Isolation of a californium(II) crown-ether complex

The actinides, from californium to nobelium (Z = 98-102), are known to have an accessible +2 oxidation state. Understanding the origin of this chemical behaviour requires characterizing Cf^II materials, but investigations are hampered by the fact that they have remained difficult to isolate. This partly arises from the intrinsic challenges of manipulating this unstable element, as well as a lack of suitable reductants that do not reduce Cf^III to Cf°. Here we show that a Cf^II crown-ether complex, Cf(18-crown-6)I₂, can be prepared using an Al/Hg amalgam as a reductant. Spectroscopic evidence shows that Cf^III can be quantitatively reduced to Cf^II, and rapid radiolytic re-oxidation in solution yields co-crystallized mixtures of Cf^II and Cf^III complexes without the Al/Hg amalgam. Quantum-chemical calculations show that the Cf‒ligand interactions are highly ionic and that 5f/6d mixing is absent, resulting in weak 5f→5f transitions and an absorption spectrum dominated by 5f→6d transitions.

Advancing the Am Extractant Design through the Interplay among Planarity, Preorganization, and Substitution Effects

Advancing the field of chemical separations is important for nearly every area of science and technology. Some of the most challenging separations are associated with the americium ion Am(III) for its extraction in the nuclear fuel cycle, ²⁴¹Am production for industrial usage, and environmental cleanup efforts. Herein, we study a series of extractants, using first-principle calculations, to identify the electronic properties that preferentially influence Am(III) binding in separations. As the most used extractant family and because it affords a high degree of functionalization, the polypyridyl family of extractants is chosen to study the effects of the planarity of the structure, preorganization of coordinating atoms, and substitution of various functional groups. The actinyl ions are used as a structurally simplified surrogate model to quickly screen the most promising candidates that can separate these metal ions. The down-selected extractants are then tested for the Am(III)/Eu(III) system. Our results show that π interactions, especially those between the central terpyridine ring and Am(III), play a crucial role in separation. Adding an electron-donating group onto the terpyridine backbone increases the binding energies to Am(III) and stabilizes Am-terpyridine coordination. Increasing the planarity of the extractant increases the binding strength as well, although this effect is found to be rather weak. Preorganizing the coordinating atoms of an extractant to their binding configuration as in the bound metal complex speeds up the binding process and significantly improves the kinetics of the separation process. This conclusion is validated by the synthesized 1,2-dihydrodipyrido[4,3-b;5,6-b]acridine (13) extractant, a preorganized derivative of the terpyridine extractant, which we experimentally showed was four times more effective than terpyridine at separating Am³⁺ from Eu³⁺ (SF_Am/Eu ∼ 23 ± 1).

Carbene Complexes of Neptunium

Since the advent of organotransuranium chemistry six decades ago, structurally verified complexes remain restricted to π-bonded carbocycle and σ-bonded hydrocarbyl derivatives. Thus, transuranium-carbon multiple or dative bonds are yet to be reported. Here, utilizing diphosphoniomethanide precursors we report the synthesis and characterization of transuranium-carbene derivatives, namely, diphosphonio-alkylidene- and N-heterocyclic carbene–neptunium(III) complexes that exhibit polarized-covalent σ²π² multiple and dative σ² single transuranium-carbon bond interactions, respectively. The reaction of [Np^IIII₃(THF)₄] with [Rb(BIPM^TMSH)] (BIPM^TMSH = {HC(PPh₂NSiMe₃)₂}^1–) affords [(BIPM^TMSH)Np^III(I)₂(THF)] (3Np) in situ, and subsequent treatment with the N-heterocyclic carbene {C(NMeCMe)₂} (I^Me4) allows isolation of [(BIPM^TMSH)Np^III(I)₂(I^Me4)] (4Np). Separate treatment of in situ prepared 3Np with benzyl potassium in 1,2-dimethoxyethane (DME) affords [(BIPM^TMS)Np^III(I)(DME)] (5Np, BIPM^TMS = {C(PPh₂NSiMe₃)₂}^2–). Analogously, addition of benzyl potassium and I^Me4 to 4Np gives [(BIPM^TMS)Np^III(I)(I^Me4)₂] (6Np). The synthesis of 3Np–6Np was facilitated by adopting a scaled-down prechoreographed approach using cerium synthetic surrogates. The thorium(III) and uranium(III) analogues of these neptunium(III) complexes are currently unavailable, meaning that the synthesis of 4Np–6Np provides an example of experimental grounding of 5f- vs 5f- and 5f- vs 4f-element bonding and reactivity comparisons being led by nonaqueous transuranium chemistry rather than thorium and uranium congeners. Computational analysis suggests that these Np^III=C bonds are more covalent than U^III=C, Ce^III=C, and Pm^III=C congeners but comparable to analogous U^IV=C bonds in terms of bond orders and total metal contributions to the M=C bonds. A preliminary assessment of Np^III=C reactivity has introduced multiple bond metathesis to transuranium chemistry, extending the range of known metallo-Wittig reactions to encompass actinide oxidation states III-VI.

