From small molecules to nano-scale architectures - a supramolecular approach

Date

2008-04-17T16:53:12Z

Journal Title

Journal ISSN

Volume Title

Publisher

Kansas State University

Abstract

We have shown that supramolecular synthons can be used to construct discrete two or three component co-crystals and 1-D inorganic-organic chains and dramatically influence the arrangement of nanoparticle assemblies. A collection of supramolecular reagents (SR's) have been designed and synthesised to carry out a systematic study into hydrogen bonding. In order to test Etter's guideline "the best proton donor and acceptor remaining after intramolecular hydrogen-bond formation will form an intermolecular hydrogen-bond" and to develop a hierarchy of interactions, a series of co-crystals between the supramolecular reagents and hydrogen-bond donors (carboxylic acids) have been synthesised. Co-crystals with pyrazole benzamide SR's have demonstrated the ability to fine-tune hydrogen-bond formation. By utilising a poor hydrogen-bond acceptor (pyrazole) the incoming carboxylic acid opts to form a heteromeric acid-amide dimer via N-H[three dots]O hydrogen bonds. Additionally, we have shown that the hydrogen-bond acceptor strength of the pyrazole can be turned up through simple covalent modifications (i.e. isomer change or addition of methyl groups to the pyrazole ring). Although the heteromeric acid-amide dimer is observed, O-H[three dots]N hydrogen bonds to the pyrazole are also observed in cases when more than one donor site is present (i.e. di-carboxylic acids and 4-hydroxybenzoic acid). Furthermore, co-crystals with picolyl-indazole and pyrimidine-pyrazole SR's agree with Etter's guideline. In all cases, the incoming carboxylic acid forms an O-H[three dots]N hydrogen bond to the best acceptor (pyridine and pyrazole, respectively). The homomeric amide-amide dimer has been used to construct inorganic-organic hybrid materials. The reaction between the pyrazole benzamide ligands with acac or "paddle-wheel" complex ions yielded 1-D chains. Furthermore, pyrimidine-bispyrazole and functionalised 1,3-bisbenzylpyrazole ligands have been utilised as chelating-ligands for reliable metal coordination. Finally, the power of supramolecular synthons to control the arrangement of much larger nanoparticle assemblies has been shown. Both homomeric (acid-acid, alcohol-alcohol) and heteromeric (acid-imidazole, alcohol-imidazole) hydrogen bonding cause significant changes in nanoparticle assemblies.

Description

Keywords

Supramolecular, Nano, Pyrazole, Supermolecule, Heterocycle

Graduation Month

May

Degree

Doctor of Philosophy

Department

Department of Chemistry

Major Professor

Christer B. Aakeröy

Date

2008

Type

Dissertation

Citation