Assisted Self-Assembly to Target Heterometallic Mn-Nd and Mn-Sm SMMs: Synthesis and Magnetic Characterisation of [Mn7Ln3(O)4(OH)4(mdea)3(piv)9(NO3)3] (Ln=Nd,Sm, Eu,Gd)**

In an assisted self-assembly approach starting from the [Mn₆O₂(piv)₁₀(4-Me-py)₂(pivH)₂] cluster a family of Mn−Ln compounds (Ln=Pr−Yb) was synthesised. The reaction of [Mn₆O₂(piv)₁₀(4-Me-py)₂(pivH)₂] ( 1 ) with N-methyldiethanolamine (mdeaH₂) and Ln(NO₃)₃ ⋅ 6H₂O in MeCN generally yields two main structure types: for Ln=Tb−Yb a previously reported Mn₅Ln₄ motif is obtained, whereas for Ln=Pr−Eu a series of Mn₇Ln₃ clusters is obtained. Within this series the Gd^III analogue represents a special case because it shows both structural types as well as a third Mn₂Ln₂ inverse butterfly motif. Variation in reaction conditions allows access to different structure types across the whole series. This prompts further studies into the reaction mechanism of this cluster assisted self-assembly approach. For the Mn₇Ln₃ analogues reported here variable-temperature magnetic susceptibility measurements suggest that antiferromagnetic interactions between the spin carriers are dominant. Compounds incorporating Ln=Nd^III( 2 ), Sm^III( 3 ) and Gd^III ( 5 ) display SMM behaviour. The slow relaxation of the magnetisation for these compounds was confirmed by ac measurements above 1.8 K.     

Neue Vertreter des Er6[Si11N20]O‐Strukturtyps Hochtemperatur‐Synthesen und Kristallstrukturen von Ln(6+x/3)[Si(11–y)AlyN(20+x–y)]O(1–x+y) mit Ln = Nd,Er, Yb,Dy und 0 ≤ x ≤ 3, 0 ≤ y ≤ 3

New Representatives of the Er₆[Si₁₁N₂₀]O Structure Type. High‐Temperature Synthesis and Single‐Crystal Structure Refinement of Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) with Ln = Nd, Er, Yb, Dy and 0 ≤ x ≤ 3, 0 ≤ y ≤ 3 According to the general formula Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) (0 ≤ x ≤ 3, 0 ≤ y ≤ 3) four nitridosilicates, namely Er₆[Si₁₁N₂₀]O, Yb_6.081[Si₁₁N_20.234]O_0.757, Dy_0.33Sm₆[Si₁₁N₂₀]N, and Nd₇[Si₈Al₃N₂₀]O were synthesized in a radiofrequency furnace at temperatures between 1300 and 1650 °C. The homeotypic crystal structures of all four compounds were determined by single‐crystal X‐ray diffraction. The nitridosilicates are trigonal with the following lattice constants: Er₆[Si₁₁N₂₀]O: a = 978.8(4) pm, c = 1058.8(3) pm; Yb_6.081[Si₁₁N_20.243]O_0.757: a = 974.9(1) pm, c = 1055.7(2) pm; Dy_0.33Sm₆[Si₁₁N₂₀]N: a = 989.8(1) pm, c = 1078.7(1) pm; Nd₇[Si₈Al₃N₂₀]O: a = 1004.25(9) pm, c = 1095.03(12) pm. The crystal structures were solved and refined in the space group P31c with Z = 2. The compounds contain three‐dimensional networks built up by corner sharing SiN₄ and AlN₄ tetrahedra, respectively. The Ln³⁺ and the “isolated” O^2– ions are situated in the voids of the structures. According to Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) an extension of the Er₆[Si₁₁N₂₀]O structure type has been found.     

