Special Issue "Metal and Molecular Clusters"

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A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (30 June 2014)

Special Issue Editor

Guest Editor
Prof. Dr. M. Samy El-Shall (Website)

Department of Chemistry, Virginia Commonwealth University, Richmond, VA 23284-2006, USA
Phone: 804-828-3518
Fax: +1 804 828 1280
Interests: molecular clusters; gas phase and cluster polymerization; nucleation phenomena and nanostructured materials

Special Issue Information

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed Open Access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 800 CHF (Swiss Francs).

Keywords

  • molecular clusters
  • molecular beam techniques
  • bound
  • mass spectrometry
  • size-dependent spectroscopic lineshifts

Published Papers (2 papers)

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Review

Open AccessReview Catalytic Reactions over Halide Cluster Complexes of Group 5–7 Metals
Metals 2014, 4(2), 235-313; doi:10.3390/met4020235
Received: 9 January 2014 / Revised: 1 June 2014 / Accepted: 4 June 2014 / Published: 23 June 2014
Cited by 4 | PDF Full-text (2653 KB) | HTML Full-text | XML Full-text
Abstract
Halide clusters of Group 5–7 metals develop catalytic activity above 150–250 °C, and the activity is retained up to 350–450 °C by taking advantage of their thermal stability, low vapor pressure, and high melting point. Two types of active site function: the [...] Read more.
Halide clusters of Group 5–7 metals develop catalytic activity above 150–250 °C, and the activity is retained up to 350–450 °C by taking advantage of their thermal stability, low vapor pressure, and high melting point. Two types of active site function: the solid Brønsted acid site and a coordinatively unsaturated site that catalyzes like the platinum metals do. Various types of catalytic reactions including new reactions and concerted catalyses have been observed over the clusters: hydrogenation, dehydrogenation, hydrogenolysis, isomerization of alkene and alkyne, and alkylation of toluene, amine, phenol, and thiol. Ring-closure reactions to afford quinoline, benzofuran, indene, and heterocyclic common rings are also catalyzed. Beckmann rearrangement, S-acylation of thiol, and dehydrohalogenation are also catalyzed. Although the majority of the reactions proceed over conventional catalysts, closer inspection shows some conspicuous features, particularly in terms of selectivity. Halide cluster catalysts are characterized by some aspects: cluster counter anion is too large to abstract counter cation from the protonated reactants, cluster catalyst is not poisoned by halogen and sulfur atoms. Among others, cluster catalysts are stable at high temperatures up to 350–450 °C. At high temperatures, apparent activation energy decreases, and hence weak acid can be a catalyst without decomposing reactants. Full article
(This article belongs to the Special Issue Metal and Molecular Clusters)
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Open AccessReview Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes
Metals 2014, 4(2), 84-107; doi:10.3390/met4020084
Received: 9 January 2014 / Revised: 4 March 2014 / Accepted: 19 March 2014 / Published: 1 April 2014
Cited by 8 | PDF Full-text (1621 KB) | HTML Full-text | XML Full-text
Abstract
Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore [...] Read more.
Halide clusters have not been used as catalysts. Hexanuclear molecular halide clusters of niobium, tantalum, molybdenum, and tungsten possessing an octahedral metal framework are chosen as catalyst precursors. The prepared clusters have no metal–metal multiple bonds or coordinatively unsaturated sites and therefore required activation. In a hydrogen or helium stream, the clusters are treated at increasingly higher temperatures. Above 150–250 °C, catalytically active sites develop, and the cluster framework is retained up to 350–450 °C. One of the active sites is a Brønsted acid resulting from a hydroxo ligand that is produced by the elimination of hydrogen halide from the halogen and aqua ligands. The other active site is a coordinatively unsaturated metal, which can be isoelectronic with the platinum group metals by taking two or more electrons from the halogen ligands. In the case of the rhenium chloride cluster Re3Cl9, the cluster framework is stable at least up to 300 °C under inert atmosphere; however, it is reduced to metallic rhenium at 250–300 °C under hydrogen. The activated clusters are characterized by X-ray diffraction analyses, Raman spectrometry, extended X-ray absorption fine structure analysis, thermogravimetry–differential thermal analysis, infrared spectrometry, acid titration with Hammett indicators, and elemental analyses. Full article
(This article belongs to the Special Issue Metal and Molecular Clusters)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Type of Paper: Review
Title: Cluster-Assembled Structure and Deformation in Metallic Glass
Authors: W. D. Liu and L. C. Zhang *
Affiliation: School of Mechanical and Manufacturing Engineering, University of New South Wales, NSW 2052 Australia; E-Mail: Liangchi.Zhang@unsw.edu.au
Abstract: Metallic glass (MG) is a newcomer of the metal family, which has a disordered structure and many outstanding properties such as ultrahigh strength, super elasticity, and excellent thermo-plasticity. However, due to the lack of translational periodicity, its cluster-assembled structure and deformation-induced collective atomic rearrangement (dynamic cluster) are long-standing mysteries without sufficient fundamental understanding. In this paper, the authors will review what have been done in the past few decades and aim to unravel the atomic-level structure of MGs and the underlying plastic deformation mechanism. The focus will be on (1) the formation of the cluster-assembled structure through glass transition, (2) structural characterization and theoretical models, (3) plastic event identification and micromechanics, and (4) the correlation between cluster-assembled structure and unique mechanical properties. A number of key questions and outlook in this research area will also be outlined.

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