Abstract Interfaces between metal atoms and organic molecules are key units of many important metal–organic systems. Presented are results of ab initio calculations for a series of complexes of 2nd-row metal atoms sandwiched between small unsaturated hydrocarbon molecules. Evolution of the system structure and stability is studied for different metal atoms, as well as upon excitation, ionization and electron attachment. Predicted interesting features include cooperative stabilization, unusual geometries, reversible charge- or excitation-governed geometry alterations. The observed variety of properties suggests potential applications of such species as intermolecular junctions and units with charge- or spin-controlled shapes in molecular devices and/or machines.