From Icosahedral Boron Subhalides to Octahedral Metalloid Aluminum and Gallium Analogues: Quo vadis, Wade's Rules?

Abstract

The synthesis and characterization of polyhedral boron hydrides [1] and boron subhalides, [2] originally regarded as curios, at a second glance have proved to be a lucky chance for progress in chemistry, as on this basis new concepts of chemical bonding were developed, e. g. the Wade-Mingos rules. [3][4][5][6][7] Two milestones in aluminum-organic chemistry with a polyhedral {Al n }-lattice are [Al 12 R 12 ] 2À (1 2À ) [8] and [Al 4 Cp* 4 ] (2; Cp* = C 5 Me 5 ) [9][10][11] (Figure 1). The polyhedral closo-cluster 1 2À is an exception compared to the common low-valent aluminum and gallium clusters which tend to be so-called metalloid clusters.[12] These are clusters mainly characterized by the fact that the topology of the "naked", that is, non-ligand bearing cluster atoms in the cluster core, in many cases reflects the topology of the atoms found in metals and elements, respectively. [13][14][15] Prior to presenting the results of quantum chemical calculations for some [M 12 X 12 ] and [M 13 X 12 ] (M = B, Al, Ga; X = halide) model compounds, we describe our most recent experimental findings which prompted us to start these investigations: [16] Mass spectrometric examinations of the structurally known metalloid-cluster anion [Ga 13 (GaR À (3 À ). [16][17][18] This anion formed during the stepwise reaction of chlorine in the gas phase and as a result of the cleavage of six GaCl moieties [Eq (1)]. The isomer 3 À , when generated from density functional theory (DFT) calculations is, with its octahedral {Ga 6 } core, 30 kJ mol À1 more stable than the icosahedral molecule with a {Ga 12 } core and 12 terminally bound ligands that would be expected according to Wades rules. Based on these surprising results [16, 19] we have performed DFT calculations to elaborate some fundamental differences between typical Wade clusters in boron chemistry and metalloid clusters in aluminum and gallium chemistry.We have examined neutral and dianionic compounds of the structure [M 12 Cl 12 ] 0,2À (M = B, Al, Ga) to determine which of the two structural patterns (icosahedral M 12 -units or clusters with an M 6 -core) is energetically favored for the particular element. For each species we calculated the isomer with an icosahedral structure and terminally bound ligands (ico) and the isomer with an octahedral core of "naked" metal atoms (hence the term "metalloid" (m)). For the metalloid clusters (m), a protecting shell results consisting of doubly oxidized MX 2 units; the bridging (M-X-M) unit contributes to the stabilization of the cluster. The energetic relations between all isomers are shown in Figure 2. Selected structural parameters of [B 12 Cl 12 ] (4), [B 12 The energy diagram (Figure 2) depicts the differences between boron-, aluminum-, and gallium clusters: The icosahedral species 4 (ico) and 4 2À (ico) are energetically favored by 600 kJ mol À1 and 918 kJ mol À1 , respectively, over the metalloid isomers 4 (m) and 4 2À (m). On the other hand, the neutral metalloid Al and Ga clusters 5 (m) and 6 (m) are,

Super‐atom properties of 13 atom clusters of group 13 elements

“…2. supports the work of Koch et al 21 that small environmental changes may tip the ground state structure between these symmetries. Several general features emerge from our calculations.…”

“…It is clear therefore that the energy differences between the different symmetries are small compared with the effect of the environment. Koch et al 21 have shown that 13 atom clusters are not necessarily the most stable configuration for Al but in some environments it is more appropriate to consider clusters a six atom core surrounded by M X n moieties.…”

Segregation of tetracarbon units in low‐energy tetracarbindane structures: Major differences from their aluminum and gallium analogs

“…Tetracarbindanes, indium clusters, density functional theory, metal-metal bonding 1 | INTRODUCTION Addition of organometallic hydride derivatives of the Group 13 metals aluminum [1][2][3][4] and gallium to the C C triple bonds in alkynes has provided a route to novel metal-carbon clusters including n-vertex clusters with central C 4 M n−4 (M = Al, Ga) units. For aluminum, these clusters include 11-vertex tetracarbalane tetracarbagallanes such as (AlMe) 7 (CEt) 4 (μ-H) 2 and (AlEt) 7 (CCH 2 Ph) 4 (C CPh)(μ-H) based on an 11-vertex central C 4 Al 7 polyhedron with no C C edges (Figure 1).…”

Hauptgruppenmetallcluster stabilisiert durch N‐heterocyclische Carbene

“…[18] Quantenchemische Methoden helfen beim Versuch, die Bindungsverhältnisse in solchen Clustern zu verstehen und systematische Zusammenhänge aufzudecken. [11,[13][14][15][16][17][18][19][20] Beispielsweise erklärt sich die Stabilität des [Ga 8 R 8 ] 2À -Clusters 4 durch eine Orbitalabfolge analog der im closo-Cluster B 8 H 8 2À . [14] Viele Galliumcluster haben jedoch eine von den Polyboranen abweichende elektronische Struktur.…”

“…[14] Viele Galliumcluster haben jedoch eine von den Polyboranen abweichende elektronische Struktur. [18][19][20] In diesen Fällen muss die Einordnung in das Wade-MingosKonzept scheitern, und eine intuitive Vorhersage von Strukturmotiven wird irreführend. Ein wesentlicher Faktor bei der Stabilisierung polyedrischer Cluster ist ihre sphärische Aromatizität, die sich durch die Berechnung von "Nucleus-Independent Chemical Shifts" (NICS) quantifizieren lässt.…”