207Pb NMR chemical shift

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

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... 

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). 

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]... 

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). 

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

Fig. 1. 62.8 MHz 2°7Pb NMR spectrum of (Cp)Fe(CO)2-PbMe3 (25 °C =5% in C6D6), recorded by using the refocused INEPT pulse sequence with CPD H decoupling (200 transients with a repetition time of 8 s and an acquisition time of 4 s).94 The line width h, /2 = 2 Hz is rather small for 207Pb NMR signals and makes it possible to observe 57Fe satellites and also 13C satellites in order to measure accurately the isotope-induced chemical shifts...

Solid-state 207Pb NMR spectra can be obtained for static samples or by MAS and CP MAS techniques,19 and for organolead compounds CP MAS techniques are definitely preferred (see Fig. 3). The huge chemical shift anisotropy is a drawback for all techniques, although, on the other hand, this parameter contains valuable additional information. 

---