Monomers, Dimers, and Helices: Complexities of Cerium and Plutonium Phenanthrolinecarboxylates

The reaction of Ce^III or Pu^III with 1,10-phenanthroline-2,9-dicarboxylic acid (PDAH₂) results in the formation of new f-element coordination complexes. In the case of cerium, Ce­(PDA)­(H₂O)₂Cl·H₂O (<b>1</b>) or [Ce­(PDAH)­(PDA)]₂[Ce­(PDAH)­(PDA)] (<b>2</b>) was isolated depending on the Ce/ligand ratio in the reaction. The structure of <b>2</b> is composed of two distinct substructures that are constructed from the same monomer. This monomer is composed of a Ce^III cation bound by one PDA^2– dianionic ligand and one PDAH^– monoanionic ligand, both of which are tetradentate. Bridging by the carboxylate moieties leads to either [Ce­(PDAH)­(PDA)]₂ dimers or [Ce­(PDAH)­(PDA)]_1∞ helical chains. For plutonium, Pu­(PDA)₂ (<b>3</b>) was the only product isolated regardless of the Pu/ligand ratio employed in the reaction. During the reaction of plutonium with PDAH₂, Pu^III is oxidized to Pu^IV, generating <b>3</b>. This assignment is consistent with structural metrics and the optical absorption spectrum. Ambiguity in the assignment of the oxidation state of cerium in <b>1</b> and <b>2</b> from UV–vis–near-IR spectra invoked the use of Ce L_3,2-edge X-ray absorption near-edge spectroscopy, magnetic susceptibility, and heat capacity measurements. These experiments support the assignment of Ce^III in both compounds. The bond distances and coordination numbers are also consistent with these assignments. <b>3</b> contains 8-coordinate Pu^IV, whereas the cerium centers in <b>1</b> and <b>2</b> are 9- and/or 10-coordinate, which correlates with the increased size of Ce^III versus Pu^IV. Taken together, these data provide an example of a system where the differences in the redox behavior between these f elements creates more complex chemistry with cerium than with plutonium

Covalency in Lanthanides. An X‑ray Absorption Spectroscopy and Density Functional Theory Study of LnCl₆^<i>x</i>– (<i>x</i> = 3, 2)

Covalency in Ln–Cl bonds of <i>O</i>_<i>h</i>-LnCl₆^<i>x</i>– (<i>x</i> = 3 for Ln = Ce^III, Nd^III, Sm^III, Eu^III, Gd^III; <i>x</i> = 2 for Ln = Ce^IV) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L_3,2-edge and M_5,4-edge XAS were also used to characterize CeCl₆^<i>x</i>– (<i>x</i> = 2, 3). The M_5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce^III and Ce^IV). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (<i>t</i>_2<i>g</i>* and <i>e</i>_<i>g</i>*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce^III to Ce^IV had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl₆^3– (formally Ln^III), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce^IV 4f-orbital mixing (<i>t</i>_1<i>u</i>* + <i>t</i>_2<i>u</i>*) in CeCl₆^2–. This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl₆^2– (M = Ti, Zr, Hf, U)

Covalency in Lanthanides. An X‑ray Absorption Spectroscopy and Density Functional Theory Study of LnCl₆^<i>x</i>– (<i>x</i> = 3, 2)

Covalency in Ln–Cl bonds of <i>O</i>_<i>h</i>-LnCl₆^<i>x</i>– (<i>x</i> = 3 for Ln = Ce^III, Nd^III, Sm^III, Eu^III, Gd^III; <i>x</i> = 2 for Ln = Ce^IV) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L_3,2-edge and M_5,4-edge XAS were also used to characterize CeCl₆^<i>x</i>– (<i>x</i> = 2, 3). The M_5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce^III and Ce^IV). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (<i>t</i>_2<i>g</i>* and <i>e</i>_<i>g</i>*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce^III to Ce^IV had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl₆^3– (formally Ln^III), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce^IV 4f-orbital mixing (<i>t</i>_1<i>u</i>* + <i>t</i>_2<i>u</i>*) in CeCl₆^2–. This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl₆^2– (M = Ti, Zr, Hf, U)

