PHOTOCHEMICAL CORE MANIPULATION IN HIGH-NUCLEARITY OS-HG CLUSTERS

The cluster dianion [Os18Hg3C2(CO)42]2- (2) has been synthesized in over 90% yield by reacting [OS10C(CO)24]2- with 1.6 equiv of Hg(O2CCF3)2, and the molecular structure of its [PPN]+ salt ([PPN]+ = bis(triphenylphosphine)iminium(1+)) was determined by X-ray crystallography. The cluster contains a central Hg3 triangle fusing two tricapped-octahedral Os9 fragments together: triclinic, P1BAR, a = 19.022 (4) angstrom, b = 15.737 (3) angstrom, c = 15.204 (3) angstrom, alpha = 115.66 (2)degrees, beta = 68.32 (2)degrees, gamma = 115.45 (3)degrees, V = 3612.2 angstrom3, Z = 1, R = 0.0859. 2 undergoes partial demercuration on irradiation with visible light to generate the corresponding dimercury cluster dianion [0s18Hg2C2(CO)42]2- (3), which thermally reincorporates metallic mercury quantitatively, thus making 2 a photochromic system. The structure of 3 contains a dimercury fragment sandwiched between the two Os9 subclusters in a uniquely compact way. Both dianions 2 and 3 can be reversibly oxidized to their corresponding monoanions that are related to each other by a similar reversible photochemical process. Quantum yields for the photolytic Hg extrusion for both systems were obtained from spectral sequences after successive irradiation with the 458-, 488-, and 514-nm lines of an Ar ion laser. They lie between 0.004 and 0.006 for the dianionic and between 0.003 and 0.005 for the monoanionic cluster, reflecting the efficiency of nonreactive deactivation pathways in these systems. Irradiation with UV light at 337 nm (N2 laser) favors the competing CO dissociation leading to a drop in the quantum efficiency of the demercuration by an order of magnitude.