Hydrogen Storage in Prussian Blue Analogues: H-2 Interaction with the Metal Found at the Cavity Surface

In open framework Prussian blue analogues, all of the metal atoms linked at the N end of the CN groups are found at the surface of the cavities with an unsaturated coordination environment. These metal sites are available for a specific interaction with guest species. To shed light on the H-2 interaction with these metal sites, H-2 adsorption isotherms in Ni3-xMnx[Co(CN)(6)](2), Ni3-xCox[Co(CN)(6)](2), Ni3-xCdx[Co-(CN)(6)](2), and Co3-xMnx[Co(CN)(6)](2) were recorded and evaluated. According to the obtained data for the adsorption heat values, the strongest H-2-metal interaction was found for Ni. The same evidence is obtained from the fitting of the isotherms using the osmotic model, where the value for the osmotic parameter (g) senses the strength for the guest-host interaction. The probable origin of that stronger interaction for the Ni atom is discussed. The information derived from these mixed series was complemented with an analogue study for T-3[Co(CN)(6)](2) and T-3[Ir(CN)(6)](2), with T = Mn, Co, Ni, Zn, Cu, and Cd. The strength for the guest-host interation in these two simple series follows the order: Ni > Cu > Co similar to Cd similar to Mn similar to Zn. For the series T-3[Co(CN)(6)](2), H-2 adsorption isotherms up to 7600 Torr were recorded, confirming that the strongest H-2-metal interation corresponds to Ni and Cu. The samples to be studied were characterized from energy-dispersed spectroscopy, X-ray diffraction infrared, and CO2 adsorption data.