The Solid Solution Sr1−xBaxGa2: Substitutional Disorder and Chemical Bonding Visited by NMR Spectroscopy and Quantum Mechanical Calculations

Complete miscibility of the intermetallic phases (IPs) SrGa₂ and BaGa₂ forming the solid solution Sr_1?xBa_xGa₂ is shown by means of X‐ray diffraction, thermoanalytical and metallographic studies. Regarding the distances of Sr/Ba sites versus substitution degree, a model of isolated substitution centres (ISC) for up to 10 % cation substitution is explored to study the influence on the Ga bonding situation. A combined application of NMR spectroscopy and quantum mechanical (QM) calculations proves the electric field gradient (EFG) to be a sensitive measure of different bonding situations. The experimental resolution is boosted by orientation‐dependent NMR on magnetically aligned powder samples, revealing in first approximation two different Ga species in the ISC regimes. EFG calculations using superlattice structures within periodic boundary conditions are in fair agreement with the NMR spectroscopy data and are discussed in detail regarding their application on disordered IPs.     

K and Ba distribution in the structures of the clathrate compounds KxBa16−x(Ga,Sn)136 (x = 0.8, 4.4, and 12.9) and KxBa8−x(Ga,Sn)46 (x = 0.3)

Studies of the K–Ba–Ga–Sn system produced the clathrate compounds K_0.8(2)Ba_15.2(2)Ga_31.0(5)Sn_105.0(5) [a = 17.0178 (4) Å], K_4.3(3)Ba_11.7(3)Ga_27.4(4)Sn_108.6(4) [a = 17.0709 (6) Å] and K_12.9(2)Ba_3.1(2)Ga_19.5(4)Sn_116.5(4) [a = 17.1946 (8) Å], with the type‐II structure (cubic, space group Fdm), and K_7.7(1)Ba_0.3(1)Ga_8.3(4)Sn_37.7(4) [a = 11.9447 (4) Å], with the type‐I structure (cubic, space group Pmn). For the type‐II structures, only the smaller (Ga,Sn)₂₄ pentagonal dodecahedral cages are filled, while the (Ga,Sn)₂₈ hexakaidecahedral cages remain empty. The unit‐cell volume is directly correlated with the K:Ba ratio, since an increasing amount of monovalent K occupying the cages causes a decreasing substitution of the smaller Ga in the framework. All three formulae have an electron count that is in good agreement with the Zintl–Klemm rules. For the type‐I compound, all framework sites are occupied by a mixture of Ga and Sn atoms, with Ga showing a preference for Wyckoff site 6c. The (Ga,Sn)₂₀ pentagonal dodecahedral cages are occupied by statistically disordered K and Ba atoms, while the (Ga,Sn)₂₄ tetrakaidecahedral cages encapsulate only K atoms. Large anisotropic displacement parameters for K in the latter cages suggest an off‐centering of the guest atoms.     

Verbindungen A3M5 (A = Erdalkalimetall,M = Triel/Tetrel): Eine Fallstudie zur strukturellen und elektronischen Stabilität polarer intermetallischer Phasen

