Ligand polyhedral model

Favorable packing of the CO ligands about the cluster core was qualitatively and later (semi)quantitatively" investigated by Johnson et al. who, while searching for the best fit between the metal cluster and the optimum ligand polyhedron, eventually derived what is known as the Ligand Polyhedral Model (LPM). According to the LPM ... 

Fluxional Molecules. - The ligand polyhedral model has been applied to carbonyl clusters containing thirteen carbonyl groups. ... 

The dianionic species, [Fe3(CO)n] 4 and [Fe4(CO)i3] 5 (see Scheme 10), are used for preparation of hetcro-nuclear cluster compounds. " Polymer-bound 4 and 5 are obtained by treatment of 1 with aminated polystyrenes in Me0H-H20. The ligand polyhedral model (LPM) has been successfully applied to [M4(CO)i3] species including It is claimed that a new neutral binary iron carbonyl formulated as Fe4(CO)i4 (characterized by IR) is formed by co-deposition of mass-selected Fc4 and... 

Attempts to distinguish between possible mechanisms for CO ligand mobility in Group 9 carbonyl clusters, i.e. merry-go-round versus Johnson and Benfield s ligand polyhedral model, have proven inconclusive. A series of Co-NMR studies on [Co4(CO)i2] and analysis of the thermal motion of the CO ligands using new structural data for [Rh4(CO)i2] failed to provide conclusive evidence for the type of fluxional processes observed. 

It is often difficult to represent inorganic compounds with the usual structure models because these structures are based on complex crystals space groups), aggregates, or metal lattices. Therefore, these compounds are represented by individual polyhedral coordination of the ligands such as the octahedron or tetrahedron Figure 2-124d). 

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