Nb28Ni33.5Sb12.5, a New Representative of the X-phase

The first ternary compound in the Nb–Ni–Sb system, Nb₂₈Ni_33.5Sb_12.5, has been synthesized and its structure has been determined by single-crystal X-ray diffraction methods. Nb₂₈Ni_33.5(2)Sb_12.5(2) adopts the X-phase structure type (orthorhombic, space group Pnnm, Z=1, a=13.2334(5) Å, b=16.5065(7) Å, c=5.0337(2) Å), which belongs to the set of tetrahedrally close-packed (TCP) structures adopted by many intermetallic compounds. Typical of such TCP structures, the atoms reside in sites of high coordination number, with Ni and Sb in CN12 and Nb in CN14, -15, and -16 sites. The relative importance of various metal–metal bonding interactions is discussed on the basis of extended Hückel band structure calculations. Nb₂₈Ni_33.5Sb_12.5 displays metallic behavior with a room-temperature resistivity of 2.3×10⁻⁴ Ω cm.     

Zintl Phases: Transitions between Metallic and Ionic Bonding

Experimental studies on compounds of alkali and alkaline earth metals with semi- and metametals have considerably broadened the basis for a discussion of the transition from metallic to ionic bonding. Current interest is focused mainly upon the elucidation of the principles governing the structure of such compounds which are subject to a wide range of variation within this class of materials. A new definition of the term Zintl phase is proposed after consideration of available findings.     

Lanthanum Gallium Tin Antimonides LaGaxSnySb2

A series of quaternary lanthanum gallium tin antimonides LaGa_xSn_ySb₂ was elaborated to trace the structural evolution between the known end members LaGaSb₂ (SmGaSb₂-type) and LaSn_ySb₂ (LaSn_0.75Sb₂-type). Five members of this series were characterized by single-crystal X-ray diffraction. For low Sn content, the Sn atoms disorder with Ga atoms in zigzag chains to form solid solutions LaGa_1-ySn_ySb₂ (0≤y≤0.2) adopting the SmGaSb₂-type structure, as exemplified by LaGa_0.92(3)Sn_0.08Sb₂ and LaGa_0.80(3)Sn_0.20Sb₂ (orthorhombic, space group D⁵₂−C222₁,Z=4). For higher Sn and lower Ga content, there is a segregation in which the Sn atoms appear in chains of closely spaced partially occupied sites as in the parent LaSn_0.75Sb₂-type structure whereas the Ga atoms remain in zigzag chains as in the parent SmGaSb₂-type structure. This feature is observed in the structures of LaGa_0.68(4)Sn_0.31(3)Sb₂, LaGa_0.62(3)Sn_0.32(3)Sb₂, and LaGa_0.43(3)Sn_0.39(3)Sb₂ (orthorhombic, space group D¹⁷_2h−Cmcm,Z=4). The last example illustrates that the combined Ga/Sn content can be substoichiometric (x+y<1). These compounds have a layered nature, with the chains of Ga or Sn atoms residing between ²_∞[LaSb₂] slabs.     

Chemical route for formation of intermetallic Zn4Sb3 phase

Synthesis of intermetallic zinc antimonide phases via low temperature solution route was investigated. Trial experiments were carried out under inert atmosphere at 70 °C using metallic Zn, SbCl₃ and NaBH₄ as reactants and tetrahydrofuran (THF), dimethylsulfoxide (DMSO) as organic media. Powder X-ray analysis confirmed the nucleation and growth of ZnSb phases in presence of excess Zn. SEM analysis revealed the existence of core-shell structure comprising of Zn core and Sb shell. Such particles get transformed into Zn₄Sb₃ crystalline phases upon thermal treatment at 300 °C/6 h in a silica tube closed under high secondary vacuum.     

