Main-group clusters symmetry

The analysis of these molecules is complicated by the presence of the d orbitals, which contribute one orbital of CT symmetry (d 2 in local axes), two of n symmetry (d and Ayg), and two of 5 symmetry (d y and dj2 j,2). There are far more examples of deviations from the usual patterns in transition metal clusters than in main group clusters, and many of these must be treated specifically, although TSH theory may again provide a useful framework in which to perform the analysis. However, in this section the objective will simply be to understand the most common patterns, as set out in Section 3, which are typically found in clusters with u-acceptor ligands such as CO. 

In the first three chapters, instances were noted where the number, symmetry characteristics and occupation numbers of the frontier orbitals of a transition-metal fragment were similar to those of a main-group fragment. Such fragments are said to be isolobal to emphasize similar bonding capabilities. Since its enunciation by Hoffmann and Mingos, the concept has been used effectively for the analysis of both organometallic and cluster problems. Let s explore the idea in a more systematic... 

The replacement of main-group atoms in clusters by transition-metal atoms generates a richer structural chemistry superimposed on the cluster basics illustrated by the p-block systems. A logical question arises here. What would a one-dimensional material containing a transition metal look like Well, the d AOs will generate bands in a similar manner as the s and p orbitals. The major novelty will be the introduction of orbitals of 8 symmetry. Let s look at a hypothetical chain composed of equidistant Ni atoms (d = 2.5 A). The computed band structure, DOS and COOP are illustrated in Figure 6.14. The COs at k = 0 and ir/d arc drawn below. As a review of the previous section, we will reconstruct it starting from the Bloch functions associated with the nine Ni AOs. 

Coordination Organometalhc Chemistry Principles Electronic Structure of Main-group Compounds Electronic Structure of OrganometaUic Compounds Electronic Structure of Clusters Ligand Field Theory Spectra Molecular Orbital Theory Symmetry Point Groups. 

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