Einfluss von Pseudohalogeniden und Carboxylaten auf die Komplexierung zweiwertiger Metallionen durch Tris(2-pyridinylen-N-oxid)triaminoguanidin

• How pseudohalides and carboxylates influence the complexation of divalent metal ions by tris(2-pyridinylen-N-oxide)triaminoguanidine

Sturm, Lisa; Oppel, Iris Marga (Thesis advisor); Albrecht, Markus (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

C3-symmetric triaminoguanidine based ligands are established as triangular building blocks in supramolecular compounds like polymers or discrete monomers, dimers, and polyhedra. The reaction of tris(2-pyridinylene-N-oxide)triaminoguanidine with zinc(II) carboxylates in presence of (pseudo)halides results in protein-sized metallocycles consisting of twelve ligands linked by octahedrally coordinated zinc(II) centers. Besides crystals of the metallocycles, the crystallization of carboxylate-bridged coordination di/polymers is observed in the same reaction vessel. To address this issue, the influence of the solvent, the chain length of the carboxylate, the co-ligands and their stoichiometry is investigated, while other factors are kept as constant as possible. In this way, a sensitive dependence of the binding motif on the stoichiometric pseudohalide-carboxylate ratio was revealed. Small or no amounts of pseudohalide combined with sufficient equivalents of carboxylate lead to the formation of carboxylate-bridged di/polymers. Increasing the pseudohalide stoichiometry results in the crystallization of mixed compounds and finally of metallocycles. By adjusting the co-ligand stoichiometry, crystallization of a desired compound can be predicted and selectively induced. Applying this principle to the chemically related cadmium(II) yields in a series of carboxylate-bridged di/polymers, whereas the addition of thiocyanate gives a cadmium(II)-bridged structure, which can be considered as metallocycle fragment. Cadmium(II) prefers coordination numbers of six and higher due to its ionic radius, which inhibits the formation of a metallocycle. Cobalt(II) ions instead built up polymers and metallocycles showing the same co-ligand dependence as zinc(II). Magnetic measurements revealed predominantly antiferromagnetic behavior of these compounds due to short Co(II)-Co(II) distances. In heterometallic metallocycles, zinc(II) ions may isolate the cobalt(II) centers, which could probably result in very large discrete molecules with interesting magnetic properties.