Synthesis, characterization, and high-pressure studies of a 3D berkelium(III) carboxylate framework material

A berkelium(III) mellitate, Bk₂[C₆(CO₂)₆](H₂O)₈·2H₂O, was synthesized and rapidly crystallized by reacting mellitic acid, C₆(CO₂H)₆, and BkBr₃·nH₂O in an aqueous medium. Single crystal X-ray diffraction shows that the compound crystallizes as a three-dimensional framework isostructural with Pu(III), Am(III), and Cm(III) mellitates. UV-vis-NIR spectroscopic studies as a function of pressure were performed using a diamond anvil cell and show that the 5f → 5f transitions of Bk³⁺ display enhanced hypsochromic shifting when compared to other An(III) mellitates.

2.2.2-Cryptand complexes of neptunium(III) and plutonium(III)

New coordination environments are reported for Np(III) and Pu(III) based on pilot studies of U(III) in 2.2.2-cryptand (crypt). The U(III)-in-crypt complex, [U(crypt)I₂][I], obtained from the reaction between UI₃ and crypt, is treated with Me₃SiOTf (OTf = O₃SCF₃) in benzene to form the [U(crypt)(OTf)₂][OTf] complex. Similarly, the isomorphous Np(III) and Pu(III) complexes were obtained similarly starting from [AnI₃(THF)₄]. All three complexes (1-An; An = U, Np, Pu) contain an encapsulated actinide in a THF-soluble complex. Absorption spectroscopy and DFT calculations are consistent with 5f³ U(III), 5f⁴ Np(III), and 5f⁵ Pu(III) electron configurations.

[AnI3(THF)4] (An = Np, Pu) Preparation Bypassing An0 Metal Precursors: Access to Np3+/Pu3+ Nonaqueous and Organometallic Complexes

Direct comparison of homologous molecules provides a foundation from which to elucidate both subtle and patent changes in reactivity patterns, redox processes, and bonding properties across a series of elements. While trivalent molecular U chemistry is richly developed, analogous Np or Pu research has long been hindered by synthetic routes often requiring scarcely available metallic-phase source material, high-temperature solid-state reactions producing poorly soluble binary halides, or the use of pyrophoric reagents. The development of routes to nonaqueous Np³⁺/Pu³⁺ from widely available precursors can potentially transform the scope and pace of research into actinide periodicity. Here, aqueous stocks of An⁴⁺ (An = Np, Pu) are dehydrated to well-defined [AnCl₄(DME)₂] (DME = 1,2-dimethoxyethane), and then a single-step halide exchange/reduction employing Me₃SiI produces [AnI₃(THF)₄] (THF = tetrahydrofuran) in a high to nearly quantitative crystalline yield (with I₂ and Me₃SiCl as easily removed byproducts). We demonstrate the synthetic utility of these An-iodide molecules, prepared by metal⁰-free routes, through characterization of archetypal complexes including the tris-silylamide, [Np{N(SiMe₃)₂}₃], and bent metallocenes, [An(C₅Me₅)₂(I)(THF)] (An = Np, Pu)─chosen because both motifs are ubiquitous in Th, U, and lanthanide research. The synthesis of [Np{N(Se═PPh₂)₂}₃] is also reported, completing an isomorphous series that now extends from U to Am and is the first characterized Np³⁺-Se bond.

