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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Operando Mechanistic Studies of CO 2 Hydrogenation by Ruthenium Complexes Using High-Pressure NMR Spectroscopy

As a result of increased energy demands, the ability to both reduce carbon dioxide with dihydrogen to formate and conduct the reverse reaction with the same catalyst is of interest as a method for potential fuel generation and use. Ruthenium bis(diphosphine) complexes with and without pendant amines were reacted with mixtures of CO 2 /H 2 gases in the presence of added base to catalytically yield formate; when the base was triethylamine, the reaction was found to be reversible. The reactions were monitored using high-pressure operando 1 H and 31 P{ 1 H} NMR spectroscopy at 18 °C in THF under 40 atm of a 1:1 mixture of H 2 and CO 2 . The rate of production of formate was correlated with the observation of specific organometallic species by NMR spectroscopy under catalytic conditions, including a hydrido–dihydrogen complex. From this operando study, a mechanism is proposed with two competing catalytic cycles for which the predominant cycle is dependent on which base and catalyst are used. Finally, the role of the base is shown to be vital for both catalytic rate and reversibility of the chemical transformation, indicating base selection should be carefully considered.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Kinetic Analysis of Proton-Coupled Electron Transfer at an Electrode-Immobilized Complex

An alkyne-terminated cobalt complex, [Co(Cp)(dppe ≡H )(Cl)] + (Cp = cyclopentadienyl; dppe ≡H = 1,2-bis-(di-(4-ethynyl-phenyl)phosphino)ethane), (Co ≡H ) was immobilized onto a glassy carbon electrode using two attachment strategies: Cu(I) catalyzed azide–alkyne click chemistry and reductive electropolymerization. The modified electrodes prepared through reductive electropolymerization exhibit current densities and peak resolutions for the electrochemical reduction of the cobalt species, which are amenable to electroanalytical quantification of coupled chemical reactions. Through peak shift analysis of cyclic voltammograms recorded in the presence of 4-chloroanilinium tetrafluoroborate, we quantified the proton transfer rate constant for the stepwise proton-coupled electron transfer reaction that reduces the electrode-immobilized [Co(Cp)(dppe ≡H )(Cl)] + to [H–Co(Cp)(dppe ≡H )] + (k PT app = (9.3 ± 1.8) × 10 5 M –1 s –1 ). In conclusion, the extraction of kinetic parameters for an elementary proton-coupled electron transfer reaction of an electrode-immobilized complex represents the first experimental measurement of its type and lays crucial groundwork for kinetic analyses of hybrid catalyst–electrode architectures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Crossover from Rouse to Reptation Dynamics in Salt-Free Polyelectrolyte Complex Coacervates

Considerable interest in the dynamics and rheology of polyelectrolyte complex coacervates has been motivated by their industrial application as viscosity modifiers. A central question is the extent to which classical Rouse and reptation models can be applied to systems where electrostatic interactions play a critical role on the thermodynamics. By relying on molecular simulations, we present a direct analysis of the crossover from Rouse to reptation dynamics in salt-free complex coacervates as a function of chain length. This crossover shifts to shorter chain lengths as electrostatic interactions become stronger, which corresponds to the formation of denser coacervates. To distinguish the roles of Coulomb interactions and density, here we compare the dynamics of coacervates to those of neutral, semidilute solutions at the same density. Both systems exhibit a universal dynamical behavior in the connectivity-dominated (subdiffusion and normal diffusion) regimes, but the monomer relaxation time in coacervates is much longer and increases with increasing Bjerrum length. This is similar to the cage effect observed in glass-forming polymers, but the local dynamical slowdown is caused here by strong Coulomb attractions (ion pairing) between oppositely charged monomers. Our findings provide a microscopic framework for the quantitative understanding of coacervate dynamics and rheology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Spatiotemporal Formation and Growth Kinetics of Polyelectrolyte Complex Micelles with Millisecond Resolution

