Heterometallic 20-membered {Fe16Ln4} (Ln = Sm, Eu, Gd, Tb, Dy, Ho) metallo-ring aggregates

The reaction of triethanolamine (teaH(3)) with [Fe(III)(3)O(O(2)CCH(3))(6)(H(2)O)(3)]Cl·6H(2)O and Ln(NO(3))(3)·6H(2)O in acetonitrile yields [Fe(16)Ln(4)(tea)(8)(teaH)(12)(μ-O(2)CCH(3))(8)](NO(3))(4)·16H(2)O·xMeCN (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6); x = 10 or 11). These 20-membered metallo-ring complexes are the largest such single-stranded oxygen-bridged rings so far reported. The structure is stabilised by two of the acetate ligands, which form anti,anti-bridges across the centre of the ring, pinching the ring and giving it rigidity. The magnetic properties are dominated by the antiferromagnetic couplings between the Fe(III) centres. Although the Fe(2) and Fe(6) sub-chains within the ring are fully spin-compensated at low temperatures with S(subchain) = 0, coupling between the Gd(III) cations and the Fe(III) centres at the ends of the sub-chains (in 3) results in a pinning of the lanthanide spins. The (57)Fe M?ssbauer spectra of 3 and 5 obtained at low temperatures are consistent with the presence of Fe(III) intracluster strong antiferromagnetic coupling. The applied field spectrum for 3 reveals no magnetic hyperfine interaction apart from that of the nucleus with the applied field, while the one for 5 is a superposition of three subspectra which show contributions from each of the peripheral as well as from the central iron sites.     

Magnetic properties of Ln2−xLn′xCo17 compounds (Ln = Gd,Dy, Ho,or Er,Ln′ = Th or Ce)

Magnetic and structural characteristics of the ternary systems Ln_2?xTh_xCo₁₇ (Ln = Gd, Dy, Ho, and Er) and Ln_2?xCe_xCo₁₇ (Ln = Gd, Dy, and Ho) are presented. Incorporation of Th in the lattice stabilizes the Th₂Zn₁₇ structure, whereas incorporation of Ce does not; if the binary system has the Th₂Ni₁₇ structure the incorporation of Ce leaves the structure unchanged. The antiferromagnetic LnCo coupling observed in the Ln₂Co₁₇ systems persists in the ternary alloys. The moment of the cobalt sublattice is decreased when more than half of the Ln is replaced by Th, suggesting that the extra electron contributed by Th enters the Co d-band or d-shell. The direction of easy magnetization is in the basal plane for all composition in the Gd, Dy, and Ho systems. In Er_2?xTh_xCo₁₇ the easy direction is along the c-axis for x = 0 and 0.2, but is in the basal plane for higher thorium contents.     

Synthese und Kristallstruktur von Ln2SeSiO4 (Ln = Sm,Dy, Ho) und Sm2TeSiO4

Synthesis and Crystal Structure of Ln₂SeSiO₄ (Ln = Sm, Dy, Ho) and Sm₂TeSiO₄ Single crystals of Ln₂SeSiO₄ (Ln = Sm, Dy, Ho) could be prepared by the reaction of lanthanide metal, selenium and iodine in the ratio 1 : 1 : 2.5 and subsequent reaction with quartz glass powder. Black crystals of Sm₂TeSiO₄ have been obtained in chemical transport experiments of SmTe₂ with iodine in evacuated quartz glass ampoules as by‐products. All chalcogenide silicates crystallize orthorhombically with the space group Pbcm (Z = 4) and the lattice constants: Sm₂SeSiO₄: a = 612.6(1) pm, b = 709.0(1) pm, c = 1094.0(2) pm; Dy₂SeSiO₄: a = 603.6(1) pm, b = 696.4(1) pm, c = 1081.2(2) pm; Ho₂SeSiO₄: a = 601.0(1) pm, b = 693.6(1) pm, c = 1078.6(2) pm; Sm₂TeSiO₄: a = 623.82(8) pm, b = 713.06(7) pm, c = 1112.26(11) pm. The crystal structure is built up of alternating Ln(Se/Te) and LnSiO₄ sheets parallel (001).     