Sr11Cd6Sb12: a new Zint1 compound with infinite chains of pentagonal tubes

A new Cd-containing transition metal Zintl phase, Sr₁₁Cd₆Sb₁₂, was obtained from a direct element combination reaction using the Sn flux method. Its structure was determined using single-crystal X-ray diffraction methods. It crystallizes in the monoclinic space group C2/m with a=32.903(3) Å, b=4.7666(5) Å, c=12.6057(13) Å, β=109.752(2)°, and Z=2. Sr₁₁Cd₆Sb₁₂ has a one-dimensional infinite chain structure consisting of double pentagonal tubes, where Sr²⁺ cations reside both within two tubes and between the infinite chains of tubes. The anionic framework [Cd₆Sb₁₂]²²⁻ has features similar to those of Eu₁₀Mn₆Sb₁₃. The difference in Eu₁₀Mn₆Sb₁₃ is that its double pentagonal tubes are further condensed to form two-dimensional layers.     

The Ternary Compounds Pd13ln5.25Sb3.75 and Pdln1.26Sb0.74: Crystal Structure and Electronic Structure Calculations

The new ternary compound Pd₁₃In_5.25Sb_3.75 was found. Its crystal structure was determined using a CCD diffractometer at room temperature. Evaluations and refinements finally yielded a C-centered monoclinic structure (space group, C2/c; Pearson symbol, mC88, Z=4) with a=15.189(2) Å, b=8.799(1) Å, c=13.602(2) Å, and β=123.83(1)°. For the entire data set of 3706 independent reflections residual values are R=0.0461 and R_w=0.0789. The structure was found to be isotypic to Pd₁₃Pb₉ with In and Sb on the Pb sites. The existence of a further ternary compound, which was already described as Pd₃In₄Sb₂, could be confirmed. Its composition range was determined by EPMA to be PdIn_1.2-1.3Sb_0.8-0.7. It does not melt congruently and we were not able to find suitable single crystals. However, we were able to prepare the pure ternary compound in order to perform X-ray powder diffraction using a Guinier image plate technique. The entire diffraction spectrum was refined by full profile Rietveld method using the program Fullprof. The α-PdSn₂ structure type (space group, I4₁/acd; Pearson symbol, t148, Z=16), proposed for this compound, was confirmed and the lattice parameters are a=6.4350(1) Å and c=24.3638(3) Å. The residual values were R_p=5.34 and R_wp=6.70. The tetragonal PdSn₂ structure type is a mixed variant of the CaF₂ type and the CuAl₂ type structure. Also in this ternary compound we assumed a random contribution of In and Sb over the 16e and 16f positions. The electronic structures of both compounds were investigated by extended Hückel calculations. Crystal orbital overlap populations show extended bonding interactions between the main group elements. The bonding interactions of the main group elements are almost optimized at the experimentally observed In/Sb ratio of the ternary compound. The In/Sb ratio in Pd₁₃In_5.25Sb_3.75 can thus be rationalized on the basis of the electronic structure.     

Thermoelectric properties and microstructure of Mg3Sb2

Mg₃Sb₂ has been prepared by direct reaction of the elements. Powder X-ray diffraction, thermal gravimetric, differential scanning calorimetery, and microprobe data were obtained on hot pressed samples. Single phase samples of Mg₃Sb₂ were prepared and found to contain oxygen at the grain boundaries and to lose Mg and oxidize at temperatures above 900 K. Thermoelectric properties were characterized by Seebeck, electrical resistivity, and thermal conductivity measurements from 300 to 1023 K, and the maximum zT was found to be 0.21 at ∼875 K.     

Synthesis and characterization of the Zintl phase Na4Ba3As6 with isolated As3 anions

The title compound was prepared by direct fusion of the corresponding elements at 800°C followed by slow cooling to room temperature. It crystallizes in the orthorhombic space group Pbcm (No. 57) with a=11.340(2), b=8.745(2), and c=14.920(2) Å, V=1479.8(5) ų, and Z=4. The structure is made of isolated V-shaped trimers As₃⁵⁻ and sodium and barium countercations. According to magnetic and resistivity measurements, Na₄Ba₃As₆ is a narrow-gap semiconductor, i.e. a closed-shell compound that fulfills the Zintl concept.     