Untersuchungen zum Existenzgebiet des CaAl2Si2-Strukturtyps bei ternären Siliciden

Investigations about the Stability Range of the CaAl₂Si₂ Type Structure in the Case of Ternary Silicides Five compounds LnAl₂Si₂ (Ln: trivalent rare-earth metal, Y) were synthesized by heating the elements at 800°–1000 °C. They are isotypic and crystallize in the CaAl₂Si₂ type structure (P 3 m1; Z = 1) (lattice constants see “Inhaltsübersicht”). The electronic structures (LMTO band structure calculations) of CaAl₂Si₂ and YAl₂Si₂, the latter one is in accordance to Ln³⁺(Al³⁺)₂(Si^4–)₂ not electrovalent, are discussed with regard to the bondings and the electrical conductivity respectively. Investigations of GdAl_2–xMn_xSi₂ mixed crystals showed, that the structure type already at low Mn content (x ≈ 0,3) changes from CaAl₂Si₂ (GdAl₂Si₂) to ThCr₂Si₂ type structure (GdMn₂Si₂).     

New developments in the chemistry of heteropolytungstates of rhodium and cerium

The heteropolytungstates [PW₁₁O₃₉RhCl]⁵⁻ (I), [PW₁₁O₃₉RhCH₂COOH]⁵⁻ (III), and [PW₁₁O₃₉Rh₂(OAc)₂]⁵⁻ (IV) are prepared by hydrothermal reaction of [PW₁₁O₃₉]⁷⁻ with RhCl₃ or Rh₂(OAc)₄ and characterized by NMR and X-ray structure determination. Electrolytic reduction of I yields the dimeric species [(PW₁₁O₃₉Rh₂)]¹⁰⁻ (II) which reacts with C₆H₅CH₂Br under photochemical conditions to yield dibenzyl and [PW₁₁O₃₉RhBr]⁵⁻ in a process analogous to Rh-porphyrins. Anion III and the corresponding Sicentered anion are rare examples of complexes with Rh-C bonds prepared in aqueous solution. Reaction of B-α [As^IIIW₉O₃₃]⁹⁻ with Ln^III yields new, massive heteropolytungstates [As₂Ln₂(H₂O)W₂₉O₁₀₃]¹⁷⁻ Ln = La, Ce(V), [Ce₄(H₂O)₄ − 4x(AsW₉O₃₃)₄As(WO₃)_{2 + x}(WO₅)]²⁵⁻, x < 0.5 (VI), and As₁₂Ln₁₆(H₂O)₃₆W₁₈₄O₃₂₄]⁷⁶⁻; Ln La,Ce (VII) with approximate relative molecular masses of 7 600, 10 500, and 40 000 respectively. Anion VII has a folded cyclic structure with a radius of 4 nm and is the largest heteropolytungstate so far reported. It is synthesized in yields of ca 30 % under mild conditions.     

Preparation and Electrical Properties of Lnx(SiO4)6O(1.5x?12) (Ln: Nd, La) with Apatite Structure

In this study, Ln_x(SiO₄)₆O_(1.5x–12) (Ln: Nd, La) materials as electrolytes for solid oxide fuel cells (SOFC) were prepared by the sol-gel process. It has been reported that the apatite structure of Ln_x(SiO₄)₆O_(1.5x–12) shows higher ionic conductivity than yttrium-stabilized zirconium oxide at the working temperature of the SOFC. Ln₁₀(SiO₄)₆O₃ is a major component of the Ln_x(SiO₄)₆O_(1.5x–12) system. Ln₁₀(SiO₄)₆O₃ consists of Ln_9.33(SiO₄)₆O₂ and a small amount of Ln₂SiO₅. It has been proposed that the ionic conductivity of Ln_x(SiO₄)₆O_(1.5x–12) decreases with increasing Ln₂SiO₅ with non-apatite structure. The object of the present study was to bring about this decrease by generating Ln₂SiO₅ in the system.Precursor solutions for synthesis of the powder were prepared using tetraethoxysilane (Si(OC₂H₅)₄) and neodymium acetate monohydrate (Nd(CH₃COO)₃·H₂O) or lanthanum acetate monohydrate (La (CH₃COO)₃·H₂O) as raw materials and acetic acid (CH₃COOH), 2-methoxyethanol (C₂H₅OCH₂CH₂OH), and triethanolamine (N(CH₂CH₂OH)₃) as solvents. To obtain the powder, the solution was dried and heat-treated at 600 °C for 2 h. Disks made from the powder were heat-treated at temperatures between 1100 and 1500 °C for 10 h. The results of an XRD investigation indicate that almost all diffraction peaks of these samples could be assigned to Ln_9.33(SiO₄)₆O₂. The sample with x = 10.00 included a small amount of Ln₂SiO₅. The ionic conductivity of this latter sample was higher than that of other samples with similar values of x (x = 9.33 and 10.67).     

