Remarkably, the bonds in the Ai phase conform to the hypercoordinated multicenter unit with the rhombohedral geometry shown in Fig. . In this geometry, three linear multicenter bonds that are not mutually perpendicular are formed from three original primary covalent ppσ-bonds and three secondary LEP-based bonds. It must be stressed that the same bond geometry is present in the rhombohedral tetradymite structure of V2-VI3 PCMs, such as Bi2Se3, β-As2Te3, Sb2Te3, Bi2Te3, and also in the related compound SnSb2Te4; all of them exhibiting MMBs .