Tire tetrahedron

Figure Bl.8.4. Two of the crystal structures first solved by W L Bragg. On the left is the stnicture of zincblende, ZnS. Each sulphur atom (large grey spheres) is surrounded by four zinc atoms (small black spheres) at the vertices of a regular tetrahedron, and each zinc atom is surrounded by four sulphur atoms. On the right is tire stnicture of sodium chloride. Each chlorine atom (grey spheres) is sunounded by six sodium atoms (black spheres) at the vertices of a regular octahedron, and each sodium atom is sunounded by six chlorine atoms.

Each object (pictured in Figure 2.32) is called a simplex - the simplest possible object in space of a given dimensionality tire dimensionality is one less than the number of factors or components in a mixture, so a tetrahedron (three dimensions) represents a four component mixture. 

In this complex, Zn2(H20)3(0H)4, each zinc ion is surrounded by four oxygen atoms (of OH"" or H O), exactly as in the hydrated zinc cation or the zincate anion the loss of water without decrease in coordination number is achieved by tire dual role played by on hydroxide oxygen atom, which serves as part of the coordination tetrahedron for both zinc ions. By continuing this process ail of the tetrahedra can be linked together into an infinite framework, in c hich each tetrahedron shares its corners with four other tetrahedra. This is the structure of the Zn(OH)o precipitate. 

Each of these reefe is made up of modules consisting of 28 scrap tires strapped together with polyester tape fastened by stainless steel chps. The tires are formed into tetrahedron module imits (TMUs) with concrete ballast in the basal tires. They are placed at carefully selected locations and in a manner to minimize any adverse enviromnental effects. Underwater monitoring programs are needed on each of these reefs to see if all reefs attract fish and support a growing population of benthic organisms. It is expected that the longevity of the materials will be retained for a minimiun of 20 years. 

The steady-state nucleation rate J is measured during the nucleation stage, when the number of precipitates is varying quite linearly with time. Slowdown of precipitation kinetics with triangle and tetrahedron order corrections can be seen on the steady-state nucleation rate (Fig. 7) without these corrections is about two times higher than when these corrections tire included. 

Braekman, J.C., Daloze, D and Macedo De Abreu, P. (1982) A novel type of bis-quinolizidine alkaloid from tire sponge Petrosia seriata. Tetrahedron Lett., 23, 4277-4280. 

Murakate, H., Mikawa, A., and Natsume, M. (1992) Total synthesis of (-F)-herbindole A, (-F)-herbindole B, and (-F)-herbindole C. Determination of tire absolute configuration of the natural herbindoles. Tetrahedron Lett., 33, 4595-4598. 

---