Ternary Rare Earth (RE) Gold Compounds REAuCd and RE2Au2Cd

New intermetallic rare earth compounds REAuCd (RE = Y, La–Nd, Sm–Yb) and RE₂Au₂Cd (RE = La, Pr, Nd, Sm) were prepared by reaction of the elements in sealed tantalum tubes in a high‐frequency furnace. The compounds were investigated by X‐ray diffraction both on powders and single crystals. The equiatomic REAuCd compounds with RE = Y, La–Nd, Sm, and Gd–Tm adopt the ZrNiAl type structure with space group P62m. Single crystal X‐ray data yielded a = 786.2(2), c = 415.9(1) pm, wR2 = 0.0337, 402 F² values for LaAuCd and a = 782.91(9), c = 410.01(5) pm, wR2 = 0.0653, 395 F² values for CeAuCd with 14 parameters for each refinement. Geometrical motifs in CeAuCd are two types of gold centered tricapped trigonal prisms: [Au1Cd₃Ce₆] and [Au2Cd₆Ce₃]. The gold and cadmium atoms form a three‐dimensional [AuCd] polyanion in which the cerium atoms fill distorted hexagonal channels. EuAuCd and YbAuCd crystallize with a TiNiSi type structure, space group Pnma: a = 755.2(1), b = 450.59(5), c = 878.6(1) pm, wR2 = 0.0904, 500 F² values for EuAuCd, and a = 731.64(3), b = 432.94(2), c = 875.80(4) pm, wR2 = 0.1192, 457 F² values for YbAuCd with 20 parameters for each refinement. In these structures the europium(ytterbium) and cadmium atoms form zig‐zag chains of egde‐ and face‐sharing trigonal prisms which are centered by the gold atoms. Also in EuAuCd and YbAuCd a three‐dimensional [AuCd] polyanion occurs in which the europium(ytterbium) atoms are embedded. Europium and ytterbium are divalent in EuAuCd and YbAuCd. Susceptibility measurements show Pauli paramagnetism for YbAuCd and Curie‐Weiss behavior above 100 K for EuAuCd with an experimental magnetic moment of 7.86(6) μ_B/Eu. Ferromagnetic ordering is detected at 28 K. The saturation magnetic moment is 7.1(1) μ_B/Eu at 1.9 K. ¹⁵¹Eu Mössbauer spectra show an isomer shift of –9.2(2) mm/s and full magnetic hyperfine field splitting at 4.2 K with an internal hyperfine field of 19.5(4) T at the europium nuclei. The RE₂Au₂Cd compounds crystallize with the Mo₂FeB₂ structure, a ternary ordered version of the U₃Si₂ type. These structures may be considered as an intergrowth of distorted CsCl and AlB₂ related slabs of compositions RECd and REAu₂. Chemical bonding in REAuCd and RE₂Au₂Cd is briefly discussed.     

Structure and magnetic properties of RE2Cu2Cd

The ternary intermetallic compounds RE₂Cu₂Cd (RE=Y, Sm, Gd-Tm, Lu) were synthesized by induction-melting of the elements in sealed tantalum tubes. The samples were characterized by X-ray powder diffraction. The structure of Gd₂Cu₂Cd was refined from single crystal X-ray diffractometer data: Mo₂FeB₂ type, space group P4/mbm, a=756.2(3), c=380.2(3) pm, wR2=0.0455, 321 F² values, 12 variables. The structures are 1:1 intergrowth variants of slightly distorted CsCl and AlB₂ related slabs of compositions RECd and RECu₂. The copper and cadmium atoms build up two-dimensional [Cu₂Cd] networks (257 pm Cu-Cu and 301 pm Cu-Cd in Gd₂Cu₂Cd) which are bonded to the rare earth atoms via short RE-Cu contacts (290 pm in Gd₂Cu₂Cd). Temperature dependent susceptibility measurements of RE₂Cu₂Cd with RE=Gd, Tb, Dy, and Tm show experimental magnetic moments which are close to the free RE³⁺ ion values. The four compounds show ferromagnetic ordering at T_C=116.7(2), 86.2(3), 48.4(1), and 14.5(1) K, respectively, as confirmed by heat capacity measurements. Dy₂Cu₂Cd shows a spin reorientation at T_N=16.9(1) K.     

Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

Synthesis and characterization of monodisperse spherical SiO2@RE2O3 (RE=rare earth elements) and SiO2@Gd2O3:Ln (Ln=Eu, Tb, Dy, Sm, Er, Ho) particles with core-shell structure

Spherical SiO₂ particles have been coated with rare earth oxide layers by a Pechini sol-gel process, leading to the formation of core-shell structured SiO₂@RE₂O₃ (RE=rare earth elements) and SiO₂@Gd₂O₃:Ln³⁺ (Ln=Eu, Tb, Dy, Sm, Er, Ho) particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and cathodoluminescence spectra as well as lifetimes were used to characterize the resulting SiO₂@RE₂O₃ (RE=rare earth elements) and SiO₂@Gd₂O₃:Ln³⁺ (Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺, Er³⁺, Ho³⁺) samples. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size ca. 380 nm), smooth surface and non-agglomeration. The thickness of shells could be easily controlled by changing the number of deposition cycles (40 nm for two deposition cycles). Under the excitation of ultraviolet, the Ln³⁺ ion mainly shows its characteristic emissions in the core-shell particles from Gd₂O₃:Ln³⁺ (Eu³⁺, Tb³⁺, Sm³⁺, Dy³⁺, Er³⁺, Ho³⁺) shells.     

Crystal structures and new perspectives on Y3Au4 and Y14Au51

Y₃Au₄ (triyttrium tetragold) and Y₁₄Au₅₁ (tetradecayttrium henpentacontagold), two binary representatives of Au‐rich rare earth (R ) systems crystallize with the space groups R and P 6/m , adopting the Pu₃Pd₄ and Gd₁₄Ag₅₁ structure types, respectively (Pearson symbols hR 42 and hP 65). A variety of binary R –Au compounds have been reported, although only a few have been investigated thoroughly. Many reports lack information or misinterpret known compounds reported elsewhere. The Pu₃Pd₄ type is fairly common for group 10 elements Ni, Pd, and Pt, while Au representatives are restricted to just five examples, i.e. Ca₃Au₄, Pr₃Au₄, Nd₃Au₄, Gd₃Au₄, and Th₃Au₄. Sm₆Au₇ is suspected to be Sm₃Au₄ due to identical symmetry and close unit‐cell parameters. The Pu₃Pd₄ structure type allows for full substitution of the position of the rare earth atom by more electronegative and smaller elements, i.e. Ti and Zr. The Gd₁₄Ag₅₁ type instead is more common for the group 11 metals, while rare representatives of group 12 are known. Y₃Au₄ can be represented as a tunnel structure with encapsulated cations and anionic chains. Though tunnels are present in Y₁₄Au₅₁, this structure is more complex and is best described in terms of polyhedral `pinwheels' around the tunnel forming polyhedra along the c axis.     

Minimization of mass interferences in quadrupole inductively coupled plasma mass spectrometric (ICP-MS) determination of palladium using a flow injection on-line displacement solid-phase extraction protocol

A flow injection on-line displacement solid-phase extraction protocol was employed to minimize mass interferences with determination of palladium by inductively coupled plasma mass spectrometry (ICP-MS). The developed method involved in on-line complexing of Ag⁺ with pyrrolidine dithiocarbamate (PDC), presorption of the resultant Ag–PDC onto a microcolumn packed with the cigarette filter, displacement sorption of Pd²⁺ through loading the sample solution onto the microcolumn due to on-line displacement reaction between Pd²⁺ and the presorbed Ag–PDC, elution of the retained Pd²⁺ with 50 μL of ethanol for on-line ICP-MS detection. Interferences from co-existing heavy metal ions with lower stability of their PDC complexes relative to Ag–PDC were minimized/eliminated. No interferences from 5 mg L^− 1 Zn and 3 mg L^− 1 Pb for ¹⁰⁴Pd, 0.4 mg L^− 1 Cu for ¹⁰⁵Pd, 6 mg L^− 1 Zn and 2 mg L^− 1 Cd for ¹⁰⁶Pd, 6 mg L^− 1 Zn and 3 mg L^− 1 Cd for ¹⁰⁸Pd, and 2 mg L^− 1 Cd for ¹¹⁰Pd were observed for the determination of 100 ng L^− 1 Pd. The enhancement factors of 71–75, sample throughput of 23 samples h^− 1 and detection limits of 2.8–3.5 ng L^− 1 were achieved with the consumption of 3.0 mL of sample solution. The precision (RSD) for eleven replicate determinations of Pd at the 100 ng L^− 1 level was 1.8–2.7%. The developed method was applied to the determination of palladium in rock samples.     

