The premier example of a complex with an unsupported metal–metal bond is dimanganese decacarbonyl, Mn(CO). Many metal clusters contain several unsupported M–M bonds.  Some examples are M(CO) (M = Ru, Os) and Ir(CO).
A subclass of unsupported metal–metal bonded arrays are linear chain compounds.  In such cases the M–M bonding is weak as signaled by longer M–M bonds and the tendency of such compounds to dissociate in solution.