Insight into chemical bonding of the transition metal-doped cluster Ge2M (M = Sc–Zn) series using NBO and NRT theory

Chemical bonding of the 3d transition metal-doped germanium Ge 2 M (M = Sc–Zn) clusters is investigated by using quantum chemical calculations combined with the analyses of natural atomic orbital (NAO), natural bond orbital (NBO) and natural resonance theory (NRT). All of the clusters have ground state structure of isosceles triangle whose chemical bonding can be described by orbital overlaps and electron transfers between M atom and Ge 2 unit. Among the series, Ge 2 Ti is found to be the most stable cluster due to the best electron pairing between AO-4 s and AOs-3 d of Ti atom and the three bonding orbitals of the Ge 2 unit, whereas Ge 2 Zn is the least stable thanks to the only overlap between AO–4 s (Zn) and MO-π y of the Ge 2 unit. While the Ge–Ge bond is of most covalent character, the Ge–M bond is of half-half covalent and ionic character. The double Ge=Ge bond of Ge 2 is either enhanced (M = Cr, Mn, Cu and Zn) or depleted (M = Sc–Ti, Fe–Ni) upon interacting with the transition metal atom due to the electron transfer between the metal atom and the Ge 2 unit. Finally, the 3d shell of the dopant atoms remains most of their own character in these clusters, especially magnetic moment, which is very interesting for potential magnetic materials.