Extended Huckel calculation, illustration

Extended Huckel calculations were performed using the crystal structure data (174) of the free dianion ligands. The frontier orbitals of the Dicyd2- are illustrated in Fig. 15 and show that both HOMO and SHOMO are of tt symmetry and span the entire molecule. A crystal structure determination of the complex [ (NH3)Ru 2( U-Dicyd)][OTs]4... 

In 22, whose structure is illustrated in Figure 3-60, the Ti atoms are formally in the oxidation state +3 (d configuration) and the cluster contains 52 valence electrons, 8 electrons less than found in many other heterocubane clusters. [91] Admittedly, other compounds are known whose electron counts fall short of this normal value and still others which exceed it. Extended Huckel calculations predict a Ti4 tetrahedron having D2d symmetry with four longer and two shorter Ti-Ti bonds for this type of structure with 52 valence electrons. [92, 93] Indeed, 22 contains two shorter Ti-Ti distances of 268.6(2) pm and four longer distances of 277.2-278.5(2) pm. 

Can we see this local, very chemical bonding construction in a delocalized band structure Most certainly. The calculated (extended Huckel) band structure and total density of states of a single Mn2P22 layer is illustrated in Fig. 27. 

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