investigation of lithium complex hydrides li2mh5 (m = b, al) as hydrogen storage materials; a theoretical study

lithium complex hydrides li₂mh₅ (m= b, al) in are potential hydrogen storage material because of their high capacity of (10, 6.5 wt. % respectively) h2. however, their high thermodynamic stability is unfavorable for dehydrogenation processes. understanding the bonding nature of al-h, b-h and li-h are essential for predicting their dehydrogenation mechanism and then improving their dehydrogenation performance. quadrupolar parameters of nuclei can be used as a tool to understand the electronic structure of compounds. in this work the charge density distribution in li₂alh₅ and li₂bh₅ was compared. thus using calculated nuclear quadrupole coupling constants (nqcc) of ²h nuclei, the electronic structure of li₂alh₅ and li₂bh₅ was studied. the results show that between two proposed dehydrogenation mechanisms for li₂mh₅, hetro phase dehydrogenation is

preferred than partial dissociation to limh₄. furthermore easier condition for hetro phase dehydrogenation is expected in li₂alh₅. the electric field gradient (efg) of quadrupolar nuclei were calculated to obtain nqcc parameters. all calculations performed using gaussian 03 at mp2/6-311g** level of theory. the selected level and basis set give the rather acceptable qualitative nqccs of hydrogen atoms.