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.