Abstract Reactions of Rh 6(CO) 16 with bidentate ligands, Ph 2P(CH 2) n PPh 2( n = 2: diphosE = 1,2-bis(diphenylphosphino)ethane; n = 4: diphosB =1,4-bis(diphenylphosphino)butane) gave RH 6(CO) 12(diphosB) 2, Rh 6(CO) 15(diphosE) and Rh 6(CO) 13(diphosE) 3. In these clusters, each phosphorus donor site of diphosB is coordinated to adjacent rhodium atom, while only one donor site of diphosE is coordinated to a rhodium atom. The other site is believed to be bound to a face-bridging carbonyl group. Carbonyl exchange with carbon monoxide in these diphos-substituted clusters is affected by the mode of coordination of the ligands. In the diphosB-substituted cluster, both terminal and face bridging carbonyl groups readily exchanged with 13CO at 20°C, while in both diphosE mono- and tri-substituted clusters only a few percent of the terminal carbonyls exchanged and the face-bridging carbonyls were not observed to undergo exchange at all under similar conditions.