Solid-state NMR study of nitric oxide adsorption in carboxylate based MOFs

Solid-state NMR study of nitric oxide adsorption in MOFs. Amine functionalized Cu3btc2 MOFs shows chemisorption of NO as NONOates. NO also adsorbed in Cu open metal site(OMS). All of these information is characterized by 1H, 13C and 15N NMR studies. NO adsoprtion in Al based MOFs MIL-100(Al) is investigated to get details about direct detection of OMS site by 27Al NMR. First time detection of 15NO as dimer is acheived by 15N NMR studies.:Contents.............................................................................. v List of Figures...................................................................... vii Abbreviations............................................................................. ix 1 Motivation .............................................................................1 2 Introduction .............................................................................3 2.1 Nitric oxide (NO): A Potent Gasotransmitter . . . . . . . . . . . . . . . . . . 3 2.1.1 Biological action in human biology: . . . . . . . . . . . . . . . . . . . . 3 2.1.2 Structure and chemistry of NO . . . . . . . . . . . . . . . . . . . . . . 4 2.2 NO storage in porous materials . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1 Physisorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.2 Chemisorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Current NO storage materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.4 Metal-organic frameworks (MOFs) . . . . . . . . . . . . . . . . . . . . . . . . 8 2.4.1 Cu3btc2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.4.2 MIL-100(Al) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3 Experimental techniques .............................................................................15 3.1 Nuclear spin interactions in solid-state NMR . . . . . . . . . . . . . . . . . . . 15 3.2 NMR Techniques and Pulse Sequences . . . . . . . . . . . . . . . . . . . . . . 19 3.3 NMR sample tube preparation . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.4 Gas adsorption procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 4 Overview and enclosed papers 29 References .............................................................................121 5 Contribution .............................................................................137Gas storage in solids is becoming more important as a technology, with applications ranging in fields such as energy, the environment, and more importantly in biology and medicine. Porous solid storage materials are also increasingly important to advancements in science, as seen through their use in emergent gas-delivery technologies that include storage of the signaling molecule, nitric oxide (NO). The deficiencies of NO biosynthesis have been interconnected to a number of diseases, such as cardiovascular dysfunction, thrombosis and cancer. To date, one of the promising NO delivery materials are the metal-organic frameworks (MOFs), a new class of porous materials, which can store significant quantities of NO and then deliver it to specific sites in the body. MOFs contain open metal sites (OMS) that can physisorbed NO. Furthermore, amine functionalized MOFs can store NO covalently as N,N -diazeniumdiolates (NONOate). The thesis at hand is a collection of the publications written and co-authored by the author. The following thesis will investigate NO adsorption of one of the most highly studied carboxylate-based MOFs, Cu3btc2, and its amine derivatives, and MIL-100(Al) [Materials Institute Lavoisier] by magic angle spinning (MAS) NMR. However, NMR observation of Cu3btc2 is quite difficult, because it behaves as a paramagnet at room temperature. This paramagnetic behavior originates from the presence of antiferromagnetically coupled Cu-Cu ions, which result in an S=1 electronic state at higher temperatures (above 90 K). In that case, a significant insight into the understanding of NO interaction and the changing of electronic properties of NO loaded Cu3btc2 and the formation of NONOate in Cu3(NH2btc)2, which is known as University of Hamburg materials (UHM-30), has been obtained by MAS NMR. In paper (A) the effect of NO adsorption on the Cu3btc2 and UHM-30 has been followed by adsorbing different amounts of NO/Cu via the gas phase. The relevant NMR parameters, e.g., chemical shift, hyperfine coupling and 1H T1 of NO loaded MOFs displayed the change of electron density at the Cu site because of NO adsorption as well as indirect suggestion of NONOate formation. Further studies are carried out on the secondary amine functionalized MOFs, Cu3(NHRbtc)2, as they opened up the greater potential for NONOate formation in the MOFs. The structural characterization of four different Cu3(NHRbtc)2 is carried out by MAS NMR in (B) which revealed better incorporation of the btc ligand compared to NHRbtc in MOFs. In (C) NO loaded UHM-37 is extensively investigated by MAS NMR in order to understand the sorption priority, e.g., chemisorption or physiosorption. The multinuclear approach together with the fact that the MOFs contain antiferromagnetically coupled Cu-Cu pairs and NO being paramagnetic shows significant effects on spectra that allow for the deduction of adsorption effects in these MOFs. In the amine-functionalized UHM-37, first chemisorption of NO takes place to form NONOates. When this reaction is completed, additional adsorption at the OMS takes place. This observation is also in accordance with observed 13C shift changes upon NO adsorption. With 15N-labeled NO, we were able to directly determine signals of NONOate formation in UHM-37. To the best of our knowledge, this is the first report on 15N NMR data of NONOates in porous systems. In (D), NO interaction of another type of carboxylate MOF, MIL-100(Al) is investigated by 1H, 13C and 27Al MAS NMR. 27Al NMR data show that half of all Al sites are free for gas adsorption and that additional Al(OH)3 is present inside the pores, which is well-documented by 27Al 1H HETCOR spectra. 1H T1 of NO loaded MIL-100(Al) decreases with NO loading representing uniform distribution of NO in the MOF. In addition, the MIL-100(Al) five-coordinated Al site intensity is decreasing with increasing NO loading, while six-coordinated site intensity is increasing and a maximum of 1 NO per Al trimer can be adsorbed. This indicates rather weak NO adsorption. The magnetic properties of NO make it quite interesting for NMR measurements. Therefore, isotopically leveled bulk 15NO is studied for the first time by NMR in (E). The manuscript is accepted for publication and is included in this thesis. 15N NMR spectra have been obtained in the liquid and the solid state. The dynamic equilibrium ranges between (NO)2 and NO is characterized in gas - liquid transition temperature of NO. The variation of 15N chemical shift, line width and 15N T1 of NO with temperature represents the fast dynamic equilibrium. SQUID measurements are carried out on the same sample for further confirmation of the NMR results.:Contents.............................................................................. v List of Figures...................................................................... vii Abbreviations............................................................................. ix 1 Motivation .............................................................................1 2 Introduction .............................................................................3 2.1 Nitric oxide (NO): A Potent Gasotransmitter . . . . . . . . . . . . . . . . . . 3 2.1.1 Biological action in human biology: . . . . . . . . . . . . . . . . . . . . 3 2.1.2 Structure and chemistry of NO . . . . . . . . . . . . . . . . . . . . . . 4 2.2 NO storage in porous materials . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1 Physisorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.2 Chemisorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Current NO storage materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.4 Metal-organic frameworks (MOFs) . . . . . . . . . . . . . . . . . . . . . . . . 8 2.4.1 Cu3btc2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.4.2 MIL-100(Al) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3 Experimental techniques .............................................................................15 3.1 Nuclear spin interactions in solid-state NMR . . . . . . . . . . . . . . . . . . . 15 3.2 NMR Techniques and Pulse Sequences . . . . . . . . . . . . . . . . . . . . . . 19 3.3 NMR sample tube preparation . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.4 Gas adsorption procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 4 Overview and enclosed papers 29 References .............................................................................121 5 Contribution .............................................................................13