Rare Earth Nitrate Hybrid Double Perovskites [Me4N]2[MLn(NO3)6] (M = Na-Cs; Ln = La-Gd, ex. Pm).

An exploration of the synthetic and structural phase space of rare earth hybrid double perovskites A2B'BX6 (A = organocation, B' = M+, B = M3+, X = molecular bridging anion) that include X = NO3- and B' = alkali metal is reported, complementing earlier studies of the [Me4N]2[KB(NO3)6] (B = Am, Cm, La-Nd, Sm-Lu, Y) (Me4N = (CH3)4N+) compounds. In the present efforts, the synthetic phase space of these systems is explored by varying the identity of the alkali metal ion at the B'-site. Herein, we report three new series of the form [Me4N]2[B'B(NO3)6] (B = La-Nd, Sm-Gd; B' = Na, Rb, Cs). The early members of the Na-series crystallize in the trigonal space group R3̅ from La to Nd where a phase transition occurs in the phase between 273 and 300 K, going from R3̅ to the high-symmetry, cubic space group Fm3̅m. The preceding trigonal members of the Na-series also undergo phase transitions to cubic symmetry at temperatures above 300 K, establishing a decreasing trend in the phase-transition temperature. The remainder of the Na-series, as well as the Rb- and Cs-series, all crystallize in Fm3̅m at 300 K. The temperature-dependent phase behavior of the synthesized phases is studied via variable-temperature spectroscopic methods and high-resolution powder X-ray diffractometry. All phases were characterized via single-crystal and powder X-ray diffraction and Fourier transform infrared (FT-IR) and Raman spectroscopic methods. These results demonstrate the versatility of the perovskite structure type to include rare earth ions, nitrate ions, and a suite of alkali metal ions and serve as a foundation for the design of functional rare earth hybrid double perovskite materials such as those possessing useful multiferroic, optical, and magnetic properties.

Hexanitrato complexes and hybrid double perovskites of Am3+ and Cm3.

The synthesis and structures of the homoleptic hexanitrato complexes of Am(III) and Cm(III), [(CH3)4N]2KAn(NO3)6 are reported. These compounds form a double perovskite structure type, A2B'BX6, crystallizing in the cubic space group Fm3̄m. Their electronic properties, as calculated using the Quantum Theory of Atoms in Molecules, are reported and compared to their lanthanide homologues Eu(III) and Gd(III).

Synthesis of an Isostructural Series of 12-Coordinate Lanthanide Nitrate Hybrid Double Perovskites with Cubic Symmetry.

In efforts to study the periodic chemical properties of the rare earth elements and their structural chemistry, a hybrid double perovskite phase A2B'BX6 with the formula ((CH3)4N)2KLn(NO3)6 (Ln = La-Lu, Y ex. Pm) was synthesized that crystallizes in the cubic space group, Fm3̅m. This series was obtained via evaporative crystallization from a mixture of Ln(NO3)3, KNO3, and (CH3)4N·NO3 in a 1:1:2 ratio from either H2O or 4.0 M HNO3. In this double perovskite structure, the B site containing the lanthanide ion is coordinated by six bidentate nitrate ligands, with the distal N═O oxygen atoms coordinating the potassium on the B' site in an octahedral six-coordinate environment. The two remaining charge-compensating (CH3)4N+ cations occupy the interstitial voids in the lattice on the A site. This periodic series was characterized via single-crystal X-ray diffraction, powder X-ray diffraction, IR, and Raman spectroscopy. Emission spectra of the Eu complex indicate a phase transition to trigonal symmetry upon cooling. This series is unique as it represents a rare isostructural series spanning the entirety of the rare earth elements excluding promethium with homoleptic 12-coordinate rare earth metal ions.

Crystal structures of metallocene complexes with uranium-germanium bonds.

The first structural examples of complexes with uranium-germanium bonds are presented, namely, bis-[3,5-bis-(tri-fluoro-meth-yl)phenyl-2κC 1](hydrido-2κH)(iodido-1κI)bis-[1,1(η5)-penta-methyl-cyclo-penta-dien-yl]germaniumuranium(Ge-U), [GeU(C10H15)2(C8H3F6)2HI], and bis-[3,5-bis-(tri-fluoro-meth-yl)phenyl-2κC 1](fluorido-1κI)(hydrido-2κH)bis-[1,1(η5)-penta-methyl-cyclo-penta-dien-yl]germaniumuranium(Ge-U), [GeU(C10H15)2(C8H3F6)2FH]. The two complexes both have a long U-Ge bond [distances of 3.0428 (7) and 3.0524 (7) Å].

