Hexanuclear iridium clusters supported on magnesium oxide

Ir4(CO)12 on the surface of MgO reacts to give HIr4(CO)11, which upon treatment with CO at 200 Deg gives Ir6(CO)152- on the surface in high yield. Treatment of the latter with a soln. of [PPN] [Cl] leads to extn. of Ir6(CO)152- by cation metathesis. The surface-bound Ir6(CO)152- was characterized by EXAFS spectroscopy, with the data indicating an av. Ir-Ir coordination no. of 4.1 and an av. Ir-Ir distance of 2.77 .ANG., in close agreement with the published crystallog. data for this anion in the solid state. The reactions of the Ir carbonyls on the basic MgO surface closely parallel those of Ir carbonyl anions in basic solns. Treatment of the MgO-supported Ir6(CO)152- in He followed by H2 at 300 Deg gives decarbonylated surface species shown by EXAFS spectroscopy to have Ir cluster frames substantially unchanged from those of the carbonyl anion precursor. The decarbonylated Ir clusters are among the most nearly uniform supported metals. [on SciFinder (R)]