When the binding enthalpy for a series of d 10 M I metals (Cu I , Ag I , and Au I ) is compared, Ag I binds the weakest among the d 10 M I metals. Consequently, all three variants of the Ag I M II 4Cl3(bta)6 cluster (M II = Zn, Mn, Cd) fall within the optimal enthalpy range (Figure ) for a hydrogen storage material, thus making Ag Ibased frameworks promising for practical hydrogen storage applications. Au I sites generally exhibit too strong H2 binding (-ΔH = 38.3-62.7 kJ/mol), as indicated by the complete dissociation of the H2 molecule. Interestingly, although Au I M II 4Cl3(bta)6 clusters feature the two-coordinate binding mode by a pair of triazolates, a larger central ion weakens the H2 binding enthalpy even for this geometry of metal sites. We reason that the size of the central ion can change the bite-angle of the two triazolate moieties for the same just as it controls the degree of pyramidality of trigonal M I sites, by tuning the π-backbonding ability.