Browsing by Author "Shores, Matthew P., advisor"
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Item Open Access A study of magnetostructural parameters related to spin crossover and single molecule magnetism(Colorado State University. Libraries, 2013) Fiedler, Stephanie R., author; Shores, Matthew P., advisor; Kennan, Alan J., committee member; Anderson, Oren P., committee member; Crans, Debbie C., committee member; Patton, Carl E., committee memberHerein are described several methods to probe transition metal complexes that were designed by systematic structural modifications to allow for comparison of the resultant magnetic properties. In Chapter 1, a brief introduction is presented to introduce the broader goal of our research: controlling spin on the synthetic level. The introduction provides background regarding spin crossover and single molecule magnetism as well as some previous research to put our projects in context relative to endeavors by other researchers. In Chapter 2, heteroleptic complexes of the form [Fe(H2bip)2(pizR)]Br2 and [Fe(H2bip)2(pizR)](BPh4)2 are described, which have the opportunity to chelate an anion via hydrogen bonding to the H2bip ligand. The third ligand, pizR, is varied between two ligands that we predict will have similar ligand field strengths: pizH and pizMe. Because pizH has an additional hydrogen-bonding site, while pizMe does not, we selected these ligands in order to understand the effect of hydrogen bonding on the anion-binding/spin-state switching event independent from ligand field strength. From these studies, the pizH anion hydrogen bond is observed in crystallographic studies, but does not affect the anion-binding or spin-state switching properties in solution. In Chapter 3, we further investigate the geometry of the pizR ligand in Fe(II) complexes. What began as attempts to study hydrogen bonding in solution revealed unexpected structural distortions of the ligand that are correlated to the spin state of the complexes. The R-substituted nitrogen atom on the imidazoline moiety of the pizR ligand switches between a planar geometry, which is observed for high-spin species, and a pyramidalized geometry, which is observed for low-spin species. We reason that this occurs as a result of the weak-field, non-pizR ligands that influence the ligand field in the high-spin species. Chapters 4 and 5 delve deeper into understanding the relationship between structural parameters and magnetic properties in complexes with non-covalent interactions. In Chapter 4, a series of complexes with metallophilic Pt-Pt interactions show antiferromagnetic magnetic coupling of non-bonded transition metals through a Pt-Pt bond. By comparing complexes with Pt-Pt interactions to those without Pt-Pt interactions, we are able to determine that the Pt-Pt bond is a unique superexchange pathway for the transition metal coupling. Off-set complexes, exhibiting two Pt S interactions instead of one Pt-Pt interaction, do not show evidence of magnetic coupling between transition metals. Furthermore, by comparing magnetic properties of complexes where the apical ligand varies, we determine that the presence or absence of intermolecular interactions is largely independent from the strength of coupling through the Pt-Pt bond. In Chapter 5, an asymmetric trinuclear manganese complex with unique magnetic exchange properties and two high-spin square planar complexes of iron and cobalt, are investigated. The trinuclear manganese complex consists of a central octahedral Mn(II) ion that is coupled antiferromagnetically to another octahedral Mn(II) ion and ferromagnetically to a terminal tetrahedral Mn(II) ion. The different coupling is rationalized as a result of the change in geometry, which affects the orbital overlap that is predicted for each pair of ions. The high-spin square-planar Fe(II) and Co(II) complexes illustrate an unusual pairing of spin-state with square-planar geometry. Moreover, the Fe(II) complex exhibits signs of easy-axis molecular anisotropy and slow-relaxation of magnetization, albeit in the presence of a magnetic field. Lastly, in Chapter 6, we investigate a trinuclear Fe(III) complex bridged by a triethynylmesitylene ligand. The magnetic properties of the complex are compared to a previous Fe(III) complex bridged by a triethynylbenzene ligand. Steric interactions between the aromatic core of the ethynylmesitylene ligand and the auxiliary dimethylphosphinoethane ligands on Fe(III) are predicted to engender a ligand conformation to promote strong orbital overlap. Magnetic susceptibility data for the two complexes both exhibit ferromagnetic coupling