The structural, energetic, and spectroscopic properties of the dihydrogen-bonded complexes LiH...H-2, LiH...CH4, LiH...C2H6, and LiH...C2H2 are investigated. In particular, the interaction energy is decomposed into physically meaningful contributions, and the calculated vibrational frequencies, the magnetic resonance shielding constants, and inter- and intramolecular spin-spin coupling constants are analyzed in terms of their correlation with the interaction energy. Unlike the other three complexes, which can be classified as weak van der Waals complexes, the LiH...C2H2 complex resembles a conventional hydrogen-bonded system. The complexation-induced changes in the vibrational frequencies and in the magnetic resonance shielding constants correlate with the interaction energy, as does the reduced coupling (2h)J(HX) between the proton of LiH and hydrogen or carbon nucleus of the proton donor, while (1h)J(HH) do not correlate with the interaction energy. The calculations have been carried out using Moller-Plesset perturbation theory, coupled-cluster theory, and density-functional theory. (C) 2003 American Institute of Physics.