A chemical view of the giant Au₁₀₂(SR)₄₄ (SR = P-Mercaptobenzoic Acid) cluster: Metalloid aluminum and gallium clusters as path making examples of this novel type open our eyes for structure and bonding of metalloid Au_n(SR)_m (n > m) clusters

The outstanding position of metalloid clusters as intermediates between the bulk metals and bulk salts on the one hand and of naked metal atom clusters and salt-like clusters on the other hand is described first. Subsequently, a different more chemical description of structure and bonding of a recently published gold-thiolate Au₁₀₂(SR)₄₄ cluster based on the results of aluminum-/gallium clusters is presented., This comparison shows that there is no principal but only a gradual difference between the Au₁₀₂ cluster and the large number of metalloid aluminum-/gallium clusters: both have a metalloid character, i.e. there is a highly mixed valent bonding situation of the metal atoms involved. Therefore these clusters represent a highly complex system and are far from being only nanoscaled metal particles surrounded by a shell of protecting ligands. In detail this comparison shows that the metalloid gold and the aluminum-/gallium clusters are similar in the center, as these metal-metal interactions are energetically similar to those of the metallic solid state. However, there are significant differences between metalloid gold and aluminum-/gallium clusters in the outer regions since the interactions of the metal atoms of the outer shell with the ligands are different: i.e. in contrast to strong Al-ligand interactions there are weaker Au-ligand bonds. Furthermore it will be shown that the special Au-ligand interactions of the Au₁₀₂ cluster, which have been discussed as a novel staple motif so far, might be better attributed to the well established structural chemistry of Au^I species. To sum up, structure and bonding of metalloid gold clusters, even if they have not been structurally characterized in detail, like the well-known Schmid cluster, show that they belong to the family of metalloid clusters like the large number of aluminum-/gallium ones; i.e. they have to be seen in a novel light. Consequently, these conclusions may have a large impact on the great variety of investigations of surface reactions between crystalline gold surfaces and sulfur-containing molecules.