Figure 6.

A demonstration of bond-topological and crystallographic equivalence for the ions of a dimeric unit (cations = white, anions = grey). Topologically equivalent ions share the same lettering, and crystallographically equivalent ions share the same lettering and subscript. Crystallographic equivalence of the constituent ions lowers from (a) the configuration of maximum symmetry about ion C to (c) the point of minimum crystallographic symmetry. Intermediate configurations are observed with progressively fewer symmetry operators (m = mirror plane), thus lowering the number of equivalent metrics (bond lengths, bond angles) from configurations (a) to (c). Bond-topological equivalence is unchanged from (a) to (c).