Phosphorus-tellurium rings

The analogous phosphorus heterocyclic systems that include selenium or tellurium are discussed in detail in Chapter 6.12, and the systems incorporating phosphorus and arsenic or antimony are covered in Chapter 6.14. In addition, numerous examples of five-membered heterocyclic systems with phosphorus and elements of group III (B, Al, Ga, In) and group IV (Si, Ge, Sn, Pb) are included in Chapters 6.16 and 6.17 of this volume. The systems with five heteroatoms in a five-membered ring (e.g., pentaphospholide anion and tetrazaphospholium cation) and the fused heterocyclic rings (see Volumes 9-11) are beyond the scope of this chapter and are not covered here. 

Initially, ring expansion by tellurium leads to a four-membered heterocycle (n = 1) intermolecular rearrangements produce additional tellurium-phosphorus hctcrocycles, which are ultimately converted by extrusion of tellurium to tetra-/-butylcyclotetra-phosphane1. 

Elements. Those elements that form extended covalent (as opposed to metallic) arrays are boron, all the Group IV elements except lead, also phosphorus, arsenic, selenium and tellurium. All other elements form either only metallic phases or only molecular ones. Some of the above elements, of course, have allotropes of metallic or molecular type in addition to the phase or phases that are extended covalent arrays. For example, tin has a metallic allotrope (white tin) in addition to that with the diamond structure (grey tin), and selenium forms two molecular allotropes containing Se8 rings, isostruc-... 

In addition, mixed sulfide selenide systems such as P4S2Se are also known, while P-Te bonds are found in BaP4Te2. This new material is generated by direct reaction of the elements at 475 °C and consists of P4Te2 chains made up of six-membered phosphorus rings linked to tellurium atoms (47). The P-Te... 

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