Universität zu Köln

Payen, Leo Michel David ORCID: 0000-0003-1291-9690 (2025). Complexes of Pt(II), Pd(II) and Ni(II) with Ring-Expanded Tridentate Cyclometalated Ligands. PhD thesis, Universität zu Köln.

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Abstract

In this work, square-planar complexes [M(L)X] of Pt(II), Pd(II) and Ni(II) with L = tridentate, cyclometalated, so-called ring-expanded ligands were studied. In a first approach, the 8-quinolinyl moiety was used to achieve the ring-expanded, six-membered metallacycle. The complexes with N^C^N or C^N^N binding motives (N = pyridyl or quinolinyl) for the tridentate ligands revealed strong geometric distortions as indicated by single crystal X-ray diffraction. This leads to nearly perfect square planar coordination at the cost of coplanarity and conjugation of the ligand backbones. Spectroscopic data, supported by DFT-calculations revealed a strong influence of the ring-expansion on MLCT absorptions. Preliminary investigations showed promising luminescence results, especially for Ni(II) compounds. Introduction of further chromophore moieties such as carbazolyl and fluorenyl resulted in even stronger structural distortions of the ligand backbone. UV/Vis-absorption spectroscopy and cyclic voltammetry confirmed carbazole-containing complexes to exhibit strong shifts of MLCT transitions as well as electrochemical potentials, due to the strong σ-donor character of the ligands. Fluorene-containing complexes showed broad UV/Vis-absorptions, but the introduction of the fluorene moiety had little impact on electrochemistry. Introduction of sulphur and oxygen into the ligand backbones expanded the scope to N^C^S and N^C^O systems. Their complexes feature interesting oxidations of the sulphur-atoms in the ligand backbone and weak coordination of oxygen-donors, prone to exchange with solvent molecules. Systematic coligand (X) exchange reactions of the [M(L)X] complexes were carried out using the nitrato derivatives [M(L)NO3] as key intermediates. This NO3-coligand was exchanged under very mild conditions, allowing for a wide range of anionic, pseudo-halogenide coligands to be introduced. This method was further adapted to introduce acetylide- or pyrrole-derived coligands, that are strong σ-donors with potential for π-backbonding. These coligands have a large impact on optical and electrochemical properties and the systematic exchange is a potent method for adjusting complex properties. Overall, this work broadens the portfolio of tridentate ligands for cyclometalated complexes, with ring-expansion opening the way to many new complex species. Their properties can be tailored to specific applications through ligand design with various donors or further tuned by coligand exchange reactions. Future work could see these methods applied towards complexes in luminescent materials and optoelectronic devices.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Payen, Leo Michel David lpayen@smail.uni-koeln.de https://orcid.org/0000-0003-1291-9690 UNSPECIFIED
Corporate Creators:	Universität zu Köln
URN:	urn:nbn:de:hbz:38-791550
Date:	2025
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Inorganic Chemistry
Subjects:	Chemistry and allied sciences
Uncontrolled Keywords:	Keywords Language Chemistry, Inorganic Chemistry, Coordination Chemistry, Nickel, Palladium, Platinum, Cyclometalated, Tridentate, Ring-Expanded English
Date of oral exam:	9 October 2025
Referee:	Name Academic Title Klein, Axel Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/79155