We have directly observed the in situ self-assembly kinetics of polyelectrolyte complex (PEC) micelles by synchrotron time-resolved small-angle X-ray scattering, equipped with a stopped-flow device that provides millisecond temporal resolution. A synthesized neutral-charged diblock polycation and homopolyanion that we have previously investigated as a model charge-matched, core-shell micelle system were selected for this work. The initial micellization of the oppositely charged polyelectrolytes was completed within the dead time of mixing of 100 ms, followed by micelle growth and equilibration up to several seconds. By combining the structural evolution of the radius of gyration (R-g) with complementary molecular dynamics simulations, we show how the self-assemblies evolve incrementally in size over time through a two-step kinetic process: first, oppositely charged polyelectrolyte chains pair to form nascent aggregates that immediately assemble into spherical micelles, and second, these PEC micelles grow into larger micellar entities. Furthermore, this work has determined one possible kinetic pathway for the initial formation of PEC micelles, which provides useful physical insights for increasing fundamental understanding self-assembly dynamics, driven by polyelectrolyte complexation that occurs on ultrafast time scales.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Nanoparticle-Induced Disorder at Complex Liquid–Liquid Interfaces: Effects of Curvature and Compositional Synergy on Functional Surfaces

The self-assembly of surfactant monolayers at interfaces plays a sweeping role in tasks ranging from household cleaning to the regulation of the respiratory system. The synergy between different nanoscale species at an interface can yield assemblies with exceptional properties, which enhance or modulate their function. However, understanding the mechanisms underlying coassembly, as well as the effects of intermolecular interactions at an interface, remains an emerging and challenging field of study. Herein, we study the interactions of gold nanoparticles striped with hydrophobic and hydrophilic ligands with phospholipids at a liquid–liquid interface and the resulting surface-bound complexes. We show that these nanoparticles, which are themselves minimally surface active, have a direct concentration-dependent effect on the rapid reduction of tension for assembling phospholipids at the interface, implying molecular coassembly. Through the use of sum frequency generation vibrational spectroscopy, we reveal that nanoparticles impart structural disorder to the lipid molecular layers, which is related to the increased volumes that amphiphiles can sample at the curved surface of a particle. The results strongly suggest that hydrophobic and electrostatic attractions imparted by nanoparticle functionalization drive lipid–nanoparticle complex assembly at the interface, which synergistically aids lipid adsorption even when lipids and nanoparticles approach the interface from opposite phases. The use of tensiometric and spectroscopic analyses reveals a physical picture of the system at the nanoscale, allowing for a quantitative analysis of the intermolecular behavior that can be extended to other systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Polyelectrolyte Complex Coacervate Assembly with Cellulose Nanofibers

Polyelectrolytes are used in paper manufacturing to increase flocculation and water drainage and improve mechanical properties. In this study, we examine the interaction between charged cellulosic nanomaterials and polyelectrolyte complex coacervates of weak polyelectrolytes, polyacrylic acid salt, and polyallylamine hydrochloride. We observe that by changing the order of addition of the polyelectrolytes to cellulose nanofibers (CNFs), we can tune the interactions between the materials, which in turn changes the degree of association of the coacervates to the CNFs and the rate at which they aggregate. Importantly for the papermaking process, when adding the polyelectrolytes sequentially to the CNFs, we found faster aggregation to the fibers and lower water retention values compared to those when preformed coacervates or CNFs by themselves were used. Coarse-grain molecular dynamic simulations further support the fundamental mechanism of aggregation by taking into consideration the interaction between cellulose and the complexes at the molecular level. The simulations corroborate the experimental observations by showing the importance of strong electrostatic interactions in aggregate formation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Sulfur Lone Pairs Control Topology in Heterotrimetallic Complexes: An Experimental and Theoretical Study