between metal centers as expected. Further studies are necessary to confirm the observed behavior, but the new triethynylmesitylene complex appears to have slightly stronger coupling than the previous triethynylbenzene complex.Item Open Access Investigating the origins of slow magnetic relaxation of S = ½ Ni(III) cyclams(Colorado State University. Libraries, 2023) Morrison, Thomas L., author; Shores, Matthew P., advisor; Zadrozny, Joe, committee member; Kennan, Alan, committee member; Gelfand, Martin, committee memberThis dissertation describes the syntheses and characterizations of several Ni(III) and Ni(II) complexes in an attempt to better understand the origin of slow magnetic relaxation, or spin reversal, in S = ½ systems by utilizing Ni(III) cyclam (1,4,8,11-tetraazacyclotetradecane) as a toy model system. The content is organized as follows: Chapter 1 provides the historical context and theory surrounding the class of materials called single molecule magnets (SMMs). Therein I describe the prototypical SMM and its primary figures of merit and characteristics, such as S and D, followed by the observation of how S = ½ systems, which have previously been shown to act as SMMs, do not fit within the context currently provided by the literature. The choice of using the Ni(III) cyclam system is then elaborated upon, along with its quirks and foibles. In Chapter 2 I describe the synthesis and magnetic characterization of three Ni(III) cyclams. The first two contain halides in the axial positions, which are 100% abundant in isotopes containing nuclear spin, and the third complex has perchlorate bound in the axial position, where oxygen is nearly nuclear spin free. Neither halide systems showed slow magnetic relaxation, but it was not clear whether it was due to the superhyperfine coupling between the nuclear and electronic spins or due to the antiferromagnetic interactions present at low temperatures. The perchlorate containing complex did show slow magnetic relaxation, consistent with the literature and our predictions. Chapter three describes the crystallographic tuning tools and corresponding magnetic properties of novel S = ½ Ni(III) cyclam complex salts: strong antiferromagnetic coupling in sulfate-bridged chain {[Ni(cyclam)(µ2-SO4)]ClO4·H2O}n and field-, temperature-, and size-dependent slow magnetic relaxation in molecular [Ni(cyclam)(HSO4)2]HSO4. I have reported two methods of manipulating the dynamic magnetic response of these coordination molecules: particle size selection and deuteration. I find that particle size dependency, which I attribute to the phonon bottleneck effect, for the magnetic dynamics in the parent protiated compound is removed in deuterated isotopologue, revealing only the faster molecular relaxation mode(s). Chapter 4 describes the synthesis and characterization of four novel Ni(III) cyclams utilizing neutral ligands in the axial positions as opposed to the anionic ones considered previously, namely [Ni(cyclam)(acetonitrile)2]X3 (X = OTf, ClO4, BF4) and [Ni(cyclam)(butyronitrile)2]OTf3. Through these complexes we probe the role of ligand charge, identity, and subtle differences in the hydrogen-bonding network on the slow magnetic relaxation of the Ni(III) ion. Chapter 5 describes the solution phase studies of [Ni(cyclam)(MeCN)2]OTf3 and [Ni(cyclam)(butyronitrile)2]OTf3 in glassy and non-glassy solvents, as well as their suitability for studying other novel species in situ that may not be able to be synthesized and measured traditionally. We find that there are significant differences in the magnetic relaxation of the Ni(III) cyclams between glassy and non-glassy solutions and discuss the possibilities these findings present. In Chapter 6 I summarize the key findings from Chapters 2-5 and propose new avenues of research for further investigating this phenomenon. Finally, in Chapter 7 I describe a different ligand involving intra-ligand π-π interactions and explore the feasibility of using such interactions for intelligently controlling and tuning the first coordination sphere geometry and electronic structure. By introducing new substituents, changes to the aromaticity, and oxidation of the ligand we are able to exhibit rational control over the crystallographic and electronic structure of the metal center.Item Open Access Investigations into photocatalysis and electronic structure for transition metal and actinide complexes(Colorado State University. Libraries, 2018) Higgins, Robert F., author; Shores, Matthew P., advisor; Rappé, Anthony K., committee member; Neilson, James R., committee member; McNally, Andrew, committee member; Wu, Mingzhong, committee