INFRARED RAMAN AND HYDROGEN-1 CARBON-13 AND LEAD-207 NUCLEAR MAGNETIC RESONANCE SPECTRA OF HEXAMETHYLDILEAD

The infrared and Raman spectra of hexamethyldilead have been recorded over the range 5000-70 cm-1, both in the solid state and in solution, and assignments for the various fundamentals made. The spectra suggest that the skeletal symmetry of the molecule is D3d. Using a simple valence force field, the following force constants were derived from the a1g skeletal frequencies: K1 = 1.81 (PbC stretching), K2 = 0.05 (CPbC bending), and K3 = 0.83 mdyn/Å (PbPb stretching). The values of K1 and K2 are very similar to the values of the corresponding force constants for tetramethyllead. From the three force constants, values for the two a2u, three eu, and three eg, skeletal frequencies have been calculated and found to be in reasonable agreement with the experimental values. The infrared spectrum of hexamethylditin has been measured in the range 200-70 cm-1 in order to locate the CSnC bending frequencies. Corresponding force constant and frequency calculations have also been carried out for this molecule, giving the results K1 = 2.21, K2 = 0.09, and K3 = 0.99 mdyn/Å. The 1H, 13C, and 207Pb nmr spectral parameters for hexamethyldilead are given and compared with the corresponding ones for hexamethylditin. The direct CPb coupling constant is surprisingly small, implying an unusually high per cent s character for the PbPb bond. The 207Pb chemical shift is to high field of that found for tetramethyllead and appears to depend on factors other than the paramagnetic contribution. © 1969, American Chemical Society. All rights reserved.