Phosphorus and Arsenic, Antimony or Bismuth

Arsaphosphorus chemistry is at present comparatively small [1-8]. Although wholly As analogues of many compounds discussed in this book are known, studies of mixed As/P analogues or compounds with As-P linkages have to date been rather limited. Even smaller are the numbers of known compounds with P-Sb or P-Bi linkages. 

Examples of simple As ions, or compounds which are known to be isostructural with their P analogues are  

Notable amongst As/P compounds (i.e. devoid of As-P linkages) are mixed AsO /PO minerals, arsenatophosphates based on As-O-P linkages (Chapter 5.4), ionic salts such as Ph4p (AsNj) , and substituted phosphorus sulphides (Chapter 4.3). 

The substitution of As for P in any compound with P-P linkages is possible, at least in principle. Amongst the simplest known examples are white phosphorus derivatives P4. As , the black phosphorus derivative AsP, AS2P and the mixed sulphides P4. tAS tS3 (Chapter 4.3). Grey arsenic and black phosphorus have been reported as forming limited solid solutions, but the composition P20AS is believed to consist of ordered chains of P atoms as in Hittorf s phosphorus. The As atoms occupy special positions which allow them to link these adjacent chains. 

Both RuP2 and RuAs2 have Marcasite-type structures and contain Pj and AS2 units, respectively. The isostructural RuPAs presumably contains either randomly distributed P-P and As-As units, or statistically orientated P-As units [5]. 

---