memberPresented herein are investigations into the electronic structure of various metal complexes and how they effect reactivity. The first chapters are centered on how [Cr(Ph2phen)3]3+ reacts as a photooxidant. The latter part of this work concerns magnetic properties of various first row transition metal and actinide complexes. In Chapter 1, I provide a background on how understanding electronic structure of transition metal complexes has motivated later work in reactivity. This Chapter also includes a detailed background in photoredox catalysis and different electronic structures of Ru-, Ir- and Cr-containing photosensitizers. It ends with a lead-in to our initial hypotheses and motivations for using Cr as a paramagnetic, Earth-abundant congener to Ru photosensitizers in photoredox manifolds. Chapters 2-4 illustrate our mechanistic studies into transformations using Cr as a photooxidant to perform [4+2] cycloaddition reactions between (trans and cis)-anethole and dienes. Chapter 2 focuses on the interactions of oxygen (O2) in the reaction of trans-anethole and isoprene mediated by [Cr(Ph2phen)3]3+. We determined three separate, yet invaluable roles that oxygen performs in this reaction, which include: (1) protection of the catalyst through excited-state energy-transfer giving 1O2, (2) 1O2 oxidation of the reduced form of the catalyst, regenerating the ground state species and giving 2O2•- as well as (3) 2O2•- reduction of the radical cation of the [4+2] product, completing the catalytic cycle. In Chapter 3, I discuss the association that trans-anethole and similar dienophiles show with [Cr(Ph2phen)3]3+ and how this affects the overall reactivity. Interestingly, diamagnetic analogues do not show the same association. Finally, in Chapter 4, trans-anethole is replaced with cis-anethole to determine how the overall reactivity changes. These data are supported by reactivity, kinetic and quenching studies to probe the reactivity. Chapters 5-7 concern similar mechanistic details involving [Cr(Ph2phen)3]3+ in photocatlytic cycloaddition reactions, except that trans-anethole, which is electron-rich, is replaced by 4-methoxychlacone, which is electron-poor. Chapter 5 discusses the synthetic utility of this reaction manifold and initial mechanistic details of the transformation, which reveal an orthogonal mechanism which proceeds through energy transfer when compared to the reactivity of trans-anethole with [Cr(Ph2phen)3]3+. In Chapter 6, the observation of enhanced regioselectivity that is observed when [Cr(Ph2phen)3]3+ is used is investigated, specifically in comparison to all other Cr- and Ru-photooxidants attempted. This regioselectivity is manifested in the stabilization of a one-bond intermediate, as well as an association between 4-methoxychalcone and [Cr(Ph2phen)3]3+. To conclude this section, Chapter 7 focuses on the interesting solution-phase equilibria of 4-methoxychalcone and how the association of 4-methoxychlacone with itself and [Cr(Ph2phen)3]3+ impacts the overall reaction mechanism. Chapter 8 provides an interesting method of using ferrocenium as an inexpensive and abundant electron-transfer reagent in reactions similar to common photoredox reactions. This uncommon reaction pathway provides an interesting reactivity compared to traditional pericyclic reactions. The remaining Chapters (9-13) explore the magnetic properties and electronic structures of a variety of first-row and actinide complexes and clusters. Chapter 9 focuses on spin-state switching through oxidation chemistry of both iron and nitrogen atoms in organometallic complexes. The ground states of these complexes can be controllably tuned through sequential oxidation reactions. In Chapter 10, I present the synthesis and magnetic properties of mono- and bis-terpyridine Co(II) complexes. These Co complexes display a variety of coordination geometries which affect their dynamic magnetic properties. Chapter 11 focuses on the reactivity and magnetic properties of a family of U-acetylide species, where interesting redox chemistry is noted upon addition of redox-inactive crown ether molecules. In Chapter 12, I discuss the magnetic properties of 3 different families of uranium complexes measured in collaboration with Prof. Suzanne Bart's group at Purdue University. Finally, in Chapter 13, I give some broad conclusions about what was learned in the mechanistic studies of Cr-photocatalysis and possible interesting avenues for future work.Item Open Access Part 1: Formation and nucleophilic interception of α,β-unsaturated platinum carbenes. Part 2: Efforts toward controlling magnetic properties of cobalt