Structural data for four closely related dinuclear nickel hydride complexes have been compared in order to gain insight into the factors governing the Ni-H-Ni geometries. The derivatives [( dippm)(2)Ni2X2]( A-H) [ dippm) 1,2-bis( diisopropylphosphino)methane] were found to contain a linear Ni - H - Ni bridge, whereas the derivatives [( dcpm)(2)Ni2X2]( mu-H) [ dcpm) 1,2-bis( dicyclohexylphosphino)-methane] were found to contain a bent Ni - H - Ni bridge. The number of internal and interatomic CH-to-halide contacts of the former were much shorter and more numerous than the latter, suggesting an important role of external forces in bridging hydride geometries.