Synthesis and Luminescence Properties of Amber Emitting La7Sr[Si10N19O3] : Eu2+ and Syntheses of the Substitutional Variants RE8-xAEx[Si10N20-xO2+x] : Eu2+ with RE=La,Ce; AE=Ca,Sr, Ba; 0≤x≤2

The oxonitridosilicate La₇Sr[Si₁₀N₁₉O₃] : Eu²⁺ and its substitutional variants RE_8-xAE_x[Si₁₀N_20-xO_2+x] : Eu²⁺ with RE=La, Ce; AE=Ca, Sr, Ba and 0≤x≤2 were synthesized starting from REN, SrN/Ca₃N₂/Ba₂N, SiO₂, amorphous Si₃N₄ and Eu₂O₃ as doping agent at 1600 °C in a radiofrequency furnace. The crystal structure of La₇Sr[Si₁₀N₁₉O₃] was solved and refined based on single-crystal X-ray diffraction data. La₇Sr[Si₁₀N₁₉O₃] crystallizes in the orthorhombic space group Pmn2₁ (no. 31). The crystal structures of the isotypic compounds RE_8-xAE_x[Si₁₀N_20-xO_2+x] were confirmed by Rietveld refinements based on powder X-ray diffraction data using the single-crystal data of La₇Sr[Si₁₀N₁₉O₃] as starting point. Crystal structure elucidation reveals a 3D network of vertex sharing SiN₄ and SiN₂(N_1/2-x/4O_1/2+x/4)₂ (0≤x≤2) tetrahedra. When excited with UV to blue light, La₇Sr[Si₁₀N₁₉O₃] : Eu²⁺ shows amber luminescence with λ_em=612 nm and fwhm=84 nm/2194 cm⁻¹, which makes it interesting for application in amber phosphor-converted light emitting diodes.     

Ionic conductivity and crystal chemistry of ramsdellite type compounds,Li2+x(LixMg1−xSn3)O8, 0 ≤ x ≤ 0.5 and Li2Mg1−xFe2xSn3−xO8, 0 ≤ x ≤ 1

Solid solution phases Li_2+x(Li_xMg_1−xSn₃)O₈: 0 ≤ x ≤ 0.5 and Li₂Mg_1−xFe_2xSn_3−xO₈: 0 ≤ x ≤ 1, both with ramsdellite type structure, have been synthesized by solid state reaction at 1773 and 1523 K, respectively. The relationship of the ramsdellite structure to the recently illustrated, tetragonal-packed structure is given. The Li_2+x(Li_xMg_1−xSn₃)O₈ solid solutions exhibit conductivities 4 × 10⁻⁶–5 × 10⁻⁴ (Ω cm)⁻¹ at 573 K and corresponding activation energies, 0.93−0.74 eV. The highest conductivity was observed for Li_2.3(Li_0.3Mg_0.7Sn₃)O₈, x = 0.3. In the solid solution series Li₂Mg_1−xFe_2xSn_3−xO₈, the highest conductivity was exhibited by Li₂Fe₂Sn₂O₈, 2 × 10⁻⁵ (Ω cm)⁻¹ at 573 K.     

