Theoretical studies on aminoborane oligomers

Abstract

Aminoborane oligomers, (NH2BH2)n are the possible dehydrogenation products of NH3BH3 and NH4BH4, which are promising materials for chemical hydrogen storage. The structure and reaction stabilities of H (NH2BH2)nH (n=1–4) are calculated by density functional theory for the zigzag, square-wave linear chain structures, along with the coil and ring type structures. We compared the structure stabilities of these oligomers in the view of total energies and found that the coil structured oligomers are stable among other structured oligomers. The reaction stabilities are studied by calculating dipole moment, band gap (ΔE(LUMO–HOMO)) and electronegativity of these oligomers. The study reveals that the dimer ring structured oligomers are found to be more stable towards the reaction compared to all other structured oligomers with high band gap values. The molecular electrostatic potential (MEP) surfaces besides with infrared and Raman spectra of aminoborane oligomers are characterized. It is found that, the B–H bonds have maximum electrostatic potential and minimum for the N–H bonds. The bond dissociation energies of N–H and B–H bonds are calculated to understand their pyrolysis mechanism at molecular level. Comparing the bond dissociation energies of N–H and B–H bonds reveal that N–H bonds are weaker.