The peculiar biferrocenium cation configurational diagram is discretized in terms of a fictitious spin S=1. At the solid state, this leads to a Blume-Emery-Griffiths Hamiltonian which is solved in the mean-field approach. Order-disorder transitions are obtained, either continuous or discontinuous, together with a thermal equilibrium between trapped and delocalized states. These features are discussed with respect to characteristics of the measuring techniques.