Family of double-cubane Mn4Ln2 (Ln = Gd, Tb, Dy, Ho) and Mn4Y2 complexes: a new Mn4Tb2 single-molecule magnet

The synthesis and characterization of a family of Mn(2)(III)Mn(2)(II)Ln(III)(2) complexes (Ln = Gd (1), Tb (2), Dy (3), and Ho (4)) of formula [Mn(4)Ln(2)O(2)(O(2)CBu(t))(6)(edteH(2))(2)(NO(3))(2)] are reported, where edteH(4) is N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine. The analogous Mn(4)Y(2) (5) complex has also been prepared. They were obtained from reaction of Ln(NO(3))(3) or Y(NO(3))(3) with Mn(O(2)CBu(t))(2), edteH(4), and NEt(3) in a 2:3:1:2 molar ratio. The crystal structures of representative 1 and 2 were obtained, and their core consists of a face-fused double-cubane [Mn(4)Ln(2)(μ(4)-O(2-))(2)(μ(3)-OR)(4)] unit. Such double-cubane units are extremely rare in 3d metal chemistry and unprecedented in 3d-4f chemistry. Variable-temperature, solid-state dc and ac magnetic susceptibility studies on 1-5 were carried out. Fitting of dc χ(M)T vs T data for 5 gave J(bb) (Mn(III)···Mn(III)) = -32.6(9) cm(-1), J(wb) (Mn(II)···Mn(III)) = +0.5(2) cm(-1), and g = 1.96(1), indicating a |n, 0, n> (n = 0-5) 6-fold-degenerate ground state. The data for 1 indicate an S = 12 ground state, confirmed by fitting of magnetization data, which gave S = 12, D = 0.00(1) cm(-1), and g = 1.93(1) (D is the axial zero-field splitting parameter). This ground state identifies the Mn(II)···Gd(III) interactions to be ferromagnetic. The ac susceptibility data independently confirmed the conclusions about 1 and 5 and revealed that 2 displays slow relaxation of the magnetization vector for the Mn(4)Tb(2) analogue 2. The latter was confirmed as a single-molecule magnet by observation of hysteresis below 0.9 K in magnetization vs dc field scans on a single crystal of 2·MeCN on a micro-SQUID apparatus. The hysteresis loops also displayed well-resolved quantum tunneling of magnetization steps, only the second 3d-4f SMM to do so.     

Microwave synthesis and photoluminescent properties of Sr2CeO4/Ln3+ (Ln = Er, Ho, Tm)

Sr₂CeO₄/Ln³⁺ (Ln = Er, Ho, Tm) phosphors were synthesized with the microwave radiation method for the first time. The luminescent properties of the samples were investigated and the up-conversion luminescence of Er³⁺, Ho³⁺ and Tm³⁺ doped Sr₂CeO₄ phosphors was observed. The spectra indicate that the energy transfer takes place from the triplet excited state of MLCT (metal-to-ligand charge transfer) state for Sr₂CeO₄ (sensitizer) to the rare earth ions (activator). __________ Translated from Journal of Hebei Normal University (Natural Science Edition), 2007, 31(2): 212–216 [译自: 河北师范大学学报 (自然科学版)]     

On the Perovskites Ba2LnSbO6 (Ln = Nd,Sm, Eu,Gd, Tb,Dy, Ho,Er, Yb)

Polycrystalline Ba₂LnSbO₆ (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb) are cubic, perovskite-type compounds, space group Fm3m (No. 225), Z = 4, with a values from a = 8.544(2) Å for Ba₂NdSbO₆ to a = 8.368(1) Å for Ba₂YbSbO₆. X-ray diffraction data for all the compounds and the results of magnetic measurements for two of them are given.     

Defect-dicubane Ni2Ln2 (Ln = Dy, Tb) single molecule magnets

Two pairs of Ni(2)Dy(2) and Ni(2)Tb(2) complexes, [Ni(2)Ln(2)(L)(4)(NO(3))(2)(DMF)(2)] {Ln = Dy (1), Tb (2)} and [Ni(2)Ln(2)(L)(4)(NO(3))(2)(MeOH)(2)]·3MeOH {Ln = Dy (3), Tb (4)} (H(2)L is the Schiff base resulting from the condensation of o-vanillin and 2-aminophenol) possessing a defect-dicubane core topology were synthesized and characterized. All four complexes are ferromagnetically coupled, and the two Dy-analogues are found to be Single Molecule Magnets (SMMs) with energy barriers in the range 18-28 K. Compound 1 displays step-like hysteresis loops, confirming the SMM behavior. Although 1 and 3 show very similar structural topologies, the dynamic properties of 1 and 3 are different with blocking temperatures (3.2 and 4.2 K at a frequency of 1500 Hz) differing by 1 K. This appears to result from a change in orientation of the nitrate ligands on the Dy(III) ions, induced by changes in ligands on Ni(II).     

