Hydration of Lanthanoids(III) and Actinoids(III): An Experimental/Theoretical Saga

The latest experimental and theoretical studies on structural and dynamical properties of lanthanoid(III) and actinoid(III) ions in water have been reviewed. In the last years, most of the issues about lanthanoid(III) hydration have been resolved combining X-ray absorption experiments and different theoretical methods. Since 2008 an effort has been made to treat the entire series thus obtaining coherent sets of experimental and theoretical results that were lately put together in such a way that it was possible to derive new basic properties, such as effective ionic radii, across the series. While for the hydration of lanthanoids(III) many experiments and simulations have been reported, the hydration of actinoids(III) was less investigated. There are some experiments performed by different research groups and few simulations that we discuss in this review. Currently, there are enough results that it is possible to gain some understanding of the hydration behavior of lanthanoids(III) and actinoids(III). The ultimate goal of this review is to provide clues on the analogies and differences between the two series. These aspects are connected to several issues: 1)?technological: the separation of these elements that is necessary for recycling and stocking of nuclear waste, 2)?practical: because experiments on actinoids need particular care, the definition of possible analogies will give the possibility to use the correct lanthanoid when the information on a specific actinoid is needed, 3)?fundamental: related to chemical similarities between the two series.     

锕酰冠醚配合物电子结构和化学成键理论研究进展

本文对锕系化合物的结构和性质的理论研究进行了规律性总结,并结合我们的研究成果,重点介绍了锕酰冠醚配合物的配位化学、电子结构和化学成键的基本特征。尽管近年来出现越来越多的光谱实验和晶体学数据报道,但是对锕系配合物的电子结构和化学成键的理论研究还不够系统。本文对锕酰冠醚配合物的配位结构、稳定能和光谱性质的计算结果进行了综述。大环配体(硫代)冠醚的腔体大小决定了配合物的结构特征。通过理论研究,在锕酰冠醚配合物中存在具有典型的An≡Oactinyl共价键和An-Oligand和An-Sligand离子键。对于离子键An-Oligand和An-Sligand,An和供电子配体之间通过价原子轨道的径向分布重叠形成微弱的共价相互作用。从U到Cm,配体向金属的电荷转移(LMCT)逐渐显著,导致Am和Cm的氧化态降低,金属离子与配体的作用变弱。这一成键规律和金属氧化态的变化规律,为实验上筛选合理且高效的镧锕分离配体提供重要理论指导。     

α-Aminophosphonates, -Phosphinates,and -Phosphine Oxides as Extraction and Precipitation Agents for Rare Earth Metals,Thorium, and Uranium: A Review

α-Aminophosphonates, -phosphinates, and -phosphine oxides are a group of organophosphorus compounds that were investigated as extraction agents for rare earth (RE) metals and actinoids for the first time in the 1960s. However, more systematic investigations of their extraction properties towards REs and actinoids were not started until the 2010s. Indeed, recent studies have shown that these α-amino-functionalized compounds can outperform the commercial organophosphorus extraction agents in RE separations. They have also proven to be very efficient extraction and precipitation agents for recovering Th and U from RE concentrates. These actinoids coexist with REs in some of the commercially important RE-containing minerals. The efficient separation and purification of REs is becoming more and more important every year as these elements have a pivotal role in many existing technologies. If one also considers the facile synthesis of α-amino-functionalized organophosphorus extractants and precipitation agents, it is expected that they will be increasingly utilized in the extraction chemistry of REs and actinoids in the future. This review collates α-aminophosphonates, -phosphinates, and -phosphine oxides that have been utilized in the separation chemistry of REs and actinoids, including their most relevant synthetic routes and molecular properties. Their extraction and precipitation properties towards REs and actinoids are also discussed.     

