In our optimization of the synthesis of Cu I -MFU-4l, we also found that treatment of Zn5Cl4(btdd)3 with copper(I) chloride dimethylsulfide in acetonitrile at 25 °C and activation of the resulting framework at 300 °C affords Cu2.4Zn2.6Cl1.6(btdd)3 (Cu2.4-MFU-4l; see Figures , S29-S30, and S35-S36). The H2 adsorption capacity measured for this material at 77 K and 1 mbar is 2.03 mmol/g, which corresponds closely to the theoretical capacity assuming binding of one molecule of H2 per Cu(I) site in the material (2.05 mmol/g) (Figure ). Advantageously, this approach affords access to Cu I -MFU-4l with a more well-defined formula and in fewer synthetic steps than the materials accessed via copper(II) substitution and autoreduction. The BET surface area of Cu2.4-MFU-4l is 3820(30) m 2 /g (Figure ), which is slightly lower than the surface area measured for Cu2.7-MFU-4l and consistent with the presence of only chloride capping ligands, in contrast to the mixture of chloride and smaller hydride ligands in Cu2.7-MFU-4l. For all O2, N2, and Ar isotherm data collection (see below), we employed Cu2.7-MFU-4l based on its slightly higher estimated copper(I) loading, while Cu2.4-MFU-4l was used for spectroscopic analyses due to its greater homogeneity of copper ions and coordinated anions.