Volume 65, Issue 8

A rich variety of chalcogenidoarsenate anions and ligands have been prepared under mild solvothermal conditions in strongly polarizing solvents such as water, methanol and amines in the temperature range 100 - 200 ◦C. This review covers synthetic and structural aspects of such species A Sx E y z− with particular emphasis being placed on the trends and differences observed for E = S, Se, Te and on developments within the past decade. These include the preparation of quaternary Main Group element chalcogenidoarsenates(III) such as Cs 3 AsGeSe 5 and polymeric selenidoarsenates(II, III) such as Cs2As 4 Se 6 . A currently expanding area of interest involves the employment of transition metal-polyamine or -polyimine fragments such as {Mn(tren)} 2+ or {Mn(terpy)} 2+ as structuredirecting agents. The metal atoms of such cations can be connected to the terminal chalcogen atoms of oligomeric or polymeric anions AsxEy z− to prevent their further condensation or can be directly incorporated into anionic or neutral networks when at least two free coordination sites are available in the fragment. This strategy has led to the characterization of novel ligands including cyclo- [As 4 S 8 ] 4− , As 2 Se 6 2− , As 2 Se 6 4− and 1 ∞ [As 4 Se 7 2− ]. The syntheses and structures of the new compounds Cs 5 As 5 Se 9 and Cs[{Mn(trien)}(AsSe 4 -K 2 Se)] ・CH 3 OH are also presented. Whereas the former phase contains infinite selenidoarsenate(II,III) chains 1 ∞ [As 5 Se 9 5− ], the [{Mn(trien)}(AsSe 4 )]− anion of the latter compound represents the first example of a transition metal-containing ternary selenidoarsenate( V) Graphical Abstract Review. Solvothermal Synthesis and Structure of Chalcogenidoarsenate Anions

A rich variety of inorganic-organic hybrid thioantimonates and thiostannates were prepared during the last few years under solvothermal conditions applying organic amine molecules or transition metal complexes as structure directors. In this review synthetic approaches to and structural features of these thiometallates are discussed. For thioantimonates(III) the structures range from well isolated thioanions to three-dimensional networks, whereas the structural chemistry of thiostannates(IV) is strongly dominated by the [Sn 2 S 6 ] 4− anion, and no three-dimensional thiostannate has been reported so far. In the structures of thioantimonates(III) several primary building units like the [SbS 3 ] trigonal pyramid, the [SbS 4 ] unit or even the [SbS 5 ] moiety are joined by vertex- and/or edge-linkages to form building blocks of higher structural hierarchy like [Sb 3 S 4 ] semi-cubes or Sb x S x heterocycles. A pronounced difference between thioantimonate and thiostannate chemistry is the tendency of Sb(III) to enhance the coordination geometry via so-called secondary bonds. In most cases the environment of Sb(III) is better described as a 3+n polyhedron with n = 1 - 3. The thioantimonate(V) structural chemistry is less rich than that of thioantimonates(III), and the [SbS 4 ] 3− anion shows no tendency for further condensation. By applying suitable multidentate amine molecules, transition metal cations which normally prefer bonding to the N atoms of the amines can be incorporated into the thiometallate frameworks Graphical Abstract Review. Synthesis of Inorganic-Organic Hybrid Thiometallate Materials with a Special Focus on Thioantimonates and Thiostannates and in situ X-Ray Scattering Studies of their Formation

This review focuses primarily on the past 10 years of our development of multifunctional coordination polymers with 1D, 2D and 3D structures employing low-temperature and cost-effective hydrothermal and solvothermal methods. The effects of the experimental conditions and parameters on the crystal formation and phase separation, including temperature and pressure, reaction pH, solvent and composition, are discussed. Our studies have shown that a variety of different types of network structures may be rationally designed and synthesized by deliberate selection and construction of metal building blocks and organic ligands, which lead to numerous interesting properties and multifunctionality that are promising for applications in gas storage and separation, catalysis and optical sensing Graphical Abstract Review. Solvothermal Synthesis of Multifunctional Coordination Polymers

Solvothermal processes are defined, and the different domains of applications are described. The main physico-chemical factors playing a key role in such processes are then analyzed. The trends characterizing the current development of solvothermal processes are outlined

Solvothermal processes, as compared to hydrothermal processes, enlarge the scope of the employed solvents from aqueous to non-aqueous media, the objective being to extend the possibilities for the preparation and/or the crystal growth of non-oxide materials. During the last fifteen years solvothermal crystal growth of materials has been investigated at two different levels: (i) the macroscopic scale, with the preparation of large single crystals of functional materials for specific applications, (ii) the nanoscale, involving the elaboration of single-crystalline nanocrystallites well defined in size and morphology, and particularly adapted to nanodevices. In the first domain, two main factors have been studied: (i) the influence of the thermodynamical parameters governing the solvothermal processes, and (ii) the purity of the components (nutrient, solvent, etc.), the main objective being to reduce drastically the density of defects inside the single crystals. In the second domain, strong efforts have been made: (i) to control the nano-size, but mainly, (ii) to induce specific morphologies, in particular 1D, appropriate to the relative nanotechnologies Graphical Abstract Review. New Trends in Solvothermal Crystal Growth at theMacro- and Nanoscale

