Harris Edward Mason

¹³ C‐ and ² H‐enriched bis((3,5‐dimethylphenyl)aminomethyl) ^tert butylphosphine (the natural abundance (NA) ligand ^Ar BiAMP ^{t Bu} ; the ² H‐ and ¹³ C‐labelled analogues are denoted as d ₄ ‐ ^Ar BiAMP ^{t Bu} and ¹³ C ₂ ‐ ^Ar BiAMP ^{t Bu} , respectively), containing two secondary amines and a tertiary phosphine, was synthesized using a Kabachnik–Fields protocol. The coordination chemistry of the ligand isotopologues (including the NA derivative) was investigated with the paramagnetic lanthanides Ce and Nd and the paramagnetic actinide elements Np and Pu, furnishing MI( ^Ar BiAMP ^{t Bu} )(thf) ₃ (M = Ce( 1 ), Nd( 2 ), Np( 3 ), Pu( 4 )), MI( d ₄ ‐ ^Ar BiAMP ^{t Bu} )(thf) ₃ (M = Ce( ² H‐1 ), Nd( ² H‐2 )) and MI( ¹³ C ₂ ‐ ^Ar BiAMP ^{t Bu} )(thf) ₃ (M = Ce( ¹³ C‐1 ), Nd( ¹³ C‐2 ), Np( ¹³ C‐3 ), Pu( ¹³ C‐4 )); each complex bears the metal in the 3+ oxidation state chelated by the amide groups and phosphorus atom of the ^Ar BiAMP ^{t Bu} ligand. Multinuclear ( ¹ H, ³¹ P, ¹³ C, and ² H) NMR characterization of the complexes revealed wide windows of paramagnetically shifted resonances; the isotopically enriched derivatives allowed for the unambiguous identification of the methylene environments, highlighting the utility of the ^Ar BiAMP ^{t Bu} ligands for providing rich spectroscopic signatures of paramagnetic f ‐element coordination complexes. A combination of single‐crystal X‐ray diffraction and UV‐vis‐NIR spectroscopic techniques was also employed for the characterization of the compounds. Actinide complexes 3 and 4 possess rare examples of molecular transuranium element–phosphorus bonds and the first examples of transuranium element–phosphine interactions.

Earth’s field NMR (EFNMR) is a useful modality for low-field NMR spectroscopy due to its availability, portability, and low cost. EFNMR can enable better line width resolution than at high fields primarily due to low magnetic susceptibility broadening. Unfortunately, EFNMR spectra are highly complex due to strong J-coupling effects and can be challenging to interpret without additional information. However, the spectral complexity paired with ultrahigh resolution offers a unique opportunity to fingerprint analytes. Herein, we show that high-field (e.g., 9.4 T) NMR and EFNMR have distinct complementary roles in explaining the NMR interactions that manifest in the respective spectra of complex molecules. Chemical shifts are nearly exclusive to high-field NMR and can enable facile observations of weak J-couplings for cursory spectral assignments, but EFNMR’s ability to resolve high-precision magnitudes and signs of J-couplings is essential for fully and accurately assigning structures with high fidelity. We demonstrate this with an important category of materials, fluorinated fentanyl analogues (i.e., fluorofentanyls) and their precursors. These systems are well suited to study due to their relevance to the synthetic opioid crisis and their similarities to fluorinated pharmaceuticals and biomolecules. Results show assignment of the magnitudes and signs of J-couplings in several fluorinated precursors using both high-field and EFNMR. In select fluorofentanyls, EFNMR can provide information on J-couplings that would otherwise be inaccessible even with 3D experiments at 9.4 T. EFNMR spectra of fluorofentanyls show a strong dependence on J-coupling between 1H or 19F and 14N nuclei, where the effects that manifest in spectra may be used to gain insights into local molecular dynamics and information on 14N electric-field gradient tensors.

Polyacenes, one-dimensional (1D) linear chains of fused benzene rings, are of significant interest because of their unique structural and optoelectronic properties.

Trends in the covalency of the U–Cl bonds were investigated using ^35/37 Cl wideline solid-state NMR and DFT calculations of solid paramagnetic uranium chlorides highlighting the ability of SSNMR to probe the electronic structure of actinide compounds.

The synthesis, characterization, and electronic structure of Cp*₂Am(^tBu₂bipy^•–) (1-Am) (Cp* = pentamethylcyclopentadienide; ^tBu₂bipy = 4,4′-di-tert-butyl-2,2′-bipyridine), the first isolated and structurally verified americium complex containing a radical ligand, is reported. Theoretical calculations (DFT and multiconfigurational methods) alongside experimental comparisons of M–N distances reveal a greater degree of metal–ligand covalency in 1-Am compared to near-isoradial lanthanide counterparts 1-Nd and 1-Sm. Electrochemical studies suggest that 1-Am may behave as an “Am(II) synthon”, and a preliminary attempt to probe the chemical reactivity of 1-Am is briefly discussed.

The synthesis, characterization, and electronic structure of Cp*2Am(tBu2bipy•−) (1-Am; Cp* = pentamethylcyclopentadienide; tBu2bipy = 4,4ʹ-di-tert-butyl-2,2ʹ-bipyridine) is reported as the first isolated and structurally- verified americium complex containing a radical ligand. Theoretical calculations (DFT and multiconfigurational methods) along with-alongside experimental comparisons of M–N distances reveal a greater degree of metal-ligand covalency in 1-Am com-pared to near-isoradial lanthanide counterparts, 1-Nd and 1-Sm. Electrochemical studies suggest 1-Am may behave as an ‘Am(II) synthon’ and a preliminary attempt to probe the chemical reactivity of 1-Am is briefly discussed.

Complexes derived from H2ExPh reveal differences in ligand framework between lanthanide and uranium ions. Structures are overlaid on the cyclic voltammogram of U(iv)ExPh.

Magnesium-ion batteries hold the potential to outperform the energy density of lithium-ion batteries, given the divalent charge carried by each Mg²⁺ cation, but remain in an early stage of development. Here, ²⁵Mg solid-state nuclear magnetic resonance (ssNMR) is used to gain insight into the local structure and Mg-ion dynamics of candidate Mg-ion solid electrolytes, the antiperovskites Mg₃SbN and Mg₃AsN. Using the highest available magnetic field (35.2 T) for high-resolution solid-state NMR, the largest ²⁵Mg quadrupole coupling constants (C_Q) yet measured of up to 22 MHz are reported and corroborated by first-principles calculations. Predicted C_Q values are shown to correlate with the antiperovskite's tolerance factor; thus, ²⁵Mg NMR linewidths can report on lattice distortions and phase stability of these antiperovskites. Variable-temperature ²⁵Mg NMR spectra demonstrate changes at elevated temperatures, ascribed to Mg-ion motional effects. ²⁵Mg T₁ relaxometry measurements at ultrahigh field reveal a lower activation energy for the more distorted Mg₃AsN phase, matching computational predictions of a lower energy barrier for Mg²⁺ ion migration and suggesting that additional scrutiny of antiperovskites as Mg-ion conductors is warranted. Given the inherent challenges of ²⁵Mg NMR, this work demonstrates the benefits of combining ultrahigh field NMR spectroscopy, advanced pulse sequences, modern signal processing, and first-principles calculations to facilitate NMR of quadrupolar nuclei as a tool to probe the local structure and ion dynamics in beyond-Li battery materials.