Fluoroplatinate(IV) der Lanthaniden LnF[PtF6]. (Ln = Pr,Sm, Gd,Tb, Dy,Ho, Er)

Fluoroplatinates(IV) of the Lanthanides LnF[PtF₆] (Ln = Pr, Sm, Gd, Tb, Dy, Ho, Er) For the first time fluorides LnF[PtF₆] (Ln = Pr, Sm, Gd, Tb, Dy, Ho, Er), all yellow have been obtained. From single crystal data they crystallize monoclinic, space group P2₁/n?C (No. 14), Z = 4, Pr: a = 1 125.77(19) pm, b = 559.04(7) pm, c = 910.27(17) pm, β = 107.29(1)°; Sm: a = 1 114.63(31) pm, b = 552.70(12) pm, c = 898.02(20) pm, β = 107.24(2)°; Gd: a = 1 112.12(15) pm, b = 551.22(7) pm, c = 891.99(11) pm, β = 107.09(1)°; Tb (Powder data): a = 1 108.88(20) pm, b = 552.71(9) pm, c = 889.56(16) pm, β = 107.30(1)°; Dy: a = 1 100.28(23) pm, b = 547.77(8) pm, c = 882.41(13) pm, β = 107.32(1); Ho: a = 1 099.11(16) pm, b = 546.16(7) pm, c = 879.45(15) pm, β = 107.34(1)°; Er: a = 1 095.10(16) pm, b = 544.82(10) pm, c = 874.85(14) pm, β = 107.37(1)°.     

Synthesis and characterization of ethylthioethylcyclopentadienyl organolanthanide complexes: CpLnCl (Ln=Gd,Dy), Cp2LnCpTh (Ln=Yb,Sm, Dy,Y) and CpThErCl2·2THF

Six new ethylthioethylcyclopentadienyl containing organolanthanide complexes CpLnCl [Ln=Gd (1), Dy (2)] and Cp₂LnCp^Th [Cp=C₅H₅, Ln=Yb (3), Sm (4), Dy (5), Y (6)] were synthesized by the reaction of ethylthioethyl‐cyclopentadienyl (Cp^Th) sodium salt with LnCl₃ or Cp₂LnCl in THF. Complexes 1–6 were characterized by elemental analyses, infrared and mass spectroscopies. The molecular structures of complexes 1–3 were also determined by the X‐ray single crystal diffraction. The results show that the side‐chain sulfur atom on the ethylthioethylcyclopentadienyl ring can form intramolecular chelating coordination to the central lanthanide ion, improving the stability of organolanthanide complexes and reducing the number of coordinated THF molecules.     

Trapping of anionic organic radicals by (TpMe2)2Ln (Ln = Sm, Eu)

Stoichiometric reaction of [ Sm(Tp(Me2))2 ], 1, with a variety of reducible ketone- and quinone-type substrates gave thermally stable, isolable radical anions/ketyls in moderate to good yields. Thus reaction with benzophenone gave [Sm(Tp(Me2))2(OCPh2)], 2, with fluorenone [Sm(Tp(Me2))2(eta1-OC13H8)], 3, and di-tert-butylparaquinone [Sm(Tp(Me2))2(eta1-OC6H2(tBu)2O)], 4, each of which was structurally characterized. In the case of the less-hindered benzoquinone, an unimetallic semiquinone [Sm(Tp(Me2))2(OC6H4O)], 5, could be isolated, although it was unstable with respect to formation of the dimetallic complex [Sm(Tp(Me2))2]2(mu-OC6H4O), 6. Compound 6 was structurally characterized, as was its anthraquinone analogue [Sm(Tp(Me2))2]2(mu-OC14H8O), 7. When the analogous reaction was carried out between the less-reducing [Eu(Tp(Me2))2] and benzoquinone, only the europium analogue of the semiquinone 5, [Eu(Tp(Me2))2(OC6H4O)], 8, could be isolated. The use of the sterically hindered 3,5-di-tert-butyl-o-benzoquinone allowed isolation of [Sm(Tp(Me2))2(DTBSQ)], 9.     

