Metalloid Aluminum and Gallium Clusters: Element Modifications on the Molecular Scale?

Abstract

As members of the same group in the periodic table, the industrially significant elements aluminum and gallium exhibit strong similarities in the majority of their compounds. In contrast there are significant differences in the structures of the two elemental forms: Aluminum forms a typical closest-packed metallic structure whereas gallium demonstrates a diversity of molecular bonding principles in its seven structural modifications. It can therefore be expected that differences between Al and Ga compounds will arise when, as for the elemental forms, many metal-metal bonds are formed. To synthesize such cluster compounds, we have developed the following synthesis procedure: Starting from gaseous monohalides at around 1000 degrees C, metastable solutions are generated from which the elements ultimately precipitate by means of a disproportionation reaction at room temperature. On the way to the elemental forms, molecular Al and Ga cluster compounds can be obtained by selection of suitable ligands (protecting groups), in which a core of Al or Ga atoms are protected from the formation of the solid element by a ligand shell. Since the arrangement of atoms in such clusters corresponds to that in the elements, we have designated these clusters as metalloid or elementoid. In accordance with the Greek word [see text] (ideal, prototype), the atomic arrangement in metalloid clusters represents the prototypic or ideal atomic arrangement in the elements at the molecular level. The largest clusters of this type contain 77 Al or 84 Ga atoms and have diameters of up to two nanometers. They hold the world record with respect to the naked metal-atom core for structurally characterized metalloid clusters.

Structure, Thermodynamics, and Energy Content of Aluminum–Cyclopentadienyl Clusters

“…In our work we observe significant relaxation of the ligands in the Al 50 Cp 12 complex, and it is possible that this is the origin of our disagreement with the previous report, which gives no information on the calculated structure or thermodynamics of Al 50 Cp 12 . As a check, we have also calculated enthalpies of formation using BP86 with an SVP basis set, similar to the methodology used in previous work.…”

“…The structure of our energy diagram is mirrored after that proposed by Huber et 12 (g) + AlCp 3 (g). In contrast with previous work, the Al 50 structures are "barrier" states in both the methylated and unmethylated systems, though we do find that this barrier is lower for the Cp clusters than in the Cp*.…”

Structure, Thermodynamics, and Energy Content of Aluminum–Cyclopentadienyl Clusters

“…In our work we observe significant relaxation of the ligands in the Al 50 Cp 12 complex, and it is possible that this is the origin of our disagreement with the previous report, which gives no information on the calculated structure or thermodynamics of Al 50 Cp 12 . As a check, we have also calculated enthalpies of formation using BP86 with an SVP basis set, similar to the methodology used in previous work.…”

“…The structure of our energy diagram is mirrored after that proposed by Huber et 12 (g) + AlCp 3 (g). In contrast with previous work, the Al 50 structures are "barrier" states in both the methylated and unmethylated systems, though we do find that this barrier is lower for the Cp clusters than in the Cp*.…”

Ga8Br8·6NEt3: Formation and Structure of Donor-Stabilized GaBr. A Nanoscaled Step on the Way to β-Gallium?

“…These thermodynamical conclusions are directly correlated to the topology of Ga atoms of 1 and 2 . Because the arrangement of the Ga-atoms in 1 is very similar to that of the low-temperature modifications of β-gallium (−16.3 °C) (cf., Figure a,b), it seems, in accordance with many of our former investigations, to be a plausible hypothesis to correlate the structure of 1 as an arrangement of gallium atoms in the direction of the formation of β-Gallium. , Because γ-gallium is formed at lower temperatures (−35.6 °C) (cf., Figure c,d), the above-mentioned hypothesis can be expanded: 2 may represent a preorientated structure of γ-gallium . This extended hypothesis is in line with the conditions under which 1 and 2 , respectively, β- and γ-gallium, are formed at different temperatures: 1 is formed at −25 °C analogous to β-Ga (<−16.3 °C), and 2 is formed at −78 °C analogous to γ-Ga (<−35 °C).…”

Correspondence: Reply to ‘On the bonding in ligand-protected gold clusters’

“…As such, one may view the ligand-protected gold clusters as the trapped intermediates on the path toward the bulk phase, but being stabilized by the ligands bounded to the surface metal atoms. A similar view has been reported previously for Al and Ga clusters 9 .…”

