Magnetic Properties of Multinuclear Titanium Complexes

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Self-assembly of well defined molecular architectures is attracting a huge international research effort. While such work has yielded systems with novel photophysical (e. g. light-harvesting) and electrochemical properties, surprisingly little work has been carried out on assemblies with novel magnetic behaviour. However, the knowledge of the magnetic behaviour of early transition metal multinuclear complexes employing d1, d2 or d3 metal centers is comparatively low. We have found, that discrete molecular architectures (molecular triangular, square and rectangular) can be build up by using low valent titanium complexes and bridging bisazine molecules like pyrazine, pyrimidine, 4,4¿-bipyridine or quinoxalines. The formation of the molecular architectures is often accompanied by simultaneously occurring C-C couplings of primary formed radical anions or by C-H bond activation and dehydrogenative C-C couplings leading to attractive trinucleare HAT type (1,4,5,8,9,12-hexaazatriphenylene) as well as HATN titanium (1,6,7,12,13,18-hexaazatrinaphthylene) complexes. Generally, polypyridyl compounds constitute an attractive class of organic ligands, which have been widely used for the preparation of supramolecular species which are potentially useful to understand energy as well as electron transfer processes. In this project we want investigate the magnetic behaviour of multinuclear low valent titanium complexes as a function of the molecular arrangement, the oxidation and the spin state of the involved metal centers in homo and mixed valent complexes. Particularly, investigation to compare the magnetic properties of molecular squares with tetrahedral like arranged aggregates depending on the nature of the bridging ligands are of interest. The magnetic properties should be correlated with the electrochemical behaviour, the photophysical properties as well as the MO situation characterized by DFT calculation. At the end switchable systems based on early transition metals could becomes possible.