The interaction between any fragments bonded to some central atom are increasingly recognized as an important factor in determining, e.g. the geometry and properties of metal complexes. Here we analyze the class of the two-legged piano stool complexes Cp′ML2 (Cp′= cyclopentadienyl or a derivative, M = Fe(II) and Ru(II), L = phosphorus and nitrogen co-ligands) with the aid of the through-space coupling (TSC) concept. This is the molecular orbital representation of van der Waals-like repulsive-attractive forces between the ligands in addition to the interactions with the metal center. The combination of both, i.e. the interaction between the new collective ligands orbitals and the metal AO's is shown to be the main determinant for deciding whether a planar or pyramidal structure is adopted and further, whether the complex is diamagnetic or paramagnetic. In addition the TSC concepts aids in understanding the effect of intercomplex interactions on the nucleophilic and electrophilic behavior of the 16e-complexes towards an incoming ligand. In fact, interpretations hitherto solely in terms of electronic ligand effects appear to be inadequate. The present paper is a continuation of our former work in which we successfully applied the TSC concept to rationalize the diverse array of structural arrangements as well as reactivities of the main-group Cp metal complexes (Sapunov et al. Coord. Chem. Reviews 214 (2001) 143).
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