SYNTHESIS, STRUCTURAL CHARACTERIZATION, SPECTROSCOPIC STUDIES AND COMPUTATIONAL INVESTIGATIONS OF 1,2,5-TELLURADIAZOLES AND THEIR SUPRAMOLECULAR ASSEMBLIES

Abstract

<p> The use of Te-N-C heterocycles as supramolecular building blocks was investigated. The propensity of the heavy main-group elements to engage in secondary bonding interactions motivated a survey of the literature that identified the supramolecular association patterns that are most frequent in the crystal structures of tellurium compounds. A notation was proposed to classify those supramolecular synthons. The shortest Te-N secondary bonding distances are observed in the crystals of 1,2,5-chalcogenadiazoles which assemble the virtual four-membered ring [Te-Nb. Detailed computational investigations (OFT) established that the Te-N secondary bonding interactions are stabilized by a combination of electrostatic and Lewis acid-base covalent contributions. The study also indicated that the [Te-N] 2 supramolecular synthon meets the requirements of strength, directionality and reversibility that are necessary in supramolecular chemistry. A general method was developed for the synthesis of a wide variety of telluradiazoles. These compounds were used in experiments that probed the ability of steric effects to disrupt the self-assembly and select dimers instead of ribbon polymers. Derivatives resulting from the addition of Lewis acids and bases were also investigated. Photoelectron spectroscopy confirmed the details of the calculated electronic structures of benzo-2, 1,3-chalcogenadiazoles and mass spectrometry provided evidence of the association of these molecules in gas phase. A molecular mechanics method was parameterized to reproduce the structural features of the [Te-N]2 supramolecular synthon and, using this information, envision new supramolecular architectures based on 1,2,5-telluradiazoles. The use of the [Te-N]2 supramolecular synthon in the design and function of materials with properties such as thermochromism and nonlinear optical responses was demonstrated. Preliminary findings also highlighted the potential use of this approach in molecular materials that conduct electricity. </P>