Probing Lead(II) Bonding Environments in 4-Substituted Pyridine Adducts of (2,6-Me2C6H3S)2Pb: An X-ray Structural and Solid-State 207Pb NMR StudyInorganic Chemistry (2007)
The effect of subtle changes in the σ-electron donor ability of 4-substituted pyridine ligands on the lead(II) coordination environment of (2,6-Me2C6H3S)2Pb (1) adducts has been examined. The reaction of 1 with a series of 4-substituted pyridines in toluene or dichloromethane results in the formation of 1:1 complexes [(2,6-Me2C6H3S)2Pb(pyCOH)]2 (3), [(2,6-Me2C6H3S)2Pb(pyOMe)]2 (4), and (2,6-Me2C6H3S)2Pb(pyNMe2) (5) (pyCOH = 4-pyridinecarboxaldehyde; pyOMe = 4-methoxypyridine; pyNMe2 = 4-dimethylaminopyridine), all of which have been structurally characterized by X-ray crystallography. The structures of 3 and4 are dimeric and have ψ-trigonal bipyramidal S3N bonding environments, with the 4-substituted pyridine nitrogen and bridging sulfur atoms in axial positions and two thiolate sulfur atoms in equatorial sites. Conversely, compound 5 is monomeric and exhibits a ψ-trigonal pyramidal S2N bonding environment at lead(II). The observed structures may be rationalized in terms of a simple valence bond model and the σ-electron donor ability of the 4-pyridine ligands as derived from the analysis of proton affinity values. Solid-state 207Pb NMR experiments are applied in combination with density functional theory (DFT) calculations to provide further insight into the nature of bonding in 4, 5, and (2,6-Me2C6H3S)2Pb(py)2 (2). The lead chemical shielding (CS) tensor parameters of 2, 4, and 5 reveal some of the largest chemical shielding anisotropies (CSA) observed in lead coordination complexes to date. DFT calculations using the AmsterdamDensity Functional (ADF) program, which take into account relativistic effects using the zeroth-order regular approximation (ZORA), yield lead CS tensor components and orientations. Paramagnetic contributions to the lead CS tensor from individual pairs of occupied and virtual molecular orbitals (MOs) are examined to gain insight into the origin of the large CSA. The CS tensor is primarily influenced by mixing of the occupied MOs localized on the sulfur and lead atoms with virtual MOs largely comprised of lead 6p orbitals.
Publication DateSeptember 15, 2007
Citation InformationGlen G. Briand, Andrew D. Smith, Gabriele Schatte, Aaron J. Rossini, et al.. "Probing Lead(II) Bonding Environments in 4-Substituted Pyridine Adducts of (2,6-Me2C6H3S)2Pb: An X-ray Structural and Solid-State 207Pb NMR Study" Inorganic Chemistry Vol. 46 Iss. 21 (2007) p. 8625 - 8637
Available at: http://works.bepress.com/aaron-rossini/25/