Synthesis and structure of metalloid aluminum clusters—intermediates on the way to the elements

Schnöckel, Hansgeorg; Köhnlein, Harald

doi:10.1016/s0277-5387(01)01028-2

Cited by 49 publications

(25 citation statements)

References 58 publications

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“…We primarily considered four isolated AlCp clusters: Al 4 Cp of which (save the unmethylated Al 50 compound) have been directly observed experimentally. [13][14][15] We find that the initial steps in the reaction are similar in all cases: oxygen diffuses through the protective ligand barrier, comes into close proximity with the aluminum core, and splits into atomic oxygen on its surface. The oxygen quickly orients itself in a motif reminiscent of small alumina clusters.…”

Section: Introductionmentioning

confidence: 80%

“…These systems, first synthesized by Schnöckel and co-workers, [10][11][12][13][14][15][16] form in a gas-phase disproportionation reaction starting from monovalent aluminum precursor compounds. The structure of the metallic core is generally dissimilar from that of the gas-phase pure metal cluster or bulk aluminum, though recent work has suggested that a modified superatom model might be used to treat its electronic structure.…”

Section: Introductionmentioning

confidence: 99%

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Oxidation of ligand-protected aluminum clusters: An ab initio molecular dynamics study

Alnemrat

Hooper

2014

The Journal of Chemical Physics

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Oxidation of ligand-protected aluminum clusters: an ab-initio molecular dynamics study. "J. Chem. Phys. 140, 104313 (2014 We report Car-Parrinello molecular dynamics simulations of the oxidation of ligand-protected aluminum clusters that form a prototypical cluster-assembled material. These clusters contain a small aluminum core surrounded by a monolayer of organic ligand. The aromatic cyclopentadienyl ligands form a strong bond with surface Al atoms, giving rise to an organometallic cluster that crystallizes into a low-symmetry solid and is briefly stable in air before oxidizing. Our calculations of isolated aluminum/cyclopentadienyl clusters reacting with oxygen show minimal reaction between the ligand and O 2 molecules at simulation temperatures of 500 and 1000 K. In all cases, the reaction pathway involves O 2 diffusing through the ligand barrier, splitting into atomic oxygen upon contact with the aluminum, and forming an oxide cluster with aluminum/ligand bonds still largely intact. Loss of individual aluminum-ligand units, as expected from unimolecular decomposition calculations, is not observed except following significant oxidation. These calculations highlight the role of the ligand in providing a steric barrier against oxidizers and in maintaining the large aluminum surface area of the solid-state cluster material. [http://dx

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Section: Introductionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Oxidation of ligand-protected aluminum clusters: An ab initio molecular dynamics study

Alnemrat

Hooper

2014

The Journal of Chemical Physics

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“…[1,2] Recently, Schnöckel and coworkers have developed a new class of group 13 metalloid systems. [3,4,5,6,7] All these systems are synthesized from monovalent aluminum halide precursors Al-(Cl, Br, or I). The metal core of these clusters range from as small as 4 metal atoms such as (Al 4 Cp * 4 ) up to large Al content such as (Al 7 7[N(SiMe 3 )] 2 ).…”

Section: Introductionmentioning

confidence: 99%

The role of reducing agents in the nucleation and growth of Al metalloid clusters: Ab initio molecular dynamics study

Alnemrat

Hooper

2018

AIP Conference Proceedings

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Abstract. Ab initio simulations are used to study the growth of metalloid aluminum clusters from their monohalide (AlCl) precursors. Larger metalloid clusters have recently been considered as a novel energetic material with fast metal oxidation kinetics, but the growth of these systems in solution is not understood. Molecular dynamics (MD) simulations are used to study the role of lithium-aluminum hydride (LiAlH 4 , LAH) and sodium borohydride (NaBH 4 , NaB) reducing agents in the nucleation and growth of these clusters. MD simulations of AlCl liquid with LAH show spontaneous metalloid cluster nucleation by rapid formation of Al-Al bonds. The growth process is initiated by Li detachment from LAH followed by hydrogen transfer from the hydride to a nearby Al. This process aids in the formation of trivalent impurities (AlH 3 ) in the solution. Growth towards larger metalloid clusters then proceeds via repeated insertion of AlCl into Al-Cl bonds. The transferred hydrogen plays a significant role in reducing monohalide species from the liquid. The energy barrier associated with the Al-Cl bond is dropped from 7.8 eV to ≈ 4.0 eV as a consequence of this transfer between Al centers. However, this process is hindered in the case of NaB due to strong ionic bonding between Na and B centers, and consequently no cluster growth is observed.

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“…All these systems are synthesized from AlX (X=Cl, Br, or I) monovalent aluminum halide precursors formed in a specialized cocondensation apparatus. [14,15,16,17,18] 12 . These clusters crystallize into low-symmetry molecular crystals that are very airsensitive; in this report we focus on isolated clusters for comparison with recent gas-phase cluster studies in ultra-high vacuum.…”

Section: Introductionmentioning

confidence: 99%

Modeling the stability and growth of metalloid clusters for energetic materials

Alnemrat¹,

Hooper²

2017

AIP Conference Proceedings

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Abstract. Metalloid clusters, defined as cluster systems with more metal/metal than metal/organic bonds, are currently under study as energetic materials that may retain the high energy density of bulk metals but offer substantially faster reaction kinetics. Considerable synthesis challenges remain, but these systems may in principle allow low-valence metals to oxidize within the reaction zone of a detonation. Here we present density functional theory and ab initio molecular dynamics simulations of ligated aluminum clusters, a prototypical metalloid system that can be reliably synthesized. Thermal decomposition and oxidation pathways are explored to gain a general understanding of how these unusual systems behave at elevated temperatures. The initial stages of cluster oxidation observed in molecular dynamics and metadynamics simulations are in good agreement with recent experimental gas-phase oxidation studies.

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Synthesis and structure of metalloid aluminum clusters—intermediates on the way to the elements

Cited by 49 publications

References 58 publications

Oxidation of ligand-protected aluminum clusters: An ab initio molecular dynamics study

Oxidation of ligand-protected aluminum clusters: An ab initio molecular dynamics study

The role of reducing agents in the nucleation and growth of Al metalloid clusters: Ab initio molecular dynamics study

Modeling the stability and growth of metalloid clusters for energetic materials

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