Zweikernige Nickel(II)-Komplexe und dreikernige Kupfer(II)-Komplexe als Baueinheiten im Molekularen Magnetismus

Abstract

This thesis deals with the design and synthesis of dinuclear Ni(II) complexes and trinuclear Cu(II) complexes and their application as building blocks in the research area of molecular magnetism.The first part of the work described herein deals with Ni(II)-azide complexes. For the preparation of dinuclear Ni(II) complexes, several pyrazolate ligands have been synthesized, each containing two particular, structurally diverse yet well-defined binding pockets. The coordination mode of the azide ligand - and therewith also its magnetic properties - as a bridging ligand between two metal atoms is dependent on the metal-metal distance, which itself can be regulated by adjusting the length of the pyrazolate ligand side arms. Long, flexible side arms result in a bridging m-1,1-azide coordination in such dinuclear Ni(II) complexes, while short side arms lead to complexes with a m-1,3-azide binding mode.The high flexibility of the coordinated bridging azide ligand is a key factor controlling the overall magnetic properties exhibited by the complexes formed. Making use of this feature, the preparation of materials with hysteretic magnetic bistability is demonstrated. The briging azide fragment can operate like a molecular switch, as elucidated by x-ray crystallographic measurements.Pyrazolate based bimetallic complexes with weakly coordinating solvent molecules or anions in terminal metal binding sites have been applied as building blocks for the preparation of tetranuclear species with different topologies as weel as for the synthesis of 1D-chain structures. Besides the formation of tetranuclear complexes with a regular rectangular coordination of the Ni(II) ions with m-1,1 and m-1,3 azide bridging ligands, the synthesis of a variety of tetranuclear Ni(II) complexes with unusual topologies including the very rare m-1,1,3 azide bridge and especially the hitherto unknown central m-1,1,3,3 azide bridging mode have been achieved. The magnetostructural correlations for these bridging azide units can be formulated as the sum of the interactions of single end-to-end and end-on fragments.The application of pyrazolate based bimetallic building blocks has also opened the targeted synthesis of J-alternating 1D-systems with S = 1 spin carriers. The magnetic properties of these chains have been analyzed using quantum Monte Carlo simulation in cooperation with theoretical physicists.The second part of this thesis focusses on the synthesis and characterization, both structurally and magnetochemically, of Cu(II) complexes with different topologies, using a triazine-based ligand. The magnetic interaction within the Cu(II)-triazine complexes is weak, because coordination of N-donor atoms of the triazine ligand to the Cu(II)-ions does not take place. In one trinuclear Cu(II) complex, incorporating two triazine ligands and displaying a wheel-like structure, the first x-ray crystallographic evidence for an anion--interaction could be established, which was in perfect agreement with theoretical predictions. Such interactions play a major role in the field of supramolecular chemistry and most likely also in biological processes.