Theoretical Studies on Dihedral Angle-Bending Isomers of M₂Pt₂^0/- Clusters

The structures and electronic properties of the gaseous M _2 Pt _2 ^0/- 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 D _2h isomers with the planar structures are more stable than the C _2v 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 D _2h symmetry, while the Pt-Pt covalent bonding leads to the C _2v isomers with bending structures. Two different crossing points are determined in the potential energy curves of Be _2 Pt _2 with the singlet and triplet states. But there is just one crossing point in potential energy curves of Ra _2 Pt _2 and Ca _2 Pt _2 ^- because of flatter potential energy curves of Ra _2 Pt _2 with the triplet state or Ca _2 Pt _2 ^- 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.