The lower surface areas of Mn(OAc)-MFU-4l and CdI-MFU-4l compared to ZnCl-MFU-4l are attributed to the larger capping anions at the peripheral metal sites of the pentanuclear clusters, as well as the greater atomic masses of Cd and iodine for CdI-MFU-4l. Indeed, the pore volumes of both Mn(OAc)-MFU-4l and CdI-MFU-4l by the Dubinin-Radushkevich method (Vp) agree within 10% of the calculated values (Vcalcd) expected from the available free volume of the structures, as modeled using Materials Studio (Table ). Successful syntheses of MX-MFU-4l frameworks prompted us to diagnose how the metal identity affects structural parameters, specifically unit cell parameters and the local geometry of the pentanuclear cluster. We therefore screened synthetic conditions for growing single crystals of MX-MFU-4l. Treatment of H2btdd with MnI2 in a DMF/CH3OH/HNO3 mixture followed by postsynthetic anion exchange with F -afforded single crystals of MnF-MFU-4l (see SI for experimental details; treatment with fluoride was implemented to resolve the anion compositional disorder present from the solvothermal synthesis). For CdI-MFU-4l, crystals were grown with a condition similar to that reported for ZnCl-MFU-4l. All MX-MFU-4l frameworks crystallize in the cubic space group Fm3 � m with slightly different unit cell parameters of a = 30.9085(3) Å for ZnCl-MFU-4l, 30.9027(9) Å for MnF-MFU-4l, and 31.1633(6) Å for CdI-MFU-4l at 100 K (Table ). Interestingly, the ionic radius of the central metal M is not reflected in the trend of these unit cell parameters. Furthermore, the unit cell parameters determined for the single crystals are smaller than those obtained for microcrystalline powders by Pawley fits against the powder x-ray diffraction data, even when considering the difference in temperature for these experiments (100 and 298 K for single-crystal x-ray diffraction and powder x-ray diffraction, respectively). We note that the btdd 2-linker is not strictly planar in the MX-MFU-4l crystal structures, because the dibenzodioxin moieties are generally found to be disordered over two bent positions due to thermal breathing motions (Figure ). Particle size and temperature variations may contribute to different degrees of linker vibrations, causing the discrepancy between the unit cell parameters determined from single-crystal and powder x-ray diffraction data. In addition, the extent to which the linker can bend becomes greater for frameworks with larger metals. This linker bending, as well as the size of the capping anion, explain the slightly smaller unit cell parameter of MnF-MFU-4l compared to ZnCl-MFU-4l, although the ionic radius of Mn II is larger than that of Zn II . Despite the counterintuitive trend of the unit cell parameter determined by single-crystal x-ray diffraction versus the size of M II ions, the geometry of a tripodal ligand scaffold reflects the size of M II ions (Figure ). A larger central M II ion forms a longer bond to the middle N1 atom of each triazolate group and a larger opening of the tripodal site for a peripheral metal site, as gauged by the distance between the closest N2 atoms of neighboring linkers.