“…In comparison with P 4 O 6 the monosubstituted compounds P 4 O 6 X (X = O, S, Se) show characteristic geometrical distortions in the first and second coordination shell of the attacked phosphorus atom [1,2,3]: the bonds between the attacked phosphorus atom and the nearest oxygen neighbours within the P 4 O 6 cage become shorter, whereas the bonds between the P V neighboring oxygen centers and the remaining phosphorus atoms become longer relative to their values in P 4 O 6 . Rather suprisingly, the changes in the bond strength induced by the various chalkogen substituents are of similar magnitude [4,5].…”