Topological atom study examples

Figure 6.9 pictures the example of the triangular-square network taken from [6.38]. Some 4-coordinated sites are seen comprising inner boundaries of this LRC. It is easy to notice that there are two 5-coordinated atoms in the first coordination sphere of each 5-coordinated atom in LRC. This circumstance follows from the fact that, in P-polyhedra, we have an even number of squares leading to the formation of the MRO, which manifests itself in the formation of chains of 5-coordinated atoms. Collins and Kawamura studied the thermodynamic properties of triangular-square lattices. Kawamura established the existence of the first-order phase transition connected with the transformation of the crystalline structure into a topologically disordered one. 

DETERMINATION OF THE CORRECT TRIAL MODEL. Before this stage can be started, all noncrystallographic structural information which can aid in producing the correct topology should be obtained. For example, this information should include data from sorption studies which can help to predict both the maximum pore opening and the framework density and solid state NMR studies which can show the number of crystal1ographically unique atoms or the coordination state of the framework atoms. 

---