Non-covalent interactions between metal cations and molecular hydrogen: spectroscopic studies of M⁺–H₂complexes

Abstract

Abstract We describe recent infrared spectroscopic investigations of charged complexes consisting of a hydrogen or deuterium molecule attached to an atomic metal cation, including complexes containing alkali metals (Li+–H2, Li+−D2, Na+–H2, Na+–D2), alkaline earth metals (Mg+–H2, Mg+–D2), main group metals and metalloids (B+–H2, B+–D2, Al+–H2) and transition metals (Cr+–D2, Mn+–H2, Zn+–D2 and Ag+–H2). These species have been probed spectroscopically through their infrared absorptions in the H–H or D–D stretch regions (3700–4160 cm−1 and 2700–3000 cm−1 ranges, respectively) by monitoring metal cation photofragments as the infrared wavelength is scanned. The spectra, which typically display resolved rotational structure, provide fundamental information on the M++H2 interaction, and can be used to develop and test intermolecular potential energy surfaces. The extended data-set for M+–H2 and M+–D2 complexes allows systematic explorations of the way in which the size and electronic structure of the metal cation influences the properties of the intermolecular M+ H2 bond. Aside from their fundamental interest, spectroscopic and theoretical investigations of M+–H2 complexes provide insights into the intermolecular forces underlying hydrogen storage in porous materials containing metal cations, including zeolites and metal organic frameworks. Keywords: molecular ionsintermolecular interactionshydrogen storagelaser spectroscopyion cluster Acknowledgement The authors have enjoyed collaborations with theoretician colleagues Prof. A. Buchachenko, Prof. J. Kłos, and former students and postdoctoral fellows, Dr B. Poad, Dr C. Emmeluth, and Dr C. Thompson who contributed to the M+–H2 spectroscopic investigations. Work described in this review was supported under the Australian Research Council's Discovery Project funding scheme (Project Numbers DP0986980, DP110100312 and DP120100100).