Compounds A₃M₅ (A = alkaline earth, M = triel/tetrel): A Case Study on Structural and Electronic Factors Stabilizing Polar Intermetallics Starting from the non electron precise binary compounds Ca₃Ga₅/Sr₃In₅ (Hf₃Ni₂Si₃ type) and Ba₃Al₅ at one hand and Ba₃Pb₅ (Pu₃Pd₅ type) at the other hand, a series of new ternary intermetallics of the general formula A₃M₅ (A: alkaline earth, M: triel/tetrel) has been synthesized, structurally characterized and studied by band structure calculations. The chemical substitution of M in A₃M₅ allows, via the continous variation of the radius ratio (r_A:r_M) and the valence electron number (VE/M) the detection of the geometrically and electronically determined stability ranges of the three structure types formed by the binary compounds. At values of r_A:r_M between 1.30 and 1.52 in the triel rich region of A₃M′_xM″_5?x the Hf₃Ni₂Si₃ type (orthorhombic, space group Cmcm) is formed: In Ca₃Ga₅ up to 1.8 Ga can be substituted by Al, in Sr₃In₅ similar amount of In can be replaced by either Al or Ga. The mixed trielide Sr₃Al_2.6Ga_2.4 (a = 468.4(1), b = 1132.5(1), c = 1570.0(2) pm, R1 = 0.0261) can be obtained, although both corresponding binary phases are not known. At larger values of the ratio r_A/r_M as in Ba₃Al₃Ga₂ (Ba₃Al₅ type, hexagonal, space group P6₃/mmc, a = 598.9(1), c = 1456.0(3) pm, R1 = 0.0353) layers of condensed M₅ building blocks with Al‐Al partial bonds are formed. Substituting one In position in Sr₃In₅ against Pb results in the isotypic, but electron precise Zintl compound Sr₃In₄Pb (a = 506.1(1), b = 1191.8(3), c = 1650.2(4) pm, R1 = 0.0286), where the Fermi level in shifted into a distinct minimum of the density of states. Conversely, at the tetrele rich end of the series A₃In_xPb_5?x, characterized by compounds of the Pu₃Pd₅ type (orthorhombic, space group Cmcm) with almost isolated nido clusters M₅, a minimum of the DOS can be reached, if Pb is partially substituted by In (A₃In_xPb_5?x with A = Sr/Ba: x = 0.7/0.6; a = 1084.6(2)/1118.6(2), b = 867.1(2)/904.4(1), c = 1104.8(2)/1133.9(2) pm, R1 = 0.0394/0.0434).     

Al14Ba8La26.3Ru18Sr53.7O167: a variant of cubic perovskite with isolated RuO6 units

The crystal structure of the title aluminium barium lanthanum ruthenium strontium oxide has been solved and refined using neutron powder diffraction to establish the parameters of the oxygen sublattice and then single‐crystal X‐ray diffraction data for the final refinement. The structure is a cubic modification of the perovskite ABO₃ structure type. The refined composition is Ba_0.167La_0.548Sr_1.118Ru_0.377Al_0.290O_3.480, and with respect to the basic perovskite structure type it might be written as (Ba₈La_13.68Sr_34.32)(Al_13.92La_12.64Ru_18.08Sr_19.36)O_192−x, with x = 24.96. The metal atoms lie on special positions. The A‐type sites are occupied by Ba, La and Sr. The Ba atoms are located in a regular cuboctahedral environment, whereas the La and Sr atoms share the same positions with an irregular coordination of O atoms. The B‐type sites are divided between two different Wyckoff positions occupied by Ru/Al and La/Sr. Only Al and Ru occupy sites close to the ideal perovskite positions, while La and Sr move away from these positions toward the (111) planes with high Al content. The structure contains isolated RuO₆ octahedra, which form tetrahedral substructural units.     

On the effect of Ga and In substitutions in the Ca11Bi10 and Yb11Bi10 bismuthides crystallizing in the tetragonal Ho11Ge10 structure type

The Ga‐ and In‐substituted bismuthides Ca₁₁Ga_xBi_10–x, Ca₁₁In_xBi_10–x, Yb₁₁Ga_xBi_10–x, and Yb₁₁In_xBi_10–x (x < 2) can be readily synthesized employing molten Ga or In metals as fluxes. They crystallize in the tetragonal space group I4/mmm and adopt the Ho₁₁Ge₁₀ structure type (Pearson code tI84; Wyckoff sequence n2 m j h2 e2 d). The structural response to the substitution of Bi with smaller and electron‐poorer In or Ga has been studied by single‐crystal X‐ray diffraction methods for the case of Ca₁₁In_xBi_10–x [x = 1.73 (2); octabismuth undecacalcium diindium]. The refinements show that the In atoms substitute Bi only at the 8h site. The refined interatomic distances show an unconventional – for this structure type – bond‐length distribution within the anionic sublattice. The latter can be viewed as consisting of isolated Bi³⁻ anions and [In₄Bi₈²⁰⁻] clusters for the idealized Ca₁₁In₂Bi₈ model. Formal electron counting and first‐principle calculations show that the peculiar bonding in this compound drives the system toward an electron‐precise state, thereby stabilizing the observed bond‐length pattern.     

