A new cubane-type Ru-4(CO)(12)(mu(3)-Se)(4) tetramer tailored for water photooxidation catalysis

In an effort to tailor a transition metal complex for photoinduced water sp litting, a new cubane-like ruthenium chalcogenide tetramer, Ru-4(CO)(12)(mu (3)-Se)(4), has been synthesized and structurally characterized by single- crystal X-ray diffraction. The orange-red compound crystallizes in the cubi c space group I(4) over bar 3m. The geometry of the Ru4Se4 units remains un distorted in the cubic symmetry 3m. Such a high symmetry is exceptional amo ng cubane-type cluster compounds. Ruthenium atoms are octahedrally coordina ted by three selenium atoms and three CO groups. Ru4Se4(CO)(12) clusters ar e linked via van der Waals forces by oxygen atoms which belong to CO ligand s of two different cluster units. By stacking of the cluster units along th e cubic axes two weakly coupled three-dimensional frameworks are formed. Fi rst principles band structure calculations reveal the strong influence of b oth the C-O bonding, which leads to a large splitting into bonding and anti bonding states, as well as of metal-ligand bonding. The latter gives rise t o several very sharp Ru d bands Of t(2g)-like symmetry just below the valen ce band maximum E-v, which are expected to be useful for oxidation catalysi s. While these states are bonding below -1.3 eV, they are antibonding near the edge of the valence band. For this reason, we expect a stabilization of the cubane core on depopulation of the highest occupied bands, Consequentl y, it is likely that a dynamic interrelation between electron transfer and crystal structure occurs.