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.     

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.     

The crystal structure and some properties of Eu2Sb3

The Mooser-Pearson phase Eu₂Sb₃ crystallizes in a new monoclinic structure type, space group $\text{P2}{}_1\text{c}$ (No. 14) with a = 6.570(1) Å, b = 12.760(2) Å, c = 15.028(2) Å, β = 90.04(1)°; Z = 8. The Sb atoms form six-membered twisted chain fragments oriented along the b-axis. The Eu atoms are eight- and nine-coordinated by Sb. The Eu₂Sb₃ structure is closely related to the structure of Ca₂As₃. The relations between their space-group symmetries are derived and hypothetical higher-symmetry structures are discussed. The semiconducting Eu₂Sb₃ is antiferromagnetic below T_N = 14.4°K. An Eu₂Sb₃-type structure was found also for Sr₂Sb₃.     

Ternary Antimonide EuSn3Sb4 and Related Metallic Zintl Phases

The ternary Zintl compound europium tin antimonide, EuSn₃Sb₄, has been synthesized at 900°C in the presence of a tin flux, and its structure has been determined by single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group D¹⁶_2h-Pnma with a=9.954(2), b=4.3516(7), c=22.650(4) Å, and Z=4 at 22°C. EuSn₃Sb₄ is isostructural to SrSn₃Sb₄; it possesses channels defined by an anionic framework of shared SnSb₄ tetrahedra, SnSb₃ trigonal pyramids, and Sb–Sb zigzag chains, and it is filled by Eu²⁺ cations. Resistivity measurements indicate weakly metallic behavior for ASn₃Sb₄ (A=Eu, Sr) and the structurally related Ba₂Sn₃Sb₆. The anisotropic metallic nature of these compounds is explained through extended Hückel band structure calculations.     

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.     

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.     

The lanthanoid polyantimonides with the ideal compositions Pr5Sb12 and Nd5Sb12 crystallizing with a new structure type and Ho2Sb5 with Dy2Sb5-type structure

The title compounds were isolated in well-crystallized form from samples with a substantial excess of antimony, annealed at temperatures slightly below the melting point of that element. Their crystal structures were determined from single-crystal diffractometer data. Pr_9-xSb_21-y and Nd_9-xSb_21-y crystallize with a new monoclinic structure type, Pearson symbol mS(62-5.4), space group Cm, Z=2 with a=2859.1(4) pm, b=426.3(1) pm, c=1356.1(2) pm, β=95.52(1)°, R=0.034 for 4351 structure factors and 188 variable parameters for Pr_9-xSb_21-y and a=2845(2) pm, b=424.7(8) pm, c=1345.9(9) pm, β=95.42(7)°, R=0.069 for 2928 F values and 188 variables for Nd_9-xSb_21-y. Of the 30 atomic sites, three show fractional occupancy corresponding to the compositions Pr_8.303(5)Sb_20.03(1) and Nd_8.30(2)Sb_19.98(9), respectively. A model for the order of occupied atomic sites with a tripled b-axis is proposed resulting in the ideal compositions Pr₅Sb₁₂ and Nd₅Sb₁₂. The holmium compound Ho₂Sb₅ has a Dy₂Sb₅-type structure: mP28, P2₁/m, a=1301.8(3) pm, b=414.9(1) pm, c=1451.1(2) pm, β=102.14(1)°, R=0.028 for 2573 F values and 86 variables. In both structure types most rare earth atoms have nine antimony neighbors forming tricapped trigonal prisms. The coordination polyhedra of the antimony atoms show a great variety, with a trigonal prism of rare earth atoms as one extreme case. The other extreme coordination of an antimony atom is a distorted octahedron formed by six antimony atoms. The differences and similarities of both structures are discussed. Chemical bonding within the antimony polyanions is analyzed on the basis of an extended Zintl-Klemm concept using bond-length-bond-strength relationships.     