Isolation and characterization of a californium metallocene

Californium (Cf) is currently the heaviest element accessible above microgram quantities. Cf isotopes impose severe experimental challenges due to their scarcity and radiological hazards. Consequently, chemical secrets ranging from the accessibility of 5f/6d valence orbitals to engage in bonding, the role of spin-orbit coupling in electronic structure, and reactivity patterns compared to other f elements, remain locked. Organometallic molecules were foundational in elucidating periodicity and bonding trends across the periodic table^1-3, with a twenty-first-century renaissance of organometallic thorium (Th) through plutonium (Pu) chemistry^4-12, and to a smaller extent americium (Am)¹³, transforming chemical understanding. Yet, analogous curium (Cm) to Cf chemistry has lain dormant since the 1970s. Here, we revive air-/moisture-sensitive Cf chemistry through the synthesis and characterization of [Cf(C₅Me₄H)₂Cl₂K(OEt₂)]_n from two milligrams of ²⁴⁹Cf. This bent metallocene motif, not previously structurally authenticated beyond uranium (U)^14,15, contains the first crystallographically characterized Cf-C bond. Analysis suggests the Cf-C bond is largely ionic with a small covalent contribution. Lowered Cf 5f orbital energy versus dysprosium (Dy) 4f in the colourless, isoelectronic and isostructural [Dy(C₅Me₄H)₂Cl₂K(OEt₂)]_n results in an orange Cf compound, contrasting with the light-green colour typically associated with Cf compounds^16-22.

Pronounced Pressure Dependence of Electronic Transitions for Americium Compared to Isomorphous Neodymium and Samarium Mellitates

The mellitate ion is relevant in spent nuclear fuel processing and is utilized as a surrogate for studying the interactions of f elements with humic acids. A wealth of different coordination modes gives the potential for diverse structural chemistry across the actinide series. In this study, an americium mellitate, ²⁴³Am₂[(C₆(COO^-)₆](H₂O)₈·2H₂O (1-Am), has been synthesized and characterized using structural analysis and spectroscopy at ambient and elevated pressures. 1-Am was then compared to isomorphous neodymium (1-Nd) and samarium (1-Sm) mellitates via bond-length analysis and pressure dependence of their Laporte-forbidden f → f transitions. Results show that the pressure dependence of the f → f transitions of 1-Am is significantly greater than that observed in 1-Nd and 1-Sm, with average shifts of 21.4, 4.7, and 3.6 cm^-1/GPa, respectively. This greater shift found in 1-Am shows further evidence that the 5f orbitals are more affected than the 4f orbitals when pressure is applied to isostructural compounds.

Stabilization of hydrated AcIII cation: the role of superatom states in actinium-water bonding

225Ac-based radiopharmaceuticals have the potential to become invaluable in designated cancer therapy. However, the limited understanding of the solution chemistry and bonding properties of actinium has hindered the development of existing and emerging targeted radiotherapeutics, which also poses a significant challenge in the discovery of new agents. Herein, we report the geometric and electronic structural properties of hydrated AcIII cations in the [AcIII(H2O) n ]3+ (n = 4-11) complexes in aqueous solution and gas-phase using density functional theory. We found that nine water molecules coordinated to the AcIII cation is the most stable complex due to an enhanced hydration Gibbs free energy. This complex adopts a closed-shell 18-electron configuration (1S 21P 61D 10) of a superatom state, which indicates a non-negligible covalent character and involves H2O → AcIII σ donation interaction between s-/p-/d-type atomic orbitals of the Ac atom and 2p atomic orbitals of the O atoms. Furthermore, potentially existing 10-coordinated complexes need to overcome an energy barrier (>0.10 eV) caused by hydrogen bonding to convert to 9-coordination. These results imply the importance of superatom states in actinide chemistry generally, and specifically in AcIII solution chemistry, and highlight the conversion mechanism between different coordination numbers.