and iron coordination complexes(Colorado State University. Libraries, 2017) Ozumerzifon, Tarik J., author; Shores, Matthew P., advisor; Kennan, Alan J., committee member; Neilson, James R., committee member; Achter, Jeffrey D., committee memberPresented in this dissertation are a series of studies describing the use of transition metals in several different applications. Part 1 concerns the development of novel platinum(II)-catalyzed reaction manifolds toward C-C bond formation, as well as the formal synthesis of a natural product. Meanwhile, Part 2 describes three separate efforts toward modulation of either single-molecule magnet properties in cobalt(II) or spin state control of iron(II) coordination complexes. The first chapter is a general introduction to single-molecule magnetism (SMM) and spin crossover, as these topics specifically relate to Co(II) and Fe(II) complexes, respectively. The physical origins of both phenomena are discussed, as well as some general terminology that are used throughout Chapters 3-5. Chapter 2 describes the use of Pt(II) salts in alkyne activation reactivity. The vinylogous addition of carbon nucleophiles into α,β-unsaturated platinum carbenes is discussed, and the optimization and scope of enol incorporation is provided. This is followed by a description of how Pt(II) catalysis enables the rapid formal synthesis of frondosin B, a sesquiterpene natural product. In Chapter 3, the synthesis and characterization of several salts of a trigonal prismatic cobalt(II) complex are detailed. The capping ligand used in these podands is cis-,cis-,1,3,5-triaminocyclohexane (tach), a rigid backbone which dictates coordination geometry and the iminopyridine contains pendant tert-butylamide moieties which are meant to enable guest association. The single-molecule magnet behavior (measured via slow magnetic relaxation) of these compounds is also explored, where the cation-binding tetraphenylborate salt shows slow magnetic relaxation at both zero and applied dc fields. A brief discussion of theoretical considerations of the effect of trigonal distortion on axial anisotropy is also presented, which suggests systems in an intermediate twisting geometry may give rise to guest-dependent magnetic properties in SMMs. Chapter 4 presents initial efforts toward the development of an Fe(II) system which can undergo a spin-state switch upon addition of a reagent. The chemoselective process is intended to be the result of an irreversible ligand modification. The first target toward this goal is manifested in desilylation of a 5-siloxy substituted podand. Spectroscopic and spectrometric as well as electrochemical and magnetic data indicate qualitatively that ligand desilylation is occurring as a function of fluoride addition, affecting a decrease in high-spin:low-spin ratio. Last, Chapter 5 details the systematic study of electronic character of 5-pyridyl substitution in the Fe(II) tren iminopyridine tripodal system. The Fe(II) species magnetic susceptibility and Ni(II) analog d-d transition energy data are compared to the Hammett parameter of the respective substituent, which define the complexes' electron-donating or -withdrawing properties. Overall, electron withdrawing substituents at this position lead to stabilization of the HS state. A comparison of these iminopyridine complexes to Fe(II) podands which undergo spin crossover is provided in an effort to explain the observed low-spin behavior of these complexes.Item Open Access Reevaluating the photophysics and electronic structure of Cr(III) and V(II) complexes: the implications of distortion on the excited state manifold(Colorado State University. Libraries, 2020) Portillo, Romeo I., author; Shores, Matthew P., advisor; Rappé, Anthony K., committee member; Chen, Eugene Y.-X., committee member; Peterson, Christopher, committee memberPresented in this dissertation are investigations into the electronic structure of chromium and vanadium complexes targeted towards photocatalysis. These studies have focused on two primary features in the excited state manifold: the energy of the excited state and the relative distortion of the excited state to the ground state. Chapter 1 provides a background on how the study of electron transfer led to the development of inorganic photocatalysis. The chapter includes the progression of photocatalysts design from [Ru(bpy)3]2+ to modern alternatives focusing on Earth-abundant reagents. Additionally, I provide my perspective on these advances and criticism of prevalent methodologies. Chapter 2 discusses the synthesis and characterization of polypyridyl-containing Cr(III) complexes. Each