According to low-temperature UV-Vis spectroscopy data, the two-step protonation of iron subgroup metal hydrides [{P(CH2CH2PPh2)(3)}MH2] (M = Fe, Ru, Os) with p-nitrophenol includes the formation of ion pairs stabilized by a hydrogen bond between the cationic dihydrogen complex and the phenolate anion. The trend of the extent of proton transfer appeared to be aperiodic, FeH much less than OsH < RuH, in contrast to the previously obtained sequence of the proton-acceptor capacity of the hydride ligand, which increases down the group.