Pair potentials which facilitate the modeling of mixed metal oxides containing Ru5+, Sb5+, and Ru4+ have been derived. It is shown that these potentials are consistent with the structural differences observed between apparently analogous Sb and Ru compounds and that they can account for the complex crystal structure of Ba4NaRu3O12. A prediction is made about the structural stability of some as yet unknown quaternary oxides of Ru.