Löffler, Susanne

Supramolecular coordination cages, assembled from organic ligands and metal cations, are of
broad interest due to their versatile topologies and properties. Discrete cages often possess a
secluded cavity, which allows the inclusion of various guest molecules (anions, cations and
neutral molecules). These structures are stabilized by non-covalent interactions and commonly
referred to as host-guest complexes.
The here presented thesis entitled “Host-Guest Chemistry of Acridone-based Coordination
Cages” focuses on the synthesis, self-assembly and host-guest chemistry of novel coordination
cages based on acridone-derived ligands L and square-planar Pd(II) metal ions. In the
first part of this thesis, the preparation and characterization of an interpenetrated coordination
cage from eight bispyridyl ligands L1 and four Pd(II) cations was studied. This [Pd4L1
8] assembly
shows the unique ability to encapsulate neutral guest molecules after activation through
addition of halide anions. It is the first example of an interpenetrated coordination cage that
shows this feature. In this project, the range of encapsulated neutral molecules was explored.
In particular, the size, shape as well as the amount and positions of heteroatoms within the
guests were varied and the influence of dispersion interactions in the formation of the hostguest
complexes was investigated (Chapter 2). Additionally, the interpenetrated coordination
cage has the unique ability to function as a photosensitizer by exciting triplet oxygen into singlet
oxygen. The reactivity of the coordination cage was discovered as the guest 1,3-cyclohexadiene
was transformed into the Hetero-Diels-Alder product 2,3-dioxabicyclo[2.2.2]oct-5ene in
presence of oxygen and light (Chapter 3). The uptake of halide anions in the interpenetrated
coordination cage occurs after an allosteric mechanism with positive cooperativity. The chloride-
binding ability of the acridone-based [Pd4L1
8] was compared with previously reported interpenetrated
coordination cages based on dibenzosuberone and phenothiazine (Chapter 6).
Introduction of a bulky adamantyl group in the novel ligand L2 prevents dimerization and results
in the formation of the monomeric cage [Pd2L2
4]. Owing to steric crowding, the adamantyl substituent
is considerably bent sideways with respect to the ligand backbone and an unprecedented
flipping motion of the free ligand was observed. Surprisingly, this unique dynamic also
occurs in the coordination cage. Despite the very dense packing within the self-assembled
structure, the cage is able to encapsulate a series of bis-anionic guests in an induced-fit fashion.
Additionally, electronic structure calculations revealed a substantial contribution from dispersion
interactions between the guest and the surrounding adamantyl groups that stabilize
the host–guest complex (Chapter 4).
X
The variation of ligand length, through introduction of different linkers between the acridone
backbone and the coordinating pyridyl groups, illustrated the remarkable influence of this ligand
feature. Depending on the length, the formation of monomeric or dimeric interpenetrated
coordination cages was achieved (Chapter 5).
The formation and characterization of these novel structures were verified with the help of NMR
spectroscopic studies, HR-MS spectrometric data and X-ray diffraction analysis of several obtained
crystal structures. The collected results give a deeper insight in the understanding of
supramolecular coordination cages, especially their formation via self-assembly, their ability to
form host-guest complexes with a variety of different guest molecules and the influence of
dispersion interactions on the stability of the systems. It broadens the scope of supramolecular
assemblies and is the basis for further applications in the field of selective recognition, tunable
guest uptake and catalysis

Georg-August-University Göttingen

Host-Guest Chemistry of Acridone-based Coordiantion Cages

https://ediss.uni-goettingen.de/bitstream/11858/00-1735-0000-002E-E415-6/1/Thesis_SL__Revision_20180531b.pdf

Host-Guest Chemistry of Acridone-based Coordiantion Cages

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Georg-August-University Göttingen