Heterotrimetallic complexes with (N 2 S 2 )M metallodithiolates, M = Ni 2+ , [Fe(NO)] 2+ , and [Co(NO)] 2+ , as bidentate chelating ligands to a central trans-Cr(NO)(MeCN) unit were characterized as the first members of a new class, NiCrNi, FeCrFe, CoCrCo. The complexes exhibit a cisoid structural topology, ascribed to the stereoactivity of the available lone pair(s) on the sulfur donors, resulting in a dispersed, electropositive pocket from the N/N and N/S hydrocarbon linkers wherein the Cr-NO site is housed. Computational studies explored alternative isomers (transoid and inverted cisoid) that suggest a combination of electronic and steric effects govern the geometrical selectivity. Electrostatic potential maps readily display the dominant electronegative potential from the sulfurs which force the NO to the electropositive pocket. The available S lone pairs work in synergy with the π-withdrawing ability of NO to lift Cr out of the S 4 plane toward the NO and stabilize the geometry. The metallodithiolate ligands bound to Cr(NO) thus find structural consistency across the three congeners. Although the dinitrosyl [(bme-dach)Co(NO)-Mo(NO)(MeCN)-(bme-dach)Co(MeCN)][PF 6 ] 2 (CoMoCo') analogue displays chemical noninnocence and a partial Mo–Co bond toward (N 2 S 2 )Co'(NCCH 3 ) in an “asymmetric butterfly” topology, the stability of the {Cr(NO)} 5 unit prohibits such bond rearrangement. Magnetism and EPR studies illustrate spin coupling across the sulfur thiolate sulfur bridges.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Escherichia coli Cas1/2 Endonuclease Complex Modifies Self-Targeting CRISPR/Cascade Spacers Reducing Silencing Guide Stability

CRISPR-based interference has become common in various applications from genetic circuits to dynamic metabolic control. In E. coli, the native CRISPR Cascade system can be utilized for silencing by deletion of the cas3 nuclease along with expression of guide RNA arrays, where multiple genes can be silenced from a single transcript. We notice the loss of spacer sequences from guide arrays utilized for dynamic silencing. Here, we report that unstable guide arrays are due to expression of the Cas1/2 endonuclease complex. We propose a model wherein basal Cas1/2 endonuclease activity results in the loss of spacers from guide arrays. Subsequently, mutant guide arrays can be amplified through selection. Replacing a constitutive promoter driving Cascade complex expression with a tightly controlled inducible promoter improves guide array stability, while minimizing leaky gene silencing. Additionally, these results demonstrate the potential of Cas1/2 mediated guide deletion as a mechanism to avoid CRISPR based autoimmunity.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Mechanochemical Regulation of Oxidative Addition to a Palladium(0) Bisphosphine Complex

Here, we report the effect of force applied to the biaryl backbone of a bisphosphine ligand on the rate of oxidative addition of bromobenzene to a ligand-coordinated palladium center. Local compressive and tensile forces on the order of 100 pN were generated using a stiff stilbene force probe. A compressive force increases the rate of oxidative addition, whereas a tensile force decreases the rate, relative to that of the parent complex of strain-free ligand. Rates vary by a factor of ~6 across ~340 pN of force applied to the complexes. The crystal structures and DFT calculations support that force-induced perturbation of the geometry of the reactant is negligible. The force-rate relationship observed is mainly attributed to the coupling of force to nuclear motion comprising the reaction coordinate. These observations inform the development of catalysts whose activity can be tuned by an external force that is adjusted within a catalytic cycle.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Trigonal Bipyramidal V 3+ Complex as an Optically Addressable Molecular Qubit Candidate

Synthetic chemistry enables a bottom-up approach to quantum information science, where atoms can be deterministically positioned in a quantum bit or qubit. Two key requirements to realize quantum technologies are qubit initialization and read-out. By imbuing molecular spins with optical initialization and readout mechanisms, analogous to solid-state defects, molecules could be integrated into existing quantum infrastructure. To mimic the electronic structure of optically addressable defect sites, we designed the spin-triplet, V 3+ complex, (C 6 F 5 ) 3 trenVCN t Bu (1).We measured the static spin properties as well as the spin coherence time of1demonstrating coherent control of this spin qubit with a 240 GHz electron paramagnetic resonance spectrometer powered by a free electron laser. We found that1exhibited narrow, near-infrared photoluminescence (PL) from a spin-singlet excited state. Using variable magnetic field PL spectroscopy, we resolved emission into each of the ground-state spin sublevels, a crucial component for spin-selective optical initialization and readout. This work demonstrates that trigonally symmetric, heteroleptic V 3+ complexes are candidates for optical spin addressability.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Characterization of Americium and Curium Complexes with the Protein Lanmodulin: A Potential Macromolecular Mechanism for Actinide Mobility in the Environment