Reactions of Neptunium(V) in Alkali-Metal Hydroxides.

The preparation of two new neptunium hydroxide compounds synthesized in concentrated potassium and rubidium hydroxide is reported. The phases K4[(NpO2)2(OH)6]·4H2O and Rb4[(NpO2)4(OH)8]·2H2O were prepared and their chemical structures determined using single-crystal X-ray diffraction. Raman spectra of the compounds are also presented. The newly synthesized phases are structurally related to Np2O5 and Na[NpO2(OH)2]. The potassium-containing phase reported here consists of infinite chains of edge-sharing neptunium hydroxide polyhedra but lacking the cation-cation interactions (CCIs) observed in Np2O5 and Na[NpO2(OH)2]. Rb4[(NpO2)4(OH)8]·2H2O is a an expanded three-dimensional framework based on NpO2+ CCIs like those observed in Np2O5 and Na[NpO2(OH)2]. Together these complexes begin to develop a structural series of neptunium(V) oxides and hydroxides of varying dimensionalities within the alkali-metal series. The potential roles of the alkali-metal cations and neptunyl(V) CCIs in directing the resulting structures are discussed.

Structural, Spectroscopic, and Computational Analysis of Heterometallic Thorium Phosphinidiide Complexes.

To synthesize complexes with thorium-phosphorus multiple-bond character, reactions of (C5Me5)2Th[P(H)Mes]2 with monovalent alkali-metal bases, MN(SiMe3)2, as well as CuMes, have been investigated. The results with MN(SiMe3)2 are phosphinidiide complexes of the form {(C5Me5)2Th[µ2-P(Mes)][µ2-P(H)Mes]M(L)n}2 (M = Na, n = 0; M = K, L = THF, n = 1; M = Rb, L = THF, n = 1; M = Cs, L = Et2O, n = 1). With CuMes, the product is a Th2Cu3P5 heterometallic structure, {(C5Me5)2Th[(µ2-P(H)Mes)P(Mes)]Cu}2Cu[µ2-P(H)Mes]. All complexes have been characterized using heteronuclear NMR and IR spectroscopy, density functional theory calculations, and their solid-state structure identified by X-ray crystallography. We also report the structure of {(C5Me5)2Th[(µ2-As(H)Mes)As(Mes)]Cu}2Cu[µ2-As(H)Mes] obtained from (C5Me5)2Th[As(H)Mes]2 with CuMes.

Backbonding in Thorium(IV) and Uranium(IV) Diarsenido Complexes with tBuNC and CO.

The coordination of tBuNC and CO with the diarsenido complexes (C5 Me5 )2 An(η2 -As2 Mes2 ), An=Th, U, has been investigated. For the first time, a comparison between isostructural complexes of ThIV and UIV has been possible with CO; density functional calculations indicated an appreciable amount of π backbonding that originates from charge transfer from an actinide-arsenic sigma bond. The calculated CO stretching frequencies in the ThIV and UIV diarsenido complexes are consistent with the experimental measurements, both show large shifts to lower frequency. We demonstrate that the π backbonding is crucial to explaining the red shifts of CO frequency upon AnIV complex formation. Interestingly, this interaction essentially correlates to the parallel orientation of π*(C-O) orbitals relative to the An-As bond.

Systematic Investigation of the Molecular and Electronic Structure of Thorium and Uranium Phosphorus and Arsenic Complexes.

