J. Appl. Cryst.の発刊に際して

This Review highlights the application of high-temperature solutions for exploratory crystal growth and materials discovery of novel complex oxides. It provides an overview of the method of flux crystal growth of complex oxides and can function as a "how to" guide for those interested in oxide crystal growth. The most commonly used fluxes are discussed in terms of their applicability for dissolving specific elements and the typical reaction conditions are compiled. A large variety of recent quaternary and higher oxides that have been grown as crystals from fluxes are used to illustrate the power of the flux method to grow oxide crystals containing specific elements.

Materials discovery by flux crystal growth: quaternary and higher order oxides.

Recent developments in actinide–ligand multiple bonding

Two isostructural series of trigonal prismatic complexes, M(BpMe)3 and M(BcMe)3 (M = Y, Tb, Dy, Ho, Er, U; [BpMe]− = dihydrobis(methypyrazolyl)borate; [BcMe]− = dihydrobis(methylimidazolyl)borate) are synthesized and fully characterized to examine the influence of ligand donor strength on slow magnetic relaxation. Investigation of the dynamic magnetic properties reveals that the oblate electron density distributions of the Tb3+, Dy3+, and U3+ metal ions within the axial ligand field lead to slow relaxation upon application of a small dc magnetic field. Significantly, the magnetization relaxation is orders of magnitude slower for the N-heterocyclic carbene complexes, M(BcMe)3, than for the isomeric pyrazolate complexes, M(BpMe)3. Further, investigation of magnetically dilute samples containing 11–14 mol % of Tb3+, Dy3+, or U3+ within the corresponding Y3+ complex matrix reveals thermally activated relaxation is favored for the M(BcMe)3 complexes, even when dipolar interactions are largely absent. Notably, ...

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Influence of Pyrazolate vs N‑Heterocyclic Carbene Ligands on the Slow Magnetic Relaxation of Homoleptic Trischelate Lanthanide(III) and Uranium(III) Complexes

Covalency in Ln–Cl bonds of Oh-LnCl6x– (x = 3 for Ln = CeIII, NdIII, SmIII, EuIII, GdIII; x = 2 for Ln = CeIV) anions has been investigated, primarily using Cl K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT); however, Ce L3,2-edge and M5,4-edge XAS were also used to characterize CeCl6x– (x = 2, 3). The M5,4-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 CeIII and CeIV). Pronounced mixing between the Cl 3p- and Ln 5d-orbitals (t2g* and eg*) was observed. Experimental results indicated that Ln 5d-orbital mixing decreased when moving across the lanthanide series. In contrast, oxidizing CeIII to CeIV had little effect on Cl 3p and Ce 5d-orbital mixing. For LnCl63– (formally LnIII), the 4f-orbitals participated only marginally in covalent bo...

Covalency in lanthanides. An X-ray absorption spectroscopy and density functional theory study of LnCl6(x-) (x = 3, 2).

In this Perspective we discuss a variety of methods that are broadly applicable to the syntheses of solid-state compounds. To illustrate the application of these methods we use solid-state actinide compounds, an area of chemistry that has been the focus of this laboratory for the last decade. We have synthesized single crystals, primarily of actinide chalcogenide compounds, by a variety of techniques. The benefits and drawbacks of each will be discussed in detail. Because of their propensity towards high coordination numbers and their ability to take on a variety of formal oxidation states, actinide compounds adopt structures illustrated here that are often different from those adopted by transition-metal or even lanthanide compounds. Often, there are corresponding differences in their physical properties, and these are touched upon here.

Syntheses and characterization of some solid-state actinide (Th, U, Np) compounds

Syntheses, structures, and magnetic and optical properties of the compounds [Hg3Te2][UCl6] and [Hg4As2][UCl6]

The compound La2U2Se9 was obtained in high yield from the stoichiometric reaction of the elements in an Sb2Se3 flux at 1123 K. The compound, which crystallizes in a new structure type in space grou...

La2U2Se9: an ordered lanthanide/actinide chalcogenide with a novel structure type.

The compounds Tl3Cu4USe6 and Tl2Ag2USe4 were synthesized by the reaction of the elements in excess TlCl at 1123 K. Both compounds crystallize in new structure types, in space groups P21/c and C2/m, respectively, of the monoclinic system. Each compound contains layers of USe6 octahedra and MSe4 (M = Cu, Ag) tetrahedra, separated by Tl+ cations. The packing of the octahedra and the tetrahedra within the layers is compared to the packing arrangements found in other layered actinide chalcogenides. Tl3Cu4USe6 displays peaks in its magnetic susceptibility at 5 and 70 K. It exhibits modified Curie–Weiss paramagnetic behavior with an effective magnetic moment of 1.58(1) μB in the temperature range 72–300 K, whereas Tl2Ag2USe4 exhibits modified Curie–Weiss paramagnetic behavior with μeff = 3.4(1) μB in the temperature range 100–300 K. X-ray absorption near-edge structure (XANES) results from scanning transmission X-ray spectromicroscopy confirm that Tl3Cu4USe6 has Se bonding characteristic of discrete Se2– units, ...

Pentavalent and tetravalent uranium selenides, Tl3Cu4USe6 and Tl2Ag2USe4: syntheses, characterization, and structural comparison to other layered actinide chalcogenide compounds.

The compound Ba(8)Hg(3)U(3)S(18) was obtained from the solid-state reaction at 1123 K of U, HgS, BaS, and S, with BaBr(2)/KBr or BaCl(2) as a flux. This material crystallizes in a new structure type in space group P6 of the hexagonal system with three formula units in a cell of dimensions a = 27.08(1) A, c = 4.208(2) A, and V = 2673(2) A(3). The structure contains infinite chains of US(6) octahedra and nearly linear [S-Hg-S](2-) dithiomercurate anions, separated by Ba(2+) cations. In the temperature range 100-300 K, the paramagnetic behavior of Ba(8)Hg(3)U(3)S(18) can be fit to the Curie-Weiss law, resulting in μ(eff) = 5.40(4) μ(B), or 3.12(2) μ(B)/U. The compound displays an antiferromagnetic transition at T(N) = 59 K. Although the formal oxidation states of Ba, Hg, and S can be assigned as +2, +2, and -2, the oxidation state of U is less certain. On the basis of interatomic distance arguments and the magnetic susceptibility data, the compound is proposed to contain U in both +4 and +5 formal oxidation states.

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Daniel E. Bugaris

Papers

Syntheses and characterization of some solid-state actinide (Th, U, Np) compounds

Syntheses, structures, and magnetic and optical properties of the compounds [Hg3Te2][UCl6] and [Hg4As2][UCl6]

La2U2Se9: an ordered lanthanide/actinide chalcogenide with a novel structure type.

Pentavalent and tetravalent uranium selenides, Tl3Cu4USe6 and Tl2Ag2USe4: syntheses, characterization, and structural comparison to other layered actinide chalcogenide compounds.

Ba8Hg3U3S18: a complex uranium(+4)/uranium(+5) sulfide.