Anthropogenic radionuclides, including long-lived heavy actinides such as americium and curium, represent the primary long-term challenge for management of nuclear waste. The potential release of these wastes into the environment necessitates understanding their interactions with biogeochemical compounds present in nature. Here, we characterize the interactions between the heavy actinides, Am 3+ and Cm 3+ , and the natural lanthanide-binding protein, lanmodulin (LanM). LanM is produced abundantly by methylotrophic bacteria, including Methylorubrum extorquens, that are widespread in the environment. We determine the first stability constant for an Am 3+ -protein complex (Am 3 LanM) and confirm the results with Cm 3 LanM, indicating a ~5-fold higher affinity than that for lanthanides with most similar ionic radius, Nd 3+ and Sm 3+ , and making LanM the strongest known heavy actinide-binding protein. The protein’s high selectivity over 243 Am’s daughter nuclide 239 Np enables lab-scale actinide-actinide separations as well as provides insight into potential protein-driven mobilization for these actinides in the environment. The luminescence properties of the Cm 3+ -LanM complex, and NMR studies of Gd 3+ -LanM, reveal that lanmodulin-bound f-elements possess two coordinated solvent molecules across a range of metal ionic radii. Finally, we show under a wide range of environmentally relevant conditions that lanmodulin effectively outcompetes desferrioxamine B, a hydroxamate siderophore previously proposed to be important in trivalent actinide mobility. Overall, these results suggest that natural lanthanide-binding proteins such as lanmodulin may play important roles in speciation and mobility of actinides in the environment; it also suggests that protein-based biotechnologies may provide a new frontier in actinide remediation, detection, and separations.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Toward Improved Charge Separation through Conformational Control in Copper Coordination Complexes

The continued development of solar energy as a renewable resource necessitates the design and study of new approaches to sustaining photodriven charge separation (CS). To this end, we present a bioinspired approach in which triggered conformational changes are used to control electron transfer (ET) events. We report, photo-induced conformational rearrangements of a ligand are translated into changes in the coordination geometry and environment about a bound metal ion. Taking advantage of the differential coordination properties of Cu I and Cu II , these dynamics facilitate intramolecular ET from Cu I to the ligand to create a CS state. The synthesis and photophysical characterization of CuCl(dpaa R ) (dpaa = dipicolylaminoacetophenone, with R = H and OMe) is presented. These ligands incorporate a fluorophore into their framework that gives rise to a twisted intramolecular charge transfer (TICT) excited state. Excited state ligand twisting provides a tetragonal coordination geometry capable of capturing Cu II in the CS state when an internal ortho-OMe binding site is present (as in dpaaOMe). We employ NMR, IR, EPR, and optical spectroscopies, X-ray diffraction, and electrochemical methods to establish the ground state properties of the Cu I and Cu II complexes. We then investigate the photophysical dynamics of these Cu I complexes via time-resolved photoluminescence (TR-PL), and optical transient absorption (OTA) spectroscopies. We show that relative to controls lacking a TICT-active ligand, the lifetime of the CS state is enhanced ~1000-fold. Further, the presence of the ortho-OMe substituent greatly enhances the lifetime of the TICT* state and biases the coordination environment toward Cu II . The presence of Cu I decreases photoinduced degradation from 14 to <2% but does not result in significant quenching via ET. Factors affecting CS in these systems are discussed, laying the groundwork for our strategy toward solar energy conversion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

π-Extended Ligands in Two-Coordinate Coinage Metal Complexes

Two-coordinate carbene-M I -amide (cMa, M I = Cu, Ag, Au) complexes have emerged as highly efficient luminescent materials for use in a variety of photonic applications, due to their extremely fast radiative rates via thermally activated delayed fluorescence (TADF) from an interligand charge transfer (ICT) process. A series of cMa derivatives were prepared to examine the variables which affect the radiative rate with the goal of understanding the parameters that control the radiative TADF process in these materials. We find that blue emissive complexes with high photoluminescence efficiency (Φ PL > 0.95) and fast radiative rates (k r = 4 x 10 6 s -1 ) can be achieved by selectively extending the π-system of the carbene and amide ligands. Of note is the role played by increasing the separation between the hole and electron in the ICT excited state. Analysis of temperature dependent luminescence data along with theoretical calculations indicate that the hole-electron separation alters the energy gap between the lowest energy singlet and triplet states (ΔE ST ) while keeping the radiative rate for the singlet state unchanged. As a result, this interpretation provides guidelines for the design of new cMa derivatives with even faster radiative rates as well as those with slower radiative rates and thus extended excited state lifetimes.

