Molecular rubies show promise toward applications in quantum information science (QIS), from networking to sensing and electronics. While S = 3/2 Cr3+ ions satisfy the requirements for realizing a spin-optical interface, there is a lack of information on their combined optical and spin relaxation properties. In this work, we study the effect of the matrix on both the spin and optical properties of prototypical octahedral (Oh) Cr(acac)3 (acac = acetylacetonate) in a series of diamagnetic M3+ hosts: CrxM1-x(acac)3 (M = Al [1]; Ga [2]; In [3]; Sc [4]; Co [5]; Rh [6]). X-ray diffraction confirms that the metal identity of the diluent influences the crystal symmetry of the host: monoclinic P21/c (1, 2, 5, 6) and orthorhombic Pbca (3,4). Continuous-wave (cw)-EPR spectroscopy reflects that the space group of the host dictates the ground-state spin Hamiltonian parameters. Pulse EPR spectroscopy shows that spin-lattice relaxation T1 depends on space group symmetry. Confocal microscopy photoluminescence confirms the low-temperature crystal symmetry of Cr(acac)3 within the diluent matrices. These results show that Cr(acac)3 hosts the requisite electronic structure for optical initialization and readout below 4 K, making this class of biocompatible ions primed for cryogenic nanoscale sensing.

Molecular qubits with the potential for optical read-out require careful ligand design to control zero-field splitting, D , for quantum manipulation. We find Ni 2+ in a sulfur ligand field in a near-ideal octahedral environment enables quantum control.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Mixed-valence complexes represent an enticing class of coordination compounds to interrogate electron transfer confined within a molecular framework. The diamagnetic heterotrimetallic anion, [V(SNS)2{Ni(dppe)}2]-, was prepared by reducing (dppe)NiCl2 in the presence of the chelating metalloligand [V(SNS)2]- [dppe = bis(diphenylphosphino)ethane; (SNS)3- = bis(2-thiolato-4-methylphenyl)amide]. Vanadium-nickel bonds span the heterotrimetallic core in the structure of [V(SNS)2{Ni(dppe)}2]-, with V-Ni bond lengths of 2.78 and 2.79 Å. One-electron oxidation of monoanionic [V(SNS)2{Ni(dppe)}2]- yielded neutral, paramagnetic V(SNS)2{Ni(dppe)}2. The solid-state structure of V(SNS)2{Ni(dppe)}2 revealed that the two nickel ions occupy unique coordination environments: one nickel is in a square-planar S2P2 coordination environment (τ4 = 0.19), with a long Ni···V distance of 3.45 Å; the other nickel is in a tetrahedral S2P2 coordination environment (τ4 = 0.84) with a short Ni-V distance of 2.60 Å, consistent with a formal metal-metal bond. Continuous-wave X-band electron paramagnetic resonance spectroscopy, electrochemical investigations, and density functional theory computations indicated that the unpaired electron in the neutral V(SNS)2{Ni(dppe)}2 cluster is localized on the bridging [V(SNS)2] metalloligand, and as a result, V(SNS)2{Ni(dppe)}2 is best described as a two-electron mixed-valence complex. These results demonstrate the important role that metal-metal interactions and flexible coordination geometries play in enabling multiple, reversible electron transfer processes in small cluster complexes.

Elucidating the role of specific vibrational modes in spin lattice relaxation is a key step to designing room temperature qubits. We executed an experimental and theoretical study on a series of Cu2+ qubits to increase their operating temperature.