Stabilization of U(III) to Oxidation and Hydrolysis by Encapsulation Using 2.2.2-Cryptand

The electrochemical properties of U(III)-in-crypt (crypt = 2.2.2-cryptand) were examined in dimethylformamide (DMF) and acetonitrile (MeCN) to determine the oxidative stability offered by crypt as a ligand. Cyclic voltammetry revealed a U(III)/U(IV) irreversible oxidation at E_PA= -0.49 V (vs Fe(C₅H₅)₂^+/0) in DMF and at E_PA= -0.31 V (vs Fe(C₅H₅)₂^+/0) in MeCN. The electrochemistry of U(III)-in-crypt complexes in the presence of water was also examined. These studies are supported by crystallographically characterized examples of U(III)-in-crypt complexes as DMF, MeCN, and water adducts.

Tris-{hydridotris(1-pyrazolyl)borato}actinide Complexes: Synthesis, Spectroscopy, Crystal Structure, Bonding Properties and Magnetic Behaviour

The isostructural compounds of the trivalent actinides uranium, neptunium, plutonium, americium, and curium with the hydridotris(1-pyrazolyl)borato (Tp) ligand An[η3 -HB(N2 C3 H3 )3 ]3 (AnTp3 ) have been obtained through several synthetic routes. Structural, spectroscopic (absorption, infrared, laser fluorescence) and magnetic characterisation of the compounds were performed in combination with crystal field, density functional theory (DFT) and relativistic multiconfigurational calculations. The covalent bonding interactions were analysed in terms of the natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) models.

Pressure-Induced Spectroscopic Changes in a Californium 1D Material Are Twice as Large as Found in the Holmium Analog

In this study, the synthesis, characterization, and pressure response of a 1D californium mellitate (mellitate = 1,2,3,4,5,6-benzenehexacarboxylate) coordination polymer, Cf₂(mell)(H₂O)₁₀·4H₂O (Cf-1), are reported. The Cf-O lengths within the crystal structure are compared to its gadolinium (Gd-1) and holmium (Ho-1) analogs as well. These data show that the average Cf-O bond distance is slightly longer than the average Gd-O bond, consistent with trends in effective ionic radii. UV-vis-NIR absorption spectra as a function of pressure were collected using diamond-anvil techniques for both Cf-1 and Ho-1. These experiments show that the Cf(III) f → f transitions have a stronger dependence on pressure than that of the holmium analog. In the former case, the shift is nearly linear with applied pressure and averages 6.6 cm^-1/GPa, whereas in the latter, it is <3 cm^-1/GPa.

Extraction of plutonium-containing microcrystals from Hanford soil using a focused ion beam for single-crystal X-ray diffraction analysis

Herein, the successful use of a focused ion beam/scanning electron microscope to prepare microsamples of radioactive single crystals for X-ray diffraction analysis is reported. This technique was used to extract and analyze crystalline Pu-containing particles as small as 28 µm3 from Hanford soil taken from the 216-Z-9 waste crib, which were then crystallographically characterized using single-crystal X-ray diffraction to confirm the cubic structure of PuO2. As a systematic proof of concept, the technique was first tested using UO2 crystals milled into cubic shapes with approximate volumes of 4620, 1331, 125, 8 and 1 µm3, in order to empirically determine the crystal size limits for characterization by a laboratory-based diffractometer with a sealed tube Mo or Ag anode X-ray source and a charge-coupled device detector.

[Am(C5 Me4 H)3 ]: An Organometallic Americium Complex

We report the small-scale synthesis, isolated yield, single-crystal X-ray structure, ¹ H NMR solution spectroscopy /solid-state UV/Vis-nIR spectroscopy, and density functional theory (DFT)/ab initio wave function theory calculations on an Am³⁺ organometallic complex, [Am(C₅ Me₄ H)₃ ] (1). This constitutes the first quantitative data on Am-C bonding in a molecular species.

