Molybdenum EDTA complexes

The reaction of Mo(H20)63+ and nitrate in aqueous solutions results in the formation of Mo2Oi(H20)62+ and nitrite. Mo(III) coordinated to oxygen and nitrogen donor atoms of EDTA also reduces nitrate in aqueous solutions. The reduction of nitrate by a Mo(III)-EDTA complex results in the formation of nitrite and a Mo(V)-EDTA complex, as determined by chemical and spectrophotometric techniques. These reactions serve as models for biological nitrate reduction. In addition, molybdate coordinates to naturally produced phenolates. The molybdenum-coordinating phenolates also coordinate tungstate and ferric iron. Two of these phenolates contain threonine, glycine, alanine, and 2,3-dihydroxybenzoic acid. 

One of the systems which fulfills these requirements is the EDTA complex of Mo (III), /A-acetato-di-/r-hydroxo-/x( N,N ) ethylenediaminetet-raacetatobis[molybdenum(III)]. The complex was originally prepared but incorrectly formulated by Kloubek and Podlaha (28). Its solid-state structure has recently been determined by Sykes et al. (Figure 2). Preliminary results in our laboratory have demonstrated that this compound... 

As the result of the performed investigations was offered to make direct photometric determination of Nd microgram quantities in the presence of 500-fold and 1100-fold quantities of Mo and Pb correspondingly. The rare earth determination procedure involves sample dissolution in HCI, molybdenum reduction to Mo (V) by hydrazine and lead and Mo (V) masking by EDTA. The maximal colour development of Nd-arsenazo III complex was obtained at pH 2,7-2,8. The optimal condition of Nd determination that was established permit to estimate Nd without separation in solution after sample decomposition. Relative standard deviations at determination of 5-20 p.g of Nd from 0,1 g PbMoO are 0,1-0,03. The received data allow to use the offered procedure for solving of wide circle of analytical problems. 

The potentially six-coordinate ligands (edta)4- and (pdta)4" (H4edta = N,N,N, N tetrakis(2-ethanoic acid)-l,2-diaminoethane, H4pdta = N,N,N, iV -tetrakis(2-ethanoic acid)-1,2-diaminopropane) add to dimeric molybdenum(V) centres to form complexes such as [Mo202Y2(edta)]2- and [Mo02Y2(pdta)]2- (Y = O, S) 425-429 The structure of... 

The diphenylcarbazide method is almost specific for chromium(Vl). Interferences result only from Fe, V, Mo, Cu, and Hg(II) present at much higher concentrations than the chromium. Iron(lll) can be masked by phosphoric acid or EDTA. Iron(III) can also be separated as Fe(OH>3, after chromium has been oxidized to Cr(VI), or by extraction. Vanadium can be separated from Cr(VI) by extraction as its oxinate at pH -4. Molybdenum is masked with oxalic acid, and Hg(II) is converted into the chloride complex. 

Transitory outbreaks of gushing have been observed due to the precipitation of microcrystals of calcium oxalate while other outbreaks have been associated with the presence of heavy metals, in particular, iron, nickel, tin, and molybdenum. Such outbreaks can often be cured by the addition of EDTA to the beer which forms complexes with calcium and heavy metals. The balance of heavy metals in beer is obviously critical for it was observed that iron and nickel only caused gushing when complexed with isohumulone. Cobalt, on the other hand, shows little tendency to cause gushing and, indeed it was found during one severe epidemic of gushing that the addition of 0-2-1 0 ppm of cobalt dramatically reduced the incidence of the complaint. However, in another case it was without effect. 

Oxidation of the molybdenum(v) dimer [Mo204(edta)] by one-electron reagents such as [IrCle] - or [Fe(phen)s] + leads ultimately to monomeric molybdenum(vi), but the kinetics are characteristic of a non-complementary reaction, with retardation by added [IrClJ - or [Fe(phen)3] + respectively. The mechanism proposed [e.g. equation (56)] contains a mixed-valence Mo Mo i complex, presumably... 

The kinetics of several electron transfer reactions of the molybdenum cuboidal system [Mo4S4(edta)2]" ( = 2, 3, 4) with cross-reactants such as [Co(edta)]-, [Fe(edta)]-, [Co(dipic)2] , [Fe(H20)e], and [Pta ] -, have been investigated. The electron self-exchange rate constants determined for the [Mo4S4(edta)2] and [Mo4S4(edta)2] couples, by an application of the Marcus relationship, are 1.5 x 10 and 7.7 x 10 M s , respectively. The rate constants for the outer-sphere oxidation of two dimeric complexes, [MoW 0)2(p-edta-AT,lV )]2- and [W2(0)2(p-0)(p-S)(p-edta-Ar,iV )] -, by [IrCl ] in addic aqueous solution have been measured. While the oxidation of the former complex shows a simple second-order rate law, the kinetics of the oxidation of the latter complex exhibited a rate retardation in the presence of the [IrCl6] complex. 

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