Using NMR Spectroscopy to Evaluate Metal-Ligand Bond Covalency for the f Elements.

ConspectusUnderstanding f element-ligand covalency is at the center of efforts to design new separations schemes for spent nuclear fuel, and is therefore of signficant fundamental and practical importance. Considerable effort has been invested into quantifying covalency in f element-ligand bonding. Over the past decade, numerous studies have employed a variety of techniques to study covalency, including XANES, EPR, and optical spectroscopies, as well as X-ray crystallography.

Synthesis and characterization of isostructural annulated actinocenes.

An isostructural series of four annulated actinocene complexes, M(hdcCOT) (M = Th, U, Np, Pu), is reported. The syntheses proceed through a trivalent starting material when M = U, Np, Pu with subsequent oxidation or, in the case of M = Th, directly from ThCl(DME). X-ray crystallography shows that each actinocene has molecular point symmetry in the solid state, with the metal atoms symmetrically bonded to two 10π-aromatic [8]annulene dianion rings.

ThCTi@(6)-C: Th═C Double Bond in a Mixed Actinide-Transition Metal Cluster.

A thorium-carbon double bond that corresponds to the sum of theoretical covalent double bond radii has long been sought after in the study of actinide-ligand multiple bonding as a synthetic target. However, the stabilization of this chemical bond remains a great challenge to date, in part because of a relatively poor energetic matching between 5f-/6d- orbitals of thorium and the 2s-/2p- frontier orbitals of carbon. Herein, we report the successful synthesis of a thorium-carbon double bond in a carbon-bridged actinide-transition metal cluster, i.

Correction: The roles of 4f- and 5f-orbitals in bonding: a magnetochemical, crystal field, density functional theory, and multi-reference wavefunction study.

Correction for 'The roles of 4f- and 5f-orbitals in bonding: a magnetochemical, crystal field, density functional theory, and multi-reference wavefunction study' by W. W. Lukens , , 2016, , 11508-11521, https://doi.

Machine Learning Mapping Approach for Computing Spin Relaxation Dynamics.

In this work, a machine learning mapping approach for predicting the properties of atomistic systems is reported. Within this approach, the atomic orbital overlap, density, or Kohn-Sham (KS) Fock matrix elements obtained at a low level of theory such as extended tight-binding have been used as input features to predict the electric field gradient (EFG) tensors at a higher level of theory such as those obtained with hybrid functionals. It is shown that the machine-learning-predicted EFG tensors can be used to compute spin relaxation rates of several ions in aqueous solutions.

Slow Magnetic Relaxation in a Californium Complex.

We report the synthesis and characterization of the macrocyclic californium derivative Na[Cf(HO)(DOTA)] (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), , which was studied in comparison to its dysprosium counterpart, Na[Dy(HO)(DOTA)], . Divergent spectroscopic and magnetic behaviors were observed between and . Based upon spectroscopic measurements, we propose that accessible 5f → 6d transitions (potentially operating in tandem with charge-transfer transitions) are the major contributors to the observed broadband photoluminescence in .

An Actinide Complex with a Nucleophilic Allenylidene Ligand.

The reaction of [CpTh(3,3-diphenylcyclopropenyl)] (Cp = η-CH) with 1 equiv of lithium diisopropylamide (LDA) results in cyclopropenyl ring opening and formation of the thorium allenylidene complex, [Li(EtO)][CpTh(CCCPh)] ([Li(EtO)][]), in good yield. Additionally, deprotonation of [CpTh(3,3-diphenylcyclopropenyl)] with 1 equiv of LDA, in the presence of 12-crown-4 or 2.2.

The Counterintuitive Relationship between Orbital Energy, Orbital Overlap, and Bond Covalency in CeF and CeCl.

The 4f orbitals of Ce(IV) have shown appreciably enhanced covalent mixing with ligand orbitals relative to those of Ce(III). Here, X-ray spectroscopy, magnetic susceptibility measurements, and theoretical methods are used to investigate 4f covalency in CeF and CeCl. These techniques show covalent mixing between Ce 4f and F 2p orbitals to be about 25% less than mixing between Ce 4f and Cl 3p orbitals, placing CeF among the most ionic Ce(IV) compounds to-date.

Preparation of Neptunyl and Plutonyl Acetates To Access Nonaqueous Transuranium Coordination Chemistry.

Uranyl diacetate dihydrate is a useful reagent for the preparation of uranyl (UO) coordination complexes, as it is a well-defined stoichiometric compound featuring moderately basic acetates that can facilitate protonolysis reactivity, unlike other anions commonly used in synthetic actinide chemistry such as halides or nitrate. Despite these attractive features, analogous neptunium (Np) and plutonium (Pu) compounds are unknown to date. Here, a modular synthetic route is reported for accessing stoichiometric neptunyl(VI) and plutonyl(VI) diacetate compounds that can serve as starting materials for transuranic coordination chemistry.

Computational exploration of the copper(I)-catalyzed conversion of hydrazones to dihalogenated vinyldiazene derivatives.

This computational study explores the copper (I) chloride catalyzed synthesis of (E)-1-(2,2-dichloro-1-phenylvinyl)-2-phenyldiazene (2Cl-VD) from readily available hydrazone derivative and carbon tetrachloride (CCl). 2Cl-VD has been extensively utilized to synthesize variety of heterocyclic organic compounds in mild conditions. The present computational investigations primarily focus on understanding the role of copper (I) and N,N,N,N-tetramethylethane-1,2-diamine (TMEDA) in this reaction, TMEDA often being considered a proton scavenger by experimentalists.

Realization of Organocerium-Based Fullerene Molecular Materials Showing Mott Insulator-Type Behavior.

