Periodic Trends in Hexanuclear Actinide Clusters

Four new Th­(IV), U­(IV), and Np­(IV) hexanuclear clusters with 1,2-phenylenediphosphonate as the bridging ligand have been prepared by self-assembly at room temperature. The structures of Th₆Tl₃[C₆H₄(PO₃)­(PO₃H)]₆(NO₃)₇(H₂O)₆·(NO₃)₂·4H₂O (<b>Th6-3</b>), (NH₄)_8.11­Np₁₂Rb_3.89[C₆H₄(PO₃)­(PO₃H)]₁₂(NO₃)₂₄·15H₂O (<b>Np6-1</b>), (NH₄)₄U₁₂Cs₈[C₆H₄(PO₃)­(PO₃H)]₁₂(NO₃)₂₄·18H₂O (<b>U6-1</b>), and (NH₄)₄­U₁₂Cs₂­[C₆H₄(PO₃)­(PO₃H)]₁₂(NO₃)₁₈·40H₂O (<b>U6-2</b>) are described and compared with other clusters of containing An­(IV) or Ce­(IV). All of the clusters share the common formula M₆(H₂O)_<i>m</i>[C₆H₃(PO₃)­(PO₃H)]₆(NO₃)_<i>n</i>^{(6–<i>n</i>)} (M = Ce, Th, U, Np, Pu). The metal centers are normally nine-coordinate, with five oxygen atoms from the ligand and an additional four either occupied by NO₃^– or H₂O. It was found that the Ce, U, and Pu clusters favor both <i>C</i>_3<i>i</i> and <i>C</i>_<i>i</i> point groups, while Th only yields in <i>C</i>_<i>i</i>, and Np only <i>C</i>_3<i>i</i>. In the <i>C</i>_3<i>i</i> clusters, there are two NO₃^– anions bonded to the metal centers. In the <i>C</i>_<i>i</i> clusters, the number of NO₃^– anions varies from 0 to 2. The change in the ionic radius of the actinide ions tunes the cavity size of the clusters. The thorium clusters were found to accept larger ions including Cs⁺ and Tl⁺, whereas with uranium and later elements, only NH₄⁺ and/or Rb⁺ reside in the center of the clusters

Periodic Trends in Hexanuclear Actinide Clusters

Four new Th­(IV), U­(IV), and Np­(IV) hexanuclear clusters with 1,2-phenylenediphosphonate as the bridging ligand have been prepared by self-assembly at room temperature. The structures of Th₆Tl₃[C₆H₄(PO₃)­(PO₃H)]₆(NO₃)₇(H₂O)₆·(NO₃)₂·4H₂O (<b>Th6-3</b>), (NH₄)_8.11­Np₁₂Rb_3.89[C₆H₄(PO₃)­(PO₃H)]₁₂(NO₃)₂₄·15H₂O (<b>Np6-1</b>), (NH₄)₄U₁₂Cs₈[C₆H₄(PO₃)­(PO₃H)]₁₂(NO₃)₂₄·18H₂O (<b>U6-1</b>), and (NH₄)₄­U₁₂Cs₂­[C₆H₄(PO₃)­(PO₃H)]₁₂(NO₃)₁₈·40H₂O (<b>U6-2</b>) are described and compared with other clusters of containing An­(IV) or Ce­(IV). All of the clusters share the common formula M₆(H₂O)_<i>m</i>[C₆H₃(PO₃)­(PO₃H)]₆(NO₃)_<i>n</i>^{(6–<i>n</i>)} (M = Ce, Th, U, Np, Pu). The metal centers are normally nine-coordinate, with five oxygen atoms from the ligand and an additional four either occupied by NO₃^– or H₂O. It was found that the Ce, U, and Pu clusters favor both <i>C</i>_3<i>i</i> and <i>C</i>_<i>i</i> point groups, while Th only yields in <i>C</i>_<i>i</i>, and Np only <i>C</i>_3<i>i</i>. In the <i>C</i>_3<i>i</i> clusters, there are two NO₃^– anions bonded to the metal centers. In the <i>C</i>_<i>i</i> clusters, the number of NO₃^– anions varies from 0 to 2. The change in the ionic radius of the actinide ions tunes the cavity size of the clusters. The thorium clusters were found to accept larger ions including Cs⁺ and Tl⁺, whereas with uranium and later elements, only NH₄⁺ and/or Rb⁺ reside in the center of the clusters

