Variable pressure (VP) and variable temperature (VT) 19F NMR investigation of molecular exchange mechanisms in octahedral cobalt(II) complexes [Articol]

Abstract

The labile cobalt(II) complex [Co(TUF)2(Pic)2] with 4,4,4-trifluoro-1-(2-thienyl)-1,3butanedione (TUF) bidentate and 4-methylpyridine (Pic) monodentate ligands was studied by variable temperature (VT) and variable pressure (VP) 19F NMR. In contrast to the solid state, all the isomers are present in a CD2Cl2 solution. Thermodynamic parameters (ΔH0, ΔS0 and ΔV0) of each isomer with reference to the trans(N)-trans(CF3)-trans isomer were obtained from the fitting of experimental mole fraction values.figureSchematic representation of the five isomers of [Co(TUF)2(Pic)2figureEvolution of the 19F NMR signals of the five isomers of [Co(TUF)2(Pic)2] with increasing temperature.A kinetics investigation of the isomerization processes was performed by lineshape analysis 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. Heterometallic μ3-oxo carboxylate complexes (Fe2Co and Fe2Ni) have been studied by 2D NMR. The magnetic properties of these compounds are compared in the solid state and in the liquid state.