M5(PO4)3F (M=Ca, Sr, Ba)中Sm3+的电荷迁移态及Sm3+和Eu3+的电荷迁移能量关系

采用高温固相反应合成了M_5-2xSm_xNa_x(PO₄)₃F(M=Ca,Sr,Ba)荧光体,研究了其在真空紫外-可见光范围的发光特性。发现在Ca₅(PO₄)₃F中Sm³⁺的电荷迁移带约在191 nm,在Sr₅(PO₄)₃F中约在199 nm,而在Ba₅(PO₄)₃F中约在204 nm,随着被取代碱土离子半径的增大电荷迁移能量逐渐减小。比较了M₅(PO₄)₃F (M=Ca,Sr,Ba)中Sm³⁺和Eu³⁺电荷迁移能量的关系。     

Partial Sn‐atom ordering in Sm3Ga0.80–2.48Sn4.20–2.52

Trisamarium digallide tristannide crystallizes with a partially ordered Pu₃Pd₅‐type structure in space group Cmcm. In a single crystal of Sm₃Ga_1.89(4)Sn_3.11(4), the 8g position is mostly occupied by Sn atoms (93% Sn and 7% Ga), while the 4c and 8f positions are occupied by a Ga/Sn statistical mixture. The evolution of the structure as a function of the Ga content has been studied by X‐ray powder diffraction on ten Sm₃Ga_5−xSn_x samples. It is shown that the 8g position remains occupied essentially exclusively by Sn atoms within the whole homogeneity range, with x ranging from 2.52 to 4.20.     

NMR spectroscopy of intermetallic compounds: an experimental and theoretical approach to local atomic arrangements in binary gallides

The results of the investigation of MGa(2) with M = Ca, Sr, Ba and of MGa(4) with M = Na, Ca, Sr, Ba by a combined application of NMR spectroscopy and quantum mechanical calculations are comprehensively evaluated. The electric-field gradient (EFG) was identified as the most reliable measure to study intermetallic compounds, since it is accessible with high precision by quantum mechanical calculations and, for nuclear spin I>1/2, by NMR spectroscopy. The EFG values obtained by NMR spectroscopy and quantum mechanical calculations agree very well for both series of investigated compounds. A deconvolution of the calculated EFGs into their contributions reveals its sensitivity to the local environment of the atoms. The EFGs of the investigated di- and tetragallides are dominated by the population of the p(x)-, p(y)-, and p(z)-like states of the Ga atoms. A general combined approach for the investigation of disordered intermetallic compounds by application of diffraction methods, NMR spectroscopy, and quantum mechanical calculations is suggested. This scheme can also be applied to other classes of crystalline disordered inorganic materials.     

M(SCN)2 (M = Eu,Sr, Ba): Kristallstruktur,thermisches Verhalten,Schwingungsspektroskopie

M(SCN)₂ (M = Eu, Sr, Ba): Crystal Structure, Thermal Behaviour, Vibrational Spectroscopy Single crystals of M(SCN)₂ (M = Eu, Sr, Ba) have been obtained via metathesis of NaSCN and MCl₂ (M = Eu, Sr, Ba) at 340 °C. The isotypic crystal structures of the thiocyanates M(SCN)₂ (C2/c, Z = 4, Eu: a = 979.3(2), b = 660.8(1), c = 815.7(2) pm, β = 91.58(3)°, R_all = 0.0245, Sr: a = 985.5(2), b = 662.9(2), c = 819.6(2) pm, β = 91.29(3)°, R_all = 0.0435, Ba: a = 1018.8(2), b = 687.2(1), c = 852.2(1) pm, β = 92.43(2)°, R_all = 0.0392) contain alternating layers of M²⁺ and SCN^–. According to M(SCN)_4/4(NCS)_4/4 M²⁺ is eight‐coordinated by four sulfur and four nitrogen atoms forming a square antiprism. Thermal investigations show that the compounds melt without decomposition. Vibrational spectroscopic investigations are presented and discussed.     

