title: A Macrocyclic Chelator That Selectively Binds Ln4+over Ln3+by a Factor of 1029.
abstract: A tetravalent cerium macrocyclic complex (CeLK4) was prepared with an octadentate terephthalamide ligand comprised of hard catecholate donors and characterized in the solution state by spectrophotometric titrations and electrochemistry and in the crystal by X-ray diffraction. The solution-state studies showed that L exhibits a remarkably high affinity toward Ce4+, with log β110= 61(2) and ΔG = -348 kJ/mol, compared with log β110= 32.02(2) for the analogous Pr3+complex. In addition, L exhibits an unusual preference for forming CeL4-relative to formation of the analogous actinide complex, ThL4-, which has β110= 53.7(5). The extreme stabilization of tetravalent cerium relative to its trivalent state is also evidenced by the shift of 1.91 V in the redox potential of the Ce3+/Ce4+couple of the complex (measured at -0.454 V vs SHE). The unprecedented behavior prompted an electronic structure analysis using L3- and M5,4-edge X-ray absorption near-edge structure (XANES) spectroscopies and configuration interaction calculations, which showed that 4f-orbital bonding in CeLK4has partial covalent character due to ligand-to-metal charge transfer (LMCT) in the ground state. The experimental results are presented in the context of earlier measurements on tetravalent cerium compounds, indicating that the amount of LMCT for CeLK4is similar to that observed for [Et4N]2[CeCl6] and CeO2and significantly less than that for the organometallic sandwich compound cerocene, (C8H8)2Ce. A simple model to rationalize changes in 4f orbital bonding for tri- and tetravalent lanthanide and actinide compounds is also provided.
authors.affiliation: University of California , Berkeley, California 94720, United States.|Lawrence Berkeley National Laboratory (LBNL) , Berkeley, California 94720, United States.
authors.forename: Tiffany A
authors.initials: TA
authors.lastname: Pham
authors.affiliation: University of California , Berkeley, California 94720, United States.|Lawrence Berkeley National Laboratory (LBNL) , Berkeley, California 94720, United States.
authors.forename: Alison B
authors.initials: AB
authors.lastname: Altman
authors.affiliation: Los Alamos National Laboratory (LANL) , Los Alamos, New Mexico 87545, United States.|California State Polytechnic University , Pomona, California 91768, United States.
authors.forename: S Chantal E
authors.initials: SC
authors.lastname: Stieber
authors.affiliation: Lawrence Berkeley National Laboratory (LBNL) , Berkeley, California 94720, United States.
authors.forename: Corwin H
authors.initials: CH
authors.lastname: Booth
authors.affiliation: Los Alamos National Laboratory (LANL) , Los Alamos, New Mexico 87545, United States.
authors.forename: Stosh A
authors.initials: SA
authors.lastname: Kozimor
authors.affiliation: Lawrence Berkeley National Laboratory (LBNL) , Berkeley, California 94720, United States.
authors.forename: Wayne W
authors.initials: WW
authors.lastname: Lukens
authors.affiliation: Lawrence Berkeley National Laboratory (LBNL) , Berkeley, California 94720, United States.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Olive
authors.affiliation: Lawrence Berkeley National Laboratory (LBNL) , Berkeley, California 94720, United States.
authors.forename: Tolek
authors.initials: T
authors.lastname: Tyliszczak
authors.affiliation: Canadian Light Source (CLS) , Saskatoon, Saskatchewan S7N 2V3, Canada.
authors.forename: Jian
authors.initials: J
authors.lastname: Wang
authors.affiliation: Lawrence Berkeley National Laboratory (LBNL) , Berkeley, California 94720, United States.
authors.forename: Stefan G
authors.initials: SG
authors.lastname: Minasian
authors.affiliation: University of California , Berkeley, California 94720, United States.|Lawrence Berkeley National Laboratory (LBNL) , Berkeley, California 94720, United States.
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Raymond