The importance of the transannular secondary bonding strength in the molecular structures of metallocanes of type [X(CH2CH2Y)2MRR′] and [X(CH2CH2Y)2M′R] (M = Ge(IV), Sn(IV), Pb(IV), M′ = As(III), Sb(III) and Bi(III); X = NR″, O, S; Y = O,

The 1-oxa-4,6-dithia-, 1,3,6-trithia-, 1-aza-4,6-dithia-, 1-aza-4,6-dioxa-, 1-thia-4,6-dioxa- and 1,3,6-trioxametallocanes possess a strong 1,5 transannular interaction through an acceptor atom M [Ge(IV), Sn(IV), Pb(IV), As(III), Sb(III) and Bi(III)] and an X donor (O, S, NR). The conformation adopted by the metallocane ring has exhibited various conformations along with the extreme conformations boat-boat, boat-chair and chair-chair. The structural diversity observed in these eight-membered rings results in a variety of coordination numbers, as well as in the presence of polymeric structures. The purpose of the present review is to highlight the relationship between the strength of the transannular bonding and the resulting molecular structures. Factors such as coordination number, electronegativity and steric effects are revised.