A series of mixed bis(mu-silylene) complexes of rhodium and iridium [RhIr(CO)(2)(mu-SiHR)(mu-(SiRR2)-R-1)(dppm)(2)] (R = R-1 = R-2 = Ph (4); R = R-1 = Ph, R-2 = Cl (5); R = R-1 = Ph, R-2 = Me (6); R = 3,5-C6H3F2, R-1 = Ph, R-2 = Me (7); R = 3,5-C6H3F2, R-1 = 2,4,6-C6H2Me3, R-2 = H (8)) have been synthesized by the reaction of the silylene-bridged dihydride complexes, [RhIr(H)(2)(CO)(2)(mu-SiHR)(dPPm)(2)] (1, R = Ph; 2, R = C6H3F2), with a number of secondary or primary silanes (Ph2SiH2, PhClSiH2, PhMeSiH2, C6H2Me3SiH3). The influence of substituents and pi-stacking interactions on the Si center dot center dot center dot Si distance (determined by X-ray crystallography) in this series and the implications regarding the nature of the Si center dot center dot center dot Si interactions are discussed. A series of novel (mu-silylene)/(mu-germylene) complexes, [RhIr(CO)(2)(mu-SiHPh)(mu-GePh2)(dppm)(2)] (9) and [RhIr(CO)(2)(mu-(SiRR2)-R-1)(mu-GeHPh)(dppm)(2)] (R-1 = Ph, R-2 = H (11); R-1 = R-2 = Ph (12); R-1 = Ph, R-2 = Me (13)), have also been synthesized by reaction of the silylene-bridged dihydride complex, [RhIr(H)(2)(CO)(2)(mu-SiHPh)(dPPm)(2)] (1), with 1 equiv of diphenylgermane and by reaction of the germylene-bridged dihydride complex, [RhIr(H)(2)(CO)(2)(mu-GeHPh)(dpPin)(2)] (3), with 1 equiv of the respective silanes. These complexes have been characterized by multinuclear NMR spectroscopy and X-ray crystallography.