Tetrahedral sulphur configurations

The structure of zinc sulphide on the basis of an ionic bond, would consist of Zn + and S ions arranged tetrahedrally. The covalent structure, however, requires the sulphur to be doubly charged, positive and tetravalent and the zinc to be doubly charged negative and tetravalent, both the Zn - and the thereby being in an i/ valency state. The actual molecule will be a superposition of these two extreme states and although the contribution of the covalent form may be small, it does nevertheless determine both the configuration of the atoms and their coordination numbers. 

These structure determinations show that thioethers and saturated cyclic sulphur compounds do not form addition compounds with HgCI as has previously been believed. The complexes formed are the result of a substitution reaction, in which one of the chlorine atoms in HgCl has been replaced by the sulphur atom of the donor molecule giving rise to positively charged mercuric complexes and negative chloride ions. The configuration of ligands around mercury in these complexes is intermediate in character between that of tetrahedrally and octahedrally coordinated mercury. 

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