Cages, borosilicate

Since 1992, three types of three-dimensional borosilicate "cage" compounds have been characterised. These may be described as columnar, 3,2 spherical, 4,3 and cuboid, 5.1 Our recent attempts to better understand the reactions which give rise to cage compounds and to extend their chemistry are the basis of this report. 

Eq. 2), and no cyclic siloxane or boroxine products could be isolated in either case. This suggested that the formation of B-O-Si bonds is favoured over Si-O-Si or B-O-B bonds when B-OH and Si-OH species react and led us to consider the possibility of systematic syntheses of three-dimensional borosilicate cages with the connector units shown below. Clearly, at least two, three-connector units are required for the formation of three-dimensional cages such as.3, 4, and 5 above. 

Figure 1.2 Various columns and materials employed for capillary gas chromatography (a) left 25 m x in. o.d. stainless steel capillary column in a pancake format, center 30 m X 0.25 mm i.d. aluminum-clad fused-silica column, right blank or uncoated stainless steel capillary tubing o.d. (b) 60 m x 0.75 mm i.d. borosilicate glass capillary column for EPA method 502.2 (c) 30 m x 0.25 mm i.d. fused-silica capillary column also pictured is a typical cage used to confine and mount a fused-silica column.

FIGURE 18. (a) A tripodal technetium chelator is based on three oxime ligands tethered through an acyclic boronate triester, (b) Borosilicate macrocycles and (c) cages have been formed as building blocks and (d) assembled via coordinative ditopic Lewis bases. 

---