The Difference of the Complex Formation of the Samarium (3+) Ion with the L-malic Acid as Compared to the Neodymium (3+) Ion

The complex formation of the neodymium Nd3+ ion and the samarium Sm3+ ion with L-malic acid (H3Mal) in the aqueous solutions was studied by pH-metric titration in pH region 2.80 to 10.00 and constant ionic strength 0.1 M KCl at 25 °C. The ratios of the concentrations of the rare-earth elements (Ln) and the L-malic acid were 1:0.5, 1:1 and 1:2. The number of experimental points of each curve of pH-metric titration was 160-190 at 5-6 independent titrations. Inasmuch as the literature data give mainly the dissociation constants for the racemic DL-malic acid, acid-base equilibria of L-malic acid at ionic strength of 0.1 M KCl were also previously studied in pH 3.1-11.0 range. The number of experimental points for the each titration curve of L-malic acid was 70-100 at 8 independent titrations. The dissociation constants of Lmalic acid were calculated. The compositions and the stability constants of the rare-earth element complexes with L-malic acid were calculated by SuperQuad program for complex equilibria. It was shown, that in addition to 1:1 and 1:2 complexes with differently deprotonated L-malic acid, the hydroxocomplexes and protonated complexes of the rare-earth elements are also formed. The difference of the complex formation of the Sm3+ ion with Lmalic acid as compared to the Nd3+ ion was discussed

Hexakis(dimethylsulfoxide-O)-cobalt(II) hexatungstate, [Co(C₂H₆OS)₆][W₆O₁₉]: synthesis from aqueous dimethylsulfoxide solution, crystal structure determination, FT-IR and Raman spectroscopy analysis, and surface micromorphology

<p>The conditions necessary for formation of hexakis(dimethylsulfoxide-O)–cobalt(II) hexatungstate [Co(C₂H₆OS)₆][W₆O₁₉] in Co(NO₃)₂-–Na₂WO₄–HCl–H₂O–DMSO solution, acidified up to , were established. The synthesized salt was examined using chemical analysis, X-ray single crystal analysis, FT-IR and Raman spectroscopy, and scanning electron microscopy. By X-ray single-crystal analysis of [Co(C₂H₆OS)₆][W₆O₁₉] main crystallographic characteristics were revealed: triclinic, <i>C</i>2/<i>c</i>, <i>a</i> = 16.3318(9) Å, <i>b</i> = 14.9160(5) Å, <i>c</i> = 17.8291(10) Å, <i>β</i> = 112.104(6)°, <i>V</i> = 4024.1(3) ų at <i>T</i> = 293(2) K, <i>Z</i> = 4, <i>d</i>_Calcd = 3.194 g cm⁻³. The structure is built from isolated cationic complexes [Co(C₂H₆OS)₆]²⁺ and hexatungstate anions [W₆O₁₉]^2–.</p