Over the last decade, the number of publications concerning the non-aqueous sol-gel synthesis of metal oxide nanostructures has rapidly increased, as this method affords an immense variety of sizes and shapes of the products. This review highlights the versatility of non-aqueous sol-gel routes, under solvothermal conditions, to metal oxide and hybrid materials. In particular, the easier control over the reaction kinetics, compared to aqueous methods, allows to better match the reactivity between metal oxide precursors. This permits to produce complex multimetal and doped oxides at low temperature, as it is discussed in detail for the case of doped group IV metal oxides Graphical Abstract Review. Non-aqueous Sol-Gel Routes to Metal Oxide Nanocrystals under Solvothermal Conditions: Review and Case Study on Doped Group IV Metal Oxides

In this paper, a hydrothermal method of high-pressure and low-temperature synthesis conditions is presented as a simple single-step technique to obtain crystalline nanoparticles of iron oxides. The aim of this work has been to demonstrate the influence of the main synthesis parameters on the formation of nanosized Fe 2 O 3 particles using statistical methods and to establish the most significant effects. Based on mathematical pre-modeling calculations, the best reaction conditions for the hydrothermal process have been chosen, and controlled crystalline nanostructures of iron oxides could be prepared Graphical Abstract The Influence of Synthesis Parameters on FeO(OH) / Fe 2 O 3 Formation by Hydrothermal Techniques

Anatase and Ca, Sr and Ca 0.5 Sr 0.5 hydroxyapatites were synthesized by conventional-hydrothermal (C-H) as well asmicrowave-hydrothermal (M-H)methods.Microwave-assisted reactions led to accelerated syntheses of anatase but no such acceleration of reactions could be detected with the syntheses of hydroxyapatites because the crystallization of the latter materials occurred at very low temperature. Cu and Au metal powders were produced by using glucose, fructose or sucrose as reducing agents under C-H conditions at 160 ℃, where fructose and sucrose were found to be stronger reducing agents than glucose. The crystallinity of all the powders was characterized by powder X-ray diffraction, and morphology and particle sizes were determined by scanning or transmission electron microscopy Graphical Abstract Solvothermal/ Hydrothermal Synthesis of Metal Oxides and Metal Powders with and without Microwaves

Calcium-deficient hydroxyapatite (CDHA) prepared by the coprecipitation method was solidified by the hydrothermal hot-pressing technique, and compacts of CDHA with high bulk density beyond 80% were obtained at 200 ℃. Each reaction parameter, viz. reaction temperature, pressure, and time, was systematically changed from the standard conditions to investigate its effects on density, Vickers hardness, and Ca/P ratio of the compacts obtained. The reaction temperature and pressure had a large effect on densification, but not the reaction time because the densification proceeds in a short time. The densification by hydrothermal hot-pressing involved dissolution and precipitation of the starting CDHA powder, so that the Ca/P ratio changed from 1.52 of the starting powders to 1.61 of the compact obtained by hydrothermal hot-pressing at 200 ℃ and 35 MPa for 24 h with the addition of 10 wt.-% water Graphical Abstract Hydrothermal Sintering under Mild Temperature Conditions: Preparation of Calcium-deficient Hydroxyapatite Compacts

The surface modification of γ -alumina nanoparticles by sebacic acid in super- and subcritical water was investigated. The modified alumina was characterised by Fourier-transform infrared spectra, X-ray diffraction patterns, transmission electron microscopy images, and thermogravimetric studies. The alumina nanoparticles were found to remain stable, and sebacic acid was bound to their surfaces at 200 ℃, but their crystallite structure was partially changed to that of boehmite above 200 ℃. Under supercritical conditions at 400 ℃, the alumina nanoparticles were totally changed to boehmite nanoparticles. The surface adsorption of sebacic acid is attributed to reactions between the surface -OH groups of alumina and the -COOH groups of sebacic acid. The modified alumina nanoparticles have -COOH groups on their surface, enabling hybridisation with various biomolecules, and thus allowing their application in several areas Graphical Abstract Hybridisation of Sebacic Acid on the Surface of γ-Alumina Nanoparticles in Sub- and Supercritical Water

Results of the investigation of the reactions of GaCl 3 , InCl 3 and InI 3 with LiNH 2 under solvothermal conditions in benzene, which lead to metal nitrides, are reported. GaN is obtained as a cubic phase or as a mixture of cubic and hexagonal phases, depending on temperature. The effect of the addition of surfactants on the formation of GaN was explored. InN products were always contaminated with indium metal, even at low reaction temperatures. The addition of excess LiNH 2 or the use of InI 3 instead of InCl 3 gave products with less In metal Graphical Abstract Solvothermal Synthesis of Gallium and Indium Nitrides Using Lithium Amide