Lead complexes tetravalent

Lead forms amphoteric compounds in +2 and +4 valence states, forming plumbous and plumbic salts, such as PbCL and PbCL, as well as plumbites and plumbates, such as Na4Pb03 and Ca2Pb04,. Over a thousand compounds of lead are known which include divalent and tetravalent salts, complexes, and organometaUics. Divalent compounds of lead are far more numerous than the tetravalent compounds. Most compounds, however, result from the reactions involving other lead compounds, rather than elemental lead. Only the reactions involving elemental lead are outlined briefly below. 

Most tetravalent vanadium complexes contain the V02+ unit which leads to a strong low-symmetry ligand field component. Three ligand field bands with 20 commonly occur, one — 13000 cm-1, one 17000 and one 25000-30000 cm-1, in VOL4 units, but their classification in formal C4v. symmetry is not clear, in spite of the availability of polarized light results.38-138-139 However, the ground term is accepted to be 2B2. 

In contrast to the sulfide of silicon (p. 187). the sulfides of tetravalent germanium (white) and tetravalent tin (yellow) are stable in water, but form complexes in the presence of excess sulfide ion. The sulfides of divalent tin and lead (both black) dissolve neither in strong base, in excess sulfide, nor in dilute acids. Note that PbS has the same structure as sodium chloride and is probably the most nearly covalent salt known having this structure, its color and metallic lustre setting it apart from the structurally similar ionic halides and oxides. 

Bromocomplexes of plutonium are limited in number tri- and tetravalent complexes with organic cations, namely C(C6 5)3P l3 PuBrg(c) (70) and [(C2H5)4N]2 PuBr5(c) (71) have been reported. Also, adducts of the type PuBr. 2L (with L = hexamethylphosphora-mide and tri phenyl phosphine oxide) are known (72.). No thermodynamic information are available on these species. More recently, however, the compound Cs2PuBr5(c) has been prepared (63) and its enthalpy of solution in 1 M HCl was measured as - 75.3 + 0.21 kJ. mol l. This measurement leads to a value of AHS(Cs2PuBr, c) =... 

The oxidation of tetravalent or reduction of hexavalent uranium compounds with the tren ligand present can produce stable U complexes. The one-electron oxidation of [U(NN3)(OBur)(OPh)Li-(THF)] by either electrolysis or chentical means yields the neutral [U(NN 3)(OBu/)(OPh)]. The reaction of U02CLi with the lithium salt of tren leads to the formation of a dinuclear trianion, [UO(/r -... 

Ureas. Urea adducts (and those of the closely related A-alkylated derivatives) may be prepared from nonaqueous solvents alternatively, preparation in aqueous alcoholic solution leads to the formation of hydrates. In contrast to the carbamides discussed above, there is relatively little variability in the coordination number of reported urea adducts of tetravalent actinides. Most complexes are either six- or seven-coordinate higher coordination numbers are observed for the larger thorium ion (Table 15). 

It is assumed CMPO eoordination with uranyl is the same as that for the trivalent and tetravalent actinides. Monodentate eoordination occurs via the phosphoryl oxygen for the nitrate eomplexes and bidentate coordination occurs through both the phosphoryl and earbonyl oxygen atoms for the chloride complex, leading to a coordination number of eight for both kinds of eomplexes." ... 

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