207Pb chemical shifts

Lead - The nuclear properties of 207Pb are conducive to straightforward observation of NMR spectra. The relative paucity of data in the published literature may, therefore, be a reflection of the lack of an extensive coordination chemistry or, at a more mundane level, a consequence of the relatively low solubility of many lead compounds. 207Pb chemical shifts are extremely sensitive to solvent, so care must be exercised when drawing conclusions from spectra recorded in different solvents even the change from H20 to D20 can lead to appreciable shifts (e.g. 31 ppm for Pb(NOj)2) (Lutz and Strieker, 1971). 

Due to the wide range of 207Pb chemical shifts, especially for lead(II) compounds, it is (in analogy to the tin compounds discussed above) impossible to recognize simple correlations between the coordination number at the lead atoms or the substituents directly bonded to lead(II) and the chemical shift value. What one can only do is make predictions within one class of compounds. 

TABLE 16. 207Pb chemical shifts of organometallic compounds... 

TABLE 7. 119Sn and 207Pb chemical shifts and J couplings of group-14 anions... 

The commonly used external reference for 207Pb chemical shifts, <5207Pb, was and will be in the future tetramethyllead, Me4Pb. However, using modern NMR... 

The fundamental quantum-mechanical interpretation by Ramsey of the NMR parameters of chemical shift [123, 124] and spin-spin J coupling [125, 126] still forms the basis of our understanding of these terms, as has been recently noted [127]. However, Ramsey neglected relativistic effects, which are very significant for the heavier nuclei such as 199Hg, 207Pb, and 203 205xi [127]. Derivations and discussion of Ramsey s theoretical results are found in the textbook by Slichter [26]... 

TABLE 13. 207Pb NMR chemical shifts and J couplings of phenyl-substituted Pb anionsa... 

Both tin and lead have suitable / = nuclei (119Sn and 207Pb), but there appear to be no chemical shift data available for either of these elements for any of the compounds described herein. 

The high sensitivity of the chemical shifts of 73Ge,119Sn and 207Pb to substituent effects calls for a detailed study of the resonance interactions in these organometallic compounds. 

The 119Sn NMR chemical shifts (Table 7) seem not to be correlated to the negative charge on the metal. Moreover, the 207Pb resonance of Pl Pb- appeared at an extremely low field shift (+1040 to +1060 ppm)116 (Table 7). 

Pb NMR Chemical Shifts for Plumbyl Cationic Compounds... 

The closely related lead analogue 81 shows essentially the same structural features, but the lead atom in 81 is less pyramidalized (355.7°, see Table XIV), which indicates weaker coordination. The NMR spectroscopic parameters for 81, such as 207Pb NMR chemical shift and scalar Pb-C(sp) coupling constants (see Section III.B.3) clearly demonstrate however the side-on complexation of the plumbyl cation by the C = C triple bond in zwitterions 81.161... 

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