In continuing to examine the interaction of actinide-ligand bonds with soft donor ligands, a comparative investigation with phosphorus and arsenic was conducted. A reaction of (C5Me5)2AnMe2, An = Th, U, with 2 equiv of H2AsMes, Mes = 2,4,6-Me3C6H2, forms the primary bis(arsenido) complexes, (C5Me5)2An[As(H)Mes]2. Both exhibit thermal instability at room temperature, leading to the elimination of H2, and the formation of the diarsenido species, (C5Me5)2An(η2-As2Mes2). The analogous diphosphido complexes, (C5Me5)2An(η2-P2Mes2), could not be synthesized via the same route, even upon heating the bis(phosphido) species to 100 °C in toluene. However, they were accessible via the reaction of dimesityldiphosphane, MesP(H)P(H)Mes, with (C5Me5)2AnMe2 at 70 °C in toluene. When (C5Me5)2AnMe2 is reacted with 1 equiv of H2AsMes, the bridging µ2-arsinidiide complexes [(C5Me5)2An]2(µ2-AsMes)2 are formed. Upon reaction of (C5Me5)2UMe2 with 1 equiv of H2PMes, the phosphinidiide [(C5Me5)2U(µ2-PMes)]2 is isolated. However, the analogous thorium reaction leads to a phosphido and C-H bond activation of the methyl on the mesityl group, forming {(C5Me5)2Th[P(H)(2,4-Me2C6H2-6-CH2)]}2. The reactivity of [(C5Me5)2An(µ2-EMes)]2 was investigated with OPPh3 in an effort to produce terminal phosphinidene or arsinidene complexes. For E = As, An = U, a U(III) cation-anion pair [(C5Me5)2U(η2-As2Mes2)][(C5Me5)2U(OPPh3)2] is isolated. The reaction of [(C5Me5)2Th(µ2-AsMes)]2 with OPPh3 does not result in a terminal arsinidene but, instead, eliminates PPh3 to yield a bridging arsinidiide/oxo complex, [(C5Me5)2Th]2(µ2-AsMes)(µ2-O). Finally, the combination of [(C5Me5)2U(µ2-PMes)]2 and OPPh3 yields a terminal phosphinidene, (C5Me5)2U(═PMes)(OPPh3), featuring a short U-P bond distance of 2.502(2) Å. Electrochemical measurements on the uranium pnictinidiide complexes demonstrate only a 0.04 V difference with phosphorus as a slightly better donor. Magnetic measurements on the uranium complexes show more excited-state mixing and therefore higher magnetic moments with the arsenic-containing compounds but no deviation from uncoupled U(IV) behavior. Finally, a quantum theory of atoms in molecules analysis shows highly polarized actinide-pnictogen bonds with similar bonding characteristics, supporting the electrochemical and magnetic measurements of similar bonding between actinide-phosphorus and actinide-arsenic bonds.

Two-Electron Reduction of a U(VI) Complex with Al(C5Me5).

The reduction of U(VI) to U(IV) is rare, especially in one step, and not observed electrochemically as a one-wave, two-electron couple. Here, we demonstrate that reduction of the uranium(VI) bis(imido) complex, (C5Me5)2U[═N(4-OiPrC6H4)]2, is readily accomplished with Al(C5Me5), forming the bridging uranium(IV)/aluminum(III) imido complex (C5Me5)2U[µ2-N(4-OiPrC6H4)]2Al(C5Me5). The structure and bonding of the bridging imido complex is examined with electrochemical measurements in tandem with density functional theory calculations.

Synthesis and Utility of Neptunium(III) Hydrocarbyl Complex.

To extend organoactinide chemistry beyond uranium, reported here is the first structurally characterized transuranic hydrocarbyl complex, Np[η4 -Me2 NC(H)C6 H5 ]3 (1), from reaction of NpCl4 (DME)2 with four equivalents of K[Me2 NC(H)C6 H5 ]. Unlike the UIII species, the neptunium analogue can be used to access other NpIII complexes. The reaction of 1 with three equivalents of HE2 C(2,6-Mes2 -C6 H3 ) (E=O, S) yields [(2,6-Mes2 -C6 H3 )CE2 ]3 Np(THF)2 , maintaining the trivalent oxidation state.

Functionalization of Carbon Monoxide and tert-Butyl Nitrile by Intramolecular Proton Transfer in a Bis(Phosphido) Thorium Complex.

We report intramolecular proton transfer reactions to functionalize carbon monoxide and tert-butyl nitrile from a bis(phosphido) thorium complex. The reaction of (C5 Me5 )2 Th[PH(Mes)]2 , Mes=2,4,6-Me3 C6 H2 , with 1 atm of CO yields (C5 Me5 )2 Th(κ2 -(O,O)-OCH2 PMes-C(O)PMes), in which one CO molecule is inserted into each thorium-phosphorus bond. Concomitant transfer of two protons, formerly coordinated to phosphorus, are now bound to one of the carbon atoms from one of the inserted CO molecules. DFT calculations were employed to determine the lowest energy pathway. With tert-butyl nitrile, t BuCN, only one nitrile inserts into a thorium-phosphorus bond, but the proton is transferred to nitrogen with one phosphido remaining unperturbed affording (C5 Me5 )2 Th[PH(Mes)][κ2 -(P,N)-N(H)C(CMe3 )P(Mes)]. Surprisingly, reaction of this compound with KN(SiMe3 )2 removes the proton bound to nitrogen, not phosphorus.