Within the framework of green chemistry, solvents occupy a strategic place. To be qualified as a green medium, these solvents have to meet different criteria such as availability, non-toxicity, biodegradability, recyclability, flammability, and low price among others. Up to now, the number of available green solvents are rather limited. Here we wish to discuss a new family of ionic fluids, so-called Deep Eutectic Solvents (DES), that are now rapidly emerging in the current literature. A DES is a fluid generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form a eutectic mixture with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C. These DESs exhibit similar physico-chemical properties to the traditionally used ionic liquids, while being much cheaper and environmentally friendlier. Owing to these remarkable advantages, DESs are now of growing interest in many fields of research. In this review, we report the major contributions of DESs in catalysis, organic synthesis, dissolution and extraction processes, electrochemistry and material chemistry. All works discussed in this review aim at demonstrating that DESs not only allow the design of eco-efficient processes but also open a straightforward access to new chemicals and materials.

Deep eutectic solvents: syntheses, properties and applications

International Tables for X-Ray Crystallography (Published for the International Union of Crystallography.) Vol. 1: Symmetry Groups. Edited by Norman F. M. Henry and Kathleen Lonsdale. Pp. xi + 558. (Birmingham: Kynoch Press, 1952.) 105s.

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International Tables for X-Ray Crystallography

The crystal structures of uranyl minerals and inorganic uranyl compounds are important for understanding the genesis of U deposits, the interaction of U mine and mill tailings with the environment, transport of actinides in soils and the vadose zone, the performance of geological repositories for nuclear waste, and for the development of advanced materials with novel applications. Over the past decade, the number of inorganic uranyl compounds (including minerals) with known structures has more than doubled, and reconsideration of the structural hierarchy of uranyl compounds is warranted. Here, 368 inorganic crystal structures that contain essential U6+ are considered (of which 89 are minerals). They are arranged on the basis of the topological details of their structural units, which are formed by the polymerization of polyhedra containing higher-valence cations. Overarching structural categories correspond to those based upon isolated polyhedra (8), finite clusters (43), chains (57), sheets (204), and frameworks (56) of polyhedra. Within these categories, structures are organized and compared upon the basis of either their graphical representations, or in the case of sheets involving sharing of edges of polyhedra, upon the topological arrangement of anions within the sheets.

U6+ minerals and inorganic compounds: insights into an expanded structural hierarchy of crystal structures

Thin zeolite films are attractive for a wide range of applications, including molecular sieve membranes, catalytic membrane reactors, permeation barriers, and low-dielectric-constant materials. Synthesis of thin zeolite films using high-aspect-ratio zeolite nanosheets is desirable because of the packing and processing advantages of the nanosheets over isotropic zeolite nanoparticles. Attempts to obtain a dispersed suspension of zeolite nanosheets via exfoliation of their lamellar precursors have been hampered because of their structure deterioration and morphological damage (fragmentation, curling, and aggregation). We demonstrated the synthesis and structure determination of highly crystalline nanosheets of zeolite frameworks MWW and MFI. The purity and morphological integrity of these nanosheets allow them to pack well on porous supports, facilitating the fabrication of molecular sieve membranes.

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Dispersible exfoliated zeolite nanosheets and their application as a selective membrane

A nomenclature for tourmaline-supergroup minerals is based on
chemical systematics using the generalized tourmaline
structural formula: XY3 Z6(T6O18)(BO3)3V3W where the common
ions at each site are X = Na1+, Ca2+, K1+ and vacancy; Y =
Fe2+, Mg2+, Al3+, Li1+, Fe3+ and Cr3+; Z = Al3+, Fe3+, Mg2+ and
Cr3+; T = Si4+, Al3+ and B3+; B = B3+; V = OH1- and O2-; and W
= OH1-, F1- and O2-. Most compositional variability occurs at
the X, Y, Z, W and V sites.

