Binuclear Bridging Research Articles

Enhancement of the transmission capacity of binuclear metalcontaining bridge groups

Enhancement of the transmission capacity of binuclear metalcontaining bridge groups

The Mechanism of Sulfate Adsorption on Iron Oxides

AbstractAdsorption isotherms were determined for sulfate adsorption on iron oxides under acid conditions. The product of the surface reaction between the iron oxides and sulfate ions was examined by infrared spectroscopy which showed four bands in the v S‐O stretching region. Thus a structural model could be obtained for the reaction. Two surface hydroxyl groups (or OH2+ ions) are replaced by one sulfate ion, and two oxygen atoms of the sulfate ion are coordinated each to a different Fe3+ ion, resulting in the binuclear bridging surface complex Fe‐O‐S(O2)‐O‐Fe. The complex is formed on the surfaces of goethite (α‐FeOOH), akaganéite (β‐FeOOH), lepidocrocite (γ‐FeOOH), hematite (α‐Fe2O3) and amorphous ferric hydroxide.

Phosphate Adsorption on an Oxisol

AbstractAdsorption isotherms for phosphate on the A and B horizon of an oxisol from Papua New Guinea showed high affinity adsorption at low solution concentrations and a linear increase in adsorption at higher solution concentrations. Adsorption increased with decrease in pH in the range 3 to 8. Comparison with data obtained under similar conditions with synthetic goethite (α‐FeOOH) and gibbsite [Al(OH)3] suggested that phosphate reacted with FeOH and FeOH2+ groups on soil iron oxide surfaces to form a binuclear bridging FeOP(O2)OFe complex and with exposed Al(OH)H2O on kaolinite edges and on hydroxy‐aluminum species to form a binuclear or bidentate phosphate complex. At higher phosphate concentrations isotherms showed continued adsorption which may be due to a further reaction involving hydroxy‐aluminum groups.

ADSORPTION ON HYDROUS OXIDES. IV. MECHANISMS OF ADSORPTION OF VARIOUS IONS ON GOETHITE

SummaryInfrared spectroscopy has been used to investigate the complexes that are formed when acids are evaporated onto goethite. It is probable that, like HPO2−4, the anions SO2−4, SeO2−3, and oxalate are adsorbed by ligand exchange and form binuclear bridging complexes where two singly coordinated A‐type OH groups are replaced by two oxygen atoms of one ligand. There is evidence that HPO2−4 and oxalate are likely to be present in this form in wet environments, and this is probably also true for SO2−4 and SeO2−3.Fluoride ions can completely replace the singly coordinated A‐type OH groups but do not replace C‐ or B‐type OH groups that are coordinated, respectively, to two and three Fe3+ ions. The other halides, nitrate, and benzoate partially replace the A‐type OH groups, benzoate being adsorbed as a monodentate ligand.Copper ions do not appear to react with A‐type OH but zinc ions are probably adsorbed on the goethite (100) face in conjunction with carbonate or bicarbonate.

Infrared spectra from binuclear bridging complexes of sulphate adsorbed on goethite (α-FeOOH)

Spectra of sulphate adsorbed on synthetic goethite (α-FeOOH) show replacement of A-type (one coordinated to Fe3+) surface hydroxyls and the formation of adsorbed sulphate groups with C2v symmetry. High affinity adsorption isotherms at low pH and replacement of all A-type hydroxyls (∼400 µmol g–1) by the adsorbed sulphate (200 µmol g–1) suggests that a binuclear bridging complex (i.e., Fe—O—SO2—O—Fe) is formed, similar to that found for phosphate adsorption on goethite.Absorption near 1300 cm–1 in the infrared spectra of the binuclear complex suggests that infrared criteria, recently suggested in the literature of metal sulphato complexes, for distinguishing between bridging (i.e., all frequencies 1200 cm–1) sulphato complexes may need to be re-examined.

Carbonyl complexes of rhodium (I) with bridge nitrogen-containing ligands

1. Mononuclear complexes of univalent rhodium with the general formula. Rh2Am(CO)2Cl, where Am represents o-phenylenediamine and m-phenylenediamine, were obtained. 2. Binuclear bridge compounds Rh2(CO)4Cl2Am were produced by the reaction of mononuclear complexes Rh2Am(CO)2Cl, containing a free amino group, with Rh2CO4Cl2. 3. Binuclear bridge complexes with the general formula Rh2(CO)4Cl2L were synthesized, where L represents p-phenylenediamine, benzidine, or 4,4′-dipyridyl.