New Neptunium(V) Borates That Exhibit the Alexandrite Effect

A new neptunium­(V) borate, K­[(NpO₂)­B₁₀O₁₄(OH)₄], was synthesized using boric acid as a reactive flux. The compound possesses a layered structure in which Np^V resides in triangular holes, creating a hexagonal-bipyramidal environment around neptunium. This compound is unusual in that it exhibits the Alexandrite effect, a property that is typically restricted to neptunium­(IV) compounds

(UO₂)₂[UO₄(trz)₂](OH)₂: A U(VI) Coordination Intermediate between a Tetraoxido Core and a Uranyl Ion with Cation–Cation Interactions

A uranyl triazole (UO₂)₂[UO₄(trz)₂]­(OH)₂ (<b>1</b>) (trz = 1,2,4-triazole) was prepared using a mild solvothermal reaction of uranyl acetate with 1,2,4-triazole. Single-crystal X-ray diffraction analysis of <b>1</b> revealed it contains sheets of uranium–oxygen polyhedra and that one of the U­(VI) cations is in an unusual coordination polyhedron that is intermediate between a tetraoxido core and a uranyl ion. This U­(VI) cation also forms cation–cation interactions (CCIs). Infrared, Raman, and XPS spectra are provided, together with a thermogravimetric analysis that demonstrates breakdown of the compound above 300 °C. The UV–vis–NIR spectrum of <b>1</b> is compared to those of another compound that has a range of U­(VI) coordination enviromments

Interstitial Incorporation of Plutonium into a Low-Dimensional Potassium Borate

The molten boric acid flux reaction of PuBr₃ with KBO₂ at 200 °C results in the formation of large light-yellow crystals of K[B₅O₇(OH)₂]·H₂O:Pu⁴⁺. Single-crystal X-ray diffraction experiments on the Pu-doped K[B₅O₇(OH)₂]·H₂O demonstrate two features: (1) K[B₅O₇(OH)₂]·H₂O:Pu⁴⁺ adopts a one-dimensional borate chain structure with void spaces between the chains. (2) The doping plutonium atoms do not reside on the potassium sites. The latter are not fully occupied. Both laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and energy-dispersive spectrometry analyses indicate that plutonium atoms are uniformly distributed in crystals of K[B₅O₇(OH)₂]·H₂O with an atomic K:Pu ratio of approximately 65:1 measured by LA-ICP-MS. UV–vis–NIR spectra taken from both freshly made and one day old crystals show that the plutonium present within the crystals is predominantly characterized by Pu(IV). A small amount of Pu(III) is also present initially, but slowly oxidized to Pu(IV) via interaction with oxygen in the air. X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopic measurements confirm that plutonium is mainly present as a form similar to that of a PuO₂ cluster. The combined results suggest that the clusters containing Pu(IV) ions are uniformly distributed in the void spaces between the borate chains

(UO₂)₂[UO₄(trz)₂](OH)₂: A U(VI) Coordination Intermediate between a Tetraoxido Core and a Uranyl Ion with Cation–Cation Interactions

A uranyl triazole (UO₂)₂[UO₄(trz)₂]­(OH)₂ (<b>1</b>) (trz = 1,2,4-triazole) was prepared using a mild solvothermal reaction of uranyl acetate with 1,2,4-triazole. Single-crystal X-ray diffraction analysis of <b>1</b> revealed it contains sheets of uranium–oxygen polyhedra and that one of the U­(VI) cations is in an unusual coordination polyhedron that is intermediate between a tetraoxido core and a uranyl ion. This U­(VI) cation also forms cation–cation interactions (CCIs). Infrared, Raman, and XPS spectra are provided, together with a thermogravimetric analysis that demonstrates breakdown of the compound above 300 °C. The UV–vis–NIR spectrum of <b>1</b> is compared to those of another compound that has a range of U­(VI) coordination enviromments

Periodic Trends in Lanthanide and Actinide Phosphonates: Discontinuity between Plutonium and Americium

