Pyridine-M2+[M = Mg, Ca]: A promising organometallic system for potential hydrogen storage: In silico study

Pyridine-M2+ [M = Mg, Ca] hosts have been identified as potent H2 storage material, and this has been explored by a variety of functionals within the density functional theory (DFT) context. Around the linearly connected metal centre, the pyridine-Mg2+ and pyridine-Ca2+ building blocks can adsorb 6 and 7H2 molecules, respectively. The stability of Pyridine-M2+ [M = Mg, Ca] hosts has been proven by chemical hardness, aromaticity, and molecular dynamic simulations. After H2 adsorption, the aromaticity still remains. Adsorption of H2 molecules at a quasi-molecular type is supported by the fact that their average adsorption energy/H2 (Eads/H2) is between 0.22 and 0.72 eV. Pyridine-Mg2+@6H2 and pyridine-Ca2+@7H2 both have very impressive gravimetric wt % values (10.43 and 10.53 respectively). Average delocalization correction energy (Delta EavCT) supports the charge transfer type interaction between metal ions and adsorbed H2 molecules. The topological analysis reflects that bonding between metals (Mg & Ca) and trapped H2 molecules are mostly non-covalent types. Gibbs free energy changes (Delta G) [eV] indicate that the molecular hydrogen adsorption process will be spontaneous at 298 K for pyridine-Mg2+@nH2 systems and at or below 205 K for pyridine-Ca2+@nH2 systems and atom centered density matrix propagation (ADMP) study suggests the higher temperature for desorption.