pH- and mol-ratio dependent tungsten(VI)–citrate speciation from aqueous solutions: syntheses, spectroscopic properties and crystal structures

Aqueous Electrodeposition of SmCo Alloys: II. Direct Current Studies

Previously, we reported the aqueous electrodeposition of rare earth - iron group alloys. A key factor was the complexation of the metal ions with various coordination compounds (e.g., aminoacetic acids), without which only the ferrous metal and rare earth hydroxides/oxides are deposited. In this work, samarium cobalt (SmCo) alloys were synthesized using direct current (DC) aqueous electrodeposition. The basic electrolyte solution consisted of 1 M samarium sulfamate, 0.05 M cobalt sulfate, and 0.15 M glycine, resulting in deposits containing >30 at% Sm at 60°C with current density of 500 mA/cm². Supporting electrolytes (i.e., ammonium salts) decreased the Sm content in the deposit. Crystallinity of deposited films altered from nanocrystalline to amorphous as the Sm content increased. Deposits with high Sm content (32 at%) became isotropic with reduction in magnetic saturation (M_s) and coercivity (H_c). A deposition mechanism involving stepwise reduction of the complexed Sm-Co ions by depositing hydrogen atoms was proposed.

NMR and DFT studies of the complexation of W(VI) and Mo(VI) with 3-phospho-D-glyceric and 2-phospho-D-glyceric acids

Multinuclear ((1)H, (13)C, (17)O, (31)P, (95)Mo, (183)W) magnetic resonance spectroscopy (1D and 2D) has been used to study the complexation of molybdate(VI) and tungstate(VI) with 3-phospho-D-glyceric and 2-phospho-D-glyceric acids. 3-Phospho-D-glyceric acid forms four and five complexes, respectively, with molybdate and tungstate. These have MO(2)(2+) centres, and involve the carboxylate and the adjacent OH groups. Two isomeric 1:2 (metal-ligand) complexes are detected, in addition to one mononuclear species having MO(3) centres and involving the ligand in a tridentate chelation and a dominant 12:4 species with both tungstate(VI) and molybdate(VI). The dominant 12:4 species can be seen as two 1:2 complexes bound together in a ring through two diphosphometalate moieties, derived from heptamolybdate or heptatungstate, respectively, by inclusion of two phosphate groups from the ligands. Tungstate is also able to form an additional 2:1 tridentate species. 2-Phospho-D-glyceric acid does not interact with tungstate but is able to form one phosphomolybdate species with molybdate, which can be regarded as a heptamolybdate derivative. Density functional theory (DFT) calculations were performed for 1:2 complexes, including calculations on the relative energies of the 1:2 complexes detected in related systems, to validate previously proposed structures. The results are compared with those obtained from multinuclear NMR spectroscopy.