Highly Stable Complexes of Divalent Metal Ions (Mg2+, Ca2+, Cu2+, Zn2+, Cd2+, and Pb2+) with a Dota‐Like Ligand Containing a Picolinate Pendant. Issue 36 (13th November 2014)

• Record Type: Journal Article
• Authors: Regueiro‐Figueroa, Martín; Ruscsák, Erika; Fra, Laura; Tircsó, Gyula; Tóth, Imre; de Blas, Andrés; Rodríguez‐Blas, Teresa; Platas‐Iglesias, Carlos; Esteban‐Gómez, David
• Is Part Of: European journal of inorganic chemistry. Issue 36(2014)
• Page Start: 6165
• Page End: 6173
• Publication Date: 2014-11-13
• Subjects: Macrocycles -- Macrocyclic li­gands -- Lead -- Copper -- Cadmium; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201402693
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract: The stability constants of complexes of the macrocyclic ligand do3a‐pic 4– (H4 do3a‐pic = 2, 2′, 2″‐{10‐[(6‐carboxypyridin‐2‐yl)methyl]‐1, 4, 7, 10‐tetraazacyclododecane‐1, 4, 7‐triyl}triacetic acid) with several divalent metal ions (Pb 2+, Cd 2+, Zn 2+, Cu 2+, Ca 2+, and Mg 2+ ) have been determined by using pH‐potentiometric titrations ( I = 0.1M KCl, 25 °C). The stability of these complexes follows the trend Cu 2+ > Cd 2+ ≈ Pb 2+ ≈ Zn 2+ >> Ca 2+ >> Mg 2+ . A particularly high stability constant has been determined for the Cu 2+ complex [log K CuL = 23.20(4)]. Analysis of the titration curves indicate the presence of protonated forms of the complexes in solution, with protonation constants of log K M(HxL) = 6.9–2.0 ( x = 1, 2, or 3). The structure of the complexes in solution has been investigated by using 1 H and 13 C NMR spectroscopy and DFT calculations performed in aqueous solution at the TPSSh/6‐31G(d) level. In the case of the Pb 2+ and Cd 2+ complexes, relativistic effects were considered with the use of relativistic effective core potentials. Calculations show that the complexes with the largest metal ions (Pb 2+ and Ca 2+ ) are nine‐coordinate, with their coordination polyhedra being best described as capped twisted square antiprisms. The Cd 2+ and Mg 2+ complexes are seven‐coordinate, with the metal ions being bound to the four nitrogen atoms of the cyclen unit and the three acetate pendant arms. Finally, in the Cu 2+ and Zn 2+ complexes, the metal ions are six‐coordinated, with the metal ions being asymmetrically placed inside the macrocyclic cavity of the ligand, and the coordination polyhedra can be described as an octahedron and a trigonal prism, respectively. Abstract : A detailed study of the thermodynamic stability of complexes formed by divalent metal ions with a macrocyclic ligand containing a picolinate arm is reported. The complexes of Cu 2+, Zn 2+, Cd 2+, and Pb 2+ present high stability constants [log K ML > 20]. DFT calculations and NMR spectroscopy point to variable coordination numbers and geometries for this series of metal complexes.