http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3257 Electrospray ionization mass spectrometry (ESI MS) has been conducted on the ammonium and alkali metal (A=Li⁺, Na⁺ and K⁺) dichromate systems. A large number of previously unknown polyoxochromate species have been characterized. Major series that have been identified include [Ax₊₁HxCrVIxO₄x]⁺ (Li⁺, x=1–5; Na+, x=1–7; K+, x=1–4) and [A₂x₋₁CrVIxO₄x₋₁]⁺ (Li⁺, x=2, 3; Na⁺, x=2–4; K⁺, x=2, 3) in the alkali metal dichromate systems, and [HCrVIxO₃x₋₁]⁻ (x=1–5) in the ammonium dichromate system. Several series also contain mixed oxidation state species, ranging from Cr(V) to Cr(II) in conjunction with Cr(VI), which is consistent with the ease of reduction of Cr(VI). Negative ion ESI MS spectra clearly demonstrate the existence of [HCrO₄]⁻ as the most abundant ion at −20 V, suggesting that its existence in solution is not just hypothetical, as was previously thought. The polymerization units for the series observed include {AHCrO₄}, {A₂CrO₄} and {CrO₃}, with the latter prominent in the alkali metal systems. This presumably arises from the fragmentation of dichromate, A₂Cr₂O₇→{A₂CrO₄}+{CrO₃}. Moreover, the ESI MS of the dichromate compounds have illustrated that the preservation of tetrahedral stereochemistry is of paramount importance for these systems, which leads to only limited polymerization compared to the related molybdate and tungstate systems. 2010-04-27T05:24:22.509Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:3255 The electrospray ionisation mass spectrometric (ESI MS) characterisation of potassium isopolyoxo-niobate and -tantalate solutions (at pH 11, 10⁻³ M), including the mixed Nb/Ta oxometalate system, primarily yields ions that are based on the M₆O₁₉ moiety (with some protonation of most species being evident). In both positive ion and negative ion modes, moieties of the form [AmM₆O₁₉]ⁿ±, [AmM₆O₁₈]ⁿ±, [AmM₆O₁₇]ⁿ± and [AmM₆O₁₆]ⁿ⁻ (with A=H and/or K, M=Nb and/or Ta) are evident, with the last three types of species being derived from a formal [M₆O₁₉]⁸⁻ species by the progressive loss of three O²⁻ ions. In negative ion mode, polymeric species containing 4, 8, 10, 12 and 14 metal atoms are also observed in the single metal systems, many of which can be related by {M₂O₅} polymerisation units. Most of these are hydrated species, such as [A₆M₈O₂₄(H₂O)n]²⁻ and [A₃M₁₂O₃₃(H₂O)n]³⁻ (both with M=Nb and Ta), [A₅Ta₁₂O₃₄(H₂O)n]³⁻ and [A₃Nb₁₄O₃₈(H₂O)n]³⁻, and are not observed in the 'mixed' Nb/Ta oxometalate system. 2010-04-27T05:24:17.609Z ]]>