Synthese und Struktur der Nitridoborat‐Nitride Ln4(B2N4)N (Ln = La,Ce) des Formeltyps Ln3+x(B2N4)Nx (x = 0, 1, 2)

Synthesis and Structure of Nitridoborate Nitrides Ln₄(B₂N₄)N (Ln = La, Ce) of the Formula Type Ln_3+x(B₂N₄)N_x (x = 0, 1, 2) The missing member of the formula type Ln_3+x(B₂N₄)N_x with x = 1 was synthesized and characterized for Ln = La and Ce. According to the single‐crystal X‐ray structure solution Ce₄(B₂N₄)N crystallizes in the space group C2/m (Z = 2) with the lattice parameters a = 1238.2(1) pm, b = 357.32(3) pm, c = 905.21(7) pm and β = 129.700(1)°. The anisotropic structure refinement converged at R1 = 0.039 and wR2 = 0.099 for all independent reflections. A powder pattern of La₄(B₂N₄)N was indexed isotypically with a = 1260.4(1) pm, b = 366.15(3) pm, c = 919.8(1) pm and β = 129.727(6)°. A structure rational for nitridoborates and nitridoborate nitrides containing B₂N₄ ions with the general formula Ln_3+x(B₂N₄)N_x with x = 0, 1, 2 is presented.     

Décomposition de l'isopropanol sur les apatites mixtes calcium-argent

Decomposition of isopropanol on mixed calcium-silver apatites. A new family of apatite materials Ca_10-xAg_x(PO₄)₆(OH)_2-x□_x were synthesized, then studied using the decomposition reaction of isopropanol. The catalytic activity of the mixed apatites was observed to correspond mainly to dehydrogenation reaction features (the formation of acetone). This phenomenon has been tentatively related to the migration of Ag⁺ ions towards the surface and to their reduction to metallic silver under catalytic reaction conditions. The catalytic tests for the isopropanol decomposition reaction show that silver substituted hydroxyapatites were more actives than pure hydroxyapatite.     

Pr10[Si10−xAlxO9+xN17−x]Cl with x ≈ 1 – an Oxonitridoaluminosilicate Chloride

The oxonitridoaluminosilicate chloride Pr₁₀[Si_10?xAl_xO_9+xN_17?x]Cl was obtained by the reaction of praseodymium metal, the respective chloride, AlN and Al(OH)₃ with “Si(NH)₂” in a radiofrequency furnace at temperatures around 1900 °C. The crystal structure was determined by single‐crystal X‐ray diffraction (Pbam, no. 55, Z = 2,a = 10.5973(8) Å, b = 11.1687(6) Å, c = 11.6179(7) Å, R1 = 0.0337). The sialon crystallizes isotypically to the oxonitridosilicate halides Ce₁₀[Si₁₀O₉N₁₇]Br, Nd₁₀[Si₁₀O₉N₁₇]Br and Nd₁₀[Si₁₀O₉N₁₇]Cl, which represent a new layered structure type. The structure refinement was performed utilizing an O/N‐distribution model according to Paulings rules, i.e. nitrogen was positioned on all bridging sites and mixed O/Noccupation was assumed on the terminal sites resulting in charge neutrality of the compounds. The Si and Al atoms were refined equally distributed on their three crystallographic sites, due to their poor distinguishability by X‐ray analysis. The tetrahedra layers of the structure consist of condensed [(Si,Al)N₂(O,N)₂] and [(Si,Al)N₃(O,N)] tetrahedra of Q² and Q³ type. The chemical composition of the compound was derived from electron probe micro analyses (EPMA).     

Transition metal iodates. VI. Preparation and characterization of the larger lanthanide iodates

In the continuation of this work, the Ln^III(IO₃)₃xH₂O type N compounds (abbreviated x_N) of La through Sm were prepared by precipitation, thermal decomposition, and by crystallization from the gel, from ambient and boiling water, and from boiling HNO₃. A total of 36 different compounds with 6 ? x ? 0 were obtained occurring in 12 structural types including one amorphous; in addition La₅(IO₆)₃ and four isostructural double salts of the type Ln(IO₃)₃·HIO₃ were obtained.Characterization techniques used included powder X-ray diffraction, differential thermal analysis, thermogravimetric analysis, second harmonic generation, and infrared spectroscopy.Out of the total of 16 crystalline iodate structures occurring for all the lanthanides, single crystals were obtainable in 11, comprising a total of 54 compounds.Including all the lanthanides (plus Y, less Pm), the x_N groups of isostructural compounds, with the number of compounds in parentheses, were the following: 6(1), 5_I(4), 5_II(2), 4(9), amorphous with 5 ? x ? 0 (15), 2_I(3), 2_II(9), 1(4), $\text{1}\text{2}\text{(2)}$, O_I(14), O_II(2), O_III(4), O_IV(3), O_V(4), and O_VI(1).     

