Functionalization of metal-organic frameworks with early transition metals : from fundamental studies to catalytic applications

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 191-215).Metal-organic frameworks (MOFs) have established themselves as some of the most versatile materials available, with applications ranging from gas sorption to separation to sensing to catalysis. With a large abundance of structural motifs published to date, research efforts have shifted towards further framework elaboration via post-synthetic modification (PSM), a method to alter the chemical structure of preformed MOFs. The secondary building units (SBUs) of MOFs, which are commonly small inorganic clusters, have been particularly interesting targets for this synthetic approach. The aim of this thesis is to further our understanding of how metal cations interact with these inorganic nodes. Additionally, the node functionalization approach is used to synthesize novel catalysts for the olefin metathesis reaction. In Chapter 1, the reader is introduced to post-synthetic modification of MOFs with a focus on early transition metal species. A review of pertinent literature is presented. Chapter 2 describes how a desire to challenge the limits of the well-precedented cation exchange process led to a serendipitous discovery of a long-sought binding mode in the iconic MOF-5 system using NbCl₄(THF)₂ as a precursor of niobium. In Chapter 3, attention shifts from fundamental studies to the development of new catalysts for olefin metathesis, a process that to (late has been not been extensively studied in MOFs. After a short introduction about the traditional olefin metathesis catalysis, the prospect of using the inorganic nodes of MOFs as supports akin to the classical platforms used in heterogeneous catalysis is explored. Chapter 4 expands the concepts developed in the previous chapter to rhenium oxide-based olefin metathesis, which is unique compared to catalysis using molybdenum and tungsten oxide systems.by Maciej Damian Korzyński.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Chemistr

Solid-state NMR spectra of protons and quadrupolar nuclei at 28.2 T: resolving signatures of surface sites with fast magic angle spinning

Advances in solid-state nuclear magnetic resonance (NMR) methods and hardware offer expanding opportunities for analysis of materials, interfaces, and surfaces. Here, we demonstrate the application of a very high magnetic field strength of 28.2 T and fast magic-angle-spinning rates (MAS, >40 kHz) to surface species relevant to catalysis. Specifically, we present as case studies the 1D and 2D solid-state NMR spectra of important catalyst and support materials, ranging from a well-defined silica-supported organometallic catalyst to dehydroxylated γ-alumina and zeolite solid acids. The high field and fast-MAS measurement conditions substantially improve spectral resolution and narrow NMR signals, which is particularly beneficial for solid-state 1D and 2D NMR analysis of 1H and quadrupolar nuclei such as 27Al at surfaces

Solid-state NMR spectra of protons and quadrupolar nuclei at 28.2 T: Resolving signatures of surface sites with fast magic angle spinning

Advances in solid-state nuclear magnetic resonance (NMR) methods and hardware offer expanding opportunities for analysis of materials, interfaces, and surfaces. Here, we demonstrate the application of a very high magnetic field strength of 28.2 T and fast magic-angle-spinning rates (MAS, >40 kHz) to surface species relevant to catalysis. Specifically, we present as case studies the 1D and 2D solid-state NMR spectra of important catalyst and support materials, ranging from a well-defined silica-supported organometallic catalyst to dehydroxylated γ-alumina and zeolite solid acids. The high field and fast-MAS measurement conditions substantially improve spectral resolution and narrow NMR signals, which is particularly beneficial for solid-state 1D and 2D NMR analysis of 1H and quadrupolar nuclei such as 27Al at surfaces.ISSN:2691-370

Tailored Lewis Acid Sites for High-Temperature Supported Single-Molecule Magnetism

Generating or even retaining slow magnetic relaxation in surface immobilized single-molecule magnets (SMMs) from promising molecular precursors remains a great challenge. Illustrative examples are organolanthanide compounds that show promising SMM properties in molecular systems while surface immobilization generally diminishes their magnetic performance. Here, we show how tailored Lewis acidic Al(III) sites on silica surface enable the synthesis of a material with SMM characteristics via chemisorption of (Cpttt)2DyCl ((Cpttt)= 1,2,4-tri(tert-butyl)- cyclopentadienide). Detailed studies of this system that also include its diamagnetic Y analogue indicate that the interaction of the metal chloride with surface Al sites results in a change of the coordination sphere around the metal center inducing for the dysprosium-containing material slow magnetic relaxation up to 51 K with hysteresis till 8 K and an effective energy barrier (Ueff) of 449 cm-1, the highest reported thus far for a supported SMM

Cyclooctatetraenide-Based Single-Ion Magnets Featuring Bulky Cyclopentadienyl Ligand

We report a family of organometallic rare-earth complexes with the general formula (COT)M(Cpttt) (where (COT)2– = cyclooctatetraenide, (Cpttt)– = 1,2,4-tri(tert-butyl)cyclopentadienide, M = Y(III), Nd(III), Dy(III) and Er(III)). Similarly to the prototypical Er(III) analog featuring pentamethylcyclopentadienyl ligand (Cp*)–, (COT)Er(Cpttt) behaves as a single-ion magnet. However, the introduction of the sterically demanding (Cpttt)– imposes geometric constraints that lead to a streamlined magnetic relaxation behavior compared to the (Cp*)– containing complexes. Consequently, (COT)Er(Cpttt) can be viewed as a model representative of this organometallic single-ion magnet architecture. In addition, we demonstrate that the increased steric profile associated with the (Cpttt)– ligand permits preparation, structural characterization and interrogation of magnetic properties of the early-lanthanide complex, (COT)Nd(Cpttt). Such a mononuclear derivative could not be obtained when a (Cp*)– ligand was employed, a testament to larger ionic radius of this early lanthanide ion