Structure, Thermodynamics, and Energy Content of Aluminum–Cyclopentadienyl Clusters

“…In our work we observe significant relaxation of the ligands in the Al 50 Cp 12 complex, and it is possible that this is the origin of our disagreement with the previous report, which gives no information on the calculated structure or thermodynamics of Al 50 Cp 12 . As a check, we have also calculated enthalpies of formation using BP86 with an SVP basis set, similar to the methodology used in previous work.…”

“…The structure of our energy diagram is mirrored after that proposed by Huber et 12 (g) + AlCp 3 (g). In contrast with previous work, the Al 50 structures are "barrier" states in both the methylated and unmethylated systems, though we do find that this barrier is lower for the Cp clusters than in the Cp*.…”

Ga8Br8·6NEt3: Formation and Structure of Donor-Stabilized GaBr. A Nanoscaled Step on the Way to β-Gallium?

“…These thermodynamical conclusions are directly correlated to the topology of Ga atoms of 1 and 2 . Because the arrangement of the Ga-atoms in 1 is very similar to that of the low-temperature modifications of β-gallium (−16.3 °C) (cf., Figure a,b), it seems, in accordance with many of our former investigations, to be a plausible hypothesis to correlate the structure of 1 as an arrangement of gallium atoms in the direction of the formation of β-Gallium. , Because γ-gallium is formed at lower temperatures (−35.6 °C) (cf., Figure c,d), the above-mentioned hypothesis can be expanded: 2 may represent a preorientated structure of γ-gallium . This extended hypothesis is in line with the conditions under which 1 and 2 , respectively, β- and γ-gallium, are formed at different temperatures: 1 is formed at −25 °C analogous to β-Ga (<−16.3 °C), and 2 is formed at −78 °C analogous to γ-Ga (<−35 °C).…”

Correspondence: Reply to ‘On the bonding in ligand-protected gold clusters’

“…As such, one may view the ligand-protected gold clusters as the trapped intermediates on the path toward the bulk phase, but being stabilized by the ligands bounded to the surface metal atoms. A similar view has been reported previously for Al and Ga clusters 9 .…”

Structure, Thermodynamics, and Energy Content of Aluminum–Cyclopentadienyl Clusters

“…In our work we observe significant relaxation of the ligands in the Al 50 Cp 12 complex, and it is possible that this is the origin of our disagreement with the previous report, which gives no information on the calculated structure or thermodynamics of Al 50 Cp 12 . As a check, we have also calculated enthalpies of formation using BP86 with an SVP basis set, similar to the methodology used in previous work.…”

“…The structure of our energy diagram is mirrored after that proposed by Huber et 12 (g) + AlCp 3 (g). In contrast with previous work, the Al 50 structures are "barrier" states in both the methylated and unmethylated systems, though we do find that this barrier is lower for the Cp clusters than in the Cp*.…”

Ga8Br8·6NEt3: Formation and Structure of Donor-Stabilized GaBr. A Nanoscaled Step on the Way to β-Gallium?

“…These thermodynamical conclusions are directly correlated to the topology of Ga atoms of 1 and 2 . Because the arrangement of the Ga-atoms in 1 is very similar to that of the low-temperature modifications of β-gallium (−16.3 °C) (cf., Figure a,b), it seems, in accordance with many of our former investigations, to be a plausible hypothesis to correlate the structure of 1 as an arrangement of gallium atoms in the direction of the formation of β-Gallium. , Because γ-gallium is formed at lower temperatures (−35.6 °C) (cf., Figure c,d), the above-mentioned hypothesis can be expanded: 2 may represent a preorientated structure of γ-gallium . This extended hypothesis is in line with the conditions under which 1 and 2 , respectively, β- and γ-gallium, are formed at different temperatures: 1 is formed at −25 °C analogous to β-Ga (<−16.3 °C), and 2 is formed at −78 °C analogous to γ-Ga (<−35 °C).…”

Correspondence: Reply to ‘On the bonding in ligand-protected gold clusters’

“…As such, one may view the ligand-protected gold clusters as the trapped intermediates on the path toward the bulk phase, but being stabilized by the ligands bounded to the surface metal atoms. A similar view has been reported previously for Al and Ga clusters 9 .…”