A Metalloid Al(14) Cluster with the Structure of a "Nano-Wheel"

Enriching Structural Diversity of Alkynyl-Protected Gold Nanoclusters with Chlorides

The synthesis and isolation of alkynyl/chloride-protected gold nanoclusters is described. Silica gel column chromatography is effective in isolating gold nanoclusters from the as-synthesized cluster mixture to give the clusters Na[Au₂₅ L₁₈ ] (Au₂₅ ), [HNEt₃ ]₃ [Au₆₇ L₃₂ Cl₄ ] (Au₆₇ ), [HNEt₃ ]₄ [Au₁₀₆ L₄₀ Cl₁₂ ] (Au₁₀₆ ), L=3,5-bis(trifluoromethyl)-phenylacetylide. Au₆₇ and Au₁₀₆ are new clusters; the structures were determined by X-ray single-crystal diffraction. Au₆₇ contains a distorted Au₁₈ Marks decahedron shelled by an irregular Au₃₂ and further protected with two V-shaped Au₂ L₃ , 13 linear AuL₂ staples and 4 chlorides. Au₆₇ is the first structurally determined 34e superatomic gold nanocluster. Au₁₀₆ is composed of 106 Au atoms co-protected by alkynyls and chlorides. It has a Au₇₉ kernel, like in Au₁₀₂ (p-MBA)₄₄ . The surface structure of Au₁₀₆ includes 20 linear Au-alkynyl staples, 5 Cl-Au-Cl and 2 Cl-Au motifs. These three gold nanoclusters show size-dependent electrochemical properties.

Heteroatomic Deltahedral Clusters: Synthesis and Structures of closo-[Bi3Ni4(CO)6]3-, closo-[Bi4Ni4(CO)6]2-, the Open Cluster [Bi3Ni6(CO)9]3-, and the Intermetalloid closo-[Nix@{Bi6Ni6(CO)8}]4-

Reactions of ethylenediamine solutions of K4Bi5 with Ni(PPh3)2(CO)2 yielded four novel hetero-atomic Bi/Ni deltahedral clusters. Three of them, the 7-atom pentagonal bipyramidal [Bi3Ni4(CO)6]3-, the 8-atom dodecahedral [Bi4Ni4(CO)6]2-, and the Ni-centered or empty 12-atom icosahedral [Nix@[Bi6Ni6(CO)8]4-, are closo-species according to both electron count and shape. The centered icosahedral cluster resembles packing in intermetallic compounds and belongs to the emerging class of intermetalloid clusters. The shape of the fourth cluster, [Bi3Ni6(CO)9]3-, can be derived from the icosahedral Ni-centered [Ni@[Bi6Ni6(CO)8]4- by removal of three Bi- and one Ni-atoms of two neighboring triangular faces. The clusters were structurally characterized by single-crystal X-ray diffraction in compounds with potassium cations sequestered by 2,2,2-crypt or 18-crown-6 ether. They were also characterized in solution by electrospray mass spectrometry.

Structure and stability of the Al14 halides Al14In− (n=1–11): Can we regard the Al14 core as an alkaline earthlike superatom?

We have studied the structures and stabilities of Al(14)I(n) (-) (n=1-11) clusters at the density functional level of theory. The experimentally observed Al(14)I(n) (-) (n=3, 5, 7, 9, and 11) [Bergeron et al., Science 307, 231 (2005)] are found to be stable both kinetically and thermodynamically. Al(14)I(3) (-), not Al(14)I(-), is the first member of the Al(14)I(n) (-) series in the mass spectrometric experiment, which is ascribable to the low kinetic stability of the Al(14)I(-) cluster. The Al(14) core in Al(14)I(3) (-) is close to neutral Al(14), both electronically and structurally. Population analysis shows that charge transfer occurs from the Al cluster to the I atoms, where the populations for Al(14) vary from -0.70(Al(14)I(-)) to +0.96(Al(14)I(11) (-)). The Al(14)I(5) (-) and Al(14)I(7) (-) clusters have the structure of Al(14)I(3) (-) as a core framework, but, for n=9 and 11, we found many more stable isomers than the isomers having the Al(14)I(3) (-) core. In particular, the shape of Al(14) in the Al(14)I(11) (-) cluster is a hexagonal wheel-shaped form, which was observed in the x-ray experiment for the metalloid complex [Al(14){N(SiMe(3))(2)}(6)I(6)Li(OEt(2))(2)](-)[Li(OEt(2))(4)](+)toluene [Kohnlein et al., Angew. Chem., Int. Ed. 39, 799 (2000)]. We have demonstrated that a simple jellium model cannot describe the structure and stability of the iodine-doped aluminum clusters, although it is successful for describing those of aluminum clusters. The electronic and geometric changes of the Al(14) (-) cluster due to the presence of iodines are very similar to the case of a magic cluster Al(13) (-). It can be concluded from our electronic and structural analysis that one cannot regard the Al(14) core as an alkaline earthlike superatom in the Al(14) iodide clusters.

Al(22)Cl(20).12L (L = THF, THP): the first polyhedral aluminum chlorides

Aluminum subhalides of the type Al(22)X(20).12L (X = Cl, Br; L = THF, THP) are the only known representatives of polyhedral aluminum subhalides and exhibit interesting multicenter bonding properties. Herein, we report on the synthesis and structural investigation of the first chlorides of this type. Additional investigations applying solid-state (27)Al NMR (MAS), XPS (of Al(4)Cp(4) and Al(22)X(20).12L), and quantum chemical calculations shed more light upon the structure of the molecules and possible Al modifications.

[Ga18(SitBu3)8] and [Ga22(SitBu3)8]--syntheses and structural characterization of novel gallium cluster compounds

The novel neutral gallium cluster compounds [Ga18R*8] (1) and [Ga22R*8] (2) are obtained by warming up a metastable solution of gallium(I) bromide in THF/C6H5CH3 after addition of equimolar amounts of supersilyl sodium NaR* from -78 degrees C to room temperature (R* = SitBu3 = supersilyl). From X-ray structure analyses, the observed arrangements of the 18 and 22 Ga atoms in 1 and 2, respectively, are comparable with an 18 atom section of the beta-Ga modification, or show at least some kind of relationship to a 22 atom section of the Ga-III modification. This allows a description of both the clusters as metalloid. The topology of the atoms in 2 is also well explained by the Wade-Mingos rules as an eightfold capped closo-Ga14 cluster, whereby the Ga atoms of Ga14 occupy the center and the corners of a cuboctahedron with one Ga3 face replaced by a Ga4 face. Some concepts are presented about the formation mechanism, the cluster growth, and the metalloid character of the two Ga cluster compounds.