Multinuclear n.m.r. studies (1H, 1H-{103Rh}, l3C, 13C-{103Rh}, and 103Rh) show that protonation of [Rh6(CO)15]2– and [Rh6(CO)15C]2– at low temperatures gives [Rh6H(CO)15]– and [Rh6H(CO)15C]– which contain terminal and triangular face-bridging hydrides respectively;warming these solutions to room temperature results in loss of hydrogen and formation of [Rh12(CO)30]2– and [Rh12(CO)24(C)2]2– respectively.