The design and synthesis of metal-amine networks with application to solar energy capture
Creators: name: Szpakolski, Katherine
Publisher: name: RMIT University
Year: 2024

description: The chemical and physical properties of coordination compounds can be tuned by altering the oxidation state of the metal ion(s), the ligands and the counter-anion. This is of great importance as it enables the design of complexes for specific applications including solar cell technology, in particular dye-sensitized solar cells (DSSC). The aim of the research presented in this thesis was to investigate and synthesize metal-amine complexes with light harvesting properties, known as “dyes” and, if possible, incorporate them in DSSC. <br><br>The most common and extensively explored “dye” species have consisted primarily of ruthenium coordination complexes, while other metal complexes with similar properties, such as copper, have not been exploited to their full potential. Therefore, the overall aim of this work was to further extend the use of ruthenium and copper coordination compounds, by tuning their properties to improve their absorption of visible light, and adsorption onto semiconductor surfaces, so as to incorporate them into DSSC. <br><br>Several new ruthenium(II) complexes with bipyridine and bipyridine type coordination, including new ligands with alternative surface binding possibilities, were synthesized and characterised as possible dyes. Initially, ruthenium complexes containing either carboxylate or phosphonate linkages were used, but due to limitations, an alternative linker, based on a silyl group, was investigated. Two new complexes, [Ru(bipy-sil)2Cl2] and [Ru(bipy-sil)2(NCS)2], which contain this linker have been synthesised and characterised. Each of the ruthenium based dyes was incorporated into a DSSC, by adhering the dye onto a semiconducting surface. The overall efficiency of the dye for solar energy capture was determined by measurement of the current and voltage. <br><br>A number of new copper(I) complexes which possess some of the favourable photochemical and photophysical properties required for “dye” species were synthesised, but were found to be unsuitable for use in a DSSC. Several copper(II) complexes were also isolated, and two of the dimeric species were examined for their magnetic properties. <br><br>The ligand 1H-[1,10]-phenanthrolin-2-one (HOphen) was synthesised hydrothermally in the presence of Cu(II). A copper(I) complex containing the HOphen ligand, [Cu2(Ophen)2] was isolated as a black compound, with favourable properties, but unfortunately it was insoluble for use in a DSSC. However, a novel dinuclear heteroleptic copper(II) complex, [Cu2(Ophen)2(phen)2](NO3)2.9H2O, was isolated as a by-product, the formation of which allowed an alternative mechanism for the formation of ‘covalent-hydrates’ to be proposed. <br><br>The final copper study investigated complexes which contained the ligand di-2-pyridyl ketone (dpk). Two copper(I) complexes were synthesised, [Cu(dpk)(NCS)]n, which were found to be polymorphs of one another. The two complexes were isolated as black crystals and exhibited favourable properties for solar energy capture. However, when the polymers were allowed to stand in the supernatant a novel dinuclear copper(II) complex, [Cu2(dpk.acetone)2(NCS)2], was isolated. A mechanism has been proposed, whereby a transition-metal-promoted aldol condensation reaction has occurred. On the basis of the formation of the novel dinuclear copper(II) complex an investigation into alternative ketones led to the isolation of five further complexes, three of which contained the ligand, picolinic acid (pic) which is believed to have formed from dpk through a novel Baeyer-Villiger rearrangement.<br>