Augmented formic acid electro-oxidation at a co-electrodeposited Pd/Au nanoparticle catalyst

In this study, the formic acid electro-oxidation reaction (FAEOR) was catalyzed on a Pd-Au co-electrodeposited binary catalyst. The kinetics of FAEOR were intensively impacted by changing the Pd²⁺:Au³⁺ molar ratio in the deposition medium. The Pd₁-Au₁ catalyst (for which the Pd²⁺:Au³⁺ molar ratio was 1:1) acquired the highest activity with a peak current density for the direct FAEOR (I_p) of 4.14 mA cm^?2 (ca. 13- times higher than that (ca. 0.33 mA cm^?2) of the pristine Pd₁-Au₀ catalyst). It also retained the highest stability that was denoted in fulfilling ca. 0.292 mA cm^?2 (ca. 19-times higher than 0.015 mA cm^?2 of the pristine Pd₁-Au₀ catalyst) after 3600 s of continuous electrolysis at 0.05 V. The CO stripping and impedance measurements confirmed, respectively, the geometrical and electronic enhancements in the proposed catalyst.     

Electrochemical cycling of Mg in Mg[TFSI]2/tetraglyme electrolytes

The electrochemical reversibility of magnesium was observed in an electrolyte consisting of 0.5 M Mg[TFSI]₂ in tetraglyme in the presence of a small amount of Mg[BH₄]₂. The cyclic efficiency of the cathodic/anodic process was found to increase initially with [BH₄]⁻ then plateau at about 75% beyond 6 mM in these experiments. This concentration is in the region of that indicated by Karl Fischer analysis of the electrolyte as required of [BH₄]⁻ as a dehydrating agent. Cyclic voltammetry showed the reduction onset potential at approximately − 0.35 V vs. Mg and subsequent oxidation around 0 V vs. Mg. Stable cyclic efficiency of approximately 75% over 500 cycles is demonstrated on a platinum substrate. Mg cycling on magnesium, copper and aluminium substrates all show stable cycling over 500 cycles with cyclic efficiency > 73%.     

Investigation of Mg modified mesoporous silicas and their CO2 adsorption capacities

CO₂ adsorption properties on Mg modified silica mesoporous materials were investigated. By using the methods of co-condensation, dispersion and ion-exchange, Mg²⁺ was introduced into SBA-15 and MCM-41, and transformed into MgO in the calcination process. The basic MgO can provide active sites to enhance the acidic CO₂ adsorption capacity. To improve the amount and the dispersion state of the loading MgO, the optimized modification conditions were also investigated. The XRD and TEM characteristic results, as well as the CO₂ adsorption performance showed that the CO₂ adsorption capacity not only depended on the pore structures of MCM-41 and SBA-15, but also on the improvement of the dispersion state of MgO by modification. Among various Mg modified silica mesoporous materials, the CO₂ adsorption capacity increased from 0.42 mmol g⁻¹ of pure silica SBA-15 to 1.35 mmol g⁻¹ of Mg–Al–SBA-15-I1 by the ion-exchange method enhanced with Al³⁺ synergism. Moreover, it also increased from 0.67 mmol g⁻¹ of pure silica MCM-41 to 1.32 mmol g⁻¹ of Mg–EDA–MCM-41-D10 by the dispersion method enhanced with the incorporation of ethane diamine. The stability test by 10 CO₂ adsorption/desorption cycles showed Mg–urea–MCM-41-D10 possessed quite good recyclability.     