14 SOLAR ENERGY↗
DOE OSTI2023

Controlled Self-Assembly of Gold Nanotetrahedra into Quasicrystals and Complex Periodic Supracrystals

The self-assembly of shape-anisotropic nanocrystals into large-scale structures is a versatile and scalable approach to creating multifunctional materials. The tetrahedral geometry is ubiquitous in natural and manmade materials, yet regular tetrahedra present a formidable challenge in understanding their self-assembly behavior as they do not tile space. Here, we report diverse supracrystals from gold nanotetrahedra including the quasicrystal (QC) and the dimer packing predicted more than a decade ago and hitherto unknown phases. We solve the complex three-dimensional (3D) structure of the QC by a combination of electron microscopy, tomography, and synchrotron X-ray scattering. Nanotetrahedron vertex sharpness, surface ligands, and assembly conditions work in concert to regulate supracrystal structure. We also discover that the surface curvature of supracrystals can induce structural changes of the QC tiling and eventually, for small supracrystals with high curvature, stabilize a hexagonal approximant. Finally, our findings bridge the gap between computational design and experimental realization of soft matter assemblies and demonstrate the importance of accurate control over nanocrystal attributes and the assembly conditions to realize increasingly complex nanopolyhedron supracrystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Cryo-EM Structure of the Mnx Protein Complex Reveals a Tunnel Framework for the Mechanism of Manganese Biomineralization

The global manganese cycle relies on microbes to oxidize soluble Mn(II) to insoluble Mn(IV) oxides. Some microbes require peroxide or superoxide as oxidants, but others can use O 2 directly, via multicopper oxidase (MCO) enzymes. One of these, MnxG from Bacillus sp. strain PL-12, was isolated in tight association with small accessory proteins, MnxE and MnxF. The protein complex, called Mnx, has eluded crystallization efforts, but we now report the 3D structure of a point mutant using cryo-EM single particle analysis, cross-linking mass spectrometry, and AlphaFold Multimer prediction. The ß-sheet–rich complex features MnxG enzyme, capped by a heterohexameric ring of alternating MnxE and MnxF subunits, and a tunnel that runs through MnxG and its MnxE 3 F 3 cap. The tunnel dimensions and charges can accommodate the mechanistically inferred binuclear manganese intermediates. Furthermore, comparison with the Fe(II)-oxidizing MCO, ceruloplasmin, identifies likely coordinating groups for the Mn(II) substrate, at the entrance to the tunnel. Thus, the 3D structure provides a rationale for the established manganese oxidase mechanism, and a platform for further experiments to elucidate mechanistic details of manganese biomineralization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Leveraging Intramolecular π-Stacking to Access an Exceptionally Long-Lived 3 MC Excited State in an Fe(II) Carbene Complex

The ability to manipulate excited-state decay cascades using molecular structure is essential to the application of abundant-metal photosensitizers and chromophores. Ligand design has yielded some spectacular results elongating charge-transfer excited state lifetimes of Fe(II) coordination complexes, but triplet metal-centered ( 3 MC) excited states - recently demonstrated to be critical to the photoactivity of isoelectronic Co(III) polypyridyls - have to date remained elusive, with temporally isolable examples limited to the picosecond regime. Here, with this report, we show how strong-field donors and intramolecular π-stacking can conspire to stabilize a long-lived 3 MC excited state for a remarkable 4.1 ± 0.3 ns in fluid solution at ambient temperature. Analysis of variable-temperature time-resolved absorption data using theoretical models ranging from Arrhenius to semiclassical Marcus theory, combined with computational modeling and X-ray crystallography, reveal a Jahn−Teller stabilized excited state with a high activation barrier for ground-state recovery. The net result is a chromophore with a 3 MC excited-state lifetime that is orders of magnitude longer than anything yet observed for an Fe(II) complex.