Structure Elucidation of Complex Endotaxially Intergrown Lanthanum Barium Oxonitridosilicate Oxides by Combination of Microfocused Synchrotron Radiation and Transmission Electron Microscopy

Single-crystalline domains in intergrown microcrystalline material of the new compounds Ba_22.5+xLa_55−x[Si₁₂₉N_240−xO_x]O₃:Ce³⁺ and Ba_25.5+xLa_77−x[Si₁₇₀N_312−xO_9+x]O₄:Ce³⁺ were identified by transmission electron microscopy (TEM). Precise diffraction data from these domains were collected with microfocused synchrotron radiation so that crystal structure elucidation of the complex disordered networks became possible. They are composed of two different interconnected slabs of which one is similar in both compounds, which explains their notorious intergrowth. The distribution of Ba and La is indicated by the analysis of bond-valence sums and by comparison with isostructural Sr_28.5+xLa_75−x[Si₁₇₀N_312−xO_9+x]O₄. Ce³⁺ doping leads to yellow luminescence. This is a showcase that highlights the discovery and accurate characterization of new compounds relevant for luminescence applications from heterogeneous microcrystalline samples by exploiting the capability of the combination of TEM and diffraction using the latest focusing techniques for synchrotron radiation.     

Two polymorphic forms of a mixed zinc/copper biquinoline dihydrogenphosphate

Two polymorphic forms of a mixed zinc/copper biquinoline dihydrogenphosphate are presented, showing almost identical monomeric units, viz. (2,2′‐biquinoline‐κ²N,N′)bis(dihydrogenphosphato‐κO)copper(II)/zinc(II), formulated as [Zn_xCu_1−x(H₂PO₄)₂(C₁₈H₁₂N₂)], with x = 0.88 (1) and 0.90 (2). The cation is tetrahedrally coordinated to a chelating biquinoline system and two diprotonated phosphate anions. The structures differ mainly in their intermolecular hydrogen‐bonding interactions, leading to different packing schemes. No significant evidence of stress due to the Zn/Cu solid solution formation was detected.     

A series of high-nuclear planar equilateral triangle-shaped {Ln6(μ3-OH)6} cluster encapsulated polyoxoniobates with frequency dependent magnetic property

The integration of lanthanide (Ln) ions and polyoxoniobates (PONbs) is challenging, and the known Ln-substituted PONbs are still scarce. This work introduces high-nuclear iso-Ln-oxo clusters into the PONb system. The first series of high-nuclear Ln-oxo clusters encapsulated heterometallic polyoxoniobates H₉[Na(H₂O)₄][Cu(en)₂]₁₀{Ln₆(μ₃-OH)₆(SiNb₁₈O₅₄)₃}·18H₂O (1-Ln, en = ethylenediamine, Ln = Dy, Gd, Tb, Ho, Er, Tm, Yb, Lu) based on flower-like {Ln₆(μ₃-OH)₆(SiNb₁₈O₅₄)₃} ({Ln₆Si₃Nb₅₄}) clusters have been successfully synthesized via one-pot hydrothermal synthesis strategy. The flower-like polyoxoanion {Ln₆Si₃Nb₅₄} is consisted of three heteropolyoxoniobate {SiNb₁₈O₅₄} clusters and one unique planar equilateral triangle-shaped {Ln₆(μ₃-OH)₆} cluster, which presents the highest nuclear iso-Ln-oxo cluster in PONb chemistry. In {Ln₆(μ₃-OH)₆} cluster, each pair of μ₃-OH groups link three Dy³⁺ ions to form a small approximate equilateral triangle-shaped {Dy₃(OH)₂} cluster. Furthermore, the three {Dy₃(OH)₂} clusters comprise a bigger approximate equilateral triangle-shaped {Dy₆(μ₃-OH)₆} cluster. The reported hexanuclear {Ln₆} cluster skeletons are mostly octahedral, however, such equilateral triangle-shaped skeleton of the hexanuclear Ln-oxo cluster is first observed. The 1-Dy exhibits good water vapor adsorption capacity and ferromagnetic properties.     