The hydrothermal reactions of trivalent lanthanide and actinide chlorides with 1,2-methylenediphosphonic acid (<b>C1P2</b>) in the presence of NaOH or NaNO₃ result in the crystallization of three structure types: RE­[CH₂(PO₃H_0.5)₂] (RE = La, Ce, Pr, Nd, Sm; Pu) (<b>A type</b>), NaRE­(H₂O)­[CH₂(PO₃)₂] (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy; Am) (<b>B type</b>), or NaLn­[CH₂(PO₃H_0.5)₂]·(H₂O) (Ln = Yb and Lu) (<b>C type</b>). These crystals were analyzed using single crystal X-ray diffraction, and the structures were used directly for detailed bonding calculations. These phases form three-dimensional frameworks. In both <b>A</b> and <b>B</b>, the metal centers are found in REO₈ polyhedra as parts of edge-sharing chains or edge-sharing dimers, respectively. Polyhedron shape calculations reveal that <b>A</b> favors a <i>D</i>_2<i>d</i> dodecahedron while <b>B</b> adopts a <i>C</i>_2<i>v</i> geometry. In <b>C</b>, Yb and Lu only form isolated MO₆ octahedra. Such differences in terms of structure topology and coordination geometry are discussed in detail to reveal periodic deviations between the lanthanide and actinide series. Absorption spectra for the Pu­(III) and Am­(III) compounds are also reported. Electronic structure calculations with multireference methods, CASSCF, and density functional theory, DFT, reveal localization of the An 5f orbitals, but natural bond orbital and natural population analyses at the DFT level illustrate unique occupancy of the An 6d orbitals, as well as larger occupancy of the Pu 5f orbitals compared to the Am 5f orbitals

Cation–Cation Interactions between Neptunyl(VI) Units

The boric acid flux reaction of NpO₂(ClO₄)₂ with NaClO₄ affords Na­[(NpO₂)₄B₁₅O₂₄(OH)₅(H₂O)]­(ClO₄)·0.75H₂O (<b>NaNpBO-1</b>). <b>NaNpBO-1</b> possesses a layered structure consisting of double neptunyl­(VI) borate sheets bridged by another Np^VI site through cation–cation interactions. The sole presence of Np^VI in <b>NaNpBO-1</b> is supported by absorption and vibrational spectroscopy

Syntheses, Structures, and Spectroscopic Properties of Plutonium and Americium Phosphites and the Redetermination of the Ionic Radii of Pu(III) and Am(III)

A series of isotypic rare earth phosphites (RE = Ce­(III), Pr­(III), Nd­(III), Pu­(III), or Am­(III)) with the general formulas RE₂(HPO₃)₃(H₂O) along with a Pu­(IV) phosphite, Pu­[(HPO₃)₂(H₂O)₂], have been prepared hydrothermally via reactions of RECl₃ with phosphorous acid. The structure of RE₂(HPO₃)₃(H₂O) features a face-sharing interaction of eight- and nine-coordinate rare earth polyhedra. By use of the crystallographic data from the isotypic series along with data from previously reported isotypic series, the ionic radii for higher coordinate Pu­(III) and Am­(III) were calculated. The ^VIIIPu­(III) radius was calculated as 1.112 ± 0.004 Å, and the ^IXPu­(III) radius was calculated to be 1.165 ± 0.002 Å. The ^VIIIAm­(III) radius was calculated as 1.108 ± 0.004 Å, and the ^IXAm­(III) radius was calculated as 1.162 ± 0.002 Å

Effects of Large Halides on the Structures of Lanthanide(III) and Plutonium(III) Borates

Reactions of LnBr₃ or LnOI with molten boric acid result in formation of Ln­[B₅O₈(OH)­(H₂O)₂Br] (Ln = La–Pr), Nd₄[B₁₈O₂₅(OH)₁₃Br₃], or Ln­[B₅O₈(OH)­(H₂O)₂I] (Ln = La–Nd). Reaction of PuOI with molten boric acid yields Pu­[B₇O₁₁(OH)­(H₂O)₂I]. The Ln­(III) and Pu­(III) centers in these compounds are found as nine-coordinate hula-hoop or 10-coordinate capped triangular cupola geometries where there are six approximately coplanar oxygen donors provided by triangular holes in the polyborate sheets. The borate sheets are connected into three-dimensional networks by additional BO₃ triangles and/or BO₄ tetrahedra that are roughly perpendicular to the layers. The room-temperature absorption spectrum of single crystals of Pu­[B₇O₁₁(OH)­(H₂O)₂I] shows characteristic f–f transitions for Pu­(III) that are essentially indistinguishable from Pu­(III) in other compounds with alternative ligands and different coordination environments