Daniel Avignant

X-ray diffraction study of brabantite-monazite solid solutions

Abstract We synthesized compounds with stoichiometry of natural brabantite M2+Th(PO4)2 with M2+=Ca, Cd, Sr, Pb, Ba at 1 bar, 1200 °C and 2.5 kbar, 700 °C. Those compounds were studied by powder X-ray diffraction and electron microprobe. For Ca, Sr, and Pb, we obtained always crystals with the monazite structure. For Cd, the monazite structure is obtained at 1 bar, but not at 2.5 kbar. For Ba, we obtained the monazite structure only at 2.5 kbar. The unit-cell parameters of the compounds with monazite structure vary regularly with the size of the M2+ ion. We studied also the solid-solution LaPO4–M2+Th(PO4)2, at 1200 °C, 1 bar. The solid solutions for Cd, Ca, and Sr are continuous, and the unit-cell parameters vary linearly with the degree of substitution. For Pb, the solid solution is continuous, but the unit-cell parameters do not vary linearly. For Ba, there is a miscibility gap, with a maximum of about 50 mol% of BaTh(PO4)2 in LaPO4. These results have several consequences for U–Th–Pb geochronology of monazite, and for utilization of monazite as a nuclear-waste ceramic.

Improved Copper(I)–NHC Catalytic Efficiency on Huisgen Reaction by Addition of Aromatic Nitrogen Donors

A simple addition with a large impact: Addition of aromatic amines such as phenanthroline and 4-DMAP (4-dimethylaminopyridine) increases copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) catalytic activity of [CuCl(SIMes)] at a large range of temperatures in such a way that efficient catalysis can safely take place in hydro-alcoholic solvents (see scheme).

Single-crystal structure refinement and luminescence analysis of β-NaEuF4

Abstract The crystal structure of β -NaEuF 4 has been refined from single-crystal diffraction data. The obtained results confirm the previous description in the hexagonal P-6-C 1 3h space group reported by Burns. Three Eu 3+ centres could have been identified analysing the luminescence spectra of the titled compound. Two of them are related to the current C 3h sites. The third one which exhibits the most intense luminescence corresponds to the 2h cationic site (Na + ) (half occupied in the structure) partially substituted by Eu 3+ . Occurrence of this third Eu 3+ site obscures the features due to the other sites in luminescence spectra and explains the disagreement already noted between the optical study results and the crystallographic data for NaYF 4 :Eu 3+ .

A platinum Chugaev carbene complex as a potent anticancer agent

A platinum Chugaev complex was synthesised and fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. This cis bis acyclic diamino carbene complex acts as a cytotoxic compound and behaves as a cisplatin equivalent by interacting with supercoiled DNA and thiols. Stability of the ligand is also discussed.

Tris(1,10-phenanthroline-κ2N,N′)iron(II) bis­(1,1,3,3-tetra­cyano-2-eth­oxy­propenide) hemihydrate

In the title hydrated molecular salt, [Fe(C12H8N2)3](C9H5N4O)2·0.5H2O, the water molecule site is half-occupied. The Fe—N bond lengths within the octahedral tris-chelate [Fe(phen)3]2+ ion (phen is 1,10-phenantroline) are indicative of a low-spin d 6 electronic configuration for the metal ion. The C—N, C—C and C—O bond lengths in the polynitrile anions indicate extensive electronic delocalization. In the crystal, the components are linked through O—H⋯N hydrogen bonds, forming [100] chains, as well as through Coulombic interactions.

Structure and crystallization of lanthanum fluorozirconate glasses

Abstract Glasses with compositions (1 − x )ZrF 4 − x LnF 3 , 0.2 ≤ x ≤ 0.4 and Ln = La or La, Eu have been synthesized and investigated using differential scanning calorimetry, X-ray diffraction, Raman scattering and Eu 3+ optical spectroscopy. Single-phase polycrystalline lanthanum fluorozirconates with ratio equal to 1, 2 and 3 have been investigated using the same techniques for comparison. The crystalline phases LnZrF 7 , LnZr 2 F 11 , LT-LnZr 3 F 15 (orthorhombic) and HT-LnZr 3 F 15 (trigonal) have been characterized in the recrystallized glasses and in samples spontaneously crystallized from the melt. Another phase has also been observed but remains undefined. The Raman scattering spectra of the vitreous samples are related to the vibration modes of [ZrF 6 ] isolated octahedra, and of [ZrF 7 ] and [ZrF 8 ] structural units with bridging fluorine ions. The Eu 3+ fluorescence data are related to a predominant local environment of the lanthanide ions in the glasses similar to that of the lanthanide in LnZrF 7 .

