Master of Science / Department of Chemistry / Tendai Gadzikwa / Molecular architecture involves the assembly of molecular building blocks to form supramolecular structures and the decoration of their interiors. The evolution and gathering of molecular building blocks into supramolecular constructs include examples such as co-crystals, micelles, nanoparticles, etc. These cases offer novel and advantageous pathways for research in supramolecular chemistry, however, a class of materials known as metal-organic frameworks (MOFs) materials has emerged as a prime candidate for molecular construction and interior design. MOFs are highly tunable materials because they can be synthesized from a wide range of metals cations and organic linkers. The organic linkers can also be functionalized after the MOF material has been synthesized through a process known as post-synthetic modification (PSM). These materials can be synthesized using two different organic linkers, resulting in a mixed-ligand MOF. If these ligands are modifiable and react independently, the resulting MOF structure will be orthogonally functionalized. Upon PSM we hypothesize that our porous, mixed-ligand MOF will contain homogenous bifunctionality as a blueprint for the construction of a uniformly orthogonally functionalized MOF. The synthesis of the first metal-organic framework, KSU-1, is the first of its kind to be developed at Kansas State University. PSM strategies used in this research show successful functionalization of each organic linker leading to uniform bifunctionality throughout our material. Characterization studies commonly used with MOFs verifies the synthesis and PSM of KSU-1.

Porous metal-organic materials (MOMs) are assembled through coordination between two types of building units, metal or metal-containing nodes and organic linkers. Metal-organic frameworks (MOFs) have 3-D infinite structures and are especially known for high porosity and enormous surface area, leading to diverse applications such as selective gas separation, gas storage and catalysis. In contrast, metal-organic polygons/polyhedra (MOPs) as discrete molecular coordination assemblies are soluble in certain solvents, allowing us to study their solution-chemistry. In the first project, a microporous MOF with 1-dimensional (1D) bridging helical chain secondary building units (SBUs) shows facile transition from micro- to mesoporosity upon activation conditions. The quickly activated MOF shows permanent microporosity while the slow removal of coordinated aqua ligand results in formation of the mesopores in the microporous MOF. Second, a strategy to introduce not only the functional groups but also functionalized meso-cavities into microporous MOFs through metal-ligand-fragment coassembly has been studied. With this functionalization, the interior of the MOFs can be tuned by a wide range of functional groups on the ligand fragments, including polar and ionic ones. Depending on the functional groups on the ligand fragments, the introduced cavities can be extended to mesopores in a controllable manner. Third, a MOF constructed from dicopper paddlewheels and a predesigned ligand bearing carboxylate, pyridine, and amide groups enables selective adsorption of CO2 over CH4 and high H2 adsorption. The cooperative catalytic activity in a tandem one-pot deacetalization-Knoevenagel condensation was demonstrated. In the fourth and fifth section, an optically and thermally switchable azobenzene was introduced into a MOF and MOPs, respectively. The freshly synthesized MOF adsorbed a significant amount of CO2. Upon light irradiation, the adsorbed gas molecules were squeezed out of the MOF due to the change of conformation of the azobenzene groups inside the pores. The adsorbent returned to its original state when allowed to stay with gentle heating. In addition, solubility of srMOPs was optically controlled by trans-cis isomerization of the azobenzene moieties. Interestingly, guest molecules were trapped during cis to trans isomerization and released in the trans to cis conversion. This srMOP can be applied to uses requiring stimuli responsive capture and release of guest molecules, such as in controlled drug delivery systems. Finally, an organic linker with multiple conformations was used to synthesize both single and core-shell molecular squares, whose formations were controlled by reaction temperatures. Intriguingly the core-shell structure assembly was successfully employed as a template to prepare a heterobimetallic assembly, in which the metal substitution occurred exclusively in the core. This work might pave the way for the exploration of enzyme-mimicking molecular catalysts.

