Ruthenium Carbon-Rich Group as a Redox-Switchable Metal Coupling Unit in Linear Trinuclear Complexes

The preparation and properties of novel ruthenium carbon-rich complexes [(Ph-C equivalent to C-)(2-n)Ru(dppe)(2)(-C equivalent to C-bipyM(hfac)(2))(n)] (n = 1, 2; M = Cu-II, Mn-II; bipy = 2,2'-bipyridin-5-yl) characterized by single-crystal X-ray diffraction and designed for molecular magnetism are reported. With the help of EPR spectroscopy, we show that the neutral ruthenium system sets up a magnetic coupling between two remote paramagnetic Cu-II units. More specifically, these copper compounds are unique examples of bimetallic and linear heterotrimetallic compounds for which a complete rationalization of the magnetic interactions could be made for exceptionally long distances between the spin carriers (8.3 angstrom between adjacent Cu and Ru centers, 16.6 angstrom between external Cu centers) and compared at two different redox states. Surprisingly, oxidation of the ruthenium redox-active metal coupling unit (MCU), which introduces an additional spin unit on the carbon-rich part, leads to weaker magnetic interactions. In contrast, in the simpler parent complexes bearing only one paramagnetic metal unit [Ph-C equivalent to C-Ru(dppe)(2)-C equivalent to C-bipyCu(hfac)(2)], one-electron oxidation of the ruthenium bis(acetylide) unit generates an interaction between the Cu and Ru spin carriers of magnitude comparable to that observed between the two far apart Cu ions in the above corresponding neutral trimetallic system. Evaluation and rationalization of this coupling with theoretical tools are in rational agreement with experiments for such complex systems.