Antimony ring systems structure

The principles needed to design a polymer of low flammability are reasonably well understood and have been systematized by Van Krevelen (5). A number of methods have been found for modifying the structure of an inherently flammable polymer to make it respond better to conventional flame retardant systems. For example, extensive work by Pearce et al. at Polytechnic (38, 39) has demonstrated that incorporation of certain ring systems such as phthalide or fluorenone structures into a polymer can greatly increase char and thus flame resistance. Pearce, et al. also showed that increased char formation from polystyrene could be achieved by the introduction of chloromethyl groups on the aromatic rings, along with the addition of antimony oxide or zinc oxide to provide a latent Friedel-Crafts catalyst. 

While many different structural types are known for heterocycles containing arsenic, antimony, or bismuth, structural diversity comes from the expanded CN that are available with these heteroatoms. Throughout the Chapter, the letter E, as used in the ring, represents As, Sb, or Bi and its use is explained in the text. Scheme, or Equation. In general, few ring systems exist that contain ring bound heteroatom substituents, and as a result, hydroxy-oxo, amino-imino, and thiol-thioxo tautomerism is nearly nonexistent. 

A six-membered ring (Sb—Ga 2.661 A) with an irregular boat conformation is present in [Bu2SbGaCl2]3 but the ring is the more usual four-membered system in [Bu2SbInCl(SbBu )]2. The structure shows some disorder but the mean Sb—In distance is 2.844 A and the ring angles at antimony and indium are 94.9 and 85.1°, respectively. 

Breunig, H. Althaus, H. Ring and chain systems in structures of organo antimony(III) and bismuth(III) halides. Phosphorus Sulfur 2001, 168. 123. 

---