A geometrical model for tri-nuclear molecules is reviewed. For an analytica
l solution the nuclei have to be prolately deformed and in a line connected
to each other. Furthermore, there have to be two heavy and one light clust
er, the latter sandwiched between the two heavy clusters. As an alternative
we also study an algebraic model of tri-cluster molecules based on a U(7)
group. This model allows arbitrary orientations of the center of masses.