Electron-rich organocerium complexes (CMeH)Ce and [(CMe)Ce(-oxa)], with redox potentials = -0.82 V and = -0.86 V versus Fc/Fc, respectively, were reacted with fullerene (C) in different stoichiometries to obtain molecular materials.

Facile Oxidation of Ce(III) to Ce(IV) Using Cu(I) Salts.

The synthesis, luminescence, and electrochemical properties of the Ce(III) compound, [(CMe)(2,6-PrCHO)Ce(THF)], , were investigated. Based on the electrochemical data, treatment of with CuX (X = Cl, Br, I) results in the formation of the corresponding Ce(IV) complexes, [(CMe)(2,6-PrCHO)Ce(X)]. Each complex has been characterized using NMR, IR, and UV-vis spectroscopy as well as structurally determined using X-ray crystallography.

Dynamic and relativistic effects on Pt-Pt indirect spin-spin coupling in aqueous solution studied by ab initio molecular dynamics and two- vs four-component density functional NMR calculations.

Treating 195Pt nuclear magnetic resonance parameters in solution remains a considerable challenge from a quantum chemistry point of view, requiring a high level of theory that simultaneously takes into account the relativistic effects, the dynamic treatment of the solvent-solute system, and the dynamic electron correlation. A combination of Car-Parrinello molecular dynamics (CPMD) and relativistic calculations based on two-component zeroth order regular approximation spin-orbit Kohn-Sham (2c-ZKS) and four-component Dirac-Kohn-Sham (4c-DKS) Hamiltonians is performed to address the solvent effect (water) on the conformational changes and JPtPt1 coupling. A series of bridged PtIII dinuclear complexes [L1-Pt2(NH3)4(Am)2-L2]n+ (Am = α-pyrrolidonate and pivalamidate; L = H2O, Cl-, and Br-) are studied.

Triplet-Singlet Emission of d-Block Metal Complexes Characterized by Spin-Orbit Natural Transition Orbitals.

Spin-orbit natural transition orbital (SO-NTO) methodology, recently developed in our group for complete and restricted active space (CAS/RAS) wavefunction calculations, is applied to analyze triplet-to-singlet emission in transition metal complexes. The lowest-energy (longest-wavelength) spin-forbidden transition is studied for for [Ir(pbt)2(acac)] and [Re(CO)4(pbt)] and the complexes [W(CO)4(bpy)] and [Mo(CO)4(bpy)]. For the latter complexes, spin-forbidden transitions from higher spin-triplet levels are additionally analyzed.

Exploring Spin-Orbit Effects in a [CuTl] Nanocluster Featuring an Uncommon Tl-H Interaction.

Reaction of [CuH(PPh)] with 1 equiv. of Tl(OTf) results in formation of [CuTlH(PPh)][OTf] ([1]OTf]), which can be isolated in good yields. Variable-temperature H NMR spectroscopy, in combination with density functional theory (DFT) calculations, confirms the presence of a rare Tl-H orbital interaction.

Structure and bonding in rhodium coordination compounds: a Rh solid-state NMR and relativistic DFT study.

This study demonstrates the application of Rh solid-state NMR (SSNMR) spectroscopy to inorganic and organometallic coordination compounds, in combination with relativistic density functional theory (DFT) calculations of Rh chemical shift tensors and their analysis with natural bond orbital (NBO) and natural localized molecular orbital (NLMO) protocols, to develop correlations between Rh chemical shift tensors, molecular structure, and Rh-ligand bonding. Rh is one of the least receptive NMR nuclides, and consequently, there are very few reports in the literature. We introduce robust Rh SSNMR protocols for stationary samples, which use the broadband adiabatic inversion-cross polarization (BRAIN-CP) pulse sequence and wideband uniform-rate smooth-truncation (WURST) pulses for excitation, refocusing, and polarization transfer, and demonstrate the acquisition of Rh SSNMR spectra of unprecedented signal-to-noise and uniformity.

Inquiring Hg NMR Parameters by Combining Ab Initio Molecular Dynamics and Relativistic NMR Calculations.

Ab initio molecular dynamics (AIMD) sampling followed by relativistic density functional theory (DFT) Hg NMR calculations were performed for Hg organometallic complexes in water, dimethyl sulfoxide, and chloroform. The spin-orbit coupling, a relativistic effect, is a key factor for predicting δ(Hg) and (Hg-C) accurately, in conjunction with a dynamic treatment of the systems. Good agreement between the theoretical and experimental results is reached by adopting implicit (based on a continuum model) and explicit (solvent molecules treated quantum mechanically) solvation models.

Quantifying Actinide-Carbon Bond Covalency in a Uranyl-Aryl Complex Utilizing Solution C NMR Spectroscopy.

Reaction of [UOCl(THF)] with generated LiFmes (FmesH = 1,3,5-(CF)CH) in EtO resulted in the formation of the uranyl aryl complexes [Li(THF)][UO(Fmes)] ([Li(THF)][]) and [Li(EtO)(THF)][UO(Fmes)] ([Li(EtO)(THF)][]) in good to moderate yields after crystallization from hexanes and EtO, respectively. Both complexes were characterized by X-ray crystallography and NMR spectroscopy. DFT calculations reveal that the C resonance in [] exhibits a deshielding of 51 ppm from spin-orbit coupling effects originating at uranium, which indicates an appreciable covalency in the U-C bonding interaction.

Actinide inverse trans influence versus cooperative pushing from below and multi-center bonding.

Actinide-ligand bonds with high multiplicities remain poorly understood. Decades ago, an effect known as 6p pushing from below (PFB) was proposed to enhance actinide covalency. A related effect-also poorly understood-is inverse trans influence (ITI).