The title compound appears to be present in solution as one major (98%) and two minor(ca, 1% each) isomers. All three isomers contain one bridging and one terminal hydride ligand. However, they differ in the location of the terminal hydride. Proton T-1 measurements at variable temperature have allowed the determination of H-T-H-B distances in each isomer. An estimation of the relative "hydridicity" of bridging and terminal hydrides has been gained by measuring the T-1 of H-2(mu-H-2)Os-3(CO)(11), while insights into the terminal/bridging hydride exchange have been gained from H-1 variable-temperature: NMR.