complex exhibits spectroscopic signatures of an unusual 4(3IL) excited state, a mixed excited state between a paramagnetic ligand and metal center. Calculations provide insight into the character of this excited state, suggesting this 4(3IL) excited state may be the lowest spinallowed excited state in some of these complexes. The minimal distortion in these excited states limit the degrees of freedom for non-radiative decay compared to the metal-based 4T2 excited state. Chapter 3 discusses the synthesis and characterization of two V(II) polypyridyl complexes. Here, I reevaluate the proposed excited state manifold in the literature which claims that the 4MLCT is the lowest energy excited state. Spectroelectrochemical and picosecond-resolved spectroscopic techniques reveal a short-lived excited state, presumably 2MLCT. A new excited state manifold is presented, suggesting doublet excited states are relevant to the understanding of V(II) photophysics. Chapter 4 discusses the differences in the electronic structure of isoelectronic V(II) and Cr(III) polypyridyls. While several factors contribute to these differences, the identity and energies of the relevant excited states lead to a completely different excited state manifold between the two systems. The chapter summarizes the work of Chapters 2 and 3. Chapter 5 discusses the synthesis and electronic structure of a tripodal ligand scaffold bound to V(II) and V(III). The differences between the hexacoordinate V(II) and heptacoordinate V(III) further our understanding of the apical nitrogen's role on the electronics of the complex. Additionally, we exploit the utility of the SHAPE program to quantify structural distortion and correlate to the species' electronic structure. Chapter 6 discusses the electronic structure of a similar vanadium tripodal complex, [V((5-CO2Me)py)3tren]2+ . This complex displays spectroscopic signals of both a V(II) complex with a neutral ligand and V(III) complex with a ligand radical. Different phenomena are proposed, but neither provide a complete explanation of the results. Chapter 7 summarizes the investigations into V(II) and Cr(III) photophysics. Additionally, I discuss how SHAPE may be used in other fields and identify important structural motifs through machine learning.Item Open Access Synthesis and characterization of low-dimensional paramagnetic acetylide complexes(Colorado State University. Libraries, 2011) Hoffert, Wesley A., author; Shores, Matthew P., advisor; Anderson, Oren P., committee member; Prieto, Amy L., committee member; Bailey, Travis, committee member; Patton, Carl, committee memberTo view the abstract, please see the full text of the document.Item Open Access Synthesis and characterization of sterically and electronically tuned ligands toward magnetic control of iron and cobalt complexes(Colorado State University. Libraries, 2015) Klug, Christina M., author; Shores, Matthew P., advisor; Rappé, Anthony K., committee member; Ackerson, Christopher J., committee member; Levinger, Nancy E., committee member; Wu, Mingzhong, committee memberPresented within this dissertation are the syntheses and characterizations of iron and cobalt complexes featuring ligands designed to tune the magnetic properties. Two key magnetic phenomena are of interest: spin crossover and single-molecule magnetism. Both of these topics are known to be significantly influenced by subtle changes in coordination and inter- and intramolecular interactions. The overarching goal is to understand how the magnetic properties of the metal center can be controlled via electronic and steric modifications. In Chapter 1, I offer a brief introduction into the background and motivation of the works presented in this dissertation in the realm of spin crossover and single-molecule magnetism. The first section of this chapter is focused on spin crossover and how host:guest interactions can be exploited to alter the magnetic behavior of first-row transition metals. Examples of Fe(II) complexes that display anion-dependent spin state behaviors in both the solid-state and in solution are discussed. Functionalized tripodal Schiff-base ligands are placed into context as an extension of previous research into tripodal ligands for use as metal-based anion-receptors and tripodal spin crossover complexes. The second section of Chapter 1 gives a brief introduction into single-molecule magnetism. An examination of mononuclear Co(II) complexes displaying slow magnetic relaxation and application of acetylide-bridged metal centers to enhance magnetic communication are also given. In Chapter 2, I discuss the preparation and characterizations