CRYSTAL ENGINEERING STUDIES ON MULTIDIMENSIONAL COORDINATION POLYMERS AND RELATED ORGANIC CRYSTALS FOR SOLID STATE PROPERTIES AND REACTIVITIES

Abstract

The design and synthesis of desired coordination polymers (CPs) are much easier than ever before due to the exploitation of crystal engineering principles successfully in recent times. For more than two decades, this active research area is very attractive to materials researchers due to its modular design, exhibits interesting properties and find potential applications in catalysis, gas storage, ion exchange, separation, polymerization, magnetism, conductivity, optics, etc. Of these, controlling the reactivity of the solids is a challenging task, but has potential applications in green synthesis of organic compounds with regio- and stereoselectivity. This thesis addresses some of these aspects including the design of crystalline solids to undergo [2+2] cycloaddition reactions. A linear Cu(II) CP was found transformed to a sheet or ladder structure by the loss of coordinated DMF when the single crystals or the ground powder respectively, were used. Further, the sheet structure rearranged to ladder polymer when the desolvated single crystals were ground to powder, as monitored by 1H-NMR spectroscopy. In another finding, two polymorphic forms of a ladder CP with parallel and crisscross alignments of the C=C bond pairs undergo 100% [2+2] cycloaddition reaction. But the one with a parallel orientation of C=C bonds retains its single crystallinity after the reaction. The reversibility of [2+2] cycloaddition reaction was studied for the first time in 2D CPs which also exhibited reversible water uptake coupled with magnetic phase transformation. While investigating the thermal cleavage of the cyclobutane rings in these systems, they also found to undergo thermal isomerization. Interestingly the simple but most popular rctt-tetrapyridyl cyclobutane (tpcb) has been found to thermally isomerize to rtct isomer cleanly in air. This has been investigated in detail along with other cyclobutane containing s-block metal complexes in the solid state. The tetrahedrally disposed rtct-tpcb ligands have been used along with rctt-1,2,3,4-tetrakis-(4'-carboxyphenyl)-cyclobutane (TCCB) to make a number of novel porous coordination polymers. Another solid-state property studied by design in CP was gas adsorption. Three dimensional interpenetrated diamondoid networks generated from asymmetric ligands were used to tune the porosity and thereby increase the gas uptake. One of the synthesized dia MOF showed the best uptake for methane.