Hydrogen adsorption properties of functionalized closo-dicarborane (C2B4H6) and boranes (B6H6) are studied and compared using quantum chemical methods. More number of H-2 molecules gets adsorbed on metal functionalized carboranes than metal functionalized boranes considered in this work. One, three and five H-2 molecules get adsorbed on each metal atom in B6H4Be2, B6H4Li2 and B6H4Sc2 complexes, respectively. One additional H-2 molecule per metal atom gets adsorbed on C2B4H4Be2, C2B4H4Li2 and C2B4H4Sc2 complexes than B6H4Be2, B6H4Li2 and B6H4Sc2 complexes, respectively. The H-2 uptake capacity of C2B4H4Be2, C2B4H4Li2 and C2B4H4Sc2 complexes is found to be 8.28, 15.92 and 13.04 wt%, respectively, whereas that of B6H4Be2, B6H4Li2 and B6H4Sc2 complexes is found to be 4.43, 12.75 and 11.26 wt%, respectively. Adsorption energy values reveal that though more number H-2 molecules get adsorbed on metal functionalized carboranes H-2 adsorption on metal functionalized carboranes is thermodynamically unfavourable even at very low temperature whereas it is favourable on B6H4Be2, B6H4Li2, and B6H4Sc2, below 185, 110 and 170 K respectively. B6H4Be2, B6H4Li2, and B6H4Sc2 as well as C2B4H4Be2, C2B4H4Li2, and C2B4H4Sc2 complexes are not promising materials for hydrogen storage at room temperature. However, metal doped B6H6 are promising candidate for hydrogen storage at low temperature and 1 atm pressure. For Be, Li and Sc doped B6H6 the H-2 adsorption is thermodynamically favourable below 185, 110 and 170 K, respectively. Zero point energy correction has the larger effect on H-2 adsorption energy for Be, Li and Sc functionalized borane than Be, Li and Sc functionalized carborane.