Structure–composition sensitivity in “Metallic” Zintl phases: A study of Eu(Ga1−xTtx)2 (Tt=Si, Ge, 0≤x≤1)

Two isoelectronic series, Eu(Ga_1−xTt_x)₂ (Tt=Si, Ge, 0≤x≤1), have been synthesized and characterized by powder and single-crystal X-ray diffraction, physical property measurements, and electronic structure calculations. In Eu(Ga_1−xSi_x)₂, crystal structures vary from the KHg₂-type to the AlB₂-type, and, finally, the ThSi₂-type structure as x increases. The hexagonal AlB₂-type structure is identified for compositions 0.18(2)≤x<0.70(2) with Ga and Si atoms statistically distributed in the polyanionic 6³ nets. As smaller Si atoms replace Ga atoms while the number of valence electrons increases, the lattice parameters, unit cell volumes, and Ga–Si distances in this phase region decrease significantly. Although aspects of X-ray diffraction results suggest puckering of the 6³ nets for the Si-richest example of the AlB₂-type Eu(Ga_1−xSi_x)₂, the complete experimental evidence remains inconclusive. On the other hand, in Eu(Ga_1−xGe_x)₂, six different structural types were observed as x varies. In addition to EuGa₂ (KHg₂-type; space group Imma) and EuGe₂ (own structure type, space group P3¯m1), the ternary phases studied show four different structures: the AlB₂-type for Ga-rich compositions; the YPtAs-type structure for EuGaGe; and two new structures, which are intergrowths of the YPtAs-type EuGaGe and EuGe₂, for Ge-rich compositions. These two Ge-rich phases include: (1) Eu(Ga_0.45(2)Ge_0.55(2))₂ containing two YPtAs-type motifs of EuGaGe plus one EuGe₂ motif; and (2) Eu(Ga_0.40(2)Ge_0.60(2))₂ containing one YPtAs-type motif alternating with a split site at and z=0.4798(2) with ca. 50% site occupancy by Ga and Ge along the c-axis. Magnetic susceptibilities of three Eu(Ga_1−xGe_x)₂ compounds display Curie–Weiss behavior above ca. 100 K, and show effective magnetic moments indicative of divalent Eu with a 4f⁷ electronic configuration, consistent with. X-ray absorption spectra (XAS). Density of states (DOS) and crystal orbital Hamilton population (COHP) analyses, based on first principles electronic structure calculations, rationalize the observed homogeneity ranges of the AlB₂-type phases in both systems and the structural variations as a function of Tt content.     

Electronic structure and properties of isolectronically substituted compounds Y1Ba2−m M m Cu3O7 and Y1Ba2−m M m Cu4O8 (M=Be,Mg, Ca,Sr, Ba,Ra)

According to cluster calculations, the electronic structures of compounds based on Y₁Ba₂Cu₃O₇ and Y₁Ba₂Cu₄O₈ with isoelectronically substituted barium have some qualitative distinctions. These compounds behave differently upon barium substitution by other elements due to differences in the character of their highest occupied and lowest unoccupied molecular orbitals. Substitution of barium by radium is expected to lead to an increase in oxygen stability without a significant decrease in the critical temperature of superconduction transition T_s. In order to raise T_s, it is of interest to study the systems YBa_2−m(Be or Mg)_mCu₃O_x and YBa_2−m(Ca, Sr)_mCu₃O_x. On partial substitution of barium by calcium in YBa₂Cu₄O₈, the mechanism of T_s elevation may involve contraction of the forbidden band due to oxygen sublattice distortions in the vicinity of Ba centers. D. I. Mendeleev Russian Chemical Engineering University, Novomoskovsk Branch. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 2, pp. 24–31, March–April, 1994. Translated by O. Kharlamova     

Ga2Br2R2 und Ga3I2R3 [R = C(SiMe3)3] — zwei neue elementorganische Galliumsubhalogenide mit einer bzw. zwei Ga‐Ga‐Bindungen