A family of 3d-4f octa-nuclear [Mn(III)(4)Ln(III)(4)] wheels (Ln = Sm, Gd, Tb, Dy, Ho, Er, and Y): synthesis, structure, and magnetism

We present the syntheses, crystal structures, and magnetochemical characterizations for a family of isostructural [Mn(4)Ln(4)] compounds (Ln = Sm, Gd, Tb, Dy, Ho, Er, and Y). They were prepared from the reactions of formic acid, propionic acid, N-n-butyl-diethanolamine, manganese perchlorate, and lanthanide nitrates under the addition of triethylamine in MeOH. The compounds possess an intriguing hetero-octanuclear wheel structure with four Mn(III) and four Ln(III) ions alternatively arranged in a saddle-like ring, where formate ions act as key carboxylate bridges. In the lattice, the molecules stack into columns in a quasi-hexagonal arrangement. Direct current (dc) magnetic susceptibility measurements indicated the depopulation of the Stark components at low temperature and/or very weak antiferromagnetic interactions between magnetic centers. The zero-field alternating current (ac) susceptibility studies revealed that the compounds containing Sm, Tb, and Dy showed frequency-dependent out-of-phase signals, indicating they are single-molecule magnets (SMMs). Magnetization versus applied dc field sweeps on a single crystal of the Dy compound down to 40 mK exhibited hysteresis depending on temperatures and field sweeping rates, further confirming that the Dy compound is a SMM. The magnetization dynamics of the Sm and Y compounds investigated under dc fields revealed that the relaxation of the Sm compound is considered to be dominated by the two-phonon (Orbach) process while the Y compound displays a multiple relaxation process.     

Syntheses, structures, and physical properties of LnAsTe (Ln = La, Pr, Sm, Gd, Dy, Er)

Six rare-earth arsenic tellurides have been synthesized by the reactions of the rare-earth elements (Ln) with As and Te at 1123 K. LaAsTe (a = 7.8354(11) A, b = 4.1721(6) A, c = 10.2985(14) A, T = 153 K), PrAsTe (a = 7.728(2) A, b = 4.1200(11) A, c = 10.137(3) A, T = 153 K), SmAsTe (a = 7.6180(16) A, b = 4.0821(9) A, c = 9.991(2) A, T = 153 K), GdAsTe (a = 7.5611(15) A, b = 4.0510(8) A, c = 9.920(2) A, T = 153 K), DyAsTe (a = 7.4951(13) A, b = 4.0246(7) A, c = 9.8288(17) A, T = 153 K), and ErAsTe (a = 7.4478(1) A, b = 4.0078(1) A, c = 9.7552(2) A, T = 153 K) crystallize with four formula units in the orthorhombic space group D2h16-Pnma. These compounds are isostructural and belong to the beta-ZrSb2 structure type. In each compound, the Ln atoms are coordinated by a tricapped trigonal prism of four As atoms and five Te atoms. The entire three-dimensional structure is built up by the motif of the LnAs4Te5 tricapped trigonal prisms. Infinite nonalternating zigzag As chains are found along the b axis, with As-As distances in these compounds ranging from 2.5915(5) to 2.6350(9) A. Conductivity measurements in the direction of these As chains indicate that PrAsTe is metallic whereas SmAsTe and DyAsTe are weakly metallic. Antiferromagnetic transitions occur in SmAsTe and DyAsTe at 3 and 9 K, respectively. DyAsTe above 9 K follows the Curie-Weiss law.     

Hydrothermal synthesis, dimension evolution and luminescence properties of tetragonal LaVO4:Ln (Ln = Eu3+, Dy3+, Sm3+) nanocrystals

Well-defined 1D and 3D t-LaVO(4):Ln (Ln = Eu(3+), Dy(3+), Sm(3+)) nanocrystals with regular and uniform shapes were synthesized through a simple hydrothermal route assisted by disodium ethylenediaminetetraacetic acid (Na(2)EDTA). X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), as well as kinetic decay curves were employed to characterize the samples. The results show that the reaction time, pH value of the initial solution, and Na(2)EDTA/La(3+) molar ratio all have an important influence on the dimension and shapes of the final products. By introducing the "splitting mechanism" to the dimension and morphology evolution process from one-dimensional (1D) to three-dimensional (3D) t-LaVO(4) crystals, the nucleation and crystal growth processes were well demonstrated. The Ln(3+) ions doped t-LaVO(4) samples exhibit respective bright red, blue-white and orange luminescence of Eu(3+), Dy(3+), and Sm(3+) under ultraviolet excitation, and have potential application in the fields of colour display, UV laser and biomedicine. The results not only expand the knowledge of the properties of lanthanide orthovanadates luminescence, but also contribute to the principles of the crystal growth and dimension transition of this kind of inorganic material.     

