Equilibrium between Different Coordination Geometries in Oxidovanadium(IV) Complexes.

In this laboratory activity, the equilibrium between square pyramidal and octahedral V(IV)O2+ complexes is described. We propose a set of experiments to synthesize and characterize two types of V(IV)O2+ complexes. The experiment allows great flexibility and may be effectively used at a variety of levels and the activity can be lengthened or shortened depending on the available time. The laboratory practice can combine various experiments: (i) synthesis of solid transition metal complexes, (ii) analysis of the solid complexes to hypothesize their coordination geometry, (iii) measurement of room temperature and frozen solution EPR (Electron Paramagnetic Resonance) spectra obtained when dissolving the solid complexes in different solvents, (iv) software simulation of room temperature and frozen solution EPR spectra, (v) measurement of UV-vis spectra of solutions obtained when dissolving the solid complexes in different solvents, (vi) optimization of the coordination geometry of V(IV)O2+ complexes with DFT calculations, (vii) calculation of the EPR parameters of V(IV)O2+ complexes with DFT methods, and (viii) influence of the temperature on the equilibrium calculated using DFT methods. The activity is organized to guide the students towards to a plausible explanation of the experimental evidence.