Diamond homonuclear

Electron-precise cluster systems can be seen to be a more complex version (three-connect units) of chains (one-connect units) and rings (two-connect units), leading up to an extended solid (four-connect units, e.g. the diamond structure). This is most easily appreciated for homonuclear examples, for example, (1) and (2). For the mixed systems like (3), two distinct descriptions are possible - as a 4-atom cluster or as a trinuclear metal complex with a /U.3-P cap. In many cases, the difference is of little consequence however, in others, proper choice of description can lead to analyses of significant conceptual value. 

Figure 1 Dissociation potentials for homonuclear diatomic molecules plotted against either atomic number (lower graph, diamonds), and for monoxides plotted against oxidized atom (upper graph, squares). The displaced peaks are due to iselectronicity.

In [236], coh of FI was predicted from SR and SO-GGA-DFT solid-state calculations. The obtained value of 0.5 eV (48.2 kJ/mol), the SO-PW91 result, is in reasonable agreement with the estimates of [207, 225] (Table 16). SO effects were shown to lower and lead to structural phase transitions for the solid H (the hep structure in contrast to the fee for Pb). In a nonrelativistic world, all group-14 elements would adopt a diamond structure. An increase in the solid-state nearest-neighbor distance is found from Pb to FI, as that in their homonuclear dimers, indicating that the nature of the chemical bond in the crystal is similar to that of M2. 

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