Synthesis, structure and magnetic properties of linear heterobimetallic trinuclear Mn2Ln (Ln = Eu, Gd, Dy) complexes

The reaction of (S)P[N(CH(3))N[double bond, length as m-dash]CH-C(6)H(3)-2-OH-3-OCH(3)](3) with a Mn(II) salt followed by a Ln(III) salt (Ln = Eu, Gd and Dy), afforded linear heterometallic complexes [L(2)Mn(2)Ln](+) that showed interesting magnetic properties.     

General synthesis and structural evolution of a layered family of Ln8(OH)20Cl4 x nH2O (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y)

The synthesis process and crystal structure evolution for a family of stoichiometric layered rare-earth hydroxides with general formula Ln(8)(OH)(20)Cl(4) x nH(2)O (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y; n approximately 6-7) are described. Synthesis was accomplished through homogeneous precipitation of LnCl(3) x xH(2)O with hexamethylenetetramine to yield a single-phase product for Sm-Er and Y. Some minor coexisting phases were observed for Nd(3+) and Tm(3+), indicating a size limit for this layered series. Light lanthanides (Nd, Sm, Eu) crystallized into rectangular platelets, whereas platelets of heavy lanthanides from Gd tended to be of quasi-hexagonal morphology. Rietveld profile analysis revealed that all phases were isostructural in an orthorhombic layered structure featuring a positively charged layer, [Ln(8)(OH)(20)(H(2)O)(n)](4+), and interlayer charge-balancing Cl(-) ions. In-plane lattice parameters a and b decreased nearly linearly with a decrease in the rare-earth cation size. The interlamellar distance, c, was almost constant (approximately 8.70 A) for rare-earth elements Nd(3+), Sm(3+), and Eu(3+), but it suddenly decreased to approximately 8.45 A for Tb(3+), Dy(3+), Ho(3+), and Er(3+), which can be ascribed to two different degrees of hydration. Nd(3+) typically adopted a phase with high hydration, whereas a low-hydration phase was preferred for Tb(3+), Dy(3+), Ho(3+), Er(3+), and Tm(3+). Sm(3+), Eu(3+), and Gd(3+) samples were sensitive to humidity conditions because high- and low-hydration phases were interconvertible at a critical humidity of 10%, 20%, and 50%, respectively, as supported by both X-ray diffraction and gravimetry as a function of the relative humidity. In the phase conversion process, interlayer expansion or contraction of approximately 0.2 A also occurred as a possible consequence of absorption/desorption of H(2)O molecules. The hydration difference was also evidenced by refinement results. The number of coordinated water molecules per formula weight, n, changed from 6.6 for the high-hydration Gd sample to 6.0 for the low-hydration Gd sample. Also, the hydration number usually decreased with increasing atomic number; e.g., n = 7.4, 6.3, 7.2, and 6.6 for high-hydration Nd, Sm, Eu, and Gd, and n = 6.0, 5.8, 5.6, 5.4, and 4.9 for low-hydration Gd, Tb, Dy, Ho, and Er. The variation in the average Ln-O bond length with decreasing size of the lanthanide ions is also discussed. This family of layered lanthanide compounds highlights a novel chemistry of interplay between crystal structure stability and coordination geometry with water molecules.     

Tuning of optical band gaps: syntheses, structures, magnetic properties, and optical properties of CsLnZnSe(3) (Ln = Sm, Tb, Dy, Ho, Er, Tm, Yb, and Y)