"Open-framework chalcogenides" are an important class of materials that combine porosity with semiconductor behavior, and yet fundamental aspects of their conductivity remain unexplored. Here, we report a combined experimental-computational approach to the iconic subclass of materials TMA(2)MGe(4)Q(10) (TMA = tetramethyl ammonium; M = Mn, Fe, Co, Ni, Zn; Q = S, Se). Direct current (DC) conductivity measurements and density functional theory (DFT) modeling reveal that metal ion and chalcogenide identities dominate key properties of the band structures, while impedance spectroscopy reveals purely electronic band-type transport in the Fe frameworks and redox-type mixed ion-electron conductivity in the others. Redox chemistry and computation suggest that the unique conductivity of Fe arises from its propensity toward Fe-2(+)/Fe3+ mixed valency as a source of p-type doping and from its highly covalent bonds that ensure high carrier mobilities. Taken together, these results demonstrate open-framework chalcogenides as a well-defined platform for understanding porous semiconductors and for achieving highly tunable electronic performance.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The inherent atomic level structural control of synthetic chemistry enables the creation of qubits, the base units of a quantum information science system, designed for a target application. For quantum sensing applications, enabling optical read-out of spin in tunable molecular systems, akin to defect-based systems, would be transformative. This approach would bring together molecular tunability with optical read-out technology. In theory, nickel ions in octahedral symmetry meet all the criteria for optical readout of spin. Yet, to the best of our knowledge, there are no pulse EPR studies on Ni2+ molecules. We identified two compounds featuring highly symmetric Ni2+ centers, thereby engendering weak zero-field splitting to enable EPR addressability: [Ni(phen)3](BF4)2 (1) and [Ni(pyr3)2](BF4)2 (2) (phen = 1,10-phenanthroline; pyr3 = tris-2-pyridyl-methane). Crucially, these complexes feature the requisite strong field ligands to enable emission for optical addressability. We extracted axial zero-field splitting parameters of D = +0.9 cm-1 and +2.7 cm-1 for 1 and 2, respectively, enabling pulse EPR measurements. Both compounds produce emission at λmax = 938-944 nm. The aggregate of these results expands the catalogue of qubit materials to Ni2+-based compounds and offers a future pathway for optical readout of these molecules.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Double deprotonation of bis(2-mercapto-4-methylphenyl)amine ([SNS]H3) followed by addition to NiCl2(PR3)2 in air-free conditions afforded [SN(H)S]Ni(PR3) (1a, R = Cy; 1b, R = Ph) complexes, characterized as diamagnetic, square-planar nickel(II) complexes. When the same reaction was conducted with 3 equiv of KH, the diamagnetic anions K{[SNS]Ni(PR3)} were obtained (K[2a], R = Cy; K[2b], R = Ph). In the presence of air, the reaction proceeds with a concomitant one-electron oxidation. When R = Cy, a square-planar, S = 1/2 complex, [SNS]Ni(PCy3) (3a), was isolated. When R = Ph, the bimetallic complex {[SNS]Ni(PPh3)}2 ({3b}2) was obtained. This bimetallic species is diamagnetic; however, in solution it dissociates to give S = 1/2 monomers analogous to 3a. Complexes 1-3 represent a hydrogen-atom-transfer series. The bond dissociation free energies (BDFEs) for 1a and 1b were calculated to be 63.9 ± 0.1 and 62.4 ± 0.2 kcal mol-1, respectively, using the corresponding p Ka and E°' values. Consistent with these BDFE values, TEMPO• reacted with 1a and 1b, resulting in the abstraction of a hydrogen atom to afford 3a and 3b, respectively.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A new multimetallic construct has been developed utilizing a redox‐active metalloligand. The molybdenum complex, Mo[SNS]2 {1; [SNS]H3 = bis(2‐mercapto‐p‐tolyl)amine}, has been shown to coordinate to Ni(dppe) {dppe = 1,2‐bis(diphenylphosphanyl)ethane} through two cis thiolate donors to generate heterobimetallic Mo[SNS]2Ni(dppe) (2) and heterotrimetallic Mo[SNS]2{Ni(dppe)}2 (3). X‐ray diffraction studies confirm the presence of formal metal–metal bonds between the molybdenum and nickel centers in the solid state; however, NMR spectroscopic studies show that intracluster interactions are dynamic in solution. The Mo[SNS]2 metalloligand engenders rich redox chemistry in 2 and 3, and in the latter case, electrochemical and spectroscopic data suggest that 3+ is a localized mixed‐valence complex, despite the metal–metal bonding network.

