Keywords: Osmium / Hydrido ligand / Proton transfer / Hydrogen bonds / Density functional calculationsThe interaction between Cp*OsH(dppe) (1) and a series of proton donors (HA) of increasing strength [indole, CFH 2 CH 2 OH (MFE), CF 3 CH 2 OH (TFE), (CF 3 ) 2 CHOH (HFIP), p-nitrophenol, and HBF 4 ·Et 2 O] has been investigated experimentally by variable temperature IR and NMR spectroscopy in solvents with different coordinating abilities (alkanes, dichloromethane and their mixtures) and computationally at the DFT/B3PW91 level using different models. Both the IR and NMR spectroscopic data for the interaction with weak proton donors conform to the criteria of M-H···H-A bond formation. Theoretical calculations, however, indicate an asymmetric bifurcated interaction with a significant contribution from the metal atom, which is greater than that previously found for the corresponding Fe system. The basicity factor of 1 (E j = 1.47) is greater than those of the Ru (1.39) and Fe (1.35) congeners, in agreement with previous studies