Application of ^204mPb Perturbed Angular Correlation of γ-rays Spectroscopy in Coordination Chemistry

^204mPb perturbed angular correlation of γ-rays (PAC) spectroscopy has been applied successfully for the first time to detect the nuclear quadrupole interaction in a lead­(II) coordination compound in a molecular crystal [tetraphenylarsonium lead­(II) isomaleonitriledithiolate ([AsPh₄]₄[Pb₂(i-mnt)₄])]. The recorded parameters from a powder crystalline sample are ν_Q = 0.178(1) GHz and η = 0.970(7). The electric field gradient (EFG) was determined at the PW91/QZ4P level including relativistic effects using the two-component zeroth-order regular approximation method for both the [Pb­(i-mnt)₂]^2– monomer and the [Pb₂(i-mnt)₄]^4– dimer. Only the EFG for the latter compares favorably with the experimental data, indicating that the picture of this complex as a prototypical hemidirected coordination geometry with a stereochemically active lone pair on lead­(II) is inadequate. Advantages and limitations of ^204mPb PAC spectroscopy as a novel technique to elucidate the electronic and molecular structures of lead-containing complexes and biomolecules are presented

Microscopic Dynamics of Li⁺ in Rutile TiO₂ Revealed by ⁸Li β‑Detected Nuclear Magnetic Resonance

We report measurements of the dynamics of isolated ⁸Li⁺ in single crystal rutile TiO₂ using β-detected nuclear magnetic resonance. From spin–lattice relaxation and motional narrowing, we find two sets of thermally activated dynamics: one below 100 K and one at higher temperatures. At low temperature, the activation barrier is 26.8(6) meV with prefactor 1.23(5) × 10¹⁰ s^–1. We suggest this is unrelated to Li⁺ motion and rather is a consequence of electron polarons in the vicinity of the implanted ⁸Li⁺ that are known to become mobile in this temperature range. Above 100 K, Li⁺ undergoes long-range diffusion as an isolated uncomplexed cation, characterized by an activation energy and prefactor of 0.32(2) eV and 1.0(5) × 10¹⁶ s^–1, respectively, in agreement with macroscopic diffusion measurements. These results in the dilute limit from a microscopic probe indicate that Li⁺ concentration does not limit the diffusivity even up to high concentrations but that some key ingredient is missing in the calculations of the migration barrier. The anomalous prefactors provide further insight into both Li⁺ and polaron motion