Crystal Structure of Ternary Molybdate Rb5FeHf(MoO4)6 — a New Phase in the Rb2MoO4-Fe2(MoO4)3-Hf(MoO4)2 System

Physicochemical analysis (XRPA, DTA) was used to study phase equilibria in a ternary salt system Rb₂MoO₄-Fe₂(MoO₄)₃-Hf(MoO₄)₂ in the subsolidus region. Ternary molybdates with compositions 5:1:3, 5:1:2, and 1:1:1 have been found and synthesized. Crystal and thermal characteristics have been determined. Single crystals of the ternary molybdate Rb₅FeHf(MoO₄)₆ with a composition of 5:1:2 were grown. The crystal structure of the compound was solved using X-ray diffractometry (CAD-4 automatic diffractometer, MoK _α radiation, 1766 F(hkl), R = 0.0298). Hexagonal crystals with unit cell dimensions: a = b = 10.124(1) Å, c =15.135(3) Å, V = 1343.4(4) ų, Z = 2, ρ_calc = 4.008 g/cm³, space group P6₃. The mixed three-dimensional framework of the structure is formed from two sorts of MoO₄ tetrahedra and Fe and Hf octahedra linked through their common O-vertices. Rubidium atoms of three varieties occupy the large voids of the framework.Original Russian Text Copyright © 2004 by B. G. Bazarov, R. F. Klevtsova, A. D. Tsyrendorzhieva, L. A. Glinaskaya, and Zh. G. Bazarova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1038–1043, November–December, 2004.     

Synthesis and Structure of Ba8Cu3In4N5 with Nitridocuprate Groups and One-Dimensional Infinite Indium Clusters

Single crystals of the quaternary compound Ba₈Cu₃In₄N₅ were prepared by heating Ba, Cu, and In in a Na flux at 1023 K under 7 MPa of N₂, and by slow cooling from this temperature. The crystal structure was analyzed by single-crystal X-ray diffraction. It crystallizes in an orthorhombic cell (space group Immm (No. 71), Z=2) with a=4.0781(6), b=12.588(2), and c=19.804(3) Å at 298 K. The structural formula is expressed as Ba₈[CuN₂]₂ [CuN]In₄. Nitridocuprates of one-dimensional chains ¹_∞[CuN_2/2] and isolated units ⁰[CuN₂], and one-dimensional indium clusters ¹_∞[In₂In_4/2] are contained in the structure. A split-site model applied for the arrangement of ¹_∞[CuN_2/2] chains suggested that there is a short-bond, long-bond alternation of the Cu-N bondings. The electrical resistivity of Ba₈Cu₃In₄N₅ was 3.44 mΩ·cm at 298 K. A metallic temperature dependence of the resistivity was observed down to 10 K.     

High-temperature thermoelectric studies of A11Sb10 (A=Yb, Ca)

Large samples (6-8 g) of Yb₁₁Sb₁₀ and Ca₁₁Sb₁₀ have been synthesized using a high-temperature (1275-1375 K) flux method. These compounds are isostructural to Ho₁₁Ge₁₀, crystallizing in the body-centered, tetragonal unit cell, space group I4/mmm, with Z=4. The structure consists of antimony dumbbells and squares, reminiscent of Zn₄Sb₃ and filled Skutterudite (e.g., LaFe₄Sb₁₂) structures. In addition, these structures can be considered Zintl compounds; valence precise semiconductors with ionic contributions to the bonding. Differential scanning calorimetry (DSC), thermogravimetry (TG), resistivity (ρ), Seebeck coefficient (α), thermal conductivity (κ), and thermoelectric figure of merit (zT) from room temperature to at minimum 975 K are presented for A₁₁Sb₁₀ (A=Yb, Ca). DSC/TG were measured to 1400 K and reveal the stability of these compounds to ∼1200 K. Both A₁₁Sb₁₀ (A=Yb, Ca) materials exhibit remarkably low lattice thermal conductivity (∼10 mW/cm K for both Yb₁₁Sb₁₀ and Ca₁₁Sb₁₀) that can be attributed to the complex crystal structure. Yb₁₁Sb₁₀ is a poor metal with relatively low resistivity (1.4 mΩ cm at 300 K), while Ca₁₁Sb₁₀ is a semiconductor suggesting that a gradual metal-insulator transition may be possible from a Ca_11−xYb_xSb₁₀ solid solution. The low values and the temperature dependence of the Seebeck coefficients for both compounds suggest that bipolar conduction produces a compensated Seebeck coefficient and consequently a low zT.     