Synthesis and single-crystal structural study of an originallow-temperatureform α of BaTbF6

BaTbF 6 is the first terbium(iv) fluoride for which a polymorphic phase transition at high temperature is evidenced. Whereas its high temperature form is isostructural with β-BaZrF 6 , the crystal structure of its low-temperature polymorph has been determined from single-crystal X-ray diffraction data and refined to conventional R=0.044 (R w =0.053) for 2880 independent reflections and 149 variable parameters. α-BaTbF 6 crystallizes in the triclinic system with space group P and unit-cell parameters a=7.344(1), b=8.4476(6), c=8.6770(9) A, α=101.63(8), β=96.89(1), γ=114.62(1)° and Z=4.  The three-dimensional structure may be regarded as a stacking along the c direction of alternated corrugated layers of Ba polyhedra and layers of Tb polyhedra built from [Ba 4 F 30 ] 22- and [Tb 4 F 26 ] 10- tetrameric complex anions respectively. The [Tb 4 F 26 ] 10- complex anion results from the association of four square antiprisms by sharing corners and edges.

Magnetic properties of the Tb4+ ion in Li2TbF6: Particular crystal chemical behavior within the Li2MIVF6 compounds

Abstract Magnetic properties of polycrystalline samples of Li2TbF6 were studied in high continuous magnetic fields up to 20 Teslas between 1.4 and 300 K. In this new structural type, all the results agree with the calculated Tb4+ free ion values ( 8 S 7 2 ground state multiplet), and the 4+ oxidation state of the terbium ion was unambiguously inferred. The particular crystal chemical behavior of the Tb4+ ion is discussed using the phase relationship within the series of Li2MIVF6 compounds.

Tetrahedral ferric iron in oxidized hydrous wadsleyite

Abstract Crystals of ferrous and ferric iron-bearing hydrous wadsleyite have been synthesized at 1400 °C and 12-13.5 GPa in a multi-anvil press. Crystal structures (atom positions, occupancies, and cell parameters) have been refined by single-crystal X‑ray diffraction at ambient conditions. Assuming cation vacancies to be in the M3 site only, their concentration has been estimated from the unit-cell parameter b/a ratio. Total refined site Fe contents are consistent with microprobe chemical analysis. There appears to be up to 11% iron (presumably ferric) in the tetrahedral site, consistent with reduced silica content (<1 Si per 4 O atoms) in the chemical analysis. Also the volume of the tetrahedron increases with increasing ferric iron content. Strong ordering of Fe in the octahedral sites is apparent in the order FeM3 ≥ FeM1 >> FeM2. The presence of ferric iron in the mantle transition zone is expected to partition preferentially into wadsleyite and may expand the stability region of wadsleyite relative to olivine and ringwoodite. Also, the observation of tetrahedral ferric iron in these samples increases the likelihood that there is compositional continuity between wadsleyite and the spinelloid III phase field observed in the Mg-free system fayalite-magnetite.

Recent progress in tetravalent terbium chemistry

Abstract The stability of the tetravalent state in Ln compounds has been the subject of numerous investigations. If tetravalent cerium compounds are among the most stable and can be handled with minor risk of decomposition, the existence of tetravalent praseodymium fluorides is of no doubt, but they cannot give rise to reliable experimental data. With regard to the terbium, it has now been established that the tetravalent oxidation state may be stabilized under certain circumstances. However, the terbium tetrafluoride itself exhibits a domain of thermal instability which has turned out to synthesize mixed-valence terbium fluorides, such as Tb 4 F 15 or KTb 3 F 12 . Up to now, there were no available crystallographic data from single-crystal works for the Tb 4+ ion. Obtaining single-crystals of Li 2 TbF 6 , KTbF 5 , CsTbF 5 , Li 2 CaTbF 8 , KTb 3 F 12 , both α and β-BaTbF 6 , represents a quantum leap in the capability of crystal structure determination and refinement. These results have brought a revival of the search for new Tb IV compounds which has lead to the discovery of a large family of LiLnTbF 8 fluorides, the structural relationships of which, with LiNaY 2 F 8 and BaY 2 F 8 , are discussed.