题目：Enthalpy and Entropy Measurements toProbe the Nature of Actinide/Lanthanide Complexes: Thermodynamics of ActinideComplexation in Solution

报告人：Rao Linfeng, Senior Scientist, LawrenceBerkeley National Laboratory, Berkeley, CA, USA

时间：10月13日（周四）上午9:00

地点：401号楼一楼会议室

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报告摘要：

Because the 5f-orbitals of the actinide elements are spatially moreextended and less shielded by the outer orbitals than the 4f-orbitals of thelanthanide elements, the 5f-electrons of the actinide elements have highertendency to participate in chemical bonding. As a result, there could be ahigher degree of “covalence” in the complexes of actinides thanthose of lanthanides. Such difference in covalence could be manifested in thecomplexation of actinides/lanthanides with ligands containing “softer” donor atoms such as nitrogen and sulfur.

Various techniques could be applied to probe the covalence inactinide/lanthanide complexes, including thermodynamic determination of theenergetics ( G, ?H, and ?S) of complexation,spectroscopic measurements of electron densities, structural characterizationof bond distances, as well as computational methods. In my group at LawrenceBerkeley National Laboratory, we emphasize the application of enthalpy/entropymeasurements to probe/quantify the degree of covalence in actinide/lanthanidecomplexes in solution.

Data from two complexation systems are presented as examples. One is thecomplexation of Am(III) and Nd(III)/Eu(III) with a new nitrogen donor ligand,2,9-di(quinazolin-2-yl)-1,10-phenanthroline (denoted as BQPhen) [1]; the otheris the complexation of Cm(III) and Nd(III) with the well-knownsulfur-containing ligand, bis(2,4,4-trimethylpentyl)-dithiophosphinate (denotedas Cyanex 301) [2]. The stability constants of the complexes were obtained byspectrophotometry. The enthalpy of complexation was directly determined bymicrocalorimetry.

In both complexation systems, results show that BQPhen or Cyanex 301forms stronger complexes with the trivalent actinides, An(III), than thetrivalent lanthanides, Ln(III), under identical experimental conditions. Inaddition, the higher binding strength of BQPhen or Cyanex 301 towards An(III)than Ln(III) is mainly due to the more favorable enthalpy of complexation forAn(III) complexes, implying a higher degree of covalence in the An(III)complexes than the Ln(III) complexes. The thermodynamic data are corroboratedwith the results from solvent extraction separations and theoreticalcomputations.

个人简介：Dr. Rao received his diploma in Radiochemistryfrom University of Science and Technology of China in1968, and his Ph. D in Inorganic Chemistry from Florida State University(Advisor: Prof. Gregory R. Choppin) in 1992. He is Senior Scientist working in LawrenceBerkeley National Laboratory and holds an Adjunct Professor position in ClemsonUniversity, College of Engineering and Science. He is engaged in actinideresearch supported by DOE’s Basic Energy Sciences (BES), EnvironmentalManagement Sciences Program (EMSP), Yucca Mountain (YM) S&T Research,Nuclear Energy Research Initiatives – Consortium (NERI-C) program, Office ofNuclear Energy (NE) Fuel Cycle Research and Development (FCRD) program, andOffice of Science Single Investigator and Small Group (SISGR) program, andserved as a member of DOE Environmental Management-Technical Expert Group(EM-TEG) advising DOE Office of EM on strategies for tank wastes andgroundwater/soil remediation. He has 170 publications in peer-reviewedjournals, 7 book/book chapters.