Structures, energy bands and conductivities of (Me3NEt)[Pd(dmit) 2]2 and (NEt4)[Pd(dmit) 2]2

The electrical conductive molecular crystals (Me₃NEt)[Pd(dmit) ₂]₂ and (NEt₄)[Pd (dmit) ₂]₂ (dmit = 4,5-dimercapto-1,3-dithiole-2-thione) have been prepared, and their crystal structures and conductivity-temperature curves have been determined. The fact that the conductivity at room temperature of (Me₃NEt)[Pd(dmit) ₂]₂ (σ = 58 Ω^-1 cm^-1) is much higher than that of (Net₄)-[Pd(dmit)₂]₂ (σ = 2.2 Ω^-1.cm^-1) has been rationally explained by the results of energy band calculations. (MeNEt₃)[Pd(dmit)₂]₂ belongs to monoclinic system, P2₁/m space group and (Net₄)[Pd (dmit)₂]₂ belongs to triclinic system, space group. The structural conducting component of the crystals is the planar coordinative anion [Pd(dmit)₂]^0.5- which forms the face-to-face dimmer. [Pd(dmit)₂]^- ₂These dimers have been further constructed to be a kind of two-dimensional (2-D) conductive molecular sheet by means of S_S intermolecular interactions. The tiny difference of the above 2-D molecular sheets of the two title crystals has resulted in one order of magnitude difference of conductivities.     

Synthesis, structure and physical properties of the new Zintl phases Eu11Zn6Sb12 and Eu11Cd6Sb12

Reported are the syntheses, crystal structure determinations from single-crystal X-ray diffraction, and magnetic properties of two new ternary compounds, Eu₁₁Cd₆Sb₁₂ and Eu₁₁Zn₆Sb₁₂. Both crystallize with the complex Sr₁₁Cd₆Sb₁₂ structure type—monoclinic, space group C2/m (no. 12), Z=2, with unit cell parameters a=31.979(4) Å, b=4.5981(5) Å, c=12.3499(14) Å, β=109.675(1)° for Eu₁₁Zn₆Sb₁₂, and a=32.507(2) Å, b=4.7294(3) Å, c=12.4158(8) Å, β=109.972(1)° for Eu₁₁Cd₆Sb₁₂. Their crystal structures are best described as made up of polyanionic and ribbons of corner-shared ZnSb₄ and CdSb₄ tetrahedra and Eu²⁺ cations. A notable characteristic of these structures is the presence of Sb-Sb interactions, which exist between two tetrahedra from adjacent layers, giving rise to unique channels. Detailed structure analyses shows that similar bonding arrangements are seen in much simpler structure types, such as Ca₃AlAs₃ and Ca₅Ga₂As₆ and the structure can be rationalized as their intergrowth. Temperature-dependent magnetization measurements indicate that Eu₁₁Cd₆Sb₁₂ orders anti-ferromagnetically below 7.5 K, while Eu₁₁Zn₆Sb₁₂ does not order down to 5 K. Resistivity measurements confirm that Eu₁₁Cd₆Sb₁₂ is poorly metallic, as expected for a Zintl phase.     

