Mooser-Pearson diagram

Ax) and the average, h, of the principal quantum number, n, of the valence electrons on the A, B atoms. Two of these Mooser Pearson diagrams are shown in Figures 8 and 9. Notice that for the AB octets such indices sort the structures of the three different coordination number structures from each other well, and also separate the wurtzite structure from the sphalerite structure. The wurtzite structure is found for the more ionic examples. 

One has to assume that an anionic tetrahedron complex is formed and one has to make also assumptions which of the elements are the cations C, the central atoms C and the anions A. The parameters used in the Mooser - Pearson diagrams to separate compounds with adamantane structure from those having no adamantane structures are also here of some relevance, if the central atom and the anion is from the second period of the Periodic Table then a planar trianguleir anion complex is preferred to a tetrahedron complex, as for example with BOs) -, (003)2- or (NOs) -. Tetrahedral complexes are also rarely found if the central atom is from a very high period. Central atoms from periods inbetween can be expected to form tetrahedral complexes, but there are exceptions. 

Notice that the aforementioned compositional scheme is a necessary condition for building the tetrahedral structures, but not every compound that fulfils this condition is a tetrahedral compound. The influence of other parameters, such as the electronegativity difference, has been pointed out. By means of diagrams, such as that reported by Mooser and Pearson (1959) (average principal quantum number vs. electronegativity difference) the separation of tetrahedral structures from other structures can be evidenced. 

The metallicity defined here, as well as the simpler earlier form, corresponds roughly to the metallization introduced earlier by Mooser and Pearson (1959). It is also the parameter (based upon earlier values) that formed the ordinate in the schematic phase diagram shown in Fig. 2-6. 

Fig. 4. (a) AB2 and (b) AB3 valence compounds shown on an h versus Ax diagram. Symbols indicate the different crystal structures given as Strukturbericht types, together with the near-neighbor coordination. After Mooser and Pearson. ... 

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