钯基氧还原和乙醇氧化反应电催化剂:关于结构和机理研究的一些近期见解

质子交换膜燃料电池和直接乙醇燃料电池已成为可持续性清洁能源研究的一个聚焦点.在燃料电池中,氧还原反应和乙醇氧化反应是两个重要的反应,其相关高活性、高稳定性并且廉价的催化剂的研发仍然存在很多问题,极大地制约了燃料电池的大规模商业化应用.其中的挑战主要来自于对纳米催化剂结构和反应机理的有限认识.由于实验表征理论计算的结合,...     

Polarizable interaction potential for molecular dynamics simulations of actinoids(III) in liquid water

In this work, we have developed a polarizable classical interaction potential to study actinoids(III) in liquid water. This potential has the same analytical form as was recently used for lanthanoid(III) hydration [M. Duvail, P. Vitorge, and R. Spezia, J. Chem. Phys. 130, 104501 (2009)]. The hydration structure obtained with this potential is in good agreement with the experimentally measured ion-water distances and coordination numbers for the first half of the actinoid series. In particular, the almost linearly decreasing water-ion distance found experimentally is replicated within the calculations, in agreement with the actinoid contraction behavior. We also studied the hydration of the last part of the series, for which no structural experimental data are available, which allows us to provide some predictive insights on these ions. In particular we found that the ion-water distance decreases almost linearly across the series with a smooth decrease of coordination number from nine to eight at the end.     

Hydrogen migrations in alkylcycloalkyl radicals: implications for chain-branching reactions in fuels

A thorough understanding of the oxidation chemistry of cycloalkanes is integral to the development of alternative fuels and improving current fuel performance. An important class of reactions essential to this chemistry is the hydrogen migration; however, they have largely been omitted from the literature for cycloalkanes. The present work investigates all of the hydrogen migration reactions available to methylcyclopentane, ethylcyclopentane, methylcyclohexane, and ethylcyclohexane. The kinetic and thermodynamic parameters have been studied by a combination of computational methods and compared to their corresponding n-alkyl and methylalkyl counterparts to determine the effect that the cycloalkane ring has on these reactions. In particular, although the alkylcycloalkyl activation energies for the dominant 1,4, 1,5, and 1,6?H-migration are higher than in n-alkyl and methylalkyl radicals, because several of the rotors needed to form the transition state are locked into place as part of the cycloalkane ring, the A-factors are higher for the alkylcycloalkyl reactions, making the rates closer to the noncyclic systems, at higher temperatures. The results presented here suggest that the relative importance of each H-migration pathway differs from the trends predicted by either the n-alkyl or methylalkyl radical systems. Of particular interest is the observation that since the barrier height of the 1,4?H-migration is only 3-5?kcal?mol(-1) higher than the 1,5?H-migration in the methyl and ethylcycloalkyl radicals, compared to a difference of roughly 7?kcal?mol(-1) in similar reactions for both the n-alkyl and methylalkyl radicals, the 1,4 H-migrations in alkylcycloalkyl radicals will be more important in the overall mechanism than would be predicted based on the n-alkyl and methylalkyl radicals. These results have important combustion model implications, particularly for fuels with high cycloalkane content.     

原子数精确的金属纳米团簇在电催化领域的应用研究进展

金属纳米团簇(MNCs)是由几个到数百个金属原子组成,其尺寸一般小于2nm.金属纳米团簇在许多催化反应中表现出高的催化活性和选择性,这与金属纳米团簇具有高的比表面积、较多暴露的活性原子,以及与金属纳米粒子(MNPs)不同的电子结构有关.金属纳米团簇确定的组成和结构使其成为一种新型模型催化剂,对纳米团簇的催化性能研究有利...     

