Elements and Paraelements in Known Structures

The structures of known compounds made up entirely of elements remain unaltered if the elements are substituted partially or totally by pseudo- or paraelements. 

By partial substitution of C—X by BH2 (pseudonitrogen) in triazine ( N=BH2)3 is first produced and this is stabilized by resonance through 

Very recently it was possible to synthesize two basic adamantanes of the formula (HSi)4S6 and (HSi)4Se6. They were made by reacting HSiCl3 with (H3Si)2E (E = S, Se). An X-ray structure determination proved the expected adamantane structure for (HSi)4S6 and spectroscopic investigations left no doubt that (HSi)4Se6 has the same structure (94). 

It is very difficult at first sight to understand why substances like P7R3, P4[Si(CH3)2]3 and also Sb73- should have the same structure as P4S3. With the aid of the element displacement principle this question can be answered without difficulty. In the cases mentioned the molecules contain a P4 and an Sl 4 unit and the other parts can be written as 

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