The Crystal Structures of the Strontium Gallates Sr10Ga6O19 and Sr3Ga2O6

The crystal structures of Sr₁₀Ga₆O₁₉ and Sr₃Ga₂O₆ have been characterized using X-ray diffraction techniques. In the case of Sr₁₀Ga₆O₁₉, the structure was determined from a single crystal diffraction data set collected at room conditions and refined to a final R index of 0.061 for 3471 observed reflections (I>2 σ(I)). The compound is monoclinic with space group C12/c1 (a=34.973(4) Å, b=7.934(1) Å, c=15.943(2) Å, β=103.55(1)°, V=4300.7(6) ų, Z=8, D_calc=4.94 g/cm³, μ(MoKα)=32.04 mm⁻¹) and can be classified as an oligogallate. It is the first example of an inorganic compound where six [TO₄]-tetrahedra of only one chemical species occupying the tetrahedral centres are linked via bridging oxygen atoms to form [T₆O₁₉] groups. The hexamers are not linear, but highly puckered. Eleven symmetrically different Sr cations located in planes parallel (100) crosslink between the oligo-groups. They are coordinated by six to eight oxygen ligands. The structure of Sr₃Ga₂O₆ has been refined from powder diffraction data using the Rietveld method (space group Pa , a=16.1049(1), V=4177.1(1) ų, Z=24, D_calc=4.75 g/cm³). The compound is isostructural with tricalcium aluminate and contains highly puckered, six-membered [Ga₆O₁₈]¹⁸⁻ rings. The rings are linked by strontium cations having six to nine nearest oxygen neighbors.     

The binary gallide Eu5Ga9 - crystal structure, chemical bonding and physical properties

The title compound was prepared from the elements by reaction in a sealed tantalum tube at 1320 K followed by slow cooling to 970 K or, alternatively, in glassy carbon crucibles with HF melting. The crystal structure of Eu₅Ga₉ was refined from single-crystal data: Cmcm, a=4.613(1) Å, b=10.902(3) Å, c=26.097(6) Å, Z=4, R_F=0.036, 811 structure factors and 46 variables. The structure is described as a three-dimensional network formed by gallium atoms with europium atoms embedded in the cavities. The bonding analysis (LMTO, ELF) confirmed this representation of the structure. Magnetic susceptibility measurements show Curie-Weiss behavior above 60 K with a magnetic moment per Eu atom of 8.12(1) μ_B, indicating divalent europium. Eu₅Ga₉ orders antiferromagnetically at 19.0(5) K with re-ordering at 6.0(5) K. The electrical resistivity shows a metallic temperature dependence and magnetic scattering. ¹⁵¹Eu Mössbauer spectroscopic experiments are compatible with divalent europium and show complex magnetic hyperfine field splitting below the ordering temperature.     

V2Cu3Ga8, Mo2Cu3Ga8 and W2Cu3Ga8—New compounds with a novel order variant of a bcc packing and motifs of self-similarity

Single crystals of the new compounds TM₂Cu₃Ga₈ (TM=V, Mo, W) were synthesised from the elements. Structure determinations of the isotypic compounds (cI104, space group , Z=8; Mo₂Cu₃Ga₈: a=11.9171(10) Å, 613 refl., 23 param., R₁(F)=0.022, wR₂(F²)=0.047; W₂Cu₃Ga₈: 11.9248(8) Å, 346 refl., 23 param., R₁(F)=0.048, wR₂(F²)=0.086; V₂Cu₃Ga₈: 11.7861(14) Å, 374 refl., 24 param., R₁(F)=0.033, wR₂(F²)=0.081) showed a new cubic structure type which can be classified as an ordered defect variant of a bcc packing with a^′=4a: [(TM)₂(Cu)₃(□)₃][Ga₈]. The coordination polyhedra of the transition metals consist of Ga₈-cubes with 3 sides capped by Cu leading to coordination number 11. The arrangement of the TMGa₈Cu₃-polyhedra is in a way they form itself a 3-fold capped cube. All compositions were confirmed by EDX measurements.     