carbene compounds↗
DOE OSTI2025

Sustained, Selective, and Efficient Photochemical CO 2 Reduction to Formate by Electron-Deficient Ruthenium Polypyridyl Complexes

Metal-hydrides play a significant role in a variety of reactions, including chemical, electrochemical, and pho-tochemical CO 2 reduction. Molecular metal-hydrides have the distinct advantage of allowing tunability of their hydricities by rational ligand modifications, with more electron-rich metal-hydrides being in general more hydridic. We report here a new approach to generate highly hydridic metal hydrides of the type [Ru(tpy)(LL)(H)] n+ by introducing electron-withdrawing substituents in the backbone of the bidentate LL ligand. This strategy enables the generation of the metal hydride, [Ru(tpy)(LL)(H)] + , at mild negative potentials and further one electron reduction to the more hydridic [Ru(tpy)(LL)(H)] 0 at a potential window that is redox silent for the more electron-rich metal hydride analogue [Ru(tpy)(bpy)(H)] + . In addition, for-mate release takes place from the hydride transfer adducts [Ru---HCOO)(tpy)(LL)] 0 rather than from the corresponding formato complexes, [Ru(tpy)(LL)(OCHO)] 0 , which would require further reduction to [Ru(tpy)(LL)(OCHO)]ˉ as demonstrated by IR-spectroelectrochemistry. The parent [Ru(tpy)(LL)(CH 3 CN)] n+ solvento complexes were then tested as catalysts for the reduction of CO 2 to formate in a 4-component homogenenous photochemical approach driven by a Ru(II) sensitizer. The re-sults showed selective (> 88%) formate production with record turnover number of ~50,000 and record turnover frequency of 4.4 s -1 when compared to other molecular catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Magnetic Blocking in Fluoflavine Radical-Bridged Dilanthanide Complexes

Magnetic exchange coupling is difficult to foster in polynuclear lanthanide (Ln) complexes and poorly understood. While coupling Ln ions through closed-shell ligands is inherently weak due to the contracted 4f orbitals, placing open-shell ligands instead has proven to promote orders of magnitude stronger coupling, giving rise to single-molecule magnets (SMMs) innate to real magnetic memory effect in the case of the anisotropic Ln ions. Notably, the impact of radical bridges with differing oxidation states on magnetic blocking remains unexplored due to lack of Ln SMMs with radicals in two distinct charge states. Herein, the first dilanthanide complexes (Ln = Gd, Dy) containing fluoflavine (flv) bridges, [(Cp* 2 Ln) 2 (μ-flv z )]X, (where X = [Al(OC{CF 3 } 3 ) 4 ] − (z = 1−•), 1-Ln; X = 0 (z = 2−), 2-Ln; X =[K(crypt-222)] + (z = 3−•), 3-Ln) are reported. 1-Ln and 3-Ln, comprising the flv 1−• and flv 3−• radical bridges, were investigated via single-crystal X-ray diffraction (SCXRD), ultraviolet−visible (UV−vis) spectroscopy, Superconducting Quantum Interference Device (SQUID) magnetometry, high-field electron paramagnetic resonance (HF-EPR) spectroscopy and broken-symmetry density functional theory (BS-DFT) calculations. 1-Dy and 3-Dy constitute the first SMMs innate to radicals in two differing oxidation states. 1-Dy exhibits a spin-reversal barrier U eff of 28.36 cm −1 and open magnetic hysteresis loops below 3 K. By contrast, 3-Dy displays a much higher U eff of 143(2) cm −1 and open hysteresis loops until 9.5 K, representing a record for dilanthanide SMMs containing an organic radical bridge. The boost in SMM properties in 3-Dy is attributed to spin-phonon coupling and improved frontier orbital structure. This study paves the way for advanced design strategies of polynuclear Ln SMMs.

Benner, Florian [Michigan State Univ., East Lansin↗