermodn. parameters (DHo and DSo) of each isomer with ref. to the trans(N)-trans(CF3)-trans isomer were obtained from the fitting of exptl. mole fraction values. A kinetics investigation of the isomerization processes was performed by lineshape anal. of the spectra using the Kubo-Sack formalism. The suggested bidentate bondrupture mechanism involves the breaking of the weakest Co-O bond (closest to the CF3 withdrawing group) with the TUF ligand.