Leading coordinates

IA Iowa Department of Public Health, Bureau of Environmental Health, State Lead Coordinator All Levels ... 

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FIGURE 87. Structure of (tr/.jPbCF projected normal to the ligand plane , showing the lead coordination environment. Reproduced by permission of the Australian Academy of Science and CSIRO from Reference 137... 

Fig. 6. 62.8 MHz solid-state 207Pb NMR (CP/MAS) spectra of organolead compounds containing a bridging methoxy and a bridging alkynyl group, all of which increase the lead coordination number in the solid state as well as in solution.36 Isotropic shifts S Pb are indicated by arrows. The <5207Pb values in solution and in solid state are as follows Me3PbOMe in CDCl3 +307.5 (1.18M), +379.9 (0.40 M), +391.2 (0.18M) solid +103.8 middle trace in CflD6 +661.0 solid +662.0 lower trace in C6D6 +667.2 solid +670.5.

The hydrocarbon database [3], [8] comprises 391 crystal structures. Of these, only 19% contain molecules with an odd number of carbon atoms, and the amount of (PE) attainable by molecules with an even number of carbons is consistently higher than for those with an odd number. Figure 12.5 shows that molecular size is the leading coordinate in determining (PE), but a spread of values is observed for mole-... 

How do trends in NMR parameters depend on the lead coordination environment ... 

Dead-207 NMR spectroscopy does not provide the details of electronic structure that can be gleaned from PES or atomic transitions, but can—at least in theory—provide complementary information about the Pb(II) coordination environment in solution. Dead-207 NMR spectroscopy is an excellent probe for the lead coordination environment due to the characteristics of the ° Pb isotope (I = j) Excellent receptivity (11.7 times greater than that of C), high natural abundance (22.6%), and large chemical shift range (>16,000 ppm) (172, 173). Although ° Pb NMR spectroscopy has been used extensively to characterize alkyl Pb(IV) derivatives and solid-state Pb(II) compounds, relatively few studies have been conducted of soluble Pb(ll) coordination compounds (171-183). Nonetheless, those studies that have been conducted to date on Pb(II) coordination compounds in solution reveal that the ° Pb chemical shift is particularly... 

Figure 8. Lead-207 NMR chemical shifts of selected lead compounds referenced to Pb(N03)2 (0 ppm). Lead chemical shifts can cover a range of I6,000 ppm and are very sensitive to the lead coordination environment. The lead resonance tends to shift upfield as the electronegativity of the ligand atom increases (S > N > O). [Reprinted with permission from E. S. Claudio, M. A. ter Horst, C. E. Eorde, C. L. Stern, M. K. Zart, and H. A. Godwin, Inorg. Chem., 39, 1391-1397 (2000). Copyright 2000 American Chemical Society.]...

Taken together, the studies that have been conducted to date on the absorption, photoelectron, vibrational, and NMR spectra of Pb(II) compounds suggest that divalent lead is far from spectroscopically silent . These studies have provided useful insights into the electronic structure of Pb(II) compounds and the role that relativistic effects play in determining the properties of Pb(II). In addition, they provide useful tools not only for characterizing the fundamental coordination chemistry of lead (Section IV), but also for determining lead coordination environments in complex environmental (Section V) and biological (Section VI) samples. 

What insights into lead coordination chemistry can be gained from EXAFS spectroscopy that are not available from X-ray crystal structures ... 

Average Pb—X Distances in Angstroms (A) in Lead(II) Coordination Compounds According to Atom, Denticity of Ligand, and Lead Coordination Number d... 

One of the greatest goals of this field is to develop a sufficiently good understanding of lead coordination chemistry to be able to rationally design improved ligands for lead that could be used as chelation therapy agents to treat... 

Here, we review the studies that have been conducted to date on the kinetics and thermodynamics of lead coordination compounds, with particular focus on addressing the following questions ... 

Lead is not spectroscopically silent. The absorption spectroscopy, photoelectron spectroscopy, and NMR spectroscopy of Pb(II) compounds have all been extensively studied. These techniques not only provide useful insights into the electronic structure and stmctures of Pb(II) compounds, but have also proven useful in the characterization of lead coordination environments in complex samples (e.g., samples of biological or environmental origin). 

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