The structural landscape in 14-vertex clusters of silicon, M@Si₁₄: when two bonding paradigms collide

Abstract

The structural chemistry of the title clusters has been the source of controversy in the computational literature because the identity of the most stable structure appears to be pathologically dependent on the chosen theoretical model. The candidate structures include a D-symmetric 'fullerene-like' isomer with 3-connected vertices (A), an 'arachno' architecture (B) and an octahedral isomer with high vertex connectivities typical of 'closo' electron-deficient clusters (C). The key to understanding these apparently very different structures is the fact that they make use of the limited electron density available from the endohedral metal in very different ways. Early in the transition series the favoured structure is the one that maximises transfer of electron density from the electropositive metal to the cage whereas for later metals it is the one that minimises repulsions with the increasingly core-like d electrons. The varying role of the d electrons across the transition series leads directly to strong functional dependency, and hence to the controversy in the literature.

Strong lowering of ionization energy of metallic clusters by organic ligands without changing shell filling

“…While these characteristics are inherent to the elements, metallic clusters also share similar features. Quantum confinement of electron gas in metallic clusters leads to a grouping of the electronic states into shells as in the atoms 1 – 6 . These shells order as 1S 2 , 1P 6 , 1D 10 , 2S 2 , 1F 14 , 2P 6 , 1G 18 … where the uppercase letters are used to distinguish them from atoms that have a different combination of the principal and angular momentum quantum numbers.…”

Electronic structure and bonding in endohedral Zintl clusters

“…Our focus in this review will be firmly on endohedral Zintl clusters [32][33][34][35][36][37] that are primarily the domain of synthetic inorganic chemistry and, very recently, materials science, but they have also been the subject of many theoretical and gas-phase spectroscopic studies. [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] Generally, Zintl clusters are anionic molecules made up of atoms from p-block (semi)metals.…”

Current advances in tin cluster chemistry

“…124,125 Later, the structural variety in 10, 12, and 14-vertex intermetalloid clusters of group 14 elements was investigated systematically in a series of quantum chemical studies. [126][127][128] These studies were sparked by the synthesis and crystallization of the isoelectronic stannide cluster [Fe@Sn 10 ] 3À , 126 which exhibits yet another cluster geometry that can be considered as an intermediate between the two extremes of a deltahedral and a pentagonal prismatic cage. A very at potential energy hypersurface was found for this anion that led to severe disorder in the solid state and very poor single crystal data.…”