Novel strategy to synthesize homonuclear cubic heteroleptic metal-organic cages using Ruthenium(II) complexes and N-donor ligands : Synthesis, Characterization, Complexation, and Attempts

Sammanfattning

Metal-Organic Frameworks (MOF) are a group of polymeric porous self-assembly structures consisting of a combination of coordinated metal ions and organic-linker molecules resulting in supramolecules with one-, two- or three-dimensional structures. The porosity of the macromolecule allows smaller molecules to enter and remain coordinated via intermolecular interactions, therefore the potential use as molecule containers, catalysts, and enzyme mimics has always been a huge topic of discussion over the decades. The smallest unit of a MOF is referred to as a metal-organic cage (MOC) and its attention is on the rise due to being superior in all the tasks mentioned due to its increased pore accessibility. Several structures of homoleptic (all organic linkers are the same) MOCs have been synthesized within these few decades but the interest of heteroleptic (variety of linkers) MOCs is on the rise due to their further versatile usage in comparisons to homoleptic structures. However, a problem is the fact that heteroleptic MOCs are structures that require difficult synthesis strategies in order to achieve the wanted product, hence demand complicated calculations and extensive understanding of the properties of the materials. In this work we propose and test a brand-new strategy to synthesize heteroleptic three-dimensional cubic MOCs, which will significantly aid future projects to synthesize cubic MOCs. The approach is robust and controlled ultimately allowing solely one type of structure to form, by using octahedral ruthenium(II) acting as corners of the cube and three different organic-linker ligands to connect the metal centers. Over the span of a year this work was divided into two parts where: 1) Metal-anchor complexes and organic-linker ligands synthesis including characterization, 2) Self-assembly complexation of the metal and ligands. The first part consisted of synthesizing and characterizing four different organic-linker ligands and their intermediates, in addition to the synthetic route of the ruthenium metal centers. The second part was the self-assembly complexation of the ruthenium complexes. Unfortunately, this work was not able to reach the final structure within time hence the furthest step achieved was potentially the first complexation step of the MOC out of three. The uncertainty of the result stems from the fact that characteristics of complexation are exhibited via NMR spectroscopy, yet due to requiring additional time to assemble it was not possible to extract the product and fully confirm its existence. For future studies, we suggest investigating more effective methods to self-assemble the complex or reviewing the metal-anchors to contain more labile ligands allowing quicker assembly to take place.