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The VV-substituted polyoxotungstate isomers 1- and 4-[S2VW17O62]5- are prepared as Bu4N+ salts from a Na2WO4-H2SO4/NH4 VO3-NaOH reaction mixture in aqueous MeCN.

UV-Vis and ESR spectroscopy have been used to study the behaviour of Cs 2 [TcNCl 5 ] and the hydrolysis product [{TcN(OH)(OH 2 )} 2 (μ-O) 2 ] ( 1 ) in concentrated and aqueous solutions of a variety of sulfur and phosphorus oxo acids ranging from the very weakly coordinating CF 3 SO 3 H to H 2 SO 4 and the coordinating acids H 3 PO 4 and H 4 P 2 O 7 . The paramagnetic monomeric Tc VI N 3− (d 1 ) forms were readily identified by ESR spectroscopy and the diamagnetic dimeric μ-oxo (Tc 2 N 2 O 4+ ) and di(μ-oxo) (Tc 2 N 2 O 2 2+ ) forms by their UV-Vis spectra. For solutions of Cs 2 [TcNCl 5 ] the chemical form of Tc VI N and the rate of the conversion of monomer→μ-oxo dimer→di(μ- oxo) dimer is dependent on the presence of Cl − and the concentration and complexing ability of the acid, with the monomeric form being favoured by the acids of greater complexing power. For solutions of 1 the reverse order of conversion was observed. In 1 M CF 3 SO 3 H, MeSO 3 H or toluene- p -sulfonic acid, 1 is converted to the di(μ-oxo) aquanitrido cation [{TcN(OH 2 ) 3 } 2 (μ-O) 2 ] 2+ while in 7.5 M CF 3 SO 3 H it is proposed that the predominant form is the μ-oxo aqua dimer [{TcN(OH 2 ) 4 } 2 (μ-O)] 4+ . In H 2 SO 4 and the phosphorus oxo acids the aqua cations are coordinated by the acid anions. The monomeric aqua cation, [TcN(OH 2 ) 5 ] 3+ , does not appear to be a viable species, as is also the case for MoO 3+ (aq), and spontaneously dimerises in 7.5 M CF 3 SO 3 H. In anhydrous CF 3 SO 3 H or H 2 SO 4 monomeric Tc VI N with CF 3 SO 3 − or HSO 4 − coordination is observed. A characteristic feature of the UV-Vis spectra of monomeric Tc VI N is a strong absorption at 266–300 nm assigned to πN→Tc charge transfer. The μ-oxo dimers show an intense visible absorption at 470–510 nm.

The synthesis, isolation, and structural characterization of the fully oxidized sulfite-based polyoxotungstate cluster (Pr4N)4{α-[W18O54(SO3)2]}·2CH3CN and the one-electron reduced form (Pr4N)5{α-[W18O54(SO3)2]}·2CH3CN has been achieved. α-[W18O54(SO3)2]5- was obtained as a Pr4N+ salt by reducing the “Trojan Horse” [W18O56(SO3)2(H2O)2]8- cluster via a template orientation transformation. Acetonitrile solutions of pure α-[W18O54(SO3)2]5- also were prepared electrochemically by one-electron bulk reductive electrolysis of α-[W18O54(SO3)2]4-. Cyclic voltammetry of α-[W18O54(SO3)2]4- and α-[W18O54(SO3)2]5- in CH3CN (0.1 M Hx4NClO4) produces evidence for an extensive series of reversible one-electron redox processes, that are associated with the tungsten−oxo framework of the polyoxometalate cluster. Hydrodynamic voltammograms in CH3CN exhibit the expected sign and magnitude of the steady-state limiting current values for the α-[W18O54(SO3)2]4-/5-/6- series and confirm the existence of a stable one-electron redu...

The reaction of (AsPh4)[TcNCl4] with KCN and added AsPh4Cl in CH3CN/H2O yields crystals of (AsPh4)2[TcN(CN)4(OH2)]·5H2O (1). The complex crystallises in the monoclinic space group P21/n with a=17.107(5), b=19.965(7), c=15.473(5)A, β= 101.70(2)° and Z=4. Refinement with 3212 data measured with Cu Kα radiation converged at R= 0.065. The geometry of the anion is distorted octahedral with a water molecule coordinated trans to the nitrido ligand (TcOH2, 2.56(1) A). The TcN distance is 1.60(1) A. ESR studies have established the presence of two paramagnetic intermediates in the conversion of [TcN(CN)4(OH2)]2− to [TcNCl]4− in HCl solutions.