FIG. . Hypercoordinated multicenter units around a central electron-rich A atom (pink color) showing the simplest linear three-center bonds in one (1D), two (2D), and three (3D) dimensions. Each unit around the A atom is defined by three numbers enclosed in parentheses, A(C,E,M), denoting the number of covalent bonds (C), LEPs (E), and linear multicenter bonds (M) that are depicted in white-pink, pink, and green color, respectively. These units are typical of molecules with electron-rich multicenter bonds (ERMBs), such as I3 ꟷ , XeF2, XeF4, XeF6, which are also present in molecular solids, such as CsI3 and Cs2TeI6. These units, but extended indefinitely in 1D, 2D, and 3D, also appear in solids with electron-deficient multicenter bonds (EDMBs), such as the octahedrally-coordinated phases of group-15 and -16 elements, in IV-VI and V2-VI3 PCMs, such as PbTe and Bi2Te3, and in other solids, such as BaZnSb2.