New tetrahedral cluster compounds of iridium. Synthesis of the anions [Ir4(CO)11X]- (X = Cl, Br, I, CN, SCN) and x-ray structure of [PPh4] [Ir4(CO)11Br]

[Ir4(CO)11X]- anions are obtained by reaction of halide and pseudo-halide ions with Ir4(CO)12. X-ray determination of the structure of [Ir4(CO)11Br]- shows that the carbonyl arrangement differs from that of the parent Ir4(CO)12, and is similar to that known for Co4(CO)12; one terminal CO group in the basal M3(CO)9 moiety is replaced by the bromide ligand, and two of the bridging CO groups become markedly asymmetric. © 1978.