Microcrystalline materials, preparation

Tin(IV) sulfide can be prepared by hydrogen sulfide precipitation of Sn(IV) from solution, to produce a microcrystalline material that is contaminated with oxide. Mosaic gold is a crystalline form of tin(IV) sulfide prepared by high-tempera-ture sublimation procedures. Mosaic gold is the reported product of heating mixtures of (1) tin and sulfur (2) tin, sulfur, and ammonium chloride (3) tin, sulfur, mercury, and ammonium chloride 9 (4) tin(II) oxide, sulfur, and ammonium chloride 9 (5) tin(II) chloride and sulfur 9 (6) tin(II) sulfide, tin(II) chloride, and sulfur.9... 

The red-brown polynuclear complex Ni4[(CH3)3CNC]7 can be recrystallized from diethyl ether in a Dry Ice-acetone bath to give a microcrystalline material which displays terminal and bridging isocyanide stretching frequencies at 2020 and 1605 cm"1, respectively. This highly air-sensitive material may be used as an intermediate in the preparation of nickel isocyanide complexes of unsaturated molecules simply by the addition of the desired molecules to a hexane or ether suspension. 

The Sm-Fe-Zr system. In the Sm-Fe-Zr system neither the 1 12 nor the A2 phase was observed for mechanically alloyed samples with a high Sm content. Instead, a (Sm,Zr)Fe3 phase forms with the rhombohedral PuNi3 crystal structure. Also this phase proved to be hard magnetic when prepared as a microcrystalline material by mechanical alloying [3.82]. Its coercivity reaches 11.8kA/cm. 

PTN(Me) is a white microcrystalline material, which is air stable in the solid state. The corresponding oxide cannot be obtained by classical P-phosphine oxidation with hydrogen peroxide, while the sulfide and selenide derivatives are easily and quantitatively prepared by reaction with the appropriate chalcogen element.6 PTN (Me) is soluble in nonpolar and polar solvents including water. At 20°C, PTN(Me), 1.18 g dissolves in 1 mL of water (6.81 x 10 2M). 

In contrast to all these attractive properties there are some disadvantages. The absorption effects of the primary radiation and the fluorescence radiation created in the analyte result in a shallow layer a few tenths of a millimeter deep that provides information on its composition. This requires a perfectly homogeneous sample, which often occurs naturally but must sometimes be produced by acid dissolution into liquids or by grinding and the preparation of pressed pellets. In both instances the feature of non-destructiveness is lost. Thin films or small amounts of microcrystalline material on any substrate are the ideal analyte where also the quantification process is simple because there is Hnearity between fluorescence intensity and concentration. In thick samples corrections for absorption and enhancement effects are necessary. 

Adel, A.M. Abd El-Wahab, Z.H. Ibrahim, A.A. Al-Shemy, M.T. Characterization of microcrystalline cellulose prepared from lignocellulosic materials. Part II Physicochemical properties. Carbohydr. Polym. 2011, 83 (2), 676-687. 

Aggregation is definitively observed, especially at high polymer concentrations and low temperatures. For example, after adding a poor solvent (e.g. methanol) to a solution of P3HT in MTHF ( 1 mg/ml) and successively cooling to — 78°C (dry ice-acetone temperature), microcrystalline material precipitates and can be collected. Powder X-ray scans of these aggregates indicate that this partially crystalline material has the same powder pattern as that of the as-prepared neutral films. 

Fraction I, a white microcrystalline material, was found to be readily soluble in water. Its sulfate, readily soluble in dilute alcohol, but quite insoluble in absolute alcohol, was prepared by acidifying an aqueous solution of fraction I to pH 2.5 with H2SO4 and adding acetone and ether. 

Certain solid phases, on the other hand, cannot be obtained (even as microcrystalline powders) by crystallization experiments, but instead can be generated only by other types of preparation procedure. Some types of preparation processes commonly (or in some cases inherently) yield microcrystaUine products, including (1) preparation of materials directly from solid-state chemical reactions (see Sect. 6.6), (2) preparation of materials by solid-state desolvation processes (see Sect. 6.4), (3) preparation of materials by solid-state grinding (mechanochemical) processes (see Sect. 6.2), and (4) preparation of materials directly by rapid precipitation from solution (as opposed to crystallization) (see Sect. 6.7). Again, structure determination from powder XRD data may represent the only opportunity for determining the structural properties of new solid phases obtained by such processes. 

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