Rare‐Earth‐Rich Magnesium Compounds RE23Rh7Mg4 (RE = La,Ce, Pr,Nd, Sm,Gd) with Tetrahedral Mg4 Clusters

The rare earth‐rich compounds RE₂₃Rh₇Mg₄ (RE = La, Ce, Pr, Nd, Sm, Gd) were prepared by induction‐melting the elements in sealed tantalum tubes. The new compounds were characterized by X‐ray powder diffraction. They crystallize with the hexagonal Pr₂₃Ir₇Mg₄ type structure, space group P6₃mc. The structures of La₂₃Rh₇Mg₄ (a = 1019.1(1), c = 2303.7(4) pm, wR2 = 0.0827, 1979 F² values, 69 variables), Nd₂₃Rh₇Mg₄ (a = 995.4(2), c = 2242.3(5) pm, wR2 = 0.0592, 2555 F² values, 74 variables) and Gd₂₃Rh_6.86(5)Mg₄ (a = 980.5(2), c = 2205.9(5) pm, wR2 = 0.0390, 2083 F² values, 71 variables) were refined from single crystal X‐ray diffractometer data. The three crystallographically different rhodium atoms have trigonal prismatic rare earth coordination with short RE–Rh distances (283–300 pm in Nd₂₃Rh₇Mg₄). The prisms are condensed via common edges, leading to a rigid three‐dimensional network in which isolated Mg₄ tetrahedra (312–317 pm Mg–Mg in Nd₂₃Rh₇Mg₄) are embedded. Temperature dependent magnetic susceptibility data of Ce₂₃Rh₇Mg₄ indicate Curie‐Weiss behavior with an experimental magnetic moment of 2.52(1) μ_B/Ce atom, indicative for stable trivalent cerium. Antiferromagnetic ordering is evident at 2.9 K.     

Raman scattering in rare earths tetraborides

The Raman spectra of single crystalline RE (rare earth) tetraborides REB₄ (RE = Y, La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu) are measured and analysed with respect to the dependence of the phonon frequencies on the rare earth metal. Phonons representing octahedral B₆ units are identified by comparison to the according phonon modes of hexaborides. Their relative force parameters are estimated.     

Separating Ag, B, Cd, Dy, Eu, and Sm in a Gd matrix using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester extraction chromatography for ICP-AES analysis

The separation procedure for Ag, B, Cd, Dy, Eu and Sm as impurities in Gd matrix using ICP-AES technique with an extraction chromatographic column has been developed. The spectral interference of the Gd matrix on the elements was eliminated using a chromatography technique with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) as the mobile phase and XAD-16 resin as the stationary phase. Ag⁺, B₄O₇²⁻, and Cd²⁺ were eluted with 0.1 M HNO₃, while rare earth ions were not. The best eluent for separating Eu and Sm in the Gd matrix was 0.3 M HNO₃. The limit of quantitation for these elements was 0.6-3.0 ng mL⁻¹. The recovery of Ag, B, and Cd was 90-104% using 0.1 M HNO₃ as the eluent, while that of Eu, Gd, and Sm ranged from 100 to 102% with 0.3 M HNO₃. Dy was recovered quantitatively with 4 M HNO₃. The relative standard deviation of the methods for a set of three replicates was between 1.0 and 15.4% for the synthetic and standard Gd solutions. The proposed separation procedure was used to measure Ag, B, Cd, Dy, Eu, and Sm in a standard Gd solution.     

