An expanded Co-IRMOF-74 material, with a similar structure to the well-known Co-MOF-74 but with wider pores has been developed using a larger organic linker containing two benzene rings instead of one. Moreover, the partial isomorphic substitution of cobalt for nickel in the inorganic cluster of the MOF was performed in gradation, obtaining a series of materials with mixed-metal Co/Ni sites in different proportion. This partial isomorphic substitution of the OMS displayed a significant enhancement of their hydrogen adsorption capacity. The presence of nickel increased the hydrogen uptake at cryogenic and ambient temperature, particularly when nickel and cobalt are present in the structure in the same ratio. This behaviour demonstrated a synergetic contribution, between both transition metal cations, related to electronic effects. This new series of expanded materials evidence the great versatility of MOF structures in tuning their porosity and chemistry, which can let eventually hosting different active species inside the pores to enhance specific properties, particularly their affinity to hydrogen molecules.