铂基金属间化合物纳米晶的最新进展:可控合成与电催化应用

铂基金属间化合物纳米晶因其高度有序的结构特点,优异的抗氧化及耐腐蚀性能,作为电极材料被广泛应用于各类电催化反应,目前已有的PtCo金属间化合物纳米晶在燃料电池阴极反应(氧还原反应)中的活性和稳定性均达到了美国能源部(DOE) 2020年的目标。为了进一步提高金属间化合物纳米晶的电催化性能,需要对影响纳米晶电催化性能的因素进行深入研究。本文综述了铂基金属间化合物纳米晶的研究现状,着重介绍了铂基金属间化合物的可控合成策略及其在电催化领域的最新研究进展,分析总结了该领域存在的问题,并展望了其未来发展方向。     

Synthesis, structure, electrochemistry, and electrochemiluminescence of thienyltriazoles

Four blue-emitting thienyltriazoles with desired N and O coordination atoms were prepared in high yield via click chemistry for potential incorporation into metal complexes. Three of their crystal structures were determined by X-ray crystallography. The electrochemical properties, electronic structures of these thienyltriazoles, 1-4, and their correlations were studied using cyclic voltammetry and differential pulse voltammetry techniques along with density function theory (DFT) calculations. All of the compounds underwent irreversible redox reactions, leading to unstable electrogenerated radical cations and anions. Electrochemical gaps determined from the differences between first formal reduction and oxidation reactions were correlated to HOMO-LUMO energy gaps obtained from UV-vis spectroscopy and the DFT calculations as well as energies of excited states measured from photoluminescence spectroscopy. We observed weak electrochemiluminescence (ECL) from annihilation of these thienyltriazole radicals in acetonitrile containing 0.1 M tetra-n-butylammonium perchlorate as electrolyte. An enhancement in ECL efficiency ranging from 0.16 to 0.50% was observed upon addition of benzoyl peroxide as a coreactant in the above electrolyte solutions. The generation of excimers in solutions of 1-4 was observed as seen by the red-shift in ECL maxima relative to their corresponding photoluminescence peak wavelengths. Our work is of importance for the development of efficient blue-emitting fluorophores via click chemistry that could be potential luminophores in metal complexes.     

Electron‐Deficient Triborane and Tetraborane Ring Compounds: Synthesis,Structure, and Bonding

Electron‐deficient small boron rings are unique in their formation of σ‐ and π‐delocalized electron systems as well as the avoidance of “classical” structures with two‐center‐two‐electron (2c,2e) bonds. These rings are tolerant of several skeletal electron numbers, which makes their redox chemistry highly interesting. In the past few decades, a range of stable compounds have been synthesized with various electron numbers in their B₃ and B₄ cores. The electronic structures were evaluated by quantum‐chemical calculations. On the other hand, the chemistry of these rings is still very much underdeveloped, being generally limited to the protonation and redox reactions of individual systems. The linkage of several B₃ and/or B₄ ring systems should give compounds with attractive electronic properties, thus leading the way to novel boron‐based materials. By summarizing important experimental and theoretical results, this Review intends to provide the basis for the exploration of the chemistry of these rings and, in particular, their integration into larger molecular architectures.     

Integrated computational strategies for UV/vis spectra of large molecules in solution

In recent years, the margin of interaction between computational chemistry and most branches of experimental chemistry has increased at a fast pace. The experimental characterization of new systems relies on computational methods for the rationalization of structural, energetic, electronic and dynamical features. In particular, novel computational approaches allow accurate estimates of molecular parameters from spectroscopic optical observables, giving rise to synergic interactions between experimentalists and theoretically-oriented chemists. Our main objective in this tutorial review is to delineate the degree of advancement of possible integrated computational approaches to the interpretation of optical spectroscopies, with an accent on large molecules in solvated environments, based on the combination of advanced quantum mechanical treatments and stochastic modelling of relaxation processes.     

Carbon-based single atom catalyst: Synthesis,characterization, DFT calculations

Carbon-based single-atom catalysts(SACs) with atomic sizes of active sites have become the promising candidates for a variety of catalytic systems because of their high atom utilization, and unique electronic structures. Different types of single-atom sites can be fabricated via multiple preparation strategies, which would demonstrate distinct different coordination configurations and electronic features, and ultimately affected the structure-catalysis relationship of SACs in targeted reactions....     

