20 research outputs found
A nucleophilic beryllyl complex via metathesis at [BeâBe] 2+
Owing to its high toxicity, the chemistry of element number four, beryllium, is poorly understood. However, as the lightest elements provide the basis for fundamental models of chemical bonding, there is a need for greater insight into the properties of beryllium. In this context, the chemistry of the homo-elemental BeâBe bond is of fundamental interest. Here the ligand metathesis chemistry of diberyllocene (1; CpBeBeCp)âa stable complex with a BeâBe bondâhas been investigated. These studies yield two complexes with BeâBe bonds: Cp*BeBeCp (2) and [K{(HCDippN)2BO}2]BeBeCp (3; Dipp = 2,6-diisopropylphenyl). Quantum chemical calculations indicate that the BeâBe bond in 3 is polarized to such an extent that the complex could be formulated as a mixed-oxidation state Be0/BeII complex. Correspondingly, it is demonstrated that 3 can transfer the âberyllylâ anion, [BeCp]â, to an organic substrate, by analogy with the reactivity of sp2âsp3 diboranes. Indeed, this work reveals striking similarities between the homo-elemental bonding linkages of beryllium and boron, despite the respective metallic and non-metallic natures of these elements
Diberyllocene, a stable compound of Be(I) with a Be-Be bond
The complex diberyllocene, CpBeBeCp (Cp, cyclopentadienyl anion), has been the subject of numerous chemical investigations over the past five decades yet has eluded experimental characterization. We report the preparation and isolation of the compound by the reduction of beryllocene (BeCp2) with a dimeric magnesium(I) complex and determination of its structure in the solid state by means of x-ray crystallography. Diberyllocene acts as a reductant in reactions that form beryllium-aluminum and beryllium-zinc bonds. Quantum chemical calculations indicate parallels between the electronic structure of diberyllocene and the simple homodiatomic species diberyllium (Be2)
Correlation-Polarization Effects in Electron/Positron Scattering from Acetylene: A Comparison of Computational Models
Different computational methods are employed to evaluate elastic
(rotationally summed) integral and differential cross sections for low energy
(below about 10 eV) positron scattering off gas-phase CH molecules. The
computations are carried out at the static and static-plus-polarization levels
for describing the interaction forces and the correlation-polarization
contributions are found to be an essential component for the correct
description of low-energy cross section behavior. The local model potentials
derived from density functional theory (DFT) and from the distributed positron
model (DPM) are found to produce very high-quality agreement with existing
measurements. On the other hand, the less satisfactory agreement between the
R-matrix (RM) results and measured data shows the effects of the slow
convergence rate of configuration-interaction (CI) expansion methods with
respect to the size of the CI-expansion. To contrast the positron scattering
findings, results for electron-CH integral and differential cross
sections, calculated with both a DFT model potential and the R-matrix method,
are compared and analysed around the shape resonance energy region and found to
produce better internal agreement
Configuration-interaction calculations of positron binding to zinc and cadmium
The configuration-interaction method is applied to the study of positronic zinc (e+Zn) and positronic cadmium (e+Cd). The estimated binding energies and annihilation rates were 0.00373 hartree and 0.42×109 sec-1 for e+Zn and 0.006 10 hartree and 0.56×109 sec-1 for e+Cd. The low-energy elastic cross section and Zeff were estimated from a model potential that was tuned to the binding energies and annihilation rates. Since the scattering lengths were positive (14.5a0 for Zn and 11.6a0 for Cd) the differential cross sections are larger at backward angles than at forward angles just above threshold. The possibilities of measuring differential cross sections to confirm positron binding to these atoms is discussed
Grammar schools: a very English solution to a very English problem
The governmentâs decision to pass new legislation for the reintroduction of grammar schools took most people by surprise and was met with outcry by quite a few working in education. Details about how these new grammar schools would work in practice are still vague â in particular how they would avoid the traditional bias towards the middle classes. However what seems to stand out strongly in the debate is the generally negative response to this policy by the experts and even those in the Conservative Party.
Despite this, Theresa May seems determined to push ahead with her plans, quite possibly because grammar schools are simply popular with the public. The cynic might well argue that the new prime minister wants to endear herself to the electorate â and what could be more convenient than to bring back a policy which resonates strongly with aspiring middle class and working class parents
Sociology of Education
âAn essential student-friendly text for Education Studies.â
Dr Gillian Forrester, Subject Head for Education & Early Childhood Studies, Liverpool John Moores University
âIntroducing students to the complexities of Education Studies is a difficult task and this book will go a long way to making it easier. I will definitely be recommending this to all my students.â
Kevin Brain, Programme Leader, Education Studies, Leeds Trinity University
This textbook explains the basic principles of sociology and relates these concepts to todayâs society and education system in order to deepen your understanding of how these issues affect our lives and the world we live in, encouraging you to think critically and to develop a âsociological imaginationâ.
Coverage includes:
the wider political and economic context for education in the UK, including an analysis of the reforms of the 2010 coalition government
childhood, schooling and pupil voice
non-traditional consideration of critical pedagogy, âraceâ and gender
the role of education in a multicultural society
inequalities in educational opportunity in terms of class, ethnicity and disability.
This is essential reading for students on undergraduate Education Studies degrees, and for sociology courses covering educational issues
A Crystalline Tri-thorium Cluster with Ï-Aromatic Metal-Metal Bonding.
From PubMed via Jisc Publications RouterHistory: received 2020-12-07, accepted 2021-08-06Publication status: aheadofprintMetal-metal bonding is a widely studied area of chemistry , and has become a mature field spanning numerous d transition metal and main group complexes . In contrast, actinide-actinide bonding is predicted to be weak , being currently restricted to spectroscopically-detected gas-phase U and Th , U H and U H in frozen matrices at 6-7 Kelvin (K) , or fullerene-encapsulated U . Conversely, attempts to prepare thorium-thorium bonds in frozen matrices produced only ThH (n = 1-4) . Thus, there are no isolable actinide-actinide bonds under normal conditions. Computational investigations have explored the likely nature of actinide-actinide bonding , concentrating on localised Ï-, Ï-, and ÎŽ-bonding models paralleling d transition metal analogues, but predictions in relativistic regimes are challenging and have remained experimentally unverified. Here, we report thorium-thorium bonding in a crystalline cluster, prepared and isolated under normal experimental conditions. The cluster exhibits a diamagnetic, closed-shell singlet ground-state with a valence-delocalised three-centre-two-electron Ï-aromatic bond that is counter to the focus of previous theoretical predictions. The experimental discovery of actinide Ï-aromatic bonding adds to main group and d transition metal analogues, extending delocalised Ï-aromatic bonding to the heaviest elements in the periodic table and to principal quantum number six, and constitutes a new approach to elaborating actinide-actinide bonding. [Abstract copyright: © 2021. The Author(s), under exclusive licence to Springer Nature Limited.