Strategies to control interpenetration

It may be desirable to avoid interpenetration, for example if we want to create a porous structure. Note, however, that porosity will not be automatically destroyed by interpenetration, and that sometimes interpenetration may actually be advantageous. It may provide additional stability to the net and it may also give the structure a larger surface area. 

In any case, if the synthetic chemist wants to have control over the material produced, both the net and the degree of interpenetration have to be mastered. There may be two slightly different ways to (eventually) get there, we can either analyse the nets themselves, or we can analyse the voids within them. 

It seems perhaps reasonable that nets built from the same kinds of nodes and having the same lengths of the links should also have the same density (counted as nodes per unit volume ), but this is not the case. In Table 11.1 we show some data from the RCSR database [I I] for four-coimected nets. 

Net Vertex Symbol Nodes/ unit cell Density[nodes/A ] Volume[A]  

There are some possible conclusions from this table. For example, the higher density of the quartz (qtz) net compared to the diamond (dia) net means that there is less space available for interpenetration in qtz structures. The table also suggest that for a given chemical system the degree of interpenetration may vary with the net adapted. 

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