The theme of this work is the observation and understanding of the effects of pore functionalization on adsorption properties of stable Metal-Organic Frameworks (MOFs). Over the first two sections of this work, sets of materials with representative pore sizes and functional groups are studied for adsorption properties. Observed trends are used to identify the best pore properties achievable via functionalization for adsorption systems. The third section of this work provides perspective on MOF materials and proposes target pore features for an efficient adsorbent for carbon dioxide capture from flue gas. First, the highly stable UiO-66 series of materials was selected for a pure-component adsorption study. The selectivity and capacity for CO2 can be best enhanced with the smallest, most polar functional group, such as an amino group, but significantly enhance water adsorption. Large, non-polar groups do not yield a completely hydrophobic material, but may be useful for humid gas separations as pore filling with water is inhibited. Next, a breakthrough study was conducted using CO2:CH4 and CO2:N2 mixtures on a set of stable MOFs. UiO-66-NH2 and UiO-66-DM, where DM=dimethyl, outperform predictions based on published isotherms and have dynamic CO2:CH4 selectivity comparable to zeolite NaY. UiO-66-DM may be a good candidate for further study due to the combination of partial hydrophobicity and good selectivity. Finally, by combining a review of literature with observations made in this work, a perspective on MOFs as efficient humid gas separation materials is provided. The presence of water vapor prevents use of current high performance adsorbents, but several MOF pore features show promise for these separations. The designable nature of MOFs allows for targeted design of size-matched pores and single-molecule traps which can selectively or cooperatively adsorb CO2 in the presence of water. Also, many MOF materials would be well suited for advanced pressure swing adsorption cycles and engineered sorbents, which enables greater material utilization and system efficiency.

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"The investigation through design and synthesis of metal-organic frameworks was conducted in an effort to create new types of porous crystalline solids. The supramolecular chemistry and crystal structures of six novel frameworks (1-Cd, 2Cd, 1-Cu, 2a-Cu, 2b-Cu, 3-Cu) are reported. We are targeting porous solids composed of the transition metals Cu2+ and Cd2+ with three related families of organic molecules: Ethyl 4-(1H-imidazol-1-yl)benzoate, 4-(1H-benzo[d]imidazol-1-yl)benzoic acid, and Ethyl 4-(2-methyl-1H-imidazol-1-yl)benzoate. These molecular building blocks self assemble via metal coordination into coordination polymers that form a variety of 1-D, 2-D, and 3-D architectures. The networks are comprised of M•••O and M•••N bonds that coordinate into different geometrical arrangements dependent on steric hindrance and the metal ions that are used. The frameworks synthesized display porous behavior using weight measurements that are also seen to be reversible in some cases using atmospheric reuptake of guest molecules from growth solution. The uptake of rhodamine b was examined for the framework 3-Cu."

Metal-Organic Frameworks (MOFs), an emerging class of porous crystalline materials, have shown promising properties for diverse applications such as catalysis, gas storage and separation. The high degree of tunability of MOFs vs other solid materials enable the assembly of advanced materials with fascinating properties for specific applications. Nevertheless, the precise control in the construction of MOFs at the molecular level remains challenging. Particularly, the formation of pre-targeted multi-nuclear Molecular Building Block (MBB) precursors to unveil materials with targeted structural characteristics is captivating. The aim of my master project in the continuous quest of the group of Prof. Eddaoudi in exploring different synthetic pathways to control the assembly of Rare Earth (RE) based MOF. After giving a general overview about MOFs, I will discuss in this thesis the results of my work on the use of tri-topic oriented organic carboxylate building units with the aim to explore the assembly/construction of new porous RE based MOFs. In chapter 2 will discuss the assembly of 3-c linkers with RE metals was then evaluated based on symmetry and angularity of the three connected linkers. The focus of chapter 3 is cerium based MOFs and heterometallic system, based on 3-c ligands with different length and symmetry. Overall, the incompatibility of 3-c ligands with the 12-c cuo MBB did not allow to any formation of higher neuclearity (˃6), but it has resulted in affecting the connectivity of the cluster.

