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      Rare earth elements: Mendeleev’s bane, modern marvels

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      Science
      American Association for the Advancement of Science (AAAS)

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          Abstract

          The rare earths (REs) are a family of 17 elements that exhibit pronounced chemical similarities as a group, while individually expressing distinctive and varied electronic properties. These atomistic electronic properties are extraordinarily useful and motivate the application of REs in many technologies and devices. From their discovery to the present day, a major challenge faced by chemists has been the separation of RE elements, which has evolved from tedious crystallization to highly engineered solvent extraction schemes. The increasing incorporation and dependence of REs in technology have raised concerns about their sustainability and motivated recent studies for improved separations to achieve a circular RE economy.

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          Molecular magnetic hysteresis at 60 kelvin in dysprosocenium

          Lanthanides have been investigated extensively for potential applications in quantum information processing and high-density data storage at the molecular and atomic scale. Experimental achievements include reading and manipulating single nuclear spins, exploiting atomic clock transitions for robust qubits and, most recently, magnetic data storage in single atoms. Single-molecule magnets exhibit magnetic hysteresis of molecular origin—a magnetic memory effect and a prerequisite of data storage—and so far lanthanide examples have exhibited this phenomenon at the highest temperatures. However, in the nearly 25 years since the discovery of single-molecule magnets, hysteresis temperatures have increased from 4 kelvin to only about 14 kelvin using a consistent magnetic field sweep rate of about 20 oersted per second, although higher temperatures have been achieved by using very fast sweep rates (for example, 30 kelvin with 200 oersted per second). Here we report a hexa-tert-butyldysprosocenium complex—[Dy(Cpttt)2][B(C6F5)4], with Cpttt = {C5H2tBu3-1,2,4} and tBu = C(CH3)3—which exhibits magnetic hysteresis at temperatures of up to 60 kelvin at a sweep rate of 22 oersted per second. We observe a clear change in the relaxation dynamics at this temperature, which persists in magnetically diluted samples, suggesting that the origin of the hysteresis is the localized metal–ligand vibrational modes that are unique to dysprosocenium. Ab initio calculations of spin dynamics demonstrate that magnetic relaxation at high temperatures is due to local molecular vibrations. These results indicate that, with judicious molecular design, magnetic data storage in single molecules at temperatures above liquid nitrogen should be possible.
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            Rare earth metals are essential for methanotrophic life in volcanic mudpots.

            Growth of Methylacidiphilum fumariolicum SolV, an extremely acidophilic methanotrophic microbe isolated from an Italian volcanic mudpot, is shown to be strictly dependent on the presence of lanthanides, a group of rare earth elements (REEs) such as lanthanum (Ln), cerium (Ce), praseodymium (Pr) and neodymium (Nd). After fractionation of the bacterial cells and crystallization of the methanol dehydrogenase (MDH), it was shown that lanthanides were essential as cofactor in a homodimeric MDH comparable with one of the MDHs of Methylobacterium extorquens AM1. We hypothesize that the lanthanides provide superior catalytic properties to pyrroloquinoline quinone (PQQ)-dependent MDH, which is a key enzyme for both methanotrophs and methylotrophs. Thus far, all isolated MxaF-type MDHs contain calcium as a catalytic cofactor. The gene encoding the MDH of strain SolV was identified to be a xoxF-ortholog, phylogenetically closely related to mxaF. Analysis of the protein structure and alignment of amino acids showed potential REE-binding motifs in XoxF enzymes of many methylotrophs, suggesting that these may also be lanthanide-dependent MDHs. Our findings will have major environmental implications as metagenome studies showed (lanthanide-containing) XoxF-type MDH is much more prominent in nature than MxaF-type enzymes. © 2013 Society for Applied Microbiology and John Wiley & Sons Ltd.
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              Selective functionalization of methane, ethane, and higher alkanes by cerium photocatalysis

              With the recent soaring production of natural gas, the use of methane and other light hydrocarbon feedstocks as starting materials in synthetic transformations is becoming increasingly economically attractive, though it remains chemically challenging. Here, we report the development of photocatalytic C–H amination, alkylation and arylation of methane, ethane, and higher alkanes under visible light irradiation at ambient temperature. High catalytic efficiency (turnover numbers up to 2900 for methane and 9700 for ethane) and selectivity were achieved using abundant, inexpensive cerium salts as photocatalysts. Ligand-to-metal charge transfer excitation generates alkoxy radicals from simple alcohols that in turn act as hydrogen atom transfer catalysts. The mixed phase gas/liquid reaction was adapted to continuous-flow, enabling the efficient use of gaseous feedstocks in scalable photocatalytic transformations.
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                Author and article information

                Journal
                Science
                Science
                American Association for the Advancement of Science (AAAS)
                0036-8075
                1095-9203
                January 31 2019
                February 01 2019
                February 01 2019
                January 31 2019
                : 363
                : 6426
                : 489-493
                Article
                10.1126/science.aau7628
                30705185
                a14eec4f-db73-438b-8a29-671cfaf64d5f
                © 2019

                http://www.sciencemag.org/about/science-licenses-journal-article-reuse

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