Some studies on the solid solutions in the systems Sr2Nb2O7Eu2Nb2O7 and Sr2Ta2O7Eu2Ta2O7

Preparation of new solid solutions containing divalent europium have been tried in the systems Eu₂Nb₂O₇Sr₂Nb₂O₇ and Eu₂Ta₂O₇Sr₂Ta₂O₇. These solid solutions described as Eu_2xSr_2(1?x)M₂O₇ (M = Nb and Ta) exist in a pure orthorhombic phase in a limited region of x from 0 to about 0.5. The compounds with compositions close to Eu₂M₂O₇ exist but techniques have not been found to prepare them in pure form.     

Reactions of the dications C7H6, C7H7, and C7H8 with methane: Predominance of doubly charged intermediates

The reactions of methane with the dications C₇H₆²⁺, C₇H₇²⁺, and C₇H₈²⁺ generated by electron ionization of toluene are studied using mass-spectrometry tools. It is shown that the reactivity is dominated by the formation of doubly charged intermediates, which can either eliminate molecular hydrogen to yield doubly charged products or undergo charge-separation reactions leading to the formation of a methyl cation and the corresponding C₇H_n+1⁺ monocation. Typical processes observed for dications, like electron transfer or proton transfer, are largely suppressed. The theoretically derived mechanism of the reaction between C₇H₆²⁺ and CH₄ indicates that the formation of the doubly charged intermediate is kinetically preferred at low internal energies of the reactants. In agreement, the experimental results show a pronounced hydrogen scrambling and dominant formation of the doubly charged products at low collision energies, whereas direct hydride transfer prevails at larger collision energies.     

Synthesis and crystal structure determination of the new ternary intermetallic phase Na17Cu6Ga46.5 (Na102Cu36Ga279)

Na₁₇Cu₆Ga_46.5 crystallizes in the trigonal system, space group with a = B = 16.183(6), C = 35.190(9) Å; Z = 6. Diffraction data were collected on a Nonius CAD 3 diffractometer within the octants hkl and of the corresponding A-centered monoclinic cell (a = 14.993(6), B = 16.184(7), C = 25.254(8) Å; β = 119.75(5)°). The 5091 reflections were transformed and averaged into 1216 observed (I> 3σ(I)) in the space group. The structure was solved by direct methods and refined by full-matrix least-squares to a final R(F) = 0.056. The structure of Na₁₀₂Cu₃₆Ga₂₇₉ contains icosahedra displaying two types of symmetry and a triply fused icosahedron which forms a very unusual polyhedral complex with a copper atom (M₂₈CuM₂₈). Clusters are linked to each other to form an intricated three-dimensional anionic lattice. Sodium cations lie inside 12-vertex (Friauf), 15-vertex, and 16-vertex polyhedral cavities. This stoichiometric phase has been interpreted in terms of electron-deficient bonding within clusters and localized (2c-2e) bonding between clusters. In association with the extended Hückel molecular orbital (EHMO) calculation, the Wade-Mingos electron counting procedure applies successfully.     

Synthesis and crystal structure determination of the new intermetallic phase Li13Cu6Ga21

Li₁₃Cu₆Ga₂₁ crystallizes in a cubic structure, space group Im3, with a = 13.568(2) Å, Z = 4. Diffraction data were collected on a NONIUS CAD 4 diffractometer in the range 4 ≤ 2θ ≤ 50° (MoKα radiation). The structure was solved by direct methods and refined by full-matrix least-squares to a final R(F) = 0.033 for 346 independent reflections with I> 3σ(I). Li₁₃Cu₆Ga₂₁ presents an interesting structure composed of Samson's polyhedral clusters (104 atoms) linked to each other through smaller junction polyhedral clusters (truncated tetrahedra and hypho-13-vertex polyhedra) containing lithium atoms in their centers.     

