Pb-X bonds

The broken bonds (boldface = dissociated atom or group), Affi°(R), kcal/mol (kJ/mol) BDEs (boldface = recommended data reference in parentheses) Methods  

Tetraethyllead (QHdaPb-CzHs 55 5 230 21 Derived from in ref. 1996NIST 

Note (1) The BDEs in the clusters and complexes of C-, Si-, Ge-, Sn-, and Pb-ions are listed in Chapter 24. (2) The BDEs in the clusters and complexes of N-, P-As-, Sb-, and Bi-ions are listed in Chapter 25. (3) The BDEs in the clusters and complexes of 0-, S-, Se-, Te-, and Po-ions are listed in Chapter 26. (4) The BDEs in the clusters and complexes of halogenated ions are listed in Chapter 27. 

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The equilibrium internuclear separation (r ) of HgO(g) is estimated from the corresponding quantity for PbO(g) and comparison of Hg-X and Pb-X bond distances for cases in which values of both distances are known. The rotational constant 8 is calculated from r. The fundamental vibrational frequency (d is estimated from Guggenhelmer s relation for multiple bonded molecules ( ). 

Germyl, Stannyl, and Plumbyl Anions The preparative methods for the synthesis of the germyl, stannyl, and plumbyl anions are essentially the same as those mentioned above for the silyl anions. The most widely used methods are (1) reduction of halides R3EX (R = alkyl, aryl E = Ge, Sn, Pb X = Cl, Br) with alkali metals and (2) reductive cleavage of the E-E bond of R3E-ER3 (R = alkyl, aryl E = Ge, Sn, Pb) with alkali metals or organolithium reagents. Due to the favorable polarization of the (E = Ge, Sn, Pb) bond, the direct metalation... 

A topological analysis of the total static density has been carried out. The analysis is not complete, and will not be discussed in any great detail in the present context. It is worth mentioning however that similar results as found for benzoylacetone were obtained. The values of pb and V2pbat the 0(1)-H(X) and 0(3)-H(X) bond critical... 

Although some review articles are now available on the synthesis of heavy ketones," they are restricted to dealing with some selected elements, especially silicon and germanium. We delineate here a more general account of the whole chemistry of stable double bonds between heavier Group 14 and Group 16 elements [i.e., RR M=X (M = Si, Ge, Sn, Pb X = O, S, Se, Te)]. 

The successful synthesis and isolation of a series of heavy ketones (r r2M = X M = Si, Ge, Sn, Pb X = S, Se, Te) using kinetic stabilization (vide infra) and the remarkable progress in the field of theoretical calculations prompted chemists to perform computational calculations on the a and it bond energies as well as on the single and double bond lengths of H2M=X at the higher level of theory.14... 

This interpretation of the experimental results was corroborated by ab initio calculations on the relative stabilities of a series of double bond compounds, [H2Pb=X] and their plumbylene type isomers, [frans-H-Pb-X-H] and [ciT-H-Pb-X-H] (X = O, S, Se, and Te) (vide supra) 6 The results of the theoretical calculations and experiments for lead-chalcogen double bond species are in sharp contrast to those of the other Group 14 element analogues which do not isomerize to the divalent compounds.14b... 

Ph3PbS2PMe2]x (with unsymmetrical bridging dithio ligands and secondary Pb S bonds),168 and monomeric Ph2Pb(S2PPh2)2 (six-coordinate lead, aniso-bidentate ligands).169... 

There is a steady decrease in the E—E bond strength (E = Ge, Sn, Pb). In general, with the exception of E—H bonds (E = Ge, Sn, Pb), the strength of other E—X bonds (X = Cl, C) diminishes less noticeably, though the absence of Ge analogues of silicone polymers speaks for the lower stability of the Ge—O—Ge linkage. 

The apparent first-order rate coefficient is 1.5x 1010 exp(—28,200/RT ) sec-1. This expression has undoubtedly been obtained for a pressure-dependent region. If, as an extreme case, it is assumed that the unimolecular process occurred in the second-order region and if approximately one half of the classical degree of vibrational freedom are active, an upper limit of kx — 1.5 x 1015 exp(—46,000/Rr) sec-1 is obtained. The mean Pb-CH3 bond dissociation energy in tetramethyl lead19,142 is 37.6 kcal.mole-1. Dx should therefore be about 40 kcal.mole-1. 

Two factors combine to lend a greater diversity in the stereochemistries exhibited by bivalent germanium, tin and lead compounds, the increased radius of Mn compared with that of Mw and the presence of a non-bonding pair of electrons. When the non-bonding pair of electrons occupies the isotropic valence level s orbital, as in, for example, the complex cations Pb[SC(NH2)2]6+ and Pb[antipyrine]6+, or when they are donated to conductance band levels, as in the binary tin and lead selenides or tellurides or the perovskite ternary phases CsMX3 (M = Sn, Pb X = Cl, Br, I), then the metal coordination is regular. However, in the majority of compounds an apparent vacancy in the coordination sphere of the metal is observed, which is usually ascribed to the presence of the non-bonding pair of electrons in a hybrid orbital and cited as evidence for a stereochemically active lone pair . 

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