A CNDO/2 approach to electron delocalization in N4S4 and N4S4F4

The electronic structure of N₄S₄ and N₄S₄F₄ molecules is investigated within the framework of the CNDO/2 approximation. A pure alternated system is obtained for the fluorinated compound with respect to the Wiberg bond populations. On the other hand, the N₄S₄ molecule appears to be composed of three highly delocalized “islands”, as defined by Dewar in the case of cyclophosphazenes. The “tub form” of N₄S₄ is due to a strong spatial interaction between non-bonded sulphur atoms and, for this reason, the N₄S₄ molecule may be called the “inorganic cyclooctatetraene”.