Here, we describe the preparation of four structurally modified MOF-5s and carried out a systematic study of the effects of the structural modifications on the evolution of the crystal structure, pore characteristics, and H-2 capacities of MOF-5s. The structural modifications were found to significantly influence the pore characteristics, and the specific surface areas of the MOF-5s decreased with the evolution of an ultrafine porosity. These changes were correlated with an increase in the H-2 storage capacity of the MOF-5 (from 1.2 to 2.0 wt% at -196 degrees C and 1 bar). The structural modifications also enhanced the thermal stability of the MOF-5s (the decomposition temperature increased from 438 degrees C to 510 degrees C). These results are particularly useful for the design of favorable MOF-based adsorbents with a high H-2 uptake coupled with a high thermal stability. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.