Author: Yim, King Him
Title: Design of lanthanide supramolecular architectures
Advisors: Law, Ga-lai (ABCT)
Wong, Wing-tak (ABCT)
Degree: Ph.D.
Year: 2022
Subject: Rare earth metals
Supramolecular chemistry
Hong Kong Polytechnic University -- Dissertations
Department: Department of Applied Biology and Chemical Technology
Pages: xiii, 350 pages : color illustrations
Language: English
Abstract: Self-assembly of supramolecular architectures have been widely used in catalysis and luminescent sensing. By contrast to transition metals, lanthanide self-assembled supramolecular complexes exhibit unique chemical and physical properties which have shown promising application in luminescent sensing and diagnostic applications. In Chapter 1, the background of supramolecular chemistry and lanthanides are briefly introduced. Since the applications of these lanthanide self assembled systems are all structure-dependent, this thesis aims to develop different lanthanide supramolecular compounds from small assembled units by targeting changes in ligand design and reaction conditions. The other goal is to create chiral functional materials to explore and develop the area of chiroptic by looking at the effect of chirality in structure and correlating to its optical properties and function. In this aspect, such assemblies require the control of stereoselectivity of the lanthanide supramolecular architectures. However, controlling the stereoselectivity of lanthanide complexes is rather challenging due to the kinetically labile properties and poor stereochemical preferences. In Chapter 2- point chirality as well as the linker/spacer effect will be explored.
In Chapter 2a, two pairs of linear biphenyl-linked chiral bis-tridentate ligands were prepared and the point chirality effect of four resulting lanthanide supramolecular bimetallic helicates were studied. By extending the point chirality from the two metal centers, the ability of chirality transfer was shown to be greatly affected and diastereoselective and nondiastereoselective formation of bimetallic triple helicates were observed.
In Chapter 2b, two C2-symmetric bis-tridentate ligands were designed based on symmetry principles where the effect of the length of the spacer towards self-assembly process was studied. Results showed that the length of the spacer greatly affected the supramolecular formation even if the offset distance of two metal chelating units remained unchanged. Higher-ordered supramolecular tetrahedron was then prepared based on the small helicate units, which resulted in an helicate-to-cage transformation. In this system, it was found that the stability of the tetrahedron was dependent on the size of the ionic radii. Hence, this study showed the importance of ionic radii and ligand design towards supramolecular transformation. Lanthanide heterometallic complexes are important for engineering optical material and is promising for creating more versatile multifunctional properties as well as improving up-conversion efficiency and enhancing optical properties. However, preparation of lanthanide heterometallic complexes is extremely difficult owing to the similar ionic radii causing issues in controlled selectively.
In Chapter 3, attempt to prepare lanthanide heterometallic tetrahedron by a simple crystallization method was reported. In this work, it was found that upon crystallization with a mixture of two different lanthanide metal helicates with very similar ionic radii, e.g. one helicate strand of Eu and Ln (Ln = Sm /Gd), a mixture of five different lanthanide tetrahedron was formed as evidenced by ESI-HRMS. The percentage amount of each tetrahedron was estimated by MS deconvolution. It was evidenced, that the self-assembly process of the tetrahedron deviated from the statistical result. The helicate-to-tetrahedron mechanism was also investigated in this chapter.
In Chapter 4, focus here is channeled to looking at point chirality and the chiral domino effect in a lanthanide system. Hence different types of small building blocks based on amino acids were used to investigate and explore the area. The construction of enantiomeric pure lanthanide supramolecular complexes strongly relies on point chirality induced by a chiral group with the strongest point chirality effect. As a result, the ligand design is restricted by the use of a specific chiral group and the distance between the point chirality and metal centers. A series of ligands which was coupled to different types of amino acid were designed and synthesized. The design principal here is based on a chiral group being attached to the C-terminal of a short peptide which is expected to transfer chiral information to the metal center via the chiral domino effect.
Rights: All rights reserved
Access: open access

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