that are considered to have the best properties for hydrogen storage as of May 2012 (in order of decreasing hydrogen storage capacity). While each MOF described has its advantages, none of these MOFs reach all of the standards set by the U.S. DOE. Therefore, it is not yet known whether materials with high surface areas, small pores, or di- or trivalent metal clusters produce the most favorable MOFs for hydrogen storage. High hydrogen uptake is attributed to overlapping attractive potentials from multiple copper paddle-wheel units: each Cu(II) center can potentially lose a terminal solvent ligand bound in the axial position, providing an open coordination site for hydrogen binding. Structural impacts on hydrogen storage capacity To date, hydrogen storage in MOFs at room temperature is a battle between maximizing storage capacity and maintaining reasonable desorption rates, while conserving the integrity of the adsorbent framework (e.g. completely evacuating pores, preserving the MOF structure, etc.) over many cycles. There are two major strategies governing the design of MOFs for hydrogen storage: 1) to increase the theoretical storage capacity of the material, and 2) to bring the operating conditions closer to ambient temperature and pressure. Rowsell and Yaghi have identified several directions to these ends in some of the early papers. Surface area The general trend in MOFs used for hydrogen storage is that the greater the surface area, the more hydrogen the MOF can store. High surface area materials tend to exhibit increased micropore volume and inherently low bulk density, allowing for more hydrogen adsorption to occur. Hydrogen adsorption enthalpy High hydrogen adsorption enthalpy is also important. Theoretical studies have shown that 22-25 kJ/mol interactions are ideal for hydrogen storage at room temperature, as they are strong enough to adsorb H2, but weak enough to allow for quick desorption. The interaction between hydrogen and uncharged organic linkers is not this strong, and so a considerable amount of work has gone in synthesis of MOFs with exposed metal sites, to which hydrogen adsorbs with an enthalpy of 5-10 kJ/mol. Synthetically, this may be achieved by using ligands whose geometries prevent the metal from being fully coordinated, by removing volatile metal-bound solvent molecules over the course of synthesis, and by post-synthetic impregnation with additional metal cations. and are great examples of increased binding energy due to open metal coordination sites; however, their high metal-hydrogen bond dissociation energies result in a tremendous release of heat upon