A detailed comparative study of the valence tautomeric interconversion of complexes 1-3 in three different environments is reported. The three environments are solid state (both crystalline and amorphous materials), solution and embedded into a polymeric matrix. The VT behavior of the three complexes strongly differs from one to the other, though no systematization can be established. In solution, different solvatational parameters seem to affect the equilibrium. However, such solvate effect cannot be translated either into the solid state or polymeric matrix, where the equilibrium is controlled by the vibrational relaxation of the network. ; We acknowledge the financial support of the Ministerio de Educación y Ciencia under grant (MAT2006-13765-C02) and the network of Excellence Magmanet. E.E. thanks the Ministerio de Educación y Ciencia for a predoctoral grant. This work was supported by the Communauté de Travail des Pyrénées program for cooperation, research and technological development. ; Peer Reviewed