Soft chemistry synthesis

Prabaharan SRS, Saparil NB, Michael SS, Massot M, Julien C (1998) Soft chemistry synthesis of electrochemically-active spinel LiMn204 for Li-ion batteries. Solid State Ionics... 

Long et al. reported the synthesis of tungsten oxychloride clusters via a soft-chemistry route [60], which confirms the potential for wide applications of the ligand combination strategy in cluster chemistry. 

Synthesis by soft chemistry made the first disodium telluride, Na2Te. This product is highly poisonous and oxidable. To make Na2Te we used the two procedures... 

In this edition, we have incorporated new material in all the chapters and updated references to the literature. New sections dealing with porous solids, fullerenes and related materials, metal nitrides, metal tellurides, molecular magnets and other organic materials have been added. Under preparative strategies, we have included new types of synthesis reported in the literature, specially those based on soft chemistry routes. We have a new section covering typical results from empirical theory and electron spectroscopy. There is a major section dealing with high-temperature oxide superconductors. We hope that this edition of the book will prove to be a useful text and reference work for all those interested in solid state chemistry and materials science. 

Materials chemistry contains all the elements of modem chemistry. These include synthesis, structure, dynamics, and properties. In synthesis, one employs all possible methods and conditions from high-temperature and high-pressure techniques to mild solution methods (chimie douce or soft chemistry).3 Chemical methods generally tend to be more delicate, often yielding novel, metastable products. Kinetic rather than thermodynamic control of reactions favors the formation of such structures. Supramolecular organization provides new ways of designing materials. 

In solid state chemistry, a special term soft chemistry was proposed to describe the methods based on preliminary synthesis of intermediate compounds which are further used to prepare final products [4]. One of the authors of this monograph has introduced the term soft mechanochemistry for mechanochemical reactions with the participation of highly reactive compounds [30]. They include the reactions with the participation of compounds containing oxygen-hydrogen groups as well as other relatively unstable compounds such as peroxides, nitrates, metal carbonates and other reactive compounds. 

Avvakumov E.G., Kosova N.V. Soft mechanochemical synthesis specific features and outlook. In Chemistry Reviews. Advances in Mechanochemistry Physical and Chemical Processes under Deformation, ed. Butaygin P.Yu., Dubinskaya A.M., Amsterdam Harwood Academic Pubhsher, 1998 23 285-312. 

Recently, renewed attention has been given to so-called soft chemistry methods of synthesis of new metastable materials [9]. The synthesis of new microporous materials containing transition metals in the framework is of growing interest due to the expected catalytic redox properties [10]. The microporous titanium(IV) silicates [11] discovered have already proven the concept by showing very good catalytic activities and are widely used nowadays [12]. Similarly, hydrothermally synthesized titanium phosphates with open-finmework or layered structures are attracting attention as potential materials with similar properties [13]. 

Remarkable advances have been made in the synthesis of N- and O-glycosylated amino acids that, in addition to the 5-fattyacyl-cysteine, are the most sensitive derivatives to the conditions of peptide synthesis. The fine tuning of both carbohydrate and peptide chemistry as well as the use of enzymatic methods are required for the synthesis of glycopeptides. " Similarly soft chemistry has to be applied in the case of S-acylated peptides, whereas fat-tyacylation at amino groups raises no additional difficulties.The state of the art in the field of glyco- and lipopeptide synthesis is discussed in details in Vol. E22b, Sections 6.3 and 6.4, respectively. 

The use of organic molecules in the synthesis of zeotype solids is an especially interesting preparative method for extended inorganic solid materials. Organic molecules cannot survive the harsh conditions of the classical high-temperature route involving reaction of the components in the solid state. Structure-directed synthesis thus belongs to the "soft chemistry" routes for the preparation of solid-state compounds [12, 13]. 

It occurs catalytically on the surface of Fe nanoparticles grown from Fe(CO)5. Also, the conventional synthesis of nanotubes by catalytic CVD from acetylene or methane can be formally considered as redox reaction. Nevertheless, the electrochemical model of carbonization (Sections 4.1.1 and 4.1.2) is hardly applicable for CVD and HiPco, since the nanotubes grow on the catalyst particle by apposition from the gas phase, and not from the barrier film (Figure 4.1). The yield and quality of electrochemically made nanotubes are usually not competitive to those of catalytic processes in carbon arc, laser ablation, CVD and HiPco. However, this methodology demonstrated that nanotubes (and also fullerenes and onions (Section 4.3)) can be prepared by soft chemistry" at room or sub-room temperatures [4,5,101]. Secondly, some electrochemical syntheses of nanotubes do not require a catalyst [4,5,95-98,100,101]. This might be attractive if high-purity, metal-free tubes are required. 

