Results and Discussion Molecular Organic Frameworks: Encapsulation effects on Diels-Alder kinetics Kassie Picard, Courtney Leo, Brady Barron, Luke Fulton, Roy Planalp Department of Chemistry, University of New Hampshire Introduction The color change from a pink to blue in the trial with thiophene as the guest using scaled down conditions can be rationalized by two different ideas. First, the guest molecule could be coordinating to the metal causing a color change. Second, is that the complex reacted with moisture in the air. This would explain the color change because water is a weak field ligand. UV/Vis spectra were obtained and analyzed for discrepancies in observed data. The synthesis of the MOF crystals were carried out in test tubes with starting material in different layers. Reaction conditions were continuously changed to promote the formation of crystals (table 1). The solutions were allowed to crystalize for seven days. Table 1. Changing reaction conditions and quantities of materials used for the synthesis of MOF crystals. Molecular organic frameworks (MOFs) are crystalline networks of metal-ligand linkages, which form capsules in the spaces between the metals and the ligands. The complex is based on an infinite ratio of M6L4 (figure 1). Figure 1. M6L4 infinite ligand structure forming the backbone of the MOF.1 The interstitial space is of interests to chemist, because of the stability that these spaces offer for small, unstable molecules, known as guests. MOFs can be used to store molecules (intermediates) that are reactive with their solvents, accelerate reaction rates, and “locking” a molecule in a specific configuration. These molecules have important functions in drug delivery techniques. The purpose of this project was to synthesize the MOF crystals with different guest molecules, and see the effects of the MOF structure on Diels-Alder kinetics.1   Layer A B C Compound Ligand Methanol Guest Absolute Methanol Co Complex Standard- Room Temp 9.37 mg 1.5 mL 6.0 mL 0.3 mL 15.76 mg Reaction in fridge Reaction in Scin Vial Scale Down 6.3 mg 1.0 mL 4.0 mL 0.2 mL 10.5 mg No Buffer- Layer 0 mL Decrease MeOH No Guest C B Figure 3. UV/Vis spectrum for the crude mixture of the ligand (1) and metal complex (2). A Future Work The original goal for this project was to synthesize MOF crystals and explore how the guest molecules, protected by the MOF structure, react when heated. Future work includes continued effort to synthesize the crystals by changing more reaction conditions like exposure to air and heating the samples. Once crystals are formed, they could be put on heat and the MOF broken down with acid. The guest molecules would be extracted and 1H NMR used see if any guest molecules underwent a Diels-Alder reaction. Results and Discussion The synthesis of MOF crystals was unsuccessful for all reaction conditions and guest molecules. This was obvious by the lack of solid, red crystals that were expected to form.2 At the start of the reaction, the layer that contained the ligand was clear, and the layer that contained the metal complex was a light pink color. The mixture of solutions was predicted to produce red crystals, but formed different colored solutions instead (table 2). Acknowledgments Methods Table 2. Color change associated with MOF synthesis for each guest molecule at different reaction conditions. Thank you to the UNH Department of Chemistry for their efforts and support during this research project. The first part of this project focused on the synthesis of the MOF crystal using 2,4,6-tris(3-pyridal) -1,3,5-triazine (1) as the ligand and cobalt (II) thiocyanate (2) using three different guests: thiophene (3), furan (4), and toluene (5). Guest Thiophene Furan Toluene Standard- Room Temp Light Pink Light Blue Purple Double Buffer Lavender Teal Reaction in Fridge Light pink Reaction in Scin Vial Dark Blue Light Purple Blue/Green- No solution Scale Down Top Light Purple/ Bottom Light Blue No Buffer- Layer Light purple/ pink Decrease MeOH Deep Blue Rose No Guest Hot Pink References Inokuma, Y.; Yoshioka, S.; Fujita, M. A Molecular Capsule Newtwork: Guest Encapsulation and Control of Diels-Alder Reactivity. Angewandte Chemie. 2010. Zhang, M.; Lu, M.; Li, J.; Bosch, M.; Chen, Y.; Liu, T.; Liua, Y.; Zhou, H. Design and Synthesis of Nucleobase-incorporated Metal–organic Materials. Royal Society of Chemistry, Journal of Inorganic Chemistry. 2014. 159-162. Plonka, A.; Chen, X.; Wang, H.; Krishna, R.; Dong, X.; Banerjee, D.; Woerner, W.; Han, W.; Li, J.; Parise, J. Light Hydrocarbon Adsorption Mechanisms in Two Calcium-Based Microporous Metal Organic Frameworks. ACS Publications. 2016. . Figure 2. Metal, ligand, and guest molecules used in the MOF synthesis.

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