Chemistry of iridium carbonyl cluster complexes. Synthesis and characterization of mixed-metal carbonyl clusters via capping reactions with HgCl2 and Au(PPh3)Cl. Crystal structures of [N(PPh3)2][Ir6(.mu.3-CO)3(CO)12(.mu.3-HgCl)].cntdot.0.5C6H12 and [NMe3(CH2Ph)][Ir6(.mu.-CO)3(CO)12[.mu.3-Au(PPh3)].cntdot.C4H8O