  We study the quantum dynamics of polygonal rare-earth molecular clusters with
Ising-type ion magnetization. It is shown that the ground state of such systems
is a non-magnetic quasi-doublet of states with oppositely twisted ion spins.
The states differ in sign of toroidal moment, which is a natural physical
quantity to characterize the spin chirality of the clusters. The possibility of
macroscopic quantum tunneling of toroidal moment between the states is
predicted. The effects of an external current is considered, both in
equilibrium and in the frames of the Landau-Zener-St\"uckelberg tunneling
model. The special treatment is given for the most important case of triangular
rare-earth clusters.