Another way of obtaining suspensions of anisotropic mineral moieties is by the spontaneous condensation of dissolved molecular species. A typical example of this process is the synthesis of V2O5 ribbons by using chimie douce (soft chemistry) techniques (Fig. 6) [35,36]. At pH=2, V(V) species exist in an octahedral coordination with a V=0 bond pointing along the Oz axis, three V-OH bonds in the xOy plane, and two bonded H2O molecules to fill the coordination sphere. Beyond a concentration threshold of 10 mol 1 , these vanadate species spontaneously condense in the xOy plane by two different reactions respectively called olation and oxolation reactions (olation V-0H-l-V-0H2 V-0H-V-i-H20 oxola-tion V-OH-l-V-OH—>V-0-V-i-H20) to form ribbons 1 nm thick, about 25 nm... 

The methods of soft chemistry include sol-gel, electrochemical, hydrothermal, intercalation and ion-exchange processes. Many of these methods are employed routinely for the synthesis of ceramic materials. - There have been recent reviews of the electrochemical methods, intercalation reactions, and the sol-gel technique. The sol-gel method has been particularly effective with wide-ranging applications in ceramics, catalysts, porous solids and composites and has given rise to fine precursor chemistry. Hydrothennal synthesis has been employed for the synthesis of oxidic materials under mild conditions and most of the porous solids and open-framework structures using organic templates are prepared hydro-thermally. The advent of supramolecular chemistry has started to make an impact on synthesis, mesoporous solids being well known examples. ... 

T.P. Feist, P.K. Davies, The soft chemical synthesis of Ti02 (B) from layered titanates . Journal of Sohd State Chemistry, 101, 275-295, (1992). 

Metal-polymer nanocomposites can be obtained by two different approaches, namely, in situ and ex situ techniques. In the in situ methods, metal particles are generated inside a polymer matrix by decomposition (e.g., thermolysis, photolysis, radiolysis, etc.) or chemical reduction of a metallic precursor dissolved into the polymer. In the ex situ approach, nanoparticles are first produced by soft-chemistry routes and then dispersed into polymeric matrices. Usually, the preparative scheme allows us to obtain metal nanoparticles whose surface has been passivated by a monolayer of -alkanethiol molecules (i.e., Crfiin+i-SH). Surface passivation has a fundamental role since it avoids aggregation and surface oxidation/contamination phenomena. In addition, passivated metal particles are hydrophobic and therefore can be easily mixed with polymers. The ex-situ techniques for the synthesis of metal/polymer nanocomposites are frequently preferred to the in situ methods because of the high optical quality that can be achieved in the final product. 

Chemically the interlayers in the modular phases described previously are relatively reactive. This has been exploited to fabricate large numbers of phases that are not available via the normal solid-state chemistry preparative method of high-temperature synthesis from mixed oxides or oxide precursors. The technique generally employs low temperatures, typically room temperature to 300°C, and long reactions times, of the order of 1 week. This procedure, termed chimie douce , is often translated as soft chemistry but is better called mild chemistry or gentle chemistry . Under such conditions, much of the stmcture remains intact, and the product phases have a strong topotactic relationship to the starting stmctures. For the modular perovskite phases, in... 

Table 14.7 illustrates soft-chemistry approach for the synthesis of metal oxide nanopowder with advantages and disadvantages. 

It was pointed out earlier that soft-chemistry routes have been receiving considerable attention recently. It would be instructive to examine a few typical examples of soft-chemical methods of material synthesis (chimie douce). Marchand et al. [6] obtained a new form of TiO by the dehydration of H TiOg-xH O, which in turn was prepared by the exchange of K+with H-tin K Ti O. The mechanism of this transformation has been described recently by Fiest and Davis [7] and we show this schematically in Figure 2.2. Rebbah et al. [8] prepared Ti Nb O by the dehydration of HTiNbOj, the... 

G.A. Seisenbaeva and V.G. Kessler, Precursor directed synthesis - molecular mechanisms in the Soft Chemistry approaches and their use for template-free synthesis of metal, metaloxide and metal chalcogenide nanoparticles and nanostructures, Nanoscale, Vol. 4, pp. 6229-6244,2004. 

---