  We investigate localized intragap states in mixed-valence bimetal chains in
an attempt to encourage further explorations into quasi-one-dimensional
halogen-bridged binuclear metal (MMX) complexes. Within a coupled
electron-phonon model, soliton and polaron excitations in the two distinct
ground states of MMX chains are numerically calculated and compared. Making a
continuum-model analysis as well, we reveal their scaling properties with
particular emphasis on the analogy between MMX chains and trans-polyacetylene.