Electron transfer in environmental systems: a frontier for theoretical chemistry

The advances in understanding the kinetic behavior of certain environmental electron transfer (ET) systems are presented. Emphasis is placed on the homogeneous ET chemistry of transition metals, particularly the Fe^II/III system, in various relevant forms. In the context of modern ET theory, we examine the utility of computational chemistry methods for the calculation of ET quantities such as the reorganization energy and electronic coupling matrix element. We discuss successful application of the methods to topics of homogeneous oxidation of dissolved metal ions by molecular oxygen in aqueous solution, as well as the prediction of electron mobility in solid phase iron oxide crystals. The examples illustrate the significant potential for many more advances in understanding environmental ET systems through the combination of ET theory and computational chemistry.     

Investigating the oxidation of alkenes by non-heme iron enzyme mimics

Iron is emerging as a key player in the search for efficient and environmentally benign methods for the functionalisation of C-H bonds. Non-heme iron enzymes catalyse a diverse array of oxidative chemistry in nature, and small-molecule complexes designed to mimic the non-heme iron active site have great potential as C-H activation catalysts. Herein we report the synthesis of a series of organic ligands that incorporate key features of the non-heme iron active site. Iron(ii) complexes of these ligands have been generated in situ and their ability to promote hydrocarbon oxidation has been investigated. Several of these systems promote the biomimetic dihydroxylation of cyclohexene at low levels, when hydrogen peroxide is used as the oxidant; allylic oxidation products are also observed. An investigation of ligand stability reveals formation of several breakdown products under the conditions of the oxidative turnover reactions. These products arise via oxidative decarboxylation, dehydration and deamination reactions. Taken together these results indicate that competing mechanisms are at play with these systems: biomimetic hydroxylation involving high-valent iron species, and allylic oxidation via Fenton chemistry and Haber-Weiss radical pathways.     

Stable dimeric magnesium(I) compounds: from chemical landmarks to versatile reagents

The chemistry of the s-block metals is dominated by the +1 oxidation state for the Alkali metals (group 1) and the +2 oxidation state for the Alkaline Earth metals (group 2). In recent years, a series of stable dimeric magnesium(I) compounds has been prepared and their chemistry has started to develop. These complexes feature "deformable" Mg-Mg single bonds and are stabilised by sterically demanding and chelating anionic N-ligands that prevent their disproportionation. They have rapidly proven useful in organic and organometallic/inorganic reduction reactions as hydrocarbon soluble, stoichiometric, selective and safe reducing agents. The scope of this perspective focuses on stable molecular compounds of the general type LMgMgL and describes their synthesis, structures, theoretical and spectroscopic studies as well as their further chemistry. Also, comparisons are drawn with related complexes including magnesium(II) hydrides and dimeric zinc(I) compounds.     

Special Collection: Computational Chemistry

Chemists know well the value of an experimental or a theoretical result, but what is the value of a computational result? Simulation is neither theory nor experience, nor a mere calculation tool, but a genuine way of approaching reality that is transforming the scientific method. In some cases, it offers explanations to observations or experiments that seem incomprehensible because they are too complex. In this case, the computation serves as a relief. An experiment that converges with a certain computation has more scientific value than an experiment that does not converge with anything at all. In other cases, contribution of computational chemistry is essential because there is no experimental manner to determine what happens during a chemical process; for instance, in the path from reactants to products in (fast) reactions. Now, computational chemistry provides additional information that is not possible to obtain from experiments, so it is a valuable complement to them. Indeed, fruitful synergy between computation and experiment has led to the approach of theory-driven experimentation. Finally, computational chemistry helps to legitimize models or theories that have little opportunity to be contrasted with reality. In this situation, computational chemistry is not experience, but it does substitute it in relation to theory. In the present special collection, we have examples of the different ways computational chemistry helps chemists to interpret the electronic and molecular structure of molecules and their reactivity.