Crabtree R.H.,Energy science Institute
Chemical Society Reviews | Year: 2017
In hypervalent bonding (HVB), secondary bonding (SB) and hydrogen bonding (HB) a nucleophilic and an electrophilic partner form a new bond that is based on a similar bonding pattern across the whole series of interactions. The electrostatic contribution is reflected in the 'σ hole' model in which a positive patch on E attracts the nucleophilic component. The nucleophile, Y, possesses a corresponding negative patch, resulting in a linear structure Y⋯E-X having one strong E-X bond and one weaker, longer Y⋯E interaction; this is considered as a SB interaction between Y and E. The covalent component, more important in the stronger interactions, HVB and strong HB, involves charge transfer between the lone pair (n) of Y, and the σ∗ orbital of E-X as emphasized in the 'n→σ∗' bonding model. For example, charge transfer from I- to I2 gives rise to the linear, symmetrical [I-I-I]- anion. We now have two short (2.95 Å) bonds of equal strength corresponding to true HVB. In HB the central element, E, is H, and we can have strong or weak hydrogen bonding. On the HVB/HB analogy, a strong symmetrical HB, as in [F-H-F]-, can be considered as containing hypervalent hydrogen. In the weak HB case, we have a lesser degree of interaction, leading to normal hydrogen bonds of type Y⋯H-X analogous to secondary bonding. Within both the HB and HVB series, strong and weak types form a smooth continuum with no sharp break in properties. HVB was once considered to involve the expansion of the octet to 10, 12 or even higher valence electron counts. Whether the σ hole or n→σ∗ model applies, any octet expansion is now seen as largely formal, however, because the central element essentially retains its eight valence electrons. Thus a range of interactions can be placed in one big tent, related by a combination of σ hole and n→σ∗ bonding contributions with retention of the octet by the central element, E. © 2017 The Royal Society of Chemistry.
Sohn S.,Yale University |
Jung Y.,Yale University |
Jung Y.,Energy science Institute |
Jung Y.,National Center for Nanosciences and Technology of China |
And 6 more authors.
Nature Communications | Year: 2015
Atomistic understanding of crystallization in solids is incomplete due to the lack of appropriate materials and direct experimental tools. Metallic glasses possess simple metallic bonds and slow crystallization kinetics, making them suitable to study crystallization. Here, we investigate crystallization of metallic glass-forming liquids by in-situ heating metallic glass nanorods inside a transmission electron microscope. We unveil that the crystallization kinetics is affected by the nanorod diameter. With decreasing diameters, crystallization temperature decreases initially, exhibiting a minimum at a certain diameter, and then rapidly increases below that. This unusual crystallization kinetics is a consequence of multiple competing factors: increase in apparent viscosity, reduced nucleation probability and enhanced heterogeneous nucleation. The first two are verified by slowed grain growth and scatter in crystallization temperature with decreasing diameters. Our findings provide insight into relevant length scales in crystallization of supercooled metallic glasses, thus offering accurate processing conditions for predictable metallic glass nanomolding © 2015 Macmillan Publishers Limited.
Jung Y.,University of Central Florida |
Zhou Y.,Yale University |
Zhou Y.,Energy science Institute |
Cha J.J.,Yale University |
Cha J.J.,Energy science Institute
Inorganic Chemistry Frontiers | Year: 2016
Intercalation is a reversible insertion process of foreign species into crystal gaps. Layered materials are good host materials for various intercalant species ranging from small ions to atoms to molecules. Given the recent intense interest in two-dimensional (2D) layered materials in thin limits, this review highlights the opportunities that intercalation chemistry can provide for nanoscale layered materials. Novel heterostructures or emergent electrical properties not found in the intrinsic host materials are possible with intercalation. In particular, we review various exfoliation methods developed for 2D layered nanomaterials based on intercalation chemistry and extensive tuning of the electrical, optical, and magnetic properties of 2D layered materials due to intercalation. © the Partner Organisations 2016.
Crabtree R.H.,Energy science Institute
Journal of Organometallic Chemistry | Year: 2014
Organometallic precatalysts are increasingly applied to oxidation catalysis, where the spectator character of such ligands as Cp and Cp* is often assumed without definite proof. A number of reports of ligand lability under oxidative conditions have now appeared in the literature, raising concerns in reactions where primary oxidants are present. In such a case, partial or complete degradative loss of the organometallic ligand from the metal may need to be considered. This loss can sometimes deactivate a catalyst but it may also activate it by opening up labile sites at the metal. The highest risk applies to oxidation of the least reactive substrates, such as alkanes, since the catalyst may then also oxidize the CH bonds of its own ligands. More reactive substrates such as alkenes are likely to provide greater stabilization to the catalysts by providing a pathway for faster reaction of the substrate with the oxidized form of the catalyst.We therefore look at these and some related reactions to probe organometallic ligand loss under oxidative conditions, a topic that has received too little attention considering its important implications. Ligand loss can also affect applications to asymmetric catalysis and heterogenized homogeneous catalysts where the organometallic ligand is functionalized with a homochiral substituent or a tether to a surface. Ligands covered include CO, alkyls, aryls, alkenes, arenes, NHCs, cyclopentadienyls and other soft ligands. © 2013 Elsevier B.V. All rights reserved.
Shen J.,Yale University |
Shen J.,Energy science Institute |
Xie Y.,Yale University |
Xie Y.,Energy science Institute |
And 2 more authors.
Nano Letters | Year: 2015
(Graph Presented). Indium (In) doping in topological crystalline insulator SnTe induces superconductivity, making In-doped SnTe a candidate for a topological superconductor. SnTe nanostructures offer well-defined nanoscale morphology and high surface-to-volume ratios to enhance surface effects. Here, we study In-doped SnTe nanoplates, InxSn1-xTe, with x ranging from 0 to 0.1 and show they superconduct. More importantly, we show that In doping reduces the bulk mobility of InxSn1-xTe such that the surface states are revealed in magnetotransport despite the high bulk carrier density. This is manifested by two-dimensional linear magnetoresistance in high magnetic fields, which is independent of temperature up to 10 K. Aging experiments show that the linear magnetoresistance is sensitive to ambient conditions, further confirming its surface origin. We also show that the weak antilocalization observed in InxSn1-xTe nanoplates is a bulk effect. Thus, we show that nanostructures and reducing the bulk mobility are effective strategies to reveal the surface states and test for topological superconductors. © 2015 American Chemical Society.