Origins of the odd optical observables in plutonium and americium tungstates

A series of f-block tungstates show atypical coloration for both the Ce(iii) and Pu(iii) compounds; whereas the other lanthanide and Am(iii) compounds possess normal absorption features. The different optical properties are actually derived from the tungstate component rather than from 5f electrons/orbitals.

A series of trivalent f-block tungstates, MW₂O₇(OH)(H₂O) (M = La, Ce, Pr, Nd, and Pu) and AmWO₄(OH), have been prepared in crystalline form using hydrothermal methods. Both structure types take the form of 3D networks where MW₂O₇(OH)(H₂O) is assembled from infinite chains of distorted tungstate octahedra linked by isolated MO₈ bicapped trigonal prisms; whereas AmWO₄(OH) is constructed from edge-sharing AmO₈ square antiprisms connected by distorted tungstate trigonal bipyramids. PuW₂O₇(OH)(H₂O) crystallizes as red plates; an atypical color for a Pu(iii) compound. Optical absorption spectra acquired from single crystals show strong, broadband absorption in the visible region. A similar feature is observed for CeW₂O₇(OH)(H₂O), but not for AmWO₄(OH). Here we demonstrate that these significantly different optical properties do not stem directly from the 5f electrons, as in both systems the valence band has mostly O-2p character and the conduction band has mostly W-5d character. Furthermore, the quasi-particle gap is essentially unaffected by the 5f degrees of freedom. Despite this, our analysis demonstrates that the f-electron covalency effects are quite important and substantially different energetically in PuW₂O₇(OH)(H₂O) and AmWO₄(OH), indicating that the optical gap alone cannot be used to infer conclusions concerning the f electron contribution to the chemical bond in these systems.

Thermodynamics of plutonium(iii) and curium(iii) complexation with a N-donor ligand

The complexation of Pu(iii) and Cm(iii) with a soft N-donor ligand was investigated using the van't Hoff method, microcalorimetry and DFT calculations. The studies revealed that the strength of the actinide-ligand bond as given by the enthalpic contribution drastically decreases on going from Pu(iii) to Cm(iii), while the complex stability remains nearly constant.

Perspectives of multiscale rare earth crystal materials

Both multisize and multiweight effects are proposed to characterize multiscale rare earth crystal materials.

Synthesis of uranium-in-cryptand complexes

The facile encapsulation of U(iii) and La(iii) by 2.2.2-cryptand (crypt) using simple starting materials is described. Addition of crypt to UI3 and LaCl3 forms the crystallographically-characterizable complexes, [U(crypt)I2]I and [La(crypt)Cl2]Cl. In the presence of water, the U(iii)-aquo adducts, [U(crypt)I(OH2)][I]2 and [U(crypt)I(OH2)][I][BPh4], can be isolated.

Syntheses, Crystal Structures, and Nonlinear Optical Activity of Cs2Ba[AnO2(C2H5COO)3]4 (An = U, Np, Pu) and Unprecedented Octanuclear Complex Units in KR2(H2O)8[UO2(C2H5COO)3]5 (R = Sr, Ba)

X-ray diffraction was applied to the elucidation of crystal structures of single crystals of Cs₂Ba[AnO₂(C₂H₅COO)₃]₄, where An = U(I), Np(II), Pu(III), and KR₂(H₂O)₈[UO₂(C₂H₅COO)₃]₅, where R = Sr(IV), Ba (polymorphs V-a and V-b). FTIR spectra were analyzed for the uranium-containing crystals I, IV, and V-b. Isostructural cubic crystals I-III are constructed of typical mononuclear anionic complex units [AnO₂(C₂H₅COO)₃]^- and charge-balancing Cs and Ba cations. Features of actinide contraction in the six U-Np-Pu isostructural series known to date are analyzed. In crystal structures of IV and V two typical complexes [UO₂(C₂H₅COO)₃]^- bind with a hydrated Sr or Ba cation to form the rare trinuclear neutral complex unit {R(H₂O)₄[UO₂(C₂H₅COO)₃]₂}, where R = Sr, Ba. Two such trinuclear units and one typical mononuclear unit further bind with a K cation to form the unprecedented octanuclear neutral complex unit K[UO₂(C₂H₅COO)₃]{R(H₂O)₄[UO₂(C₂H₅COO)₃]₂}₂. As the derived polynuclear complexes of uranyl ion with carboxylate ligands in the crystal structures of IV and V are not the first but are rare examples, the equilibrium between mono and polynuclear complex units in aqueous solutions is discussed. The two polymorphic modifications V-a and V-b were studied at 100 K and at room temperature, respectively. Peculiarities of noncovalent interactions in crystal structures of the two polymorphs are revealed using Voronoi-Dirichlet tessellation. The nonlinear optical activity of noncentrosymmetric crystals I was estimated by its ability for second harmonic generation.