Lanthanum (Oxo)nitridosilicates: From Ordered to Disordered Crystal Structures

The homeotypic compounds La_16.32Ba_1.82Sr_7.86[Si₆₀N_92.32O_3.68]O₁₂ and La_13.68Sr_12.32[Si₆₀N₉₆]F_6.32O_5.68 were synthesized at high temperature (1600/1500 °C) in a radio‐frequency furnace. The crystal structures [I$\bar{4}$ m (no. 217), Z = 1, a = 13.3360(10)/13.3258(10) Å and V = 2371.8(5)/2366.4(5) ų] were solved and refined on basis of single‐crystal X‐ray diffraction data and were corroborated by lattice‐energy calculations (Madelung part of lattice energy, MAPLE) powder X‐ray diffraction data and FTIR spectroscopy. They consist of a three‐dimensional network of allside corner sharing SiN_4–xO_x tetrahedra. The framework is characterized by double dreier rings. La_16.32Ba_1.82Sr_7.86[Si₆₀N_92.32O_3.68]O₁₂ represents an oxonitridosilicate oxide and La_13.68Sr_12.32[Si₆₀N₉₆]F_6.32O_5.68 a nitridosilicate fluoride oxide, as the crystal structures contain non‐condensed (O^[0]/O,F^[0]) anions. The first compound is isotypic to Sr₃Ln₁₀Si₁₈Al₁₂O₁₈N₃₆ (Ln = Ce, Pr, Nd; Z = 2), whereas the latter describes a disordered model of the crystal structure, which is homeotypic to the mentioned SiAlONs.     

Structural and dynamical studies of δ-Bi2O3 oxide-ion conductors: II. A structural comparison of (Bi2O3)1−x(M2O3)x for M = Y,Er, and Yb

We report the results of diffuse elastic neutron scattering studies of the superionic solid solutions (Bi₂O₃)_1−x(Er₂O₃)_x and (Bi₂O₃)_1−x(Yb₂O₃)_x, and also the result of a Bragg diffraction study of (Bi₂O₃)_0.75(Er₂O₃)_0.25. All the data suggest that Er³⁺-doped δ-Bi₂O₃ is structurally very similar to the fluorite-related solid solution (Bi₂O₃)_1−x(Y₂O₃)_x studied previously, both in terms of the average structure as determined by Bragg scattering and in terms of local ordering on the anion sublattice as detected by diffuse scattering. The ordered regions are described as microdomains of a rhombohedral phase. The Yb³⁺-doped materials also show short-range anion ordering, but over shorter distances than in the other two cases. There is evidence of cation ordering between Bi³⁺ and Yb³⁺ near the low-dopant boundary of the fluorite phase. The possible use of quasi elastic neutron scattering to monitor oxide-ion transport in the system (Bi₂O₃)_1−x(Er₂O₃)_x is discussed.     

Synthesis and physical and chemical characterization of Ca10−xAgx(PO4)6(OH)2−xx apatites

The synthesis of calcium-silver hydroxyapatites of composition Ca_10−xAg_x(PO₄)₆(OH)_2−xx is discussed, together with their physical and chemical properties. Samples prepared both by dry process and by double decomposition were characterized using a variety of analytical techniques (chemical analysis, X-ray diffraction, infrared spectroscopy). The lattice parameters a and c increase linearly with the amount of silver added. The increase is attributed to the preferential substitution of the silver ion in site me (I) of these apatites.     

