Bistiboles thermochromism

The thermochromic effect of distibines has been treated in three papers by Hoffmann and colleagues using a tight bonding model based on extended Hiickel calculations (33,47,48). These calculations treated only unsaturated distibines, and major attention was focused on bistibole (47). The important orbitals of the stacked bistibole are derived from molecular orbitals of the SbC4H4 unit (see Fig. 6). The HOMO results from the in-phase mixing of the Sb(pz) and Sb(n ) orbitals and is largely localized on the Sb atoms. At the zone center (k = 0) this band has primarily lone pair... 

Distibanes and dibismuthanes in which the antimony or bismuth atoms are incorporated in five-membered heterocycles are named bistiboles and bibismoles. This important class of thermochromic compounds has been studied intensively by the group of Ashe. The synthesis and X-ray structure determination of tetramethylbistibole. 

The thermochromic effect of heterocyclic bistiboles has been the subject of several theoretical publications " " with focus on the unsaturated compounds. Band structures have been calculated for the antimony chain of... 

Preparation of 1,1 -biheterole systems containing arsenic, antimony, and bismuth has been important in understanding thermochromic behavior in terms of structure and bonding. Their interesting solid state structures help explain why some show color transitions, while others do not (see Section 2.16.11.2). The coupled products are sometimes very air-sensitive, but can be isolated by low temperature crystallization for nonpolar solvents or by sublimation. The biarsoles, bistiboles, and bibismoles tend to be thermally stable, while the bibismolanes usually decompose at room temperature. In this section, the different methods by which these compounds may be prepared and isolated are examined. 

---