Proton magnetic resonance and Raman spectroscopic studies of methylmercury (II) complexes of inorganic anions

Abstract

. Conlplexation of methylmercury(I1) by sulfate, selenate, carbonate, sulfite, selenite, thiocyanate, selenocyanate, sulfide, and selenide in aqueous solution has been studied by proton magnetic resonance and Raman spectroscopy. Formation constants were determined for the SO$, Se042-, C032-, S032-, Se032-, Se03H-, SCN-, and SeCN-complexes from the p H dependence of the chemical shift and the 199Hg-IH spin-spin coupling constant of the methyl group of CH3Hg(II) in solutions containing both CH3Hg(II) and ligand. The chemical shift and the 199Hg-lH spin-spin coupling constant of the CH3Hg(II) in each of the complexes were also obtained from the same measurements. Proton magnetic resonance parameters were measured for several complexes with sulfide and selenide. The ligand donor atom in each of the complexes was identified using the formation constants, the I99Hg-lH spin-spin coupling constant of the complexed methylmercury and the Raman spectral data. It is of particular interest that, in the selenite complex, the methylmercury is bonded to an oxygen atom whereas sulfur is the donor atom in the sulfite complex. Chem. 54,2517Chem. 54, (1976.On a CtudiC, par rmn et par spectroscopie Raman, la complexation du mCthylmercure(l1) par les ions sulfate, sCl6nate, carbonate, sulfite, sClCnite, thiocyanate, sClCnocyanate, sulfure et s6lCnure en solution aqueuse. On a dCterminC les constantes de formation des complexes du S0,2-, Se042-, C032-, S032-, Se032-, Se03H-, SCN-et SeCN-B partir de la d6pendance des dkplacenlents chimiques sur le pH et des constantes de couplage spin-spin 199Hg-lH des groupes mkthyles du CH3Hg(II) dans des solutions contenant B la fois du CH3Hg(II) et du ligand. On a aussi obtenu, B partir des mCmes mesures, les dCplacements chimiques et les constantes de couplage spin-spin 199Hg-lH du CH3Hg(II) dans chacun des complexes. On a mesurC les paramktres rmp de plusieurs complexes avec le sulfure et le selenure. On a identifie, dans chaque complexe, l'atome agissant comnle ligand donneur en faisant appel aux constantes de formation, aux constantes de couplage spin-spin 199Hg-HI du mCthylmercure complex6 et aux donnks des spectres Raman. I1 est important de noter que dans le complexe sClCnite, le mCthylmercure est liC L l'atome d'oxygkne alors que le soufre est l'atome donneur dans le complexe sulfite.[Traduit par le journal]

Complexation of CH3Hg+ with chloride, sulfate and carbonate in NaClO4: construction of thermodynamic models

“…. The other stoichiometric constant value taken from the literature (log 1 b 11 = 0.94 in 0.7 mol dm À3 Na 2 SO 4 ), 17 taking into account that the ionic medium is different, is in agreement with the value proposed in the present work.…”

“…17 The proton mag- 17 led to a stoichiometric constant value for a 1:1 complex of log I b 11 = 6.10 in Na 2 SO 4 of ionic strength <1.0 mol dm À3 . A comparison between the experimental data and two simulations of the potentiometric titration, achieved using the computer program SOLGASWATER, 44 one without a methylmercury±carbonate complex (Figure 5a) and the other with the complex reported by Rabenstein et al 17 (Figure 5b), shows a better fit for the simulation without the carbonate complex, mainly in the last part of the titration curve±where it is supposed to exist as the complex according to Rabenstein et al 17 (Figure 6). So, in the conditions of this study, no carbonate complexes are necessary to explain the experimental data better.…”

“…In a general sense, we can conclude that the aqueous species and solid forms of chemical elements in natural Figure 6. Theoretical logarithmic diagram of methylmercury species as a function of the pH at 25°C and constant ionic strength (NaClO 4 , 0.1 mol dm À3 ) also using in the model the carbonate species (CH 3 HgCO 3 ) À proposed by Rabenstein et al 17 (log I b 11 = 6.10 in Na 2 SO 4 , ionic strength <1.0 mol dm À3 ; c CH 3 Hg = 5 Â 10 À3 mol dm À3 , c CO 3 = 10 À2 mol dm À3 ).…”

A Raman spectroscopic study of the complexation of the methylmercury(II) cation by amino acids

“…On the other hand, a new band at 458 cm-' in the spectrum can be unambiguously assigned to the v(N-Hg) vibration of the CH3NH2HgCH3+ species, by comparison with similar complexes with glycine (460 cm-') (10,12), alanine (476 cm-') (lo), glycylglycine (462 cm-') (1 I), and even the NH4+ ion (468 cm-') ( Table 1). This characteristic band is accompanied by a weaker peak at 232 cm-I, assigned to the N-Hg-CH3 bending mode of the complex, as this type of vibration in similar molecules has been found to occur in this region (15,(18)(19)(20)(21).…”

An assessment of thermodynamic reaction constants for simulating aqueous environmental monomethylmercury speciation

“…The one log unit variation in the reported constants between pure compound laboratory values and those observed with natural organic carbon is rather remarkable given the variaNicholas T. Loux 189 (Rabenstein et al, 1976) et al (Erni, 1996) CH 3 Hg þ þ CH 3 À ()(CH 3 ) 2 Hg * 37 (Erni, 1996) Erni, 1996) Hg 2 þ þ CH 3 À ()CH 3 Hg þ * 50 (Erni, 1996) CH 4 (aqu. )()CH 3 Erni,1996) Erni, 1996) tions among constants reported in previous tables.…”