Theoretical Studies on Dihedral Angle-Bending Isomers of M2Pt20/-Clusters

The structures and electronic properties of the gaseous Mbegin{document}$ _2 $end{document}Ptbegin{document}$ _2 $end{document}begin{document}$ ^{0/-} $end{document} clusters (M represents the alkaline earth metal) were investigated using the density functional theory (B3LYP and PBE0) and wave function theory (SCS-MP2, CCSD and CCSD (T)). The results indicate that the Dbegin{document}$ _{2{h}} $end{document} isomers with the planar structures are more stable than the Cbegin{document}$ _{2v} $end{document} isomers with smaller dihedral angles and shorter Pt-Pt bond lengths. The mutual competition of M(s, p)-Pt(5d) interaction and Pt-Pt covalent bonding contributes to the different stabilizations of the two kinds of isomers. The M(s, p)-Pt(5d) interaction favors the planar isomers with Dbegin{document}$ _{2h} $end{document} symmetry, while the Pt-Pt covalent bonding leads to the Cbegin{document}$ _{2v} $end{document} isomers with bending structures. Two different crossing points are determined in the potential energy curves of Bebegin{document}$ _2 $end{document}Ptbegin{document}$ _2 $end{document} with the singlet and triplet states. But there is just one crossing point in potential energy curves of Rabegin{document}$ _2 $end{document}Ptbegin{document}$ _2 $end{document} and Cabegin{document}$ _2 $end{document}Ptbegin{document}$ _2 $end{document}begin{document}$ ^- $end{document} because of flatter potential energy curves of Rabegin{document}$ _2 $end{document}Ptbegin{document}$ _2 $end{document} with the triplet state or Cabegin{document}$ _2 $end{document}Ptbegin{document}$ _2 $end{document}begin{document}$ ^- $end{document} with quartet state. The results reveal a unique example of dihedral angle-bending isomers with the smallest number of atoms and may help the understanding of the bonding properties of other potential angle-bending isomers.