Metalloid gold clusters - past, current and future aspects.

Gold chemistry and the synthesis of colloidal gold have always caught the attention of scientists. While Faraday was investigating the physical properties of colloidal gold in 1857 without probably knowing anything about the exact structure of the molecules, 150 years later the working group of Kornberg synthesized the first structurally characterized multi-shell metalloid gold cluster with more than 100 Au atoms, Au(SR). After this ground-breaking result, many smaller and bigger metalloid gold clusters have been discovered to gain a better understanding of the formation process and the physical properties.

Au(EtP)Cl: a structurally related cluster to Au(EtP)Cl gives insight into the formation process.

The reaction of Et3PAuCl with NaBH4 in EtOH leads to the metalloid gold cluster Au32(Et3P)12Cl8 (Au32) or Au54(Et3P)18Cl12 (Au54) depending on the work-up procedure of the reaction mixture. The molecular structure of Au54 is determined by X-ray diffraction and can be described as a fusion of two Au32 clusters showing a similar solubility. The metalloid cluster Au54 can be either described by a shell model or as a combination of tetrahedral Au4X units (X = Cl, Et3P); edge and face sharing, whereas tetrahedral Au4 units are a central motif in gold cluster chemistry.

Synthesis and Characterization of Three Multi-Shell Metalloid Gold Clusters Au (R P) Cl.

Three multi-shell metalloid gold clusters of the composition Au (R P) Cl (R=Et, Pr, Bu) were synthesized in a straightforward fashion by reducing R PAuCl with NaBH in ethanol. The Au core comprises two shells, with the inner one constituting a tilted icosahedron and the outer one showing a distorted dodecahedral arrangement. The outer shell is completed by eight chloride atoms and twelve R P groups.

AuS(PPh): an intermediate sized metalloid gold cluster stabilized by the AuS ring motif and Au-PPh groups.

Reducing (PhP)AuSC(SiMe) with l-Selectride® gives the medium-sized metalloid gold cluster AuS(PPh). Computational studies show that the phosphine bound Au-atoms not only stabilize the electronic structure of AuS(PPh), but also behave as electron acceptors leading to auride-like gold atoms on the exterior.

Au S (PPh ) : A Highly Symmetric Nanoscale Gold Cluster Confirms the General Concept of Metalloid Clusters.

The reduction of (Ph P)AuCl with NaBH in the presence of HSC(SiMe ) , leads to one of the largest metalloid gold clusters: Au S (PPh ) (1). Within 1 an octahedral Au core of gold atoms arranged as in Au metal is surrounded by 48 oxidized Au atoms of an Au S shell, a novel building block in gold chemistry. The protecting Au S shell is completed by additional 16 Au(PPh ) units, leading to a complete protection of the gold core.