Ceramic and porous framework metal silicates and phosphates from molecular precursors: an ever-evolving ambient synthesis approach

Abstract

Metal oxides, silicates and phosphates represent three of the major classes of materials which have been extensively investigated owing to their enormous application potential. Although these materials are found to occur widely in nature, the last few decades have seen a lot of activity in the laboratory synthesis of these zeolites. Our research group has been investigating aspects of molecular silicates and phosphates by carrying out appropriate chemistries in an organic medium, as against the hydrothermal conditions. Subsequent to the forays in using silanols (silanetriols RSi(OH)3, in particular) as primary building blocks in modelling zeolitic materials, we turned our attention to a thermally labile diester of phosphoric acid, viz. di-tert-butylphosphate, as a means to prepare a multitude of discrete and polymeric metal organophosphates which cleanly decomposed to nanoscopic ceramic metal phosphates at temperatures as low as 300 °C. By switching over to a bulky monoaryl ester of phosphoric acid, viz. 2,6-diisopropylphenyl phosphate, it has been possible to build several 0-D cage structures which resemble the D4R, D6R and D8R (and even other less common) secondary building blocks of zeolites. The clusters possessing D4R architecture were further investigated for their framework forming capabilities using hydrogen bonding and covalent-coordinate bonding interactions. This article is a compilation of contributions from our laboratory with some historical perspective and hence not considered an exhaustive review of the subject.