Eight new quaternary selenides CsSmZnSe(3), CsTbZnSe(3), CsDyZnSe(3), CsHoZnSe(3,) CsErZnSe(3), CsTmZnSe(3), CsYbZnSe(3), and CsYZnSe(3) have been synthesized with the use of high-temperature solid-state experimental methods. These compounds are isostructural with KZrCuS(3), crystallizing with four formula units in the orthorhombic space group Cmcm. The structure of these CsLnZnSe(3) compounds is composed of [LnZnSe(3)(-)] layers separated by Cs atoms. The Ln atom is octahedrally coordinated by six Se atoms, the Zn atom is tetrahedrally coordinated by four Se atoms, and the Cs atom is coordinated by a bicapped trigonal prism of eight Se atoms. Because there are no Se-Se bonds in the structure, the oxidation state of Cs is 1+, that of Ln is 3+, and that of Zn is 2+. CsYbZnSe(3) exhibits an antiferromagnetic transition at 11 K, whereas CsSmZnSe(3) does not follow a Curie-Weiss law. The remaining rare-earth compounds are paramagnetic, and the calculated effective magnetic moments of the rare-earth ions agree well with their theoretical values. Optical absorption data on face-indexed single crystals of CsSmZnSe(3), CsErZnSe(3), CsYbZnSe(3), and CsYZnSe(3) demonstrate that the optical band gap changes by more than 0.75 eV with the composition and by as much as 0.20 eV with the crystal orientation. The optical band gaps range from 2.63 eV (CsSmZnSe(3), CsErZnSe(3)) to 1.93 eV (CsYbZnSe(3)) for the (010) crystal face and 2.56 eV (CsErZnSe(3)) to 1.88 eV (CsYbZnSe(3)) for the (001) crystal face. The difference in the optical band gap of the (010) face vs the (001) face varies from +0.05 eV (CsYbZnSe(3)) to +0.20 eV (CsSmZnSe(3)).     

A new family of octanuclear Cu4Ln4 (Ln = Gd, Tb and Dy) spin clusters

The reaction of Cu(OAc)2 and Ln(OAc)3 (Ln = Gd, Tb and Dy) with 2-amino-2-methyl-1,3-propanediol (ampdH2) under solvothermal conditions has afforded a new family of isostructural octanuclear Cu4Ln4 complexes with the formula [Cu4Ln4(OAc)12(ampdH)8(OH2)2] (Ln = Gd (1), Tb (2) and Dy(3)) in good yield. Variable temperature magnetic susceptibility measurements reveal weak intramolecular exchange interactions for 1 and 2. Ferromagnetic coupling is observed for 1 and attributed to Cu...Gd interactions. In contrast, the magnetic susceptibility behaviour of 2 arises from a combination of intramolecular exchange interactions and the crystal field splitting of the (7)F6 ground state of the Tb(III) ions.     

Structure determination of KScS2, RbScS2 and KLnS2 (Ln = Nd,Sm, Tb,Dy, Ho,Er, Tm and Yb) and crystal–chemical discussion

The title structures of KScS₂ (potassium scandium sulfide), RbScS₂ (rubidium scandium sulfide) and KLnS₂ [Ln = Nd (potassium neodymium sufide), Sm (potassium samarium sulfide), Tb (potassium terbium sulfide), Dy (potassium dysprosium sulfide), Ho (potassium holmium sulfide), Er (potassium erbium sulfide), Tm (potassium thulium sulfide) and Yb (potassium ytterbium sulfide)] are either newly determined (KScS₂, RbScS₂ and KTbS₂) or redetermined. All of them belong to the α‐NaFeO₂ structure type in agreement with the ratio of the ionic radii r³⁺/r⁺. KScS₂, the member of this structural family with the smallest trivalent cation, is an extreme representative of these structures with rare earth trivalent cations. The title structures are compared with isostructural alkali rare earth sulfides in plots showing the dependence of several relevant parameters on the trivalent cation crystal radius; the parameters thus compared are c, a and c/a, the thicknesses of the S—S layers which contain the respective constituent cations, the sulfur fractional coordinates z(S²⁻) and the bond‐valence sums.     

Structures of nonlinear hexagonal boratotungstates Ln3BWO9 (Ln = La, Pr, Nd, Sm, Gd, Tb, Dy)

Polycrystalline boratotungstates of composition Ln₃BWO₉ (Ln = Pr, Nd, Sm, Gd, Tb, Dy) are prepared by solid-phase synthesis and structurally studied. The structures are refined using the Rietveld method for hexagonal space group P6₃ (Z = 2). The boratotungstate structures are frameworks. The rare-earth cations in the structure are coordinated by an array of nine oxygen atoms (three oxygen atoms from borato groups BO₃ and six from WO₆ polyhedra). The nature of the optical nonlinearity in the hexagonal boratotungstates Ln₃BWO₉ is a direct consequence of the acentricity of both the tungstate and the rare-earth polyhedra in the structure. Dimorphism is discovered in polycrystalline La₃BWO₉.