With respect to the first principle calculations, we predicted that two pairs of transition metals （e.g., Sc2 and Ti2） can be interbedded between two tetranitrogen rings to form two sandwich-like binuclear complexes respectively （e.g. N4Sc2N4 and NaTi2N4）. These two complexes can adsorb up to eight and ten hydrogen molecules, corresponding to a gravimetric storage capacity of 7.7 and 9.9 wt%, respectively. These sandwich-type complexes proposed in this work are favorable for reversible adsorption and desorption of hydrogen at ambient conditions. The results are helpful for the development of a new class of high-capacity hydrogen-storage media.
The coordination complex of Co（Ⅲ） based on a macrocyclic triamine ligand 1,4-diacetate-1,4,7-triazacyclodecane （L） has been synthesized and characterized. The metal cation is bonded with three nitrogen atoms and two oxygen atoms of L and one chloride ion to form a distorted octahedral geometry. This complex coordinated with macrocyclic ligand possesses large pore volume that will be contributed to observe high H2 adsorption. With respect to the first-principles electronic structure calculations, the feasibility to store hydrogen in the complex is explored. Indeed, the complex has shown a very high total H2 adsorption of 7.2 wt% （wt% = （weight of adsorbed H2）/（weight of host material））, with a binding energy of 0.03 eV/H2