Cobalt Centered Trigonal RE6 Prisms and Mg4 Clusters as Basic Structural Units in RE4CoMg (RE = Y,La, Pr,Nd, Sm,Gd–Tm)

The new rare earth metal rich intermetallic compounds RE₄CoMg (RE = Y, La, Pr, Nd, Sm, Gd–Tm) were prepared via melting of the elements in sealed tantalum tubes in a water‐cooled sample chamber of a high‐frequency furnace. The compounds were investigated by X‐ray diffraction of powders and single crystals: Gd₄RhIn type, , a = 1428.38(9) pm, wR2 = 0.0638, 680 F² values, 20 variables for La₄CoMg, a = 1399.5(2) pm, wR2 = 0.0584, 589 F² values, 20 variables for Pr₄CoMg, a = 1390.2(3) pm, wR2 = 0.0513, 634 F² values, 20 variables for Nd_3.90CoMg_1.10, a = 1381.0(3) pm, wR2 = 0.0730, 618 F² values, 22 variables for Sm_3.92Co_0.93Mg_1.08, a = 1373.1(4) pm, wR2 = 0.0586, 611 F² values, 20 variables for Gd_3.92CoMg_1.08, a = 1362.1(3) pm, wR2 = 0.0576, 590 F² values, 20 variables for Tb_3.77CoMg_1.23, a = 1344.8(2) pm, wR2 = 0.0683, 511 F² values, 20 variables for Dy_3.27CoMg_1.73, and a = 1343.3(2) pm, wR2 = 0.0560, 542 F² values, 20 variables for Er_3.72CoMg_1.28. The cobalt atoms have trigonal prismatic rare earth coordination. Condensation of the CoRE₆ prisms leads to a three‐dimensional network which leaves larger voids that are filled by regular Mg₄ tetrahedra at a Mg–Mg distance of 316 pm in La₄CoMg. The magnesium atoms have twelve nearest neighbors (3 Mg + 9 RE) in icosahedral coordination. In the structures with Nd, Sm, Gd, Tb, Dy, and Er, the RE1 positions which are not involved in the trigonal prismatic network reveal some RE1/Mg mixing and the Sm_3.92Co_0.93Mg_1.08 structure shows small cobalt defects. Considering La₄CoMg as representative of all studied systems an analysis of the chemical bonding within density functional theory closely reproduces the crystal chemistry scheme and shows the role played by the valence states of the different constituents in the electronic band structure. Strong bonding interactions were observed between the lanthanum and cobalt atoms within the trigonal prismatic network.     

Hydrothermal ethanol conversion on Ag,Cu, Au/TiO2

The effect UV irradiation and silver, copper, and gold ions (M ^z+) supported on titania (anatase) have on the activity of M/TiO₂ samples in ethanol conversion at 150–400°C is examined. After UV irradiation, the yields of acetaldehyde and ethylene increase for TiO₂ and Ag/TiO₂ samples, while the activity of Cu²⁺/TiO₂ decreases. The activation energy of ethanol dehydration declines in the order TiO₂ > Au³⁺ > Cu²⁺ > Ag⁺ and correlates linearly with a reduction in the radius of M ^z+ in crystal. The number of acidic sites on a M/TiO₂ surface titrated via pyridine adsorption grows upon the introduction of M. Unlike Cu²⁺/TiO₂, these sites are not activated after the irradiation of TiO₂, Ag⁺/TiO₂, and Au³⁺/TiO₂. According to IR spectral data on adsorbed pyridine, all samples contain Lewis and Brönsted acidic sites.     

Synthesis and VUV-UV spectroscopic properties of rare earth borosilicate oxyapatite: RE5Si2BO13:Ln (RE=La, Gd, Y; Ln=Eu, Tb)

Three rare earth borosilicate oxyapatites, RE₅Si₂BO₁₃ (RE=La, Gd, Y), were synthesized via wet chemical method, of which RE₅Si₂BO₁₃ (RE=Gd, Y) were first reported in this work. In the three oxyapatites, [BO₄] and [SiO₄] share the [TO₄] tetrahedral oxyanion site, and RE³⁺ ions occupy all metal sites. The differential scanning calorimetry-thermo gravimetry measurements and high temperature powder X-ray diffraction pattern revealed a vitrification process within 300-1200 °C, which was due to the glass-forming nature of borosilicates. From the VUV excitation spectra of Eu³⁺ and Tb³⁺ in RE₅Si₂BO₁₃, the optical band gaps were found to be 6.31, 6.54 and 6.72 eV for RE₅Si₂BO₁₃ (RE=La, Gd, Y), respectively. The emission and excitation bands of Eu³⁺ and Tb³⁺ are discussed relating with their coordination environments. Among the three hosts, Y₅Si₂BO₁₃ would be the best for Eu³⁺ and Tb³⁺-doped phosphors.     

