New Transition Metal Clusters with Ligands from Main Groups Five and Six

Abstract

Dedicated to Professor Hans Bock on the occasion of his 60th birthdayIn both physics and chemistry, increased attention is being paid to metal clusters. One reason for this attitude is furnished by the surprising results that have been obtained from studies of the preparation, structural characterization and physical and chemical properties of the clusters. Whereas investigations of cluster reactivity are at present generally limited to three-or four-membered clusters, successful syntheses of clusters with many more metal atoms have recently been designed. These substances occupy an intermediate position between solid state chemistry and the chemistry of metal complexes. This review presents a versatile method for synthesizing metal clusters: the reaction of complexes of transition metal halides with silylated compounds such as E(SiMe,)' (E = S, Se, Te) and E'R(SiMe3)2 (R = Ph, Me, Et; E' = P, As, Sb). Although some of the compounds thus formed have already been prepared by other routes, the method affords ready access to both small and large transition metal clusters with unusual structures and valence electron concentrations: a variety of reactions in the ligand sphere are also possible.

Large Semiconductor Molecules

“…The reaction between the nickel(II) source and the silylated selenium reagent invariably results in a distribution of products formed, however these provide mechanistic insight into the manner in which the columnar cluster forms. These products include triangular [Ni 3 Se 2 X 2 (PR 3 ) 4 ] (X ¼ Cl, SeSiMe 3 ), which can be viewed as the building blocks leading to the higher nuclearity complex 5 [26]. Recent theoretical work suggests that continued condensation of such Ni 3 units to yield clusters [Ni 3n Se 3n (PR 3 ) 6 ] (n ¼ 6-9) should be accessible [27], consistent with the previous experimental observations [26].…”

“…The synthesis and structural characterization of the spherical nanocluster [Ni 34 Se 22 (PPh 3 ) 10 ] 6 ( Figure 13.5) illustrates clearly that nanometer-sized pieces of the binary material can be accessed [28]. Cluster 6 is formed from the reaction of NiCl 2 (PPh 3 ) 2 and Se(SiMe 3 ) 2 .…”

“…The former are each cluster is bound covalently to its neighbours via sharing of a thiolate ligand at the corners of the tetrahedra, resulting in an extended network [72]. The intercluster thiolate bridges are displaced with strong donor solvents, allowing a comparison of the spectral features of molecular ''Cd 17 S 4 (SCH 2 CH 2 OH) 26 '' and the solid network. Although very similar, the UV spectrum of the solid is slightly redshifted relative to that observed for the individual molecules in solution.…”

“…Both solid-state and solution absorption spectra of [Cd 17 S 4 (SCH 2 CH 2 OH) 26 ] display a sharp, discrete maximum (@4.3 eV) that is markedly blue-shifted from the absorption onset of bulk CdS (2.4 eV); this is assigned to the excitonic transition. This transition is observed in the absorption spectra of XII-XVI colloids and clusters as a sharp absorption near the absorption edge, the energy of which is a measure of the size of the ''band gap'' of the nanoparticles [74].…”

Single-particle selection and alignment with heavy atom cluster-antibody conjugates

“…The ideal heavy atom cluster would be the smallest clearly visible particle, and several candidates exist, including Au 39 (19), Au͞Ag alloys of 25, 37, and 38 heavy atoms (20), W 30 (21), Ni 34 (22), Ni 38 (23), and Pd 38 (24). The minimal visible cluster has not been determined, but Undecagold, which contains 11 gold atoms in an approximately spherical volume 8 Å in diameter, is not seen in individual images at low dose, and it can be located only by averaging many particles, for example over a two-dimensional array (25).…”