Building a bridge between coordination compounds and clusters: Bonding analysis of the icosahedral molecules [M(ER)₁₂] (M = Cr, Mo, W; E = Zn, Cd, Hg)

The bonding situation of the icosahedral compounds [M(EH)₁₂] (M = Cr, Mo, W; E = Zn, Cd, Hg), which are model systems for the isolated species [Mo(ZnCp*)₃(ZnMe)₉] possessing the coordination number 12 at the central atom M, have been analyzed with a variety of charge and energy decomposition methods (AIM, EDA-NOCV, WBI, MO). The results give a coherent picture of the electronic structure and the nature of the interatomic interactions. The compounds [M(EH)₁₂] are transition metal complexes that possess 12 M-EH radial bond paths (AIM) that can be described as 6 three-center two-electron bonds (MO). The radial M-EH bonds come from the electron sharing interactions mainly between the singly occupied valence s and d AOs of the central atom M and the singly occupied EH valence orbitals (MO, EDA-NOCV). The orbital interactions provide ∼42% of the total attraction, while the electrostatic attraction contributes ∼58% to the metal-ligand bonding (EDA-NOCV). There is a weak peripheral E-E bonding in [M(EH) ₁₂] that explains the unusually high coordination number (MO). The peripheral bonding leads for some compounds [M(EH)₁₂] to the emergence of E-E bond paths, while in others it does not (AIM). The relative strength of the radial and peripheral bonding in [Al₁₃]^- and [Pt@Pb₁₂]^2- is clearly different from the situation in [M(EH)₁₂], which supports the assignments of the former species as cluster compounds or inclusion compounds (MO, WBI). The bonding situation in [WAu₁₂] is similar to that in [M(EH)₁₂].