<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> / Thesis / Doctor of Philosophy (PhD)

Regensburg und Mailand, Univ., Diss., 2008.

Techn. Hochsch., Diss., 2001--Aachen.

Zugl.: Karlsruhe, Univ., Diss., 2005

Zugl.: Marburg, Univ., Diss., 2005

Zugl.: Stuttgart, Univ., Diss., 2007

Universiẗat-Gesamthochsch., Diss.--Paderborn, 1997.

Universiẗat, Diss.--Paderborn, 2001.

Universiẗat, Diss., 2001--Regensburg. / Erscheinungsjahr an der Haupttitelstelle: 2001.

Crystal engineering offers a rational way of analyzing crystal structures and designing new structures with properties. The supramolecular synthon concept was introduced in 1995 and has shown versatility and utility in the design of molecular solids. Chapter 1 gives a general introduction about the development of the concept of supramolecular synthons over the years which has seen a transition from synthesis to structures and dynamics. This thesis focuses on the later phase of the development of the concept of supramolecular synthons. Chapter 2 introduces the idea of structural landscape and describes a structural landscape of a conformationally flexible molecule, orcinol, and explores the synthon preferences of this particular molecule towards cocrystal formation. Chapter 3 explores a combinatorial matrix to show both global and local features of a structural landscape. Chapter 4 takes a component of this landscape namely 4,4'-bipyridine and 4-hydroxybenzoic acid and shows the occurrence of synthon polymorphism in cocrystals which originates from the interplay of geometrical and chemical factors. Chapter 5 introduces a four step method for the identification of multiple synthons by FTIR spectroscopy. Along with, it shows that the rarity of synthon polymorphism is not a case of overlooking of crystals in the process of selecting good looking crystals. Chapter 6 takes a series of dihalogenated phenols and indicates that the Br prefers type II. This chapter also explains elastic bending on the basis of halogen bonds. Chapter 7 attempts to explore the Cl/Br isostructurality in the light of type I and type II contacts and concludes that Cl/Br isostructurality arises from a geometrical model and therefore it is quite similar to Cl/Me isostructurality. Chapter 8 attempts to analyze the class of trichlorophenols and reveals structural modularity in this class of compounds. The modularity of 3,4,5-trichlorophenol is explored in crystal design in chapter 9 in terms of LSAM (Long Range Synthon Aufbau Module) A subsequent study in solution by NMR reveals the presence of LSAM in solution and establishes a hierarchy of the dissociation of its components. The concept of supramolecular synthon has come a long way from being a tool in a crystal engineer’s toolbox to a structural unit responsible for crystallization and therefore offer multiple possibilities both in terms of structures and dynamics. This thesis attempts to explore some of these possibilities based mainly on the concepts of structural landscape and halogen bonds which are blended with the concept of supramolecular synthons.