A remarkable mixture of germanium with phosphorus and arsenic atoms making stable pentagonal hetero-prisms [M@Ge(5)E(5)](+), E = P, As and M = Fe, Ru, Os

A pentagonal hetero-prismatic structural motif was found for singly transition metal doped M@Ge(5)E(5)(+) clusters, where the transition metal atom is located at the centre of a (5/5) Ge(5)E(5) prism in which Ge is mixed with either P or As atoms. Structural characterization indicates that each (5/5) Ge(5)E(5) prism is established by joining of two Ge(3)E(2) and Ge(2)E(3) strings in a prismatic fashion rather than two Ge(5) and E(5) strings. Each string results from a remarkable mixture of Ge and E atoms and contains only one E–E connection due to the fact that Ge–E bonds are much stronger than E–E connections. From the donor–acceptor perspective, the Ge(5)E(5) tube donates electrons to the M center, which behaves as an acceptor. NBO atomic charge and ELI_D analyses demonstrate such electrostatic interactions of the M dopant with a Ge(5)E(5)(+) tube which likely induce thermodynamic stability for the resulting M@Ge(5)E(5)(+) cluster. CMO analysis illustrates that the conventional 18 electron count is recovered in the M@Ge(5)E(5)(+) cations.