Cation‐Directed Dimeric versus Tetrameric Assemblies of Lanthanide‐Stabilized Dilacunary Keggin Tungstogermanates

Reaction of mid‐ to late lanthanide ions with GeO₂ and Na₂WO₄ in NaOAc buffer results in a library of [Ln₂(GeW₁₀O₃₈)]^6? clusters ( Ln₂ ), which consist of dilacunary Keggin fragments stabilized by the insertion of 4f atoms in the vacant sites and show the ability to undergo cation‐directed self‐assembly processes. In the presence of Na⁺, two β‐ Ln₂ subunits assemble by means of Ln‐O(WO₅)‐Ln bridges to form the chiral [Ln₄(H₂O)₆(β‐GeW₁₀O₃₈)₂]^12? dimeric anions (ββ‐ Ln₄ , Ln=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). When Cs⁺ is present, two Ln₄ ‐like dimers further assemble into the [{Ln₄(H₂O)₅(GeW₁₀O₃₈)₂}₂]^24? species ( Ln₈ , Ln=Ho, Er, Tm, Yb, Lu). Two types of tetramers coexist in the solid state: One shows a full ββ‐ Ln₈ architecture, whereas the other one is a mixed αβ‐ Ln₈ assembly in which each β‐subunit is linked to its corresponding α‐ Ln₂ derivative. Regardless of differences in isomeric forms and the relative arrangement of Ln₂ subunits, all anions display virtually identical {Ln₄} cores as a common structural feature. A combination of ESI mass spectrometry and ¹⁸³W NMR spectroscopy experiments indicates that Ln₈ tetramers fragment into Ln₄ dimers upon dissolution, which undergo partial dissociation into Ln₂ monomers and slow dimer/monomer equilibration. This is most likely followed by β‐to‐α isomerization of Ln₂ clusters with consequent reassembly, as indicated by isolation of three additional αα‐ Ln₄ derivatives. Magnetic and photoluminescence properties in the Na ‐ββ‐ Ln₄ series are also discussed.     

Trigonal Prismatic Coordination of Discrete Rare Earth Ions,Enforced by the Polyoxotungstate [P4W27O99(H2O)]16–

A family of solution-stable polyanions [Na⊂{Ln^III(H₂O)}{W^VIO(H₂O)}P^V₄W^VI₂₆O₉₈]¹²⁻ (Ln=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) represent the first examples of polyoxometalates comprising a single lanthanide(III) or yttrium(III) ion in a rare trigonal prismatic O₆ environment. Their synthesis exploits the reactivity of the organophosphonate-functionalized precursor [P₄W₂₄O₉₂(C₆H₅P^VO)₂]¹⁶⁻ with heterometal ions and yields hydrated potassium or mixed lithium/potassium salts of composition K_xLn_yH_12–x–y[Na⊂{Ln(H₂O)}{WO(H₂O)}P₄W₂₆O₉₈]⋅nH₂O⋅mLiCl (x=8.5–11; y=0–2; n=24–34; m=0–1.5). The Dy, Ho, Er and Yb derivatives are characterized by slow magnetization relaxation.     

Unexpected Luminescence Properties of Sr0.25Ba0.75Si2O2N2:Eu2+—A Narrow Blue Emitting Oxonitridosilicate with Cation Ordering

Owing to a parity allowed 4f⁶(⁷F)5d¹→4f⁷(⁸S_7/2) transition, powders of the nominal composition Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ (2 mol % Eu²⁺) show surprising intense blue emission (λ_em=472 nm) when excited by UV to blue radiation. Similarly to other phases in the system Sr_1?xBa_xSi₂O₂N₂:Eu²⁺, the described compound is a promising phosphor material for pc‐LED applications as well. The FWHM of the emission band is 37 nm, representing the smallest value found for blue emitting (oxo)nitridosilicates so far. A combination of electron and X‐ray diffraction methods was used to determine the crystal structure of Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺. HRTEM images reveal the intergrowth of nanodomains with SrSi₂O₂N₂ and BaSi₂O₂N₂‐type structures, which leads to pronounced diffuse scattering. Taking into account the intergrowth, the structure of the BaSi₂O₂N₂‐type domains was refined on single‐crystal diffraction data. In contrast to coplanar metal atom layers which are located between layers of condensed SiON₃‐tetrahedra in pure BaSi₂O₂N₂, in Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ corrugated metal atom layers occur. HRTEM image simulations indicate cation ordering in the final structure model, which, in combination with the corrugated metal atom layers, explains the unexpected and excellent luminescence properties.