Introduction “Green” chemistry and atom efficient transformations have garnered increased attention with the reemergence of global climate concerns. Efficient access to and facile derivatization of small complex molecules continues to be an important facet of synthetic organic chemistry. The Brook rearrangement, discovered and studied by Adrian Brook in the 1960’s and 70’s, provides an unconventional mode for coupling chemistry. Generally initiated by the addition of a nucleophile to a carbonyl, a Brook rearrangement is a silyl group migration from carbon to oxygen. The nucleophile is usually a Grignard or organolithium reagent. The rearrangement is thermodynamically driven and proceeds with high stereochemical fidelity1. Anion relay chemistry (ARC) developed by Amos Smith III capitalizes on the mechanism of the Brook rearrangement, employing aldehydes and epoxides to trap the carbanion generated by the Brook rearrangement2. The concurrent formation of a C-C bond and a protected alcohol make this a compelling strategy for the rapid assembly of small complex molecules.

Author(s): Wojnar, Michael Kenneth | Advisor(s): Heyduk, Alan F. | Abstract: The theme of this dissertation centers around the synthesis and characterization of heteromultimetallic systems incorporating a redox-active metalloligand, a metal complex that acts as a ligand toward other metal centers. The redox-active metalloligand is comprised of two tridentate non-innocent ligands coordinated to a redox-active metal center.Chapter 2 describes the synthesis and characterization of heterobimetallic Mo[SNS]2Ni(dppe) and heterotrimetallic Mo[SNS]2{Ni(dppe)}2 complexes that include Mo[SNS]2 as the metalloligand ([SNS] = bis(2-mercapto-p-tolyl)amine). These systems involve molybdenum-nickel metal-metal bonds, through a two-center two-electron bond in the bimetallic systems, and through a three-center four-electron bonding scheme in the trimetallic complex. Electrochemistry, supported by density functional theory (DFT) calculations, is in agreement with nickel-localized oxidations, making the heterotrimetallic Mo[SNS]2{Ni(dppe)}2 a viable molecular study of mixed valency in linear trinuclear systems.Chapter 3 discusses the installation of a copper center on the the Mo[SNS]2 metalloligands. Considered as a one-electron-reduced form of Mo[SNS]2Ni(dppe), these bimetallic systems are best described as copper in its monovalent form coordinated to the monoanion of the metalloligand, Mo[SNS]2–1. Variation of the ligand on the copper centers leads to distinct changes in the metal-metal bond distance via X-ray crystallography, while spectroscopic techniques confirm almost identical electronic structures that are unperturbed by the ancillary ligand identity. Solid-state- and solution-based characterization methods lead to electronic structure assessment of these bimetallic molybdenum–copper systems as dynamic Mo(V)–Cu(I) ions in solution.Chapter 4 revolves around a library of trimetallic systems incorporating the late transition metal centers cobalt, nickel, and copper, with the general formula, Mo[SNS]2{M(dppe)}2 (M= Co, Ni, Cu). As these trimetallic cluster compounds incorporate three-center bonding schemes, variation of the metal center from cobalt to nickel to copper leads to distinct variations in the coordination geometry of the metalloligandbridge, as well as metal-metal bond length.Chapter 5 focuses on a library of metalloligands of the general formula, Kx[M[SNS]2]. Electrochemical, spectroscopy, structural, and computational studies measure the HOMO-LUMO gaps of these compounds. Based on these methods, the covalency of these systems can be tuned through judicious choice of metal ion.Chapter 6 describes the synthesis and characterization of a mixed-valent molecule, V[SNS]2{Ni(dppe)}2, which is the one-electron oxidized version of [K][V[SNS2{Ni(dppe)}2]. Oxidation of these trimetallic systems leads to metal-metal bond scission and localization of valence on the metalloligand. It is hypothesized that the energetic and spatial mismatch between the nickel and vanadium metal centers (as seen through the dative character of the metal-metal bonds) leads to valence trapping