The synthesis and characterization of two new metal–organic frameworks (MOFs) UHM-2 and UHM-4, which are isoreticular to PCN-12 and UHM-3 (see Inorg. Chem., 2009, 48, 6559), are presented. Both materials comprise dicopper paddle-wheel units and the new tetracarboxylic acid linkers 5,5′-(propane-2,2-diyl)diisophthalic acid and 5,5′-(dimethylgermanediyl) diisophthalic acid, respectively. In addition, isoreticular mixed-linker MOFs were synthesized with the silicon- and germanium containing linkers. UHM-2 to -4 constitute a homologous series allowing a systematic study on how the incorporation of atoms with higher polarizability in linkers may enhance the overall hydrogen uptake of MOFs. The experimental work is complemented by dispersion-corrected DFT calculations on C2v conformers of model systems representing the linkers of these MOFs.