Covalency in Lanthanides. An X‑ray Absorption Spectroscopy and Density Functional Theory Study of LnCl₆^<i>x</i>– (<i>x</i> = 3, 2)

Covalency in Ln–Cl bonds of <i>O</i>_<i>h</i>-LnCl₆^<i>x</i>– (<i>x</i> = 3 for Ln = Ce^III, Nd^III, Sm^III, Eu^III, Gd^III; <i>x</i> = 2 for Ln = Ce^IV) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L_3,2-edge and M_5,4-edge XAS were also used to characterize CeCl₆^<i>x</i>– (<i>x</i> = 2, 3). The M_5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce^III and Ce^IV). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (<i>t</i>_2<i>g</i>* and <i>e</i>_<i>g</i>*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce^III to Ce^IV had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl₆^3– (formally Ln^III), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce^IV 4f-orbital mixing (<i>t</i>_1<i>u</i>* + <i>t</i>_2<i>u</i>*) in CeCl₆^2–. This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl₆^2– (M = Ti, Zr, Hf, U)

Covalency in Lanthanides. An X‑ray Absorption Spectroscopy and Density Functional Theory Study of LnCl₆^<i>x</i>– (<i>x</i> = 3, 2)

Covalency in Ln–Cl bonds of <i>O</i>_<i>h</i>-LnCl₆^<i>x</i>– (<i>x</i> = 3 for Ln = Ce^III, Nd^III, Sm^III, Eu^III, Gd^III; <i>x</i> = 2 for Ln = Ce^IV) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L_3,2-edge and M_5,4-edge XAS were also used to characterize CeCl₆^<i>x</i>– (<i>x</i> = 2, 3). The M_5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce^III and Ce^IV). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (<i>t</i>_2<i>g</i>* and <i>e</i>_<i>g</i>*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce^III to Ce^IV had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl₆^3– (formally Ln^III), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce^IV 4f-orbital mixing (<i>t</i>_1<i>u</i>* + <i>t</i>_2<i>u</i>*) in CeCl₆^2–. This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl₆^2– (M = Ti, Zr, Hf, U)

Covalency in Lanthanides. An X‑ray Absorption Spectroscopy and Density Functional Theory Study of LnCl₆^<i>x</i>– (<i>x</i> = 3, 2)

Covalency in Ln–Cl bonds of <i>O</i>_<i>h</i>-LnCl₆^<i>x</i>– (<i>x</i> = 3 for Ln = Ce^III, Nd^III, Sm^III, Eu^III, Gd^III; <i>x</i> = 2 for Ln = Ce^IV) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L_3,2-edge and M_5,4-edge XAS were also used to characterize CeCl₆^<i>x</i>– (<i>x</i> = 2, 3). The M_5,4-edge XAS spectra were modeled using configuration interaction calculations. The results were evaluated as a function of (1) the lanthanide (Ln) metal identity, which was varied across the series from Ce to Gd, and (2) the Ln oxidation state (when practical, i.e., formally Ce^III and Ce^IV). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (<i>t</i>_2<i>g</i>* and <i>e</i>_<i>g</i>*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing Ce^III to Ce^IV had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl₆^3– (formally Ln^III), the 4f-orbitals participated only marginally in covalent bonding, which was consistent with historical descriptions. Surprisingly, there was a marked increase in Cl 3p- and Ce^IV 4f-orbital mixing (<i>t</i>_1<i>u</i>* + <i>t</i>_2<i>u</i>*) in CeCl₆^2–. This unexpected 4f- and 5d-orbital participation in covalent bonding is presented in the context of recent studies on both tetravalent transition metal and actinide hexahalides, MCl₆^2– (M = Ti, Zr, Hf, U)