Ga₂Br₂R₂ and Ga₃I₂R₃ [R = C(SiMe₃)₃] — Two New Organoelement Subhalides of Gallium Containing One or Two Ga‐Ga Single Bonds The oxidation of the tetrahedral tetragallium cluster Ga₄[C(SiMe₃)₃]₄ ( 1 ) with elemental bromine in the presence of AlBr₃ yielded the corresponding gallium subhalide Ga₂Br₂R₂ [ 4 , R = C(SiMe₃)₃], which remains monomer even in the solid state and in which the Ga^II atoms are connected by a short Ga‐Ga single bond [243.2(2) pm]. The analogous diiodide Ga₂I₂R₂ ( 3 ), which was obtained on a similar route by our group only recently, did not react with lithium tert‐butanolate by substitution as originally expected. Instead, partial disproportionation occurred with the formation of the trigallium diiodide Ga₃I₂R₃ ( 6 ), in which three Ga atoms are connected by two Ga‐Ga single bonds (255.1 pm on average). Both terminal Ga atoms have a coordination number of four owing to the bridging function of both iodine atoms, while the inner one which has an oxidation number of +1 remains coordinatively unsaturated. An average oxidation state of 1.66 resulted for all atoms of the chain. The Ga^III compound {[GaI(R)(OCMe₃)(OH)]Li}₂ ( 7 ) was isolated as the second product of the disproportionation. It is a dimer in the solid state via Li‐O bridges and shows a hindered rotation of its tert‐butyl group.     

From 3D to 2D: Structural,Spectroscopic and Theoretical Investigations of the Dimensionality Reduction in the [PtAl2]δ− Polyanions of the Isotypic MPtAl2 Series (M=Ca–Ba,Eu)

Four new MPtAl₂ (M=Ca, Sr, Ba, Eu) compounds, adopting the orthorhombic MgCuAl₂-type structure, have been synthesized from the elements using tantalum ampoules. All compounds are obtained as platelet-shaped crystallites and exhibit an increasing moisture sensitivity with increasing size of the formal M cation. Structural investigations indicate a pronounced elongation of the crystallographic b-axis, which results in a significant distortion of the [PtAl₂]^δ− polyanion. Within the polyanion, layer-like arrangements can be found with bonding Pt−Al interactions within the slab; the increase of the b-axis can be attributed to increasing Al−Al distances and therefore decreasing interactions between the slabs, caused by the differently-sized formal M cations. While the alkaline earth (M=Ca, Sr) representatives exhibit Pauli paramagnetism, BaPtAl₂ shows diamagnetic behavior, finally EuPtAl₂ is ferromagnetic with T_C=54.0(5) K. The effective magnetic moment indicates that the Eu atoms are in a divalent oxidation state, which is confirmed by ¹⁵¹Eu Mössbauer spectroscopic investigations. Measurements below the Curie-temperature show a full magnetic hyperfine field splitting with B_hf=21.7(1) T. ²⁷Al and ¹⁹⁵Pt magic-angle spinning NMR spectroscopy corroborates the presence of single crystallographic sites for the Pt and Al atoms. The large ²⁷Al nuclear electric quadrupolar coupling constants confirm unusually strong electric field gradients, in agreement with the structural distortions and the respective theoretical calculations. X-ray photoelectron spectroscopy has been utilized to investigate the charge transfer within the polyanion. The Pt 4f binding energy decreases with decreasing electronegativity / ionization energy of the alkaline earth elements, suggesting an increasing electron density at the Pt atoms. Theoretical investigations underline the platinide character of the investigated compounds by Bader charge calculations. The analysis of the integrated crystal orbital Hamilton population (ICOHP) values, electron localization function (ELF) and isosurface analyses lead to a consistent structural picture, indicating stable layer-like arrangements of the [PtAl₂]^δ− polyanion.     

