Aromaticity and hydrogen storage capability of planar and rings

Theoretical investigation on planar N 6 4 - and N 4 2 - rings has been performed. The aromaticity of the rings has been analyzed through their nucleus independent chemical shift (NICS) values as well as the σ- and π-contribution of the Z-component of the induced magnetic field. Counter to a previously reported result [Chem. Phys. Lett. 432 (2006) 331], the N 6 4 - ring is found to be a local minimum and aromatic with planar D6h symmetry. The N 4 2 - ring exhibits conflicting aromaticity like Al 4 4 - . Both the N 6 4 - and N 4 2 - rings can be stabilized in presence of suitable counter cations and systems like N6Ca2 and N4Li2 can trap molecular hydrogen.