DFT study of coinage metal-hydrogen associations as hydrogen storage materials stabilized by weakly coordinating anions

Abstract

Density Functional Theory (DFT) calculations were employed to study a series of coinage metal-hydrogen associations formulated as [M(Η2)n][A] (M = CuI, AgI or AuI, n = 1–5). The [M(Η2)n][A] salts utilize both their anions and cations for H2 storage. The [M(Η2)n]+ cations could be stabilized in the solid state by voluminous counter-anions, i.e. the [(H3B) (BH2NH2)5(NH2)]-, [B(CNBH3)3]- and [B12H12]- anions. The estimated bond dissociation energies (BDEs) of the M···(η2-H2) bonds are 5–17, 4–11 and 1–26 kcal/mol for the [Cu(Η2)4]+, [Ag (Η2)4]+ and [Au (Η2)4]+ cationic species respectively, while the fifth H2 molecule is estimated to be very loosely associated to the metal center. Four H2 molecules could be exploited from the [Cu(Η2)n][A] and [Ag (Η2)n][A] molecules in addition to the amount of H2 stored in the anion [A]-. Among the [M(Η2)n][A] salts optimal gravimetric, kinetic and thermodynamic properties and relatively low cost, are predicted for [Cu(Η2)n][(H3B) (BH2NH2)5(NH2)].