Trends in the stability of alpha- and beta-Keggin heteropolytungstates of the second-row main-group heteroatoms Al(III), Si(IV), and P(V) are elaborated by data that establish the roles of kinetic and thermodynamic control in the formation and isomerization of Keggin tungstoaluminates. Slow, room-temperature co-condensation of Al(III) and W(VI) (2:11 molar ratio) in water gives a pH 7 solution containing beta(1) and beta(2) isomers of [Al(AlOH(2))W(11)O(39)](6)(-) (beta(1)- and beta(2)-1). Partial equilibration of this kinetic product mixture by gentle heating (2 h at 100 degrees C) or, alternatively, co-condensation of Al(III) and W(VI) for 2.5 h at 100 degrees C both give mixtures of beta(2)-, beta(3)-, and alpha-1. Full equilibration, by prolonged heating (25 days at 100 degrees C), gives an isomerically pure solution of alpha-1, thus demonstrating that isomerization occurs in the direction beta(1) --> beta(2) --> beta(3) --> alpha. Furthermore, kinetically controlled conversions of 1 to H(5)[AlW(12)O(40)] (2)-achieved by heating pH 0-0.2 solutions of 1 for 5 days at 100 degrees C-occur with retention of isomeric integrity, such that alpha-1 is converted to alpha-2 (92%; 8% beta), while mixtures of beta(2)- and beta(3)-1 are converted to beta-2 (87%; 13% alpha). These data, when combined with previously reported observations (equilibria between alpha- and beta-2, kinetically controlled hydrolyses of alpha-2 to alpha-[AlW(11)O(39)](9)(-) (alpha-3) and of beta-2 to beta(2)-3, and equilibria between beta(3)- and alpha-3), provide a comprehensive picture regarding the roles of kinetic and thermodynamic control. Finally, a general method for preparation of the isomerically pure derivatives alpha-K(9)(-)(n)()[AlM(n)()(+)W(11)O(39)] (4), M(n)()(+) = Al(III), [V(IV)O](2+), [V(V)O](3+), Mn(II), Mn(III), Mn(IV), Co(II), and Co(III), is provided. The presence of Mn(IV) is confirmed by cyclic voltammetry, pK(a) values of the aquo ligands on 4 are determined by pH titration, and the isomeric structure of these derivatives is established by (27)Al, (51)V, and (183)W NMR and IR spectroscopies and X-ray crystallography.

Fully oxidized alpha-AlIIIW12O40(5-) (1ox), and one-electron-reduced alpha-AlIIIW12O40(6-) (1red), are well-behaved (stable and free of ion pairing) over a wide range of pH and ionic-strength values at room temperature in water. Having established this, 27Al NMR spectroscopy is used to measure rates of electron exchange between 1ox (27Al NMR: 72.2 ppm relative to Al(H2O)63+; nu(1/2) = 0.77 Hz) and 1red (74.1 ppm; nu(1/2) = 0.76 Hz). Bimolecular rate constants, k, are obtained from line broadening in 27Al NMR signals as ionic strength, mu, is increased by addition of NaCl at the slow-exchange limit of the NMR time scale. The dependence of k on is plotted using the extended Debye-Hückel equation: log k = log k0 + 2alphaz1z2mu(1/2)/(1 + betarnu(1/2)), where z1 and z2 are the charges of 1ox and 1red, alpha and beta are constants, and r, the distance of closest contact, is fixed at 1.12 nm, the crystallographic diameter of a Keggin anion. Although not derived for highly charged ions, this equation gives a straight line (R2 = 0.996), whose slope gives a charge product, z1z2, of 29 +/- 2, statistically identical to the theoretical value of 30. Extrapolation to mu = 0 gives a rate constant k11 of (6.5 +/- 1.5) x 10(-3) M(-1) s(-1), more than 7 orders of magnitude smaller than the rate constant [(1.1 +/- 0.2) x 10(5) M(-1) s(-1)] determined by 31P NMR for self-exchange between P(V)W12O40(3-) and its one-electron-reduced form, P(V)W12O40(4-). Sutin's semiclassical model reveals that this dramatic difference arises from the large negative charges of 1ox and 1red. These results, including independent verification of k11, recommend 1red as a well-behaved electron donor for investigating outer-sphere electron transfer to molecules or nanostructures in water, while addressing a larger issue, the prediction of collision rates between uniformly charged nanospheres, for which 1ox and 1red provide a working model.

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The [Ru04]" ion can be generated in aqueous base at pH 11 from aquated ruthenium trichloride with excess brómate, and this reagent will catalytically oxidize primary alcohols, activated alkyl halides, aldehydes, 1,2-diols, and nitroalkanes to carboxylic acids, while secondary alcohols and secondary halides are oxidized to ketones, brómate being the cooxidant. These oxidations are compared with those effected catalytically by Irani-[Ru(0H)203]1 2" in aqueous base at pH 14 with persulfate as cooxidant. A new preparation for organic-soluble salts of [Ru04]" avoiding the use of Ru04 is described.Oxo complexes of ruthenium are effective catalysts for the selective oxidation of various organic substrates.2 Thus the ruthenate ion Irani-[Ru(0H)203]2", which is stable above pH 12 in aqueous base,3 4"5 with persulfate as cooxidant will oxidize primary alcohols to carboxylic acids and secondary alcohols to ketones;6•7 the perruthenate ion [Ru04]", which is stable from pH 8 to 12 in aqueous base,3"5 will also effect such oxidations stoichiometrically in solution.6 The organic-soluble "TPAP" ((n-Pr4N)[Ru04]) with /V-methylmorpholine /V-oxide is an efficient selective catalyst for converting primary alcohols to aldehydes and secondary alcohols to ketones.8Here we report a simple means of generating [Ru04]" in aqueous base and using this catalytically with Br03" as cooxidant. Comparative studies on irani-[RuVI(0H)203]2" with persulfate as cooxidant are also reported, notwithstanding the necessary pH differences of the solutions used, since differences in reactivity and oxidative selectivity might be expected between ruthenium-

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The new complexes OsO 4 ؒnmo (nmo = N-methylmorpholine N-oxide) and OsO 4 ؒnmm (nmm = Nmethylmorpholine) have been made, their crystal structures determined, and their possible involvement in the catalysed dihydroxylation of alkenes considered. The use of cis-[OsO 4 (OH) 2 ] 2Ϫ as a catalyst for the oxidation of alcohols, aldehydes and alkyl halides to carboxylic acids with [Fe(CN) 6 ] 3Ϫ and other co-oxidants and also for the cleavage and dihydroxylation of alkenes with [Fe(CN) 6 ] 3Ϫ has been investigated.

The simple salt CuCl 2 •2H 2 O, and the new Cu-substituted polyoxometalate (POM), Na 7 [CuCoW 11 O 39 ]•5H 2 O 1 are highly efficient catalysts for the oxidation of ascorbic acid by peroxynitrite.