The interaction between (CF3)(2)CHOH and OsHCl(CO)((PBu2Me)-Bu-t)(2) in toluene and hexane is shown by H-1 NMR (chemical shift, NOE and relaxation times) and IR (v(CO), v(Os)-H, and v(Os)-(Cl)) spectroscopies:to involve -Delta H degrees approximate to 3-4 kcal/mol and -Delta S degrees approximate to 7-9 cal mol(-1) K-1. Integrated molecular orbital/molecular mechanics calculations show definitively that the hydrogen bond acceptor is chloride and that steric effects preclude any O-->Os donation by the alcohol. Analysis of the calculated energies and structures shows that such hydrogen bonding increases the electrophilic character of the unsaturated osmium.