Siloxane ditrigonal cavity

Surface complexes between metal cations and siloxane ditrigonal cavities on 2 1 phyllosilicates, shown in exploded view. 

Explain the Lewis-base properties of a siloxane ditrigonal cavity. 

Figure 7. Space-filled [001] projection of the siloxane ditrigonal cavity of kaolinite. Space-filled structure of hydrazine is also shown, drawn to the same scale.

Figure 4.3. Schematic of inner- and outer-sphere complexes between metal cations and the siloxane ditrigonal cavities of 2 1 day minerals (from Sposito, 1984a, with permission).

Another interesting aspect of the simulation results concerns the location of the counterions in the interlayer space. The (001) perspective of simulated Cs+-mont-morillonite (Fig. 8- 4) shows that, at a water content [ 150 g H20 kg-1] approximately corresponding to a monolayer, the cations always adopted locations such that they were aligned with the center of a siloxane ditrigonal cavity on the basal surface of one clay layer and with the base of an SiC>4 tetrahedron on the basal surface of the opposing clay layer. At lower water contents this configuration was not stable, and the interlayer counterions tended to align themselves with the centers of siloxane cavities on the basal surfaces of both clay layers. 

Fig. 8-4. (a) Representative snapshots of equilibrated Cs-montmorillonile. The cations and day were solvated by a monolayer of water, as shown in the (010) view, (b) The (001) [>crspective shows that the aqueous cations adopted locations where they always bridged between a siloxane ditrigonal cavity on one crystal layer and a tetrahedral site on the opposing layer. I Vhydiaiing the system caused the cations to align themselves with the centers of siloxane cavities on both layers. 

Figure 1.7. The siloxane ditrigonal cavity in a distorted tetrahedral sheet of a phyllosilicate. (Original computer-drawn figure courtesy of C. T. Johnston)...

The configuration of water molecules between the basal planes in vermiculite depends sensitively on the nature of the cation complexed on these surfaces to balance the negative charge produced by isomorphic substitution of for in the tetrahedral sheet. Because of this substitution, the siloxane ditrigonal cavities exhibit a relatively ItKulized... 

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