The structures and electronic properties of the gaseous M2Pt20/? clusters (M represents the alkaline earth metal) are investigated using the density functional theory (B3LYP and PBE0) and wave function theory (SCS-MP2, CCSD and CCSD (T)). The results show that the D2h isomers with the planar structures are more stable than the C2V isomers with smaller dihedral angles and shorter Pt-Pt bond lengths. In this work we show that 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 D2h symmetry, while the Pt-Pt covalent bonding leads to the C2V isomers with bending structures. Two different crossing points are determined in the potential energy curves of Be2Pt2 with the singlet and triplet states. But there is just one crossing point in potential energy curves of Ra2Pt2 and Ca2Pt2? because of flatter potential energy curves of Ra2Pt2 with the triplet state or Ca2Pt2? 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.