The metal-organic framework (MOF) research activities can be classified into MOF preparation, MOF processing, and MOF application. Processing MOFs into specially ordered shapes and morphologies is of great importance, since it bridges MOFs to real-life applications. Additionally, creating higher-order mesoscopic architectures with MOF particles as building blocks can introduce novel properties besides the inherent features of MOFs, thus opening a door to enhancing their performance in various applications. This thesis focused on the fabrication of MOFs into zero-dimensional and three-dimensional MOF architectures via various concepts inspired by polymerization and interfacial techniques. • A raspberry-like MOF-polymer microsphere was prepared via dispersion polymerization. MOFs were found to be a good stabilizer and could be bound to polymer core with the help of polyvinylpyrrolidone. The prepared microsphere could be further developed into a polymer@MOF core-shell structure. • A multilayered MOF colloidosome (MOFsome) was prepared through transient Pickering emulsion. The obtained MOFsome could be used as a stimulus-responsive carrier and as a general platform for construction of multicomponent colloidosomes. • A porous MOF monolith was obtained using high internal phase emulsion template (HIPE). MOF particles were able to stabilize HIPE with internal phase up to 90 % of the volume. The obtained monoliths were ultralight with density as low as 12 mg/cm3. • A flexible and porous nanocellulose aerogel with high MOF loadings was prepared through a straightforward sol-gel process, followed by freeze-drying. The hierarchical porous hybrid aerogel remained intact under compression and was demonstrated to be an ideal absorbents for water purification. • A shapeable and versatile platform was demonstrated for in situ growth of MOF particles. The metal ion cross-linked alginate hydrogels were converted into MOF-alginate composites through a post-treatment of the hydrogels with MOF ligand solution. The macroscopic shape of the composite could be controlled and it was demonstrated to be an effective absorbent for water purification. / Dissertation / Doctor of Philosophy (PhD)

Thesis advisor: Chia-Kuang Tsung / Incorporating shape and size controlled metal nanoparticles (NPs) into metal-organic-frameworks (MOFs) shows great potential in heterogeneous catalysis. The combination of ordered nanoporous structure of MOFs and the well-defined surfaces of metal NPs provides a new tool to modulate the catalysis on the metal surface. Due to the large pore size, framework flexibility and selective interaction with gas molecules, MOFs have been widely used for gas storage with high selectivity. Among which have been developed to date, Zeolitic Imidazolate Frameworks-8 (ZIF-8) and UiO-66 show advantageous properties. The solvent resistivity and high thermal stability makes them stand out to be good candidates as shell materials in core shell catalysts. In our work, we developed an efficient way to create a yolk-shell structure of Pd nanoparticles in ZIF-8 and, at the same time, a method to incorporate the shape/size controlled Pt nanoparticles into well-defined octahedral UiO-66 nanocrystals with the control of concentration and dispersion. The formation mechanisms of both yolk-shell and core-shell structures were also studied in the work. / Thesis (MS) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

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In this work, a systematic study relating the surface morphologies, electrical and structural properties of both doped and undoped InAs and InAsSb epitaxial films grown by metalorganic chemical vapour deposition (MOCVD) was undertaken. A comparative study using TBAs and AsH3 as the group V source in the growth of InAs revealed a considerable improvement, primarily in the electrical properties of InAs grown using TBAs with no significant difference in the surface morphology. InAs layers grown using TBAs, exhibited superior 77 K mobilities of up to 46 000 cm2/Vs, exceeding the best MOCVD data to date. The feasibility of tetraethyl tin (TESn) as an n-type dopant in InAs was to our knowledge investigated for the first time. The incorporation efficiency of this dopant was extensively studied as a function of substrate temperature, V/III ratio, substrate orientation and TESn flow rate. Results from this study show that the doping efficiency is temperature dependent and is not influenced by a variation of the V/III ratio or substrate orientation. Furthermore, Sn doping concentrations could be controlled over 2 orders of magnitude ranging between 2.7 x 1017 and 4.7 x 1019 cm-3 with 77 K mobilities ranging from 12 000 to 1300 cm2/Vs. The electrical properties of zinc doped InAs employing dimethyl zinc (DMZn) as the ptype dopant, were studied as a function of V/III ratio and substrate orientation. The effect of a variation of these parameters on the structural properties and surface morphology of InAs is also reported. The substrate orientation appears to have no influence on the Zn incorporation. An increase in Zn incorporation resulted in a deterioration of both the surface morphology and structural quality of the InAs layers. The incorporation efficiency of DMZn in InAsSb was studied as a function of growth temperature, V/III ratio and DMZn flow rate. A higher Zn incorporation was observed in InAsSb epitaxial layers grown at a lower temperature and V/III ratio as opposed to the layers grown at a higher temperature and V/III ratio. This study also revealed that the use of DMZn caused a dopant memory effect. A two-layer model proposed by Nedoluha and Koch (1952) was used to simulate the Hall measurements of Zn doped InAs and InAsSb in order to correct the shortcomings of conventional Hall measurements in determining the electrical properties exhibited by these materials.