Mn2@Si15: the smallest triple ring tubular silicon cluster

The smallest triple ring tubular silicon cluster Mn-2@Si-15 is reported for the first time. Theoretical structural identification shows that the Mn-2@Si-15 tubular structure whose triple ring is composed by three five-membered Si rings in anti-prism motif, is stable in high symmetry (D-5h) and singlet ground state ((1)A(1)'). The dimer Mn-2 is placed inside the tubular along the C-5 axis, and the Mn dopant form single Si-Mn bonds with Si skeleton, whereas the Mn-Mn is characterized as a triple bond. The effect of Mn-2 on the stability of the Si-15 triple ring structure arises from strong orbital overlap of Mn-2 with Si-15.