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Nomenclature of the tourmaline-supergroup minerals

In order to clarify inconsistencies in the literature and to verify assumed ternary solubilities, the phase equilibria in the Y2O3–Al2O3 –SiO2 system at 1600, 1400, and 1300 °C were experimentally determined using x-ray diffraction (XRD), scanning electron microscope with attached energy-dispersive detector system (SEM-EDX), and electron probe microanalyzer (EPMA). Six quasibinary phases were observed: Y4Al2O9 (YAM), YAlO3 (YAP), Y3Al5O12 (YAG), Y2SiO5, Y2Si2O7 (C and D modifications), and ˜3Al2O3· 2SiO2 (mullite). Y4Al2O9 forms an extended ternary solid solution with the formula Y4Al2(1-x)Si2xO9+x (x = 0 2 ˜0.31). The lowest ternary eutectic temperature was determined at 1371 ± 5 °C by high-temperature differential scanning calorimetry (DSC). The results were compared with previous data available for the Y2O3–Al2O3 –SiO2 system and with data for other RE2O3–Al2O3 –SiO2 (RE = rare earth element) systems.

Phase equilibria and crystal chemistry in the Y2O3–Al2O3–SiO2 system

Minamiite has been discredited and renamed natroalunite-2 c to show a double unit-cell structure and natroalunite can be designated as natroalunite-1 c to show a single unit-cell structure. Kintoreite can be designated as kintoreite-1 c to show the same single unit-cell structure, and IMA 1993-039 is a new superstructure of kintoreite and can be designated as kintoreite-2 c to show a double unit-cell structure. Beaverite has been renamed beaverite-(Cu). The Zn-bearing beaverite of Sato et al. (2008) has been named “beaverite-(Zn)”, but data for the mineral have not been approved by the CNMNC. Orpheite has been discredited as P-rich hinsdalite. Proposal 07-D was approved by the CNMNC.

Alunite supergroup: recommended nomenclature

Mixed-valence Cu(II)/Cu(I) complex of quinolone ciprofloxacin isolated by a hydrothermal reaction in the presence of L-histidine: comparison of biological activities of various copper-ciprofloxacin compounds.

The crandallite, beudantite and alunite (jarosite) mineral groups are reviewed, with an emphasis on the evaluation of their suitability as storage materials for toxic metals. New data on the highly flexible crystal chemistry, crystallography and thermodynamic stability fields of both natural and synthetic members are summarised and critically discussed. These compounds can safely incorporate a large number of toxic and radioactive metals. Extensive solid solubilities have been observed. The majority of the members are characterised by very low solubilities over a wide range of pH and Eh conditions, and by high temperature stabilities (up to 400-500°C). It is suggested, also by comparison with other mineral waste hosts (apatites, pyrochlores), that these materials can be favourably used for the long-term fixation and immobilisation of toxic ions of elements such as As, Pb, Bi, Hg, Tl, Sb, Cr, Se, and of radioactive isotopes of K, Sr, Th, U and REE.

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Crystal chemistry of the crandallite, beudantite and alunite groups: a review and evaluation of the suitability as storage materials for toxic metals

A comprehensive critical review of the phase fields, metastable modifications, solid solution ranges and phase transitions of monazite- and zircon-type REE X O 4 ( X = P, As, V) compounds is given. Monazite-type REEPO 4 compounds are stable for REE = La to Gd and metastable for Tb to Ho; zircon-type members exist for REE = Gd to Lu, and Y, Sc. REEAsO 4 compounds with monazite-type structure exist for REE = La to Nd, while zircon-type compounds are known for REE = Pm to Lu, and Y, Sc; no metastable arsenate members are known. The only stable monazite-type REEVO 4 is LaVO 4 , but metastable members are known for REE = Ce to Nd. Zircon-type REEVO 4 compounds are stable for REE = Ce to Lu, and Y, Sc, and metastable for REE = La. Solid solution series are complete only if minor size differences exist between REE 3+ or X 5+ cations in respective end-members. Phase transitions occur under pressure (zircon → (monazite →) scheelite) and at very low temperatures. The evaluation of the metastable phase fields and of naturally occurring members suggests that metastable modifications of REE X O 4 compounds can occur in nature under certain conditions (formation at temperatures

Uwe Kolitsch

Papers

Phase equilibria and crystal chemistry in the Y2O3–Al2O3–SiO2 system

Alunite supergroup: recommended nomenclature

Mixed-valence Cu(II)/Cu(I) complex of quinolone ciprofloxacin isolated by a hydrothermal reaction in the presence of L-histidine: comparison of biological activities of various copper-ciprofloxacin compounds.

Crystal chemistry of the crandallite, beudantite and alunite groups: a review and evaluation of the suitability as storage materials for toxic metals

Crystal chemistry of REEXO4 compounds (X = P,As, V). II. Review of REEXO4 compounds and their stability fields