Hydrothermal Synthesis and Spectroscopic and Magnetic Behavior of the Mn7(HOXO3)4(XO4)2(X=As, P) Compounds. Crystal Structure of Mn7(HOAsO3)4(AsO4)2

The Mn₇(HOXO₃)₄(XO₄)₂ (X=As, P) compounds have been synthesized by using hydrothermal conditions. The arsenate phase was obtained under autogeneous pressure at 170°C. However, more drastic conditions at both pressure and temperature were necessary in the attainment of the phosphate compound. The crystal structure of Mn₇(HOAsO₃)₄(AsO₄)₂ was solved using single-crystal data. The unit-cell parameters are a=6.810(3) Å, b=8.239(2) Å, c=10.011(4) Å, α=104.31(2)°, β=108.94(3)°, γ=101.25(2)°. Triclinic, P-1 with Z=1. The isostructural Mn₇(HOPO₃)₄(PO₄)₂ phase was characterized from X-ray powder diffraction techniques. The crystal structure of both compounds consists of zig-zag chains constructed by dimeric edge-sharing Mn₂O₁₀ octahedra linked through the MnO₅ trigonal bipyramids. The three-dimensional framework is completed by the connection between isolated MnO₆ entities to the dimers octahedra and trigonal bipyramids. The existence of hydrogenarsenate and hydrogenphosphate anions has been confirmed by IR and Raman spectroscopies. Magnetic measurements indicate the existence of antiferromagnetic interactions in both compounds, which are slightly stronger in the arsenate phase.     

Gallium substitutions as a means to stabilize alkaline-earth and rare-earth metal pnictides with the cubic Th3P4 type: Synthesis and structure of A7Ga2Sb6 (A=Sr, Ba, Eu)

Three new compounds—Sr_7.04(2)Ga_1.94(2)Sb₆, Ba_7.02(3)Ga_1.98(3)Sb₆ and Eu_7.04(3)Ga_1.90(3)Sb₆—have been synthesized from reactions of the corresponding elements using gallium as a metal flux. Their crystal structures (space group I4¯3d (No. 220), Z=2 with unit cell parameters: a=9.9147(9) Å for the Sr-compound; a=10.3190(9) Å for the Ba-compound; and a=9.7866(8) Å for the Eu-compound) have been established by single-crystal X-ray diffraction. The structures are best described as Ga-stabilized derivatives of the hypothetical Sr₄Sb₃, Ba₄Sb₃ and Eu₄Sb₃ phases with the cubic Th₃P₄ type. Such an inclusion of interstitial Ga atoms in this atomic arrangement results in the formation of isolated [Ga₂Sb₆]¹⁴⁻ fragments, isoelectronic and isostructural with the [Sn₂Te₆]⁶⁻ anions in the K₃SnTe₃ type, and allows for the attainment of a charge-balanced electron count. In that sense, the Sr₄Sb₃, Ba₄Sb₃ and Eu₄Sb₃ binaries, which are expected to be electron-deficient and are currently unknown, can be “turned” into Sr₇Ga₂Sb₆, Ba₇Ga₂Sb₆ and Eu₇Ga₂Sb₆, whose structures are readily rationalized following the Zintl concept.     

X-ray photoelectron spectroscopy studies of Yb14MnSb11 and Yb14ZnSb11

Measurements of core and valence electronic states of single crystals of the rare earth transition metal Zintl phases Yb₁₄MnSb₁₁ and Yb₁₄ZnSb₁₁ were performed using the X-ray photoelectron spectroscopy station of Beamline 7 at the Advanced Light Source. Sample surfaces of Yb₁₄MnSb₁₁ and Yb₁₄ZnSb₁₁ were measured as received, after Ar⁺ ion bombardment, and after cleaving in situ. The single crystal structure of Yb₁₄ZnSb₁₁ is also reported. Both compounds are air-sensitive and show Yb³⁺ due to surface oxidation. In the case of Yb₁₄MnSb₁₁, there is no evidence for Yb³⁺ that would be intrinsic to the sample, consistent with previously reported X-ray magnetic circular dichroism studies. Detailed analyses of the Yb₁₄ZnSb₁₁ surfaces reveal a significant contribution of both Yb³⁺ and Yb²⁺ 4f states in the valence band region. This result is predicted for the Zn analog by Zintl counting rules and support the mixed valency of Yb for Yb₁₄ZnSb₁₁. Further detailed analysis of the core and valence band structure of both Yb₁₄MnSb₁₁ and Yb₁₄ZnSb₁₁ is presented.     

