Tetravalent complexes

When 4g of potassium hydrogen fluoride are dissolved in the clear brown liquid (reserved as directed) and the mixture is allowed to stand in ice overnight, crystals of red-brown potassium hexafluoromanganate (III) can be isolated from the solution by the method just outlined for the tetravalent complex fluoride. 

Although both the brown [Os(NH3)6] and the yellow [Os(NH3)6]Br have been claimed as products of the reaction of [Os(NH3)6]Br3 with potassium in liquid ammonia,54 the products were not well characterized and could be hydrido ammines or mixtures. There is evidence from the polarographic reduction of [Os(NH3)6]3+ for the existence of [Os(NH3)6]2+ but it appears to be labile to substitution and has not been isolated 55 in this respect osmium differs significantly from ruthenium, for [Ru(NH3)6]2+ is isolable and is in fact a useful synthetic precursor. The tetravalent complex [Os(NH3)s]4+ has also been detected electrochemically, by cyclic voltammetric oxidation of [Os(NH3)6]3+ 55 in acidic solution however, the first product of one-electron oxidation of [Os(NH3)s]3+ is probably [Os(NH3)s(NH2)]3+.ss... 

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) =... 

Homoleptic amido compounds of U, U(NR2)5, have been synthesized by oxidation of anionic tetravalent complexes, [U(NR2)5]. A unique hexakisamido U complex has been isolated using 2,3 5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene. The [U(dbabh)] anion can be oxidized to form a species both of which have a near-perfect octahedral geometry with the six antido ligands. ... 

Hexavalent. The majority of An(VI) coordination chemistry with N-donors has been explored with the uranyl cation, 50i. Stable adducts with the hgands discussed in the tri- and tetravalent complexes have been described, for example, U02X2L (X = halide, OR, NO3, RCO2). The coordination numbers observed for these complexes are typically 6, 7, or 8 with octahedral, pentagonal bipyramidal, or hexagonal bipyramidal geometries, respectively. Neutral and anionic thiocyanates have also been isolated, for example [U02(NCS)j2- yH20(x = 2 5). 

Oxidations of metallocorroles have also been investigated by Vogel and co-workers." For instance, these researchers found that treatment of a-phenyl-cobalt(III) corrole 2.182 with Fe(C104)3 resulted in oxidation to cation 2.191 (Scheme 2.1.64). They also found that iron(III) salts could be used to effect oxidation of nitrosyl iron(III) corrole 2.192. In this case, however, it was a ic-cation radical species (i.e., 2.193), which was obtained upon by treatment with, for instance, iron(III) chloride (Scheme 2.1.65)." Similar oxidations of tetravalent complexes have also been carried out by Vogel and coworkers (see Scheme 2.1.60)." ... 

Hydroxamate. Hydroxamate complexes of trivalent actinides can be prepared directly in aqueous solution and other polar solvents and extracted into organic solvents, but due to the high thermodynamic stability of the corresponding tetravalent actinide complexes they are rapidly oxidized. They can also be prepared in solution via electrochemical reduction of the tetravalent complexes. These complexes have been studied for their role in separating high and low valent actinides in nuclear fuel processing schemes. ... 

Amines, hydrazines, and hydroxylamines. Amine complexes are known for tetravalent complexes of the earliest actinides (Th, U), particularly for the halides, nitrates, and oxalates. The complexes are generated either in neat amine, or by addition of amine to the parent compound in a nonaqueous solvent. Some of the known simple amine compounds are presented in Table 6. The molecular structure of ThCl4(NMe3)3 has been determined. The coordination environment about the metal is a chloride capped octahedron. A very limited number of adducts exist in which a tetravalent actinide is coordinated by a hydrazine or hydroxylamine ligand the parent compound is generally a halide or sulfate complex. Cationic metal hydrates coordinated with primary, secondary, or tertiary amines have also been isolated with acetylacetonate, nitrate, or oxalate as counterions. 

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