The transition metal halides Re(H-2)Br-2(NO)((PPr3)-Pr-i)(2) and MHCl(CO)((PPr3)-Pr-i)(2), M = Ru, Os afforded the hydrido(tertiary phosphine)metalates [ReH3(NO)((PPr3)-Pr-i)(2)](-) and [MH3(CO)((PPr3)-Pr-i)(2)](-), M=Ru, Os in reactions with KH in the presence of crown ethers (2.2.2-crypt, 18-crown-6, 1-aza-18-crown-6) under H-2. The anionic hydrides [RuH3(PPh3)(3)](-) and [MH5((PPr3)-Pr-i)(2)](-), M = RU, Os were also efficiently prepared by this method. The trihydrides [K(18-crown-6)][OsH3(CO)((PPr3)-Pr-i)(2)] and [K(1-aza-18-crown-6)][OsH3(CO)((PPr3)-Pr-i)(2)] were characterized by single-crystal X-ray diffraction and possess the mer structure with two trans hydride ligands. Unlike the former structure, the latter is chain polymeric via CO ... K+ links and NH ... HOs hydrogen bends; this is the first one-dimensional network to be held together by proton-hydride bonding. The [K(1-aza-18-crown-6)](+) N-H IR band shift (Delta v) indicates the increasing strength of hydrogen bonding with the following hydrides: [ReH3(NO)((PPr3)-Pr-i)(2)](-) (102 cm(-1)) < [OsH3(CO)((PPr3)-Pr-i)(2)](-) (116 cm(-1)) < [RuH3(CO)((PPr3)-Pr-i)(2)](-) (136 cm(-1)). The order of acidity of the conjugate acid forms follows a different trend: Os(H-2)(H)(2)(CO)((PPr3)-Pr-i)(2) > Re(H)(4)(NO)((PPr3)-Pr-i)(2) > Ru(H-2)(H)(2)(CO)((PPr3)-Pr-i)(2). The crypt-containing cations interact weakly with the anions in [K(2.2.2-crypt][OsH3(CO)((PPr3)-Pr-i)(2)] and [K(2.2.2-crypt)][RuH3(CO)((PPr3)-Pr-i)(2)] in toluene or tetrahydrofuran THF). This results in the formation of only the mer isomers. Substantial ion-pairing between IK(18-crown-6)](+) and the trihydrides results in the stabilization of the fac isomers to a greater degree in toluene than in polar THF. Use of [K(1-aza-18-crown-6)](+) results in even greater stabilization of the fac isomers both in THF and toluene. Nuclear Overhauser effect (NOE) experiments reveal that NH ... HM hydrogen bonds cause tighter ion pairing in this case.