title: A thermodynamical and structural study on the complexation of trivalent lanthanides with a polycarboxylate based concrete superplasticizer.
abstract: The complexation of trivalent lanthanides with a commercial polycarboxylate based concrete superplasticizer (Glenium® 51) is investigated using different spectroscopic techniques. Time-resolved laser fluorescence spectroscopy (TRLFS) in combination with a charge neutralization model is used to determine temperature dependent conditional stability constants (log β'(T)) for the complexation of Eu(iii) with Glenium® 51 in 0.1 mol kg-1NaCl solution in the temperature range of 20-90 °C. Only one complex species is observed, and log β'(T) (given in kg per mol eq) shows a very slight increase with temperature from 7.5 to 7.9. The related conditional molar reaction enthalpy (ΔrH'm) and entropy (ΔrS'm) obtained using the Van't Hoff equation show that the complexation reaction is slightly endothermic and entropy driven. The thermodynamic investigations are complemented by structural data for complexes formed with Gd(iii) or Tb(iii) and Glenium® 51 using extended X-ray absorption fine structure (EXAFS) spectroscopy. The results imply a non-chelate coordination of the trivalent metals through approximately three carboxylic functions of the polycarboxylate comb polymer which are attached predominantly in a bidentate fashion to the lanthanide under the given experimental conditions.
authors.affiliation: Ruprecht-Karls-Universität Heidelberg, Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany. daniel.froehlich@partner.kit.edu.
authors.forename: Daniel R
authors.identifier: http://orcid.org/0000-0001-8380-8598
authors.initials: DR
authors.lastname: Fröhlich
authors.affiliation: Ruprecht-Karls-Universität Heidelberg, Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany. daniel.froehlich@partner.kit.edu and Karlsruher Institut für Technologie, Institut für Nukleare Entsorgung, P.O. Box 3640, 76021 Karlsruhe, Germany.
authors.forename: Martin M
authors.initials: MM
authors.lastname: Maiwald
authors.affiliation: Technische Universität Dresden, Fakultät Mathematik und Naturwissenschaften, Fachrichtung Chemie und Lebensmittelchemie, Professur für Radiochemie/Radioökologie, 01062 Dresden, Germany.
authors.forename: Franziska
authors.initials: F
authors.lastname: Taube
authors.affiliation: Technische Universität München, Lehrstuhl für Bauchemie, Lichtenbergstr. 4, 85747 Garching, Germany.
authors.forename: Johann
authors.initials: J
authors.lastname: Plank
authors.affiliation: Ruprecht-Karls-Universität Heidelberg, Physikalisch-Chemisches Institut, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany. daniel.froehlich@partner.kit.edu and Karlsruher Institut für Technologie, Institut für Nukleare Entsorgung, P.O. Box 3640, 76021 Karlsruhe, Germany.
authors.forename: Petra J
authors.initials: PJ
authors.lastname: Panak