Synthesis and solid state studies on Mb2Sb2O7 and (Mn1−xCdx)2Sb2O7 pyrochlores

Pyrochlore oxides of the type Mn₂Sb₂O₇ and (Mn_1?xCd_x)₂Sb₂O₇ have been synthesized by high-temperature solid state reactions and characterized by X-ray diffraction and chemical analysis. X-Ray diffraction studies showed that the compound Mn₂Sb₂O₇ has a rhombohedrally distorted pyrochlore structure. In the solid solutions (Mn_1?xCd_x)₂Sb₂O₇, the phases with x ≥ 0.6 are cubic. Magnetic and ¹²¹Sb Mössbauer studies indicate that all the Mn and Sb are present in the +2 and +5 state occupying A and B sites, respectively, in the pyrochlore structure. Electrical measurements indicate that the compounds are insulators or semiconductors exhibiting p-type behavior. The stoichiometry and probable cause of the rhombohedral distortion in Mn₂Sb₂O₇ and solid solutions are discussed.     

Structure and properties of rhombohedral CePd3Ga8: A variant of the cubic parent compound with BaHg11 structure type

Single crystals of a new intermetallic gallide, R-CePd₃Ga₈, have been synthesized from excess molten gallium. Single-crystal X-ray diffraction reveals that R-CePd₃Ga₈ crystallizes in the R-3m space group with a=b=c=8.4903(10) Å and α=β=γ=89.993(17). R-CePd₃Ga₈ is a variant of the cubic BaHg₁₁ structure type with three structural units: a Ce-centered polyhedron, a distorted cube of Pd₂Ga₆ and a Pd-centered cuboctahedron. The distortions of these units are compared to undistorted analogous units in intermetallic compounds with BaHg₁₁ structure type. Field and temperature-dependent magnetization measurements on R-CePd₃Ga₈ reveal a paramagnetic material with strong antiferromagnetic correlations and a magnetization consistent with Ce³⁺. Electrical resistance measurements indicate Kondo behavior between localized Ce³⁺ magnetic moments.     

Structure and magnetic properties of ScFe6Ga6-type RCo5Ga7 (R=Y, Tb, Dy, Ho and Er)

The structure and magnetic properties of the RCo₅Ga₇ (R=Y, Tb, Dy, Ho and Er) compounds with the ScFe₆Ga₆-type structure have been studied. The stability of RCo₅Ga₇ is closely related with the ratio of the metal radii R_RE/R_(Co,Ga). With R_RE/R_(Co,Ga)?1.36, the compounds can be stabilized in the ScFe₆Ga₆-type structure. The lattice of RCo₅Ga₇ shrinks as the atomic order of R increases, and it is consistent with the lanthanide contraction. The structure analysis based on X-ray diffraction patterns reveals that in the orthorhombic RCo₅Ga₇ (Immm), R occupies the 2a site, and Co enters into the 8k and the 4h sites, and Ga is at the 4e, 4f, 4g, 4h and 8k sites. The interatomic distances and the coordination numbers of RCo₅Ga₇ are provided from the refinement results. The short interatomic distance (less than 2.480 Å) between the Co ions results in the negative magnetic interaction, which does not favor ferromagnetic ordering. The magnetic moment of YCo₅Ga₇ is absent, and RCo₅Ga₇ (R=Tb, Dy, Ho and Er) may have long-range magnetic ordering with the paramagnetic Curie temperature lower than 5 K.     

Eu2(p-ClC6H4COO)6(C12H8N2)2配合物热分解机理及非等温动力学

The thermal decomposition behaviour of europium p-chlorobenzoate complex with 1, 10-phenanthroline and its kinetics were studied in nitrogen by non-isothermal thermogravimetry.Its thermal decomposition occurs mainly in three steps..The intermediate and residue for each step of decomposition were identified from TGcurve.The kinetic parameters were obtained from analysis of the TG-DTG curves by the Achar method.the Madhusudanan- Krishnan-Niman (MKN) method and Ozawa method respectively.The most probable mechanisms function for the first and second stage were suggested by comparing the kinetic parameters.     

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.