¹³C CP/MAS NMR and Crystallographic Investigations of the Structure and Solid-State Transformations of Lead(II) Acetate Trihydrate

Lead(II) acetate trihydrate undergoes solid-state transformations at room temperature, resulting in anomalous and variable peaks in the ¹³C cross-polarization magic-angle-spinning (CP/MAS) NMR spectra of powder samples of this compound. Isotropic chemical shift differences of up to 12 ppm are observed for the carboxyl carbons as a result of these rearrangements; 2 ppm differences are observed for the methyl carbons. We have demonstrated the usefulness of ¹³C CP/MAS NMR studies in conjunction with X-ray crystallographic analysis for monitoring solid-state reactions and providing a structural basis for some of the observed spectral features. The ¹³C CP/MAS NMR spectrum of lead(II) acetate trihydrate changes from a single sharp resonance at 51 ppm (relative to benzene) for the carboxyl carbon and at-103 ppm for the methyl group, to patterns having several lines in the carboxyl region and two lines in the methyl region. X-ray crystal structure analysis of lead(II) acetate shows that there are two crystallographically nonequivalent acetate groups per molecule that differ in their intermolecular interactions; however, these chemical differences are not sufficient to yield resolvable isotropic chemical shifts for the carboxyl or methyl groups. Crystal data: PbC₄0₇H₁₂, a = 15.803 (2) Å, b = 7.269 (2) Å, c = 9.049 (2) Å, β = 109.55 (3)°; monoclinic, Cl/m, Z = 4, 1526 unique reflections, collected on an automatic diffractometer, 1124 with I > 3(7) used for structure solution; Patterson and Fourier syntheses used for structure solution; full-matrix least-squares refinement to R = 0.043. The lead atom is nine-coordinate with two bidentate acetate groups, three coordinated water molecules, and two bridging bonds to oxygens on neighboring acetate groups. Intramolecular Pb-O distances range from 2.446 (8) to 3.11 (1) Å.