Synthesis and Characterization of the Actinium Aquo Ion

Metal aquo ions occupy central roles in all equilibria that define metal complexation in natural environments. These complexes are used to establish thermodynamic metrics (i.e., stability constants) for predicting metal binding, which are essential for defining critical parameters associated with aqueous speciation, metal chelation, in vivo transport, and so on. As such, establishing the fundamental chemistry of the actinium(III) aquo ion (Ac-aquo ion, Ac(H₂O) _x³⁺) is critical for current efforts to develop ²²⁵Ac [t_1/2 = 10.0(1) d] as a targeted anticancer therapeutic agent. However, given the limited amount of actinium available for study and its high radioactivity, many aspects of actinium chemistry remain poorly defined. We overcame these challenges using the longer-lived ²²⁷Ac [t_1/2 = 21.772(3) y] isotope and report the first characterization of this fundamentally important Ac-aquo coordination complex. Our X-ray absorption fine structure study revealed 10.9 ± 0.5 water molecules directly coordinated to the Ac^III cation with an Ac-O_H2O distance of 2.63(1) Å. This experimentally determined distance was consistent with molecular dynamics density functional theory results that showed (over the course of 8 ps) that Ac^III was coordinated by 9 water molecules with Ac-O_H2O distances ranging from 2.61 to 2.76 Å. The data is presented in the context of other actinide(III) and lanthanide(III) aquo ions characterized by XAFS and highlights the uniqueness of the large Ac^III coordination numbers and long Ac-O_H2O bond distances.

Identifying Coordination Geometries of Metal Aquaions in Water: Application to the Case of Lanthanoid and Actinoid Hydrates

The angular distribution function (ADF) associated with the oxygen-metal ion-oxygen angle (OMO) of several trivalent lanthanoid and actinoid aquaions has been used to identify the most probable coordination geometry of these aquaions in aqueous solutions. The ADFs extracted from the molecular dynamics trajectories have been compared with continuous distribution functions corresponding to the geometry of a reference polyhedron pattern. The procedure incorporates specific quantum-mechanical information on the aquaion under study. The new method is applied to the analysis of four M(H₂O)_n³⁺ aquaions in water, M = Lu and Cf for n = 8, and M = La and Ac for n = 9. For those that are 8-coordinated, the square antiprism (SA) coordination geometry is preferred. For the 9-fold coordination, the simulation ADFs are more similar to the continuous ADF derived from a Gyro-elongated-SA rather than to the usually proposed trigonal tricapped prism. Advantages of these continuous distributions with respect to the usually employed discrete distributions are emphasized as well as further applications are suggested.

First structural characterization of Pa(iv) in aqueous solution and quantum chemical investigations of the tetravalent actinides up to Bk(IV): the evidence of a curium break

More than a century after its discovery the structure of the Pa(4+) ion in acidic aqueous solution has been investigated for the first time experimentally and by quantum chemistry. The combined results of EXAFS data and quantum chemically optimized structures suggest that the Pa(4+) aqua ion has an average of nine water molecules in its first hydration sphere at a mean Pa-O distance of 2.43 Å. The data available for the early tetravalent actinide (An) elements from Th(4+) to Bk(4+) show that the An-O bonds have a pronounced electrostatic character, with bond distances following the same monotonic decreasing trend as the An(4+) ionic radii, with a decrease of the hydration number from nine to eight for the heaviest ions Cm(4+) and Bk(4+). Being the first open-shell tetravalent actinide, Pa(4+) features a coordination chemistry very similar to its successors. The electronic configuration of all open-shell systems corresponds to occupation of the valence 5f orbitals, without contribution from the 6d orbitals. Our results thus demonstrate that Pa(iv) resembles its early actinide neighbors.

