Hydrothermal synthesis carboxylates

Plater M. J., Foreman M. R. St J., Howie R. A., Skakle J. M. S. and Slawin A. M. Z., Hydrothermal synthesis of polymeric metal carboxylates from benzene-1,2,4,5-tetracarboxylic acid and benzene-1,2,4-tricarboxylic acid, Inorg. Chim. Acta 315 (2001) pp. 126-132... 

The closed-shell nature of aluminosilicates renders them ineffective for certain reactions favoured by transition (d-block) elements. Haushalter has made efforts to prepare stable shape-selective microporous solids involving molybdenum phosphates [15]. These solids are prepared hydrothermally in aqueous HjPO in the presence of cationic templates along with anionic octahedral-tetrahedral frameworks containing Mo in oxidation state less than 5+ and possessing Mo-Mo bonds. Some of these contain around 40 vol% accessible internal void space. There is rich chemistry in these systems and there is considerable potential for applications. Based on this approach one may indeed discover novel microporous and catalytic oxide systems. Several open-framework metal phosphates [16] and carboxylates [17] with different connectivities have been prepared by hydrothermal synthesis. 

The literature on inorganic open-framework materials abounds in the synthesis and characterization of metal silicates, phosphates and carboxylates. Most of these materials have an organic amine as the template. In the last few years, it has been shown that anions such as sulfate, selenite and selenate can also be employed to obtain organically templated open-framework materials. This tutorial review provides an up-to-date survey of organically templated metal sulfates, selenites and selenates, prepared under hydrothermal conditions. The discussion includes one-, two-, and three-dimensional structures of these materials, many of which possess open architectures, The article should be useful to practitioners of inorganic and materials chemistry, besides students and teachers. The article serves to demonstrate how most oxy-anions can be used to build complex structures with metal-oxygen polyhedra. 

Alternatively, hydrolysis of presumably not so soluble lanthanide carboxylate complexes may be possible by carrying out the hydrolysis under hydrothermal conditions. It appears that such conditions (high temperature and high pressure) are particularly conducive to the formation of polynuclear lanthanide complexes, often with unpredictable but nevertheless interesting structure. Under ambient pressure, analogous synthesis generally produces complexes with carboxylate coordination only and without any involvement of hydroxo groups. 

The diversity of ordered porous solids increases at an astonishing rate, particularly among the readily crystallised MOFs, and continues to olfer novel materials properties. There is no obvious barrier to the synthesis of a myriad of new zeolite, zeotype or hybrid structures. Challenges remain, however. For zeolitic aluminosilicates, the 10 A pore size restriction remains an important barrier, and an enantiomerically pure zeolite is still out of reach. For nonsilicate crystalline microporous solids, thermal and hydrothermal stability, rather than framework geometry, limit their applicability, since fully crystalline germanates and carboxylates with pores in the mesoporous range now exist, and these solids have enormous specific surface areas. In these hybrid solids the ability to choose chirality in the building units indicates that it will be possible to prepare these in chiral form the first examples have already been prepared. 

These considerations are general to the synthesis of open framework solids. Details specific to particular chemical compositions are given below. By far the largest amount of synthetic work has been devoted to the aluminosilicates and other metallosilicates and silicas, which are synthesised hydrothermally at alkaline pHs (or pH 7 for fluoride syntheses). Phosphate-based solids have also received much attention and there is much current interest in inorganic-organic hybrid solids, such as carboxylates and phosphonates, which tend to have higher solubilities than silicates, and crystallise at more acidic pHs. 

A report in the same line [380] involves suspension of ZnS.Mn nanoparticles in microemulsions, with the surface modified by polyoxyethylene(l)laurylether phosphoric acid or polyoxyethylene(4.5)laurylether acetic acid. The coated particles exhibited several times higher photoluminescence intensity and quantum efficiency compared to the uncoated ones. The phosphate group P = O or the carboxyl group C = O, with their luminescent centers, were functional in this improvement, thus opening new routes for imparting superior optical properties on microemulsion-synthesized particles. Gan etaL [376] used four routes for the synthesis of ZnS Mn (i) the relatively new route that involved hydrothermal... 

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