of a Fe(II) complex coordinated by the alcohol functionalized hexadentate tripodal iminopyridine L6-OH with varying anions. Solid-state magnetic susceptibility measurements of [FeL6-OH]X2 (X = OTf-, Br-, I-, or BPh4-) reveal an anion-dependence on the magnetic behavior. Magnetostructural correlations indicate that stronger hydrogen-bonding interactions are achieved with larger anions, which are better able to undergo bifurcated interactions with the hydroxyl groups from two of the arms. Removal of the tether between the ligand arms leads to the formation of [Fe(L2)2](OTf)2, a bis(tridentate) complex that remains high spin at all temperatures. Variable temperature magnetic measurements in d3-methanol reveal that the high spin state of [FeL6-OH]2+ persists regardless of the anion down to 183 K. In Chapter 3, attempts towards synthesizing the heteroarmed tris(imine) [FeL556]2+ and analogous bis(imine)-mono(amine) [FeL556-NH]2+ complexes are discussed. Several routes are attempted to synthesize the tris-iminopyridine species including selective deprotonation of tris(2-aminoethyl)amine*3 HCl, in situ complex formation via metal-templated self-assembly, and use of presynthesized ligands. Analyses of the reaction mixtures by mass spectrometry suggest that mixtures of products are formed regardless of the method. An anion and solvent dependence leads to preferential formation of the low-spin species [FeL5-ONHtBu]2+, while using solvents such as acetonitrile and ethanol lead to increased production of the desired [FeL556]2+. To test if anion-dependent magnetic behavior can be observed with this ligand type, the comparable complex [FeL556-NH]2+ was synthesized and characterized. Variable temperature solution measurements in d3-acetonitirile suggest that host:guest interactions in solution induce a stabilization of the low-spin state for [FeL556-NH]2+ as indicated by a decrease in susceptibility at lower temperatures for the Cl- salt. In Chapter 4, the preparation, structural, and magnetic characterizations for a family of Fe(II) complexes of tripodal ligands based on L5-ONHtBu are presented. The series of ligands aim to tune the ligand field by selectively reducing imines to amines, producing the ligands L5-(NH)x (x = 1 - 3, number of amines). In the solid state, the three Fe(II) complexes formed are high spin, but significant differences in the structural distortion of both the coordination environment of the Fe(II) center as well as the anion-binding pocket of the amides are noted. In solution, the complexes [FeL5-(NH)3]2+ and [FeL5-NH]2+ are high spin between 183 and 308 K in d6-acetone but interestingly, [FeL5-(NH)2]2+ undergoes a spin-state change with decreasing temperature. Variable temperature studies in d6-acetone and anion titrations in d3-acetonitrile at room temperature monitored by Evans' method of [FeL5-(NH)2]2+ show host:guest interactions stabilize the high spin state. These studies suggest a viable method of ligand tuning for spin-state control by host:guest interactions. In Chapter 5, I discuss the structural and magnetic properties of [Co5-ONHtBu]X2 (X = Cl-, Br-, I-, and ClO4-). These hexadentate Co(II) complexes vary only in the charge-balancing anion, but marked differences in their magnetic properties are observed. Investigation of the magnetic anisotropy of the various salts reveal that the chloride salt possesses the most axial anisotropy, which manifests as an exhibition of slow magnetic relaxation under application of an external field. To my knowledge this is the first example of anion-binding influencing the magnetic anisotropy and 'turning on' single-molecule magnet-like behavior. Lastly, Chapter 6 describes the syntheses and magnetic properties of a series of mono-and dinuclear Fe(III) complexes bridged by ethynylmesitylene ligands. Inclusion of steric bulk onto the bridging-aryl ligand is predicted to increase orbital overlap between the singly-occupied molecular orbital of the metal center and the π-system of the aryl linker. The addition of methyl groups to the aryl ring cements the desired equatorial ligand orientation with respect to the π-system. This leads to an increase in ferromagnetic coupling between the metal centers.Item Open Access Synthesis and characterization of uranium(IV) compounds: from mononuclear complexes to multinuclear assemblies(Colorado State University. Libraries, 2011) Newell, Brian S., author; Shores, Matthew P., advisor; Anderson, Oren P., advisor; Chen, Eugene Y., committee member; Levinger, Nancy E., committee member; Wu, Mingzhong, committee memberThis dissertation describes the synthesis of multinuclear compounds