New Gallium Phosphate Frameworks Containing 1,4-Diaminobutane and 1,5-Diaminopentane: [NH3(CH2)xNH3][Ga4(PO4)4(HPO4)] and [NH3(CH2)xNH3][Ga(PO4)(HPO4)] (x=4 and 5)

Two new gallium phosphates, [NH₃(CH₂)₄NH₃][Ga₄(PO₄)₄ (HPO₄)] (I) and [NH₃(CH₂)₄NH₃][Ga(PO₄)(HPO₄)] (II), have been synthesized under solvothermal conditions in the presence of 1,4-diaminobutane and their structures determined using room-temperature single-crystal X-ray diffraction data. Compound (I) (M_r=844.90, triclinic, space group P-1, a=9.3619(3), b=10.1158(3) and c=12.6456(5) Å, α=98.485(1), β=107.018(2) and γ=105.424(1)°; V=1070.39 ų, Z=2, R=3.68% and R_w=4.40% for 2918 observed data [I>3(σ(I))]) consists of GaO₄ and PO₄ tetrahedra and GaO₅ trigonal bipyramids linked to generate an open three-dimensional framework containing 4-, 6-, 8-, and 12-membered rings of alternating Ga- and P-based polyhedra. 1,4-Diaminobutane dications are located in channels bounded by the 12-membered rings in the two-dimensional pore network and are held to the framework by hydrogen bonding. Compound (II) (M_r=350.84, monoclinic, space group P2₁/c, a=4.8922(1), b=18.3638(6) and c=13.7468(5) Å, β=94.581(1)°; V=1227.76 ų, Z=4, R=2.95% and R_w=3.37% for 2050 observed data [I>3(σ(I))]) contains chains of edge-sharing 4-membered rings of alternating GaO₄ and PO₄ tetrahedra constituting a backbone from which hang ‘pendant’ PO₃(OH) groups. Hydrogen bonding between the GaPO framework and the diamine dications holds the structure together. A previously reported phase, [NH₃(CH₂)₄NH₃][Ga₄(PO₄)₄(HPO₄)] (V), structurally related but distinct from its stoichiometric equivalent, (I), has been prepared as a pure phase by this method. Two further materials, [NH₃(CH₂)₅NH₃][Ga₄(PO₄)₄(HPO₄)] (III) (tricli- nic, lattice parameters from PXD: a=9.3565(4), b=5.0156(2) and c=12.7065(4) Å, α=96.612(3), β=102.747(4) and γ=105.277(3)°) and [NH₃(CH₂)₅NH₃][Ga(PO₄)(HPO₄)] (IV) (M_r=364.86, monoclinic, space group P2₁/n, a=4.9239(2), b=13.2843(4) and c=19.5339(7) Å, β=96.858(1)°; V=1268.58 ų, Z=4, R=3.74% and R_w=4.44% for 2224 observed room-temperature data [I>3(σ(I))]), were also prepared under similar conditions in the presence of 1,5-diaminopentane. (III) and (IV) are structurally related to, yet distinct from (I) and (II) respectively.     

Ga-Ga bonding and tunnel framework in the new Zintl phase Ba3Ga4Sb5

A new Zintl phase Ba₃Ga₄Sb₅ was obtained from the reaction of Ba and Sb in excess Ga flux at 1000°C, and its structure was determined with single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group Pnma (No. 62) with a=13.248(3) Å, b=4.5085(9) Å, c=24.374(5) Å and Z=4. Ba₃Ga₄Sb₅ has a three-dimensional [Ga₄Sb₅]⁶⁻ framework featuring large tunnels running along the b-axis and accommodating the Ba ions. The structure also has small tube-like tunnels of pentagonal and rhombic cross-sections. The structure contains ethane-like dimeric Sb₃Ga-GaSb₃ units and GaSb₄ tetrahedra that are connected to form 12- and 14-membered tunnels. Band structure calculations confirm that the material is a semiconductor and indicate that the structure is stabilized by strong Ga-Ga covalent bonding interactions.