Sr substitution effects on atomic and local electronic structure of Ca2AlMnO5+δ

We performed the first-principle calculations based on spin-polarized density functional theory to investigate the Sr substitution effects on the atomic and local electronic structure of Ca₂AlMnO_5+δ. The ionic radius of Sr²⁺ is larger than that of Ca²⁺; thus, the lattice expansion occurs with Sr substitution. From the total energy calculations, we found that Sr substitution makes the oxygen-absorbed phase unstable and realizes the lower operation temperature. From the point of atomic structure, Sr substitution lengthens the bond length between Mn and O atoms connecting Mn and Al atoms in Al tetrahedral (O_Mn-Alt) in oxygen-absorbed phase, because the large Sr²⁺ prevents the release of the Jahn-Teller distortion. We also found that the covalent bonding between Mn and O_Mn-Alt atoms weaken with Sr substitution by the local electronic structure analysis, which results in the unstable oxygen-absorbed phase and weak prepeak and main peak intensity near the onset of O-K edge ELNES of O_Mn-Alt atoms.     

Synergistic extraction of alkaline earth cations with 3-phenyl-4-benzoyl-isoxazol-5-one and tri-n-octylphosphine oxide in toluene

The synergistic extraction of alkaline earth cations from 1M NaNO₃ aqueous solutions with 3-phenyl-4-benzoylisoxazol-5-one (HPBI) and tri-n-octylphosphine oxide (TOPO) in toluene at 25°C has been studied. The extraction efficiency follows the order Ba²⁺<Sr²⁺<Ca²⁺<Mg²⁺, which is the same as that previously observed with 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one (HPMBP). The extraction occurs at a lower pH range than with HPMBP because of the higher acidity of HPBI. The extracted species are M(PBI)₂(TOPO) _x withx=2 for M=Mg, Ca, Sr and Ba (logK _1,2,2=3.91, 1.18 and 0.29 respectively) and withx=3 for M=Sr and Ba (logK _1,2,3=3.28 and 2.07 respectively). The strong interactions which occur between HPBI and TOPO (logK _int=1.84) have been considered in the extraction constant calculations..     

Die Clusterazide M2[Nb6Cl12(N3)6]·(H2O)4—x (M = Ca,Sr, Ba)

The Cluster Azides M₂[Nb₆Cl₁₂(N₃)₆]·(H₂O)_4—x (M = Ca, Sr, Ba) The isotypic cluster compounds M₂[Nb₆Cl₁₂(N₃)₆] · (H₂O)_4—x (M = Ca (1) , M = Sr (2) and M = Ba (3) ) have been synthesized by the reaction of an aequeous solution of Nb₆Cl₁₄ with M(N₃)₂. 1 , 2 and 3 crystallize in the space group Fd3¯ (No. 227) with the lattice constants a = 1990.03(23), 2015.60(12) and 2043, 64(11) pm, respectively. All compounds contain isolated 16e— clusters whose terminal positions are all occupied by orientationally disordered azide ligands.     

Theoretical study on 19F magnetic shielding constants of some metal fluorides

A study is presented of ¹⁹F NMR magnetic shielding constants of MF₂ (M = Zn, Cd), β‐PbF₂, MF₃ (M = Al, Ga, In), AMF₃ (A = K, Rb, Cs, Ba; M = Mg, Ca, Li, Zn, Cd), BaMgF₄, BaZnF₄ and Ba₂ZnF₆ using the DFT/GIAO method. The aug‐cc‐pVTZ basis set was used for the fluorine atom under investigation and LanL2DZ for the remaining fluorine atoms. The 3–21G(2d) basis set was used for the aluminum atom and CRENBL for the other metal atoms. When appropriate cluster models were employed, the theoretical results obtained from the B3LYP/GIAO calculations are in good agreement with experimental measurements and may be better than those obtained from empirical calculations. The correlation coefficient and the slope of the fitting line between our theoretical predictions and the experimental observations are close to unity. Copyright © 2003 John Wiley & Sons, Ltd.     