that possess magnetically-coupled actinide, namely uranium-238, clusters. These assemblies are supported by both acetylide-type ligands as well as triamidoamine or softer phosphine ligands. Synthetic inorganic chemists have been able to synthesize molecules and clusters with increased spin, S, or axial anisotropy, D, in an effort to augment the spin-reversal barriers and create better single-molecule magnets (SMMs). However, efforts to simultaneously increase these parameters are complicated. One potential route utilizes heavy atoms as a result of their larger single-ion anisotropy and believed ability to modulate the magnetism of other systems. My research is placed in this context in Chapter 1, where recent efforts to incorporate heavy atoms into expanded clusters are discussed. In Chapter 2, the preparation and magnetic property investigations of a structurally related family of mono-, di- and trinuclear U(IV) aryl acetylide complexes are presented. The reaction between [(NN′3)UCl] and lithiated aryl acetylides leads to the formation of hexacoordinate compounds. In contrast, combining the uranacycle [(bit-NN′3)U] (bit-NN′3 = [N(CH2CH2NSitBuMe2)2(CH2CH2SitBuMeCH2]) with stoichiometric amounts of mono-, bis-, and tris(ethynyl) benzenes affords pentacoordinate arylacetylide complexes, where NN′3 = [N(CH2CH2NSitBuMe2)3]. The measured magnetic susceptibilities for these compounds trend toward non-magnetic ground states at low temperatures. Nevertheless, the di- and trinuclear pentacoordinate compounds appear to display weak magnetic communication between the uranium centers. This communication is modeled by fitting of the DC magnetic susceptibility data, using the spin Hamiltonian. Geometry-optimized Stuttgart/6-31g* B3LYP hybrid DFT calculations were carried out (spin-orbit coupling omitted) on model complexes and the electrochemistry of the monomeric phenylacetylide complex exhibits a reversible redox couple at -1.02 V versus [Cp2Fe]+/0, assignable to an oxidation of U(IV) to U(V). Efforts to study the magnetic correlations as a result of cubic ligands fields are presented in Chapter 3, whereby a neutral bidentate phosphine ligand was utilized. In the course of structurally characterizing previously reported complexes based on the 1,2-bis(dimethylphosphino)ethane)) (dmpe) ligand ([(dmpe)2UCl4] (3.1) and [(dmpe)2UMe4] (3.2)), we found that adjusting the U:dmpe ratio leads to an unprecedented species. Whereas the use of two or three equivalents of dmpe relative to UCl4 produces 3.1 as a blue-green solid, use of a 1:1 dmpe:UCl4 stoichiometry yields [(dmpe)4U4Cl16]•2CH2Cl2•(3.3•2CH2Cl2) as a green solid. In turn, 3.3 is used to prepare a mixed-chelating ligand complex featuring the bidentate ligand 4,4′-dimethyl-2,2′-bipyridine (dmbpy), [(dmpe)(dmbpy)UCl4] (3.4). The measured magnetic susceptibilities for 3.1-3.4 trend toward non-magnetic ground states at low temperatures. In Chapter 4, we hypothesized that preparing complexes that contain U(IV) in a cubic ligand field environment, using acetylide ligands, might allow for the isolation of compounds exhibiting enhanced magnetic coupling. In that vein, we report the synthesis and characterization of [(dmpe)2U(CCPh)4] (4.1) (CCPh = phenylacetylide) and [(dmpe)2U(CCPh)5(Li∙Et2O)] (4.2). No reproducible magnetic susceptibility data were obtained and a discussion about these difficulties is presented. In the course of studying the crystal structure of the mixed-chelating ligand complex [(dmpe)(dmbpy)UCl4] (3.4) an interesting effect on the U-Cl⋯H was observed. Several computation methods were utilized to determine that the M-Cl⋯HC distance based on approach angles is suggestive that Cl is acting more like chlorine and less like chloride. This provides a route to study U-L bonding and is presented in Chapter 5. Finally, in Chapter 6, efforts to synthesize a mixed-metal complex are discussed and preliminary characterization of a dinuclear ethynylbenzene 5f-3d complex (6.3) is presented. While an unambiguously paramagnetic metal-complex was not isolated, initial electrochemical studies indicate a redox process takes place. A short discussion about the temperature dependence of the magnetic susceptibility is given.Item Open Access "You are young and can afford to do something stupid": fostering an understanding of electronic spin in chemistry(Colorado State University. Libraries, 2021) Joyce, Justin P., author; Shores, Matthew P., advisor; Rappé, Anthony K., advisor; Neilson, James R., committee member; Reynolds, Melissa M., committee member; Ross, Kathryn A., committee memberTo view the abstract, please see the full text of the document.