Towards functional coordination solids: Hydrogen storage materials and microporous magnets

In Chapter 2, the porosity and hydrogen storage properties for the dehydrated Prussian blue analogues M3[Co(CN)6]2 (M = Mn, Fe, Co, Ni, Cu, Zn) are reported. Argon sorption isotherms measured at 87 K afford BET surface areas ranging from 560 m2/g for Ni 3[Co(CN)6]2 to 870 m2/g for Mn 3[Co(CN)6]2; the latter value is comparable to the highest surface area reported for any known zeolite. All six compounds show significant hydrogen sorption at 77 K and 890 torr, varying from 1.4 wt. % and 0.018 kg H2/L for Zn3[Co(CN)6] 2 to 1.8 wt. % and 0.025 kg H2/L for Cu3[Co(CN) 6]2. Fits to the sorption data employing the Langmuir-Freundlich equation give maximum uptake quantities, resulting in a predicted storage capacity of 2.1 wt. % and 0.029 kg H2/L for Cu3[Co(CN) 6]2 at saturation. Enthalpies of adsorption for the frameworks were calculated from hydrogen isotherms measured at 77 K and 87 K, and found to increase with M varying in the order Mn < Zn < Fe < Co < Cu < Ni. In all cases, the binding enthalpies, which lie in the range 5.3-7.4 kJ/mol, are higher than the 4.7-5.2 kJ/mol measured for Zn4O(1,4-benzendicarboxylate) 3.; In Chapter 3, the porosity and hydrogen storage properties of the dehydrated Prussian blue type solids Ga[Co(CN)6], Fe4[Fe(CN) 6]3, M2[Fe(CN)6] (M = Mn, Co, Ni, Cu), and Co3[Co(CN)5]2 are reported and compared to those of the M3[Co(CN)6]2 type compounds described in Chapter 2. Nitrogen sorption measurements suggest partial framework collapse for M2[Fe(CN)6] (M = Co, Ni) and Co3[Co(CN) 5]2, and complete collapse for Mn2[Fe(CN) 6]. Hydrogen sorption isotherms measured at 77 K reveal a correlation between uptake capacity and the concentration of framework vacancies, with Langmuir-Freundlich fits predicting saturation values of 1.4 wt % for Ga[Co(CN) 6], 1.6 wt % for Fe4[Fe(CN)6]3, 2.1 wt % for Cu3[Co(CN)6]2, and 2.3 wt % for Cu2[Fe(CN)6]. Enthalpies of H2 adsorption were calculated from isotherms measured at 77 and 87 K. Importantly, the values obtained for compounds with framework vacancies are not significantly greater than for the fully-occupied framework of Ga[Co(CN)6] (6.3-6.9 kJ/mol). This suggests that the exposed metal coordination sites in these materials do not dominate the hydrogen binding interaction.; In Chapter 4, the impact of coordinatively-unsaturated alkali metal ions on hydrogen adsorption is studied in dehydrated variants of the compounds A2Zn3[Fe(CN)6]2· xH2O (A = H, Li, Na, K, Rb). All five compounds show similar hydrogen uptake at 77 K and 890 torr, ranging from 1.1 wt % for H2Zn 3[Fe(CN)6]2·2H2O to 1.2 wt % for K2Zn3[Fe(CN)6]2. Enthalpies of adsorption, calculated from hydrogen isotherms measured at 77 K and 87 K were found to vary with A, with maximum enthalpies ranging from 7.7 kJ/mol for A = Na to 9.0 kJ/mol for A = K, the highest yet reported for a metal-cyanide compound.; Chapter 5 describes the reaction of the microporous metal-organic framework Zn4O(BDC)3 (BDC2- = 1,4-benzenedicarboxylate) with Cr(CO)6 at 140°C in a 6:1 mixture of dibutylether and THF to afford ZN4O[(BDC)Cr(CO)3]3 ( 5.1). This compound retains the porous cubic structure of the parent framework, but features Cr(CO)3 groups attached in an eta 6 fashion to all of the benzene rings. Compound 5.1 is also microporous, exhibiting a BET surface area of 2130 m2/g. It can be fully decarbonylated by heating at 200°C, but the resulting grey solid (5.2) shows little affinity for N2 or H 2 at 298 K, suggesting aggregation of the chromium atoms. In contrast, photolysis of 5.1 using 450nm light in an atmosphere of N 2 or H2 produces solids with infrared spectra indicative of Zn4O[(BDC)Cr(CO)2(N2)]3 ( 3) and Zn4O[(BDC)Cr(CO)2(H2)] 3 (5.4). Under an N2 atmosphere, compound 5.4 completely converts into compound 5.3 over the course of 12 h, demonstrating the lability of the Cr0-H2 bond. Owing to isolation of the metal centers within the rigid, evacuable framework structures, the N2- and H2-substituted com...