The Hydrogenation of the Zintl Phase NdGa Studied by in situ Neutron Diffraction

The hydrogenation of the Zintl phase NdGa was studied by in situ neutron powder diffraction. We find a compositional range of 0.1 < x < 0.8 in NdGaH_1+x. Hydrogen atoms are located in two different positions, in HNd₄ tetrahedra, and close to the polyanionic chains. For the latter, the Ga–H distance in NdGaH_1.66 is quite long (ca. 200 pm) with a trigonal bipyramidal Nd₃Ga₂ surrounding of hydrogen atoms. Hydrogen poor NdGaH_<1 phases as known for similar systems were not observed. The changing hydrogen content shows no measureable effect on the unit cell volume, but on lattice parameter ratios. Superstructures occur for 0.53 < x < 0.66 and 0.73 < x < 0.8, leading to a doubling or tripling of the lattice parameter a. They are probably caused by partial hydrogen ordering. The threefold superstructure contains a ¹_∞[(Ga–H–Ga–H–Ga)^6–] moiety with hydrogen bridging two gallium chains.     

Etude des systemes CaHPO4−MHPO4−H2O (M=Sr,Ba) A 50°C

The systems CaHPO₄−MHPO₄−H₂O (M=Sr, Ba) were studied at 50°C. ForM=Sr, the series of single phases, Ca_1−xSr_xHPO₄ for 0.95<X<0.75 and Ca_xSr_1−xHPO₄ for 0.4<X<1 have been prepared. These solid solution were caracterized by their infrared spectra and their crystallographic unit cell parameters. ForM=Ba a new phase Ca₂Ba(HPO₄)₃ has been determined. It was characterized by DRX, IR, ATD and chemical analyses.

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Zusammenfassung Bei 50°C wurde das System CaHPO₄−MHPO₄−H₂O (mitM=Sr, Ba) untersucht. FürM=Sr wurden Serien von Einzelphasen erhalten: Ca_1−xSr_xHPO₄ für 0.95<X< 0.75 und Ca_xSr_1−xHPO₄ für 0.4<X<1. Diese Mischkristalle wurden anhand ihrer Infrarotspektren und ihrer kristallographischen Elementarzellenparameter charakterisiert. FürM=Ba wurde die neue Phase Ca₂Ba(HPO₄)₃ ermittelt. Sie wurde mittels DRX, IR, ATD und chemischer Analyse charakterisiert.

     

Magnetic Investigations and 151Eu Mössbauer Spectroscopy of MYbSi4N7 with M = Sr,Ba, Eu

The isotypic nitridosilicates MYb[Si₄N₇] (M = Sr, Ba, Eu) were obtained by the reaction of the respective metals with Si(NH)₂ in a radiofrequency furnace below 1600 °C. On the basis of powder diffraction data of MYb[Si₄N₇] Rietveld refinements of the lattice constants were performed; these confirmed the previously published single‐crystal data. The compounds contain a condensed network of corner‐sharing [N(SiN₃)₄] units. The central nitrogen thus exhibits ammonium character. Magnetic susceptibility measurements of MYb[Si₄N₇] (M = Sr, Ba, Eu) show paramagnetic behavior with experimental magnetic moments of 3.03(2), (Sr), 2.73(2) (Ba), and 9.17(2) (Eu) μ_B per formula unit. In EuYbSi₄N₇ the europium and ytterbium atoms are in stable divalent and trivalent states, respectively. According to the non‐magnetic character of the alkaline earth cations, ytterbium has to be in an intermediate valence state Yb^III‐x in the strontium and barium compound. Consequently, either a partial exchange N^3—/O^2— resulting in compositions MYb^III‐x[Si₄N_7—xO_x] or an introduction of anion defects according to MYb^III‐x[Si₄N_7—x/3□_x/3] has to be assumed. The phase width 0 ≤ x ≤ 0.4 was estimated according to the magnetic measurements. ¹⁵¹Eu Mössbauer spectra of EuYb[Si₄N₇] at 78 K show a single signal at an isomer shift of δ = —12.83(3) mm s^—1 subject to quadrupole splitting of ΔE_Q = 5.7(8) mm s^—1, compatible with purely divalent europium.