A NOVEL UNSATURATED TETRAHEDRAL HYDRIDO-CARBONYL CLUSTER ANION OF RHENIUM - SYNTHESIS AND X-RAY CHARACTERIZATION OF {[RE4(MU-H)3(MU-3-H)2(CO)12]-}

The reaction of the anion [Re4(\u3bc-H)6(CO) 12]2- with acids affords the unsaturated (58 valence electron) anion [Re4H5(CO)12]-, which contains a distorted tetrahedral cluster, with Re-Re bond lengths in the range 2.857(1)-3.251(1) \uc5, bearing three edge-bridging and two face-capping hydride ligands, completely fluxional in solution down to -90 \ub0C