Magnetic susceptibility of actinide(iii) cations: an experimental and theoretical study

Radioactive decay on magnetic susceptibility measurements by the Evans's method has been characterized on two uranium isotopes and on tritiated water. Quantum chemistry calculations have been performed to explain Pu(iii), Am(iii) and Cm(iii) magnetic susceptibilities corrected from the radioactivity effects.

Emergence of californium as the second transitional element in the actinide series

A break in periodicity occurs in the actinide series between plutonium and americium as the result of the localization of 5f electrons. The subsequent chemistry of later actinides is thought to closely parallel lanthanides in that bonding is expected to be ionic and complexation should not substantially alter the electronic structure of the metal ions. Here we demonstrate that ligation of californium(III) by a pyridine derivative results in significant deviations in the properties of the resultant complex with respect to that predicted for the free ion. We expand on this by characterizing the americium and curium analogues for comparison, and show that these pronounced effects result from a second transition in periodicity in the actinide series that occurs, in part, because of the stabilization of the divalent oxidation state. The metastability of californium(II) is responsible for many of the unusual properties of californium including the green photoluminescence.

The chemistry of the post-plutonium actinides is thought to resemble lanthanides in that bonding is primarily ionic. Here, the authors show that a californium(III) complex displays significantly different properties to those predicted for the free ion owing to a second break in actinide periodicity.

Magnetic polarization of the americium J=0 ground state in AmFe(2)

Trivalent americium has a nonmagnetic (J=0) ground state arising from the cancellation of the orbital and spin moments. However, magnetism can be induced by a large molecular field if Am^{3+} is embedded in a ferromagnetic matrix. Using the technique of x-ray magnetic circular dichroism, we show that this is the case in AmFe_{2}. Since ⟨J_{z}⟩=0, the spin component is exactly twice as large as the orbital one, the total Am moment is opposite to that of Fe, and the magnetic dipole operator ⟨T_{z}⟩ can be determined directly; we discuss the progression of the latter across the actinide series.

NMR and TRLFS studies of Ln(iii) and An(iii) C5-BPP complexes

C5-BPP is a highly efficient N-donor ligand for the separation of trivalent actinides, An(iii), from trivalent lanthanides, Ln(iii). The molecular origin of the selectivity of C5-BPP and many other N-donor ligands of the BTP-type is still not entirely understood. We present here the first NMR studies on C5-BPP Ln(iii) and An(iii) complexes. C5-BPP is synthesized with 10% 15N labeling and characterized by NMR and LIFDI-MS methods. 15N NMR spectroscopy gives a detailed insight into the bonding of C5-BPP with lanthanides and Am(iii) as a representative for trivalent actinide cations, revealing significant differences in 15N chemical shift for coordinating nitrogen atoms compared to Ln(iii) complexes. The temperature dependence of NMR chemical shifts observed for the Am(iii) complex indicates a weak paramagnetism. This as well as the observed large chemical shift for coordinating nitrogen atoms show that metal-ligand bonding in Am(C5-BPP)3 has a larger share of covalence than in lanthanide complexes, confirming earlier studies. The Am(C5-BPP)3 NMR sample is furthermore spiked with Cm(iii) and characterized by time-resolved laser fluorescence spectroscopy (TRLFS), yielding important information on the speciation of trace amounts of minor complex species.

The reactions of TiCl3, and of UF4with TiCl3in liquid ammonia: unusual coordination spheres in [Ti(NH3)8]Cl3·6NH3and [UF(NH3)8]Cl3·3.5NH3

TiCl₃and NH₃form octaammine titanium(iii) chloride ammonia (1/6), [Ti(NH₃)₈]Cl₃·6NH₃, which is the first structurally characterized octaammine complex of a transition metal.