Preparation and up-conversion fluorescence of rare earth (Er or Yb/Er)-doped TiO2 nanobelts

Anatase TiO₂ nanobelts doped with rare earth (RE) ions Yb³⁺, Er³⁺ or Yb³⁺/Er³⁺ have been prepared using layered titanate nanobelts (LTO NBs) with RE ions as the precursor obtained by ion-exchange between LTO NBs and RE ions under hydrothermal process. Various measurement results demonstrate that the RE ions have doped into the lattice of TiO₂, and the Er³⁺ or Yb³⁺/Er³⁺ doped nanobelts show strong visible up-conversion (UC) fluorescence under 980 nm excitation. The UC emission intensity of LTO NBs embedded with Er³⁺ or Yb³⁺/Er³⁺ is slightly higher than that of the corresponding TiO₂ nanobelts doped with RE ions, whereas higher RE doping content leads to the decrease of UC emission intensity due to the concentration-quenching effect.     

A Tray‐Shaped,PdII‐Clipped Au3 Complex as a Scaffold for the Modular Assembly of [3×n] Au Ion Clusters

A tray‐shaped Pd^II₃Au^I₃ complex ( 1 ) is prepared from 3,5‐bis(3‐pyridyl)pyrazole by means of tricyclization with Au^I followed by Pd^II clipping. Tray 1 is an efficient scaffold for the modular assembly of [3×n] Au^I clusters. Treatment of 1 with the Au^I₃ tricyclic guest 2 in H₂O/CH₃CN (7:3) or H₂O results in the selective formation of a [3×2] cluster ( 1 ? 2 ) or a [3×3] cluster ( 1 ? 2 ? 1 ), respectively. Upon subsequent addition of Ag^I ions, these complexes are converted to an unprecedented Au₃–Au₃–Ag–Au₃–Au₃ metal ion cluster.     

A Tray‐Shaped,PdII‐Clipped Au3 Complex as a Scaffold for the Modular Assembly of [3×n] Au Ion Clusters

A tray‐shaped Pd^II₃Au^I₃ complex ( 1 ) is prepared from 3,5‐bis(3‐pyridyl)pyrazole by means of tricyclization with Au^I followed by Pd^II clipping. Tray 1 is an efficient scaffold for the modular assembly of [3×n] Au^I clusters. Treatment of 1 with the Au^I₃ tricyclic guest 2 in H₂O/CH₃CN (7:3) or H₂O results in the selective formation of a [3×2] cluster ( 1 ⋅ 2 ) or a [3×3] cluster ( 1 ⋅ 2 ⋅ 1 ), respectively. Upon subsequent addition of Ag^I ions, these complexes are converted to an unprecedented Au₃–Au₃–Ag–Au₃–Au₃ metal ion cluster.     

La6Pd13Cd4 and Ce6Pd13Cd4 with palladium-centred rare earth octahedra: synthesis, structure, and chemical bonding

Abstract  

The palladium-rich cadmium compounds La₆Pd₁₃Cd₄ and Ce₆Pd₁₃Cd₄ were synthesized by induction melting the elements in sealed tantalum ampoules and subsequent annealing. They were characterized by X-ray powder and single-crystal diffraction: Na₁₆Ba₆N type, Im[`3] mIm\overline{3} m, a = 988.12(9) pm, wR2 = 0.0463, 225 F ² values, and 12 variables for La₆Pd₁₃Cd₄, and a = 982.1(2) pm, wR2 = 0.0521, 215 F ² values, and 12 variables for Ce₆Pd₁₃Cd₄. The striking structural motifs are palladium-centred La₆ and Ce₆ octahedra, which are packed in a bcc fashion. Further palladium and cadmium atoms built up three-dimensional [Pd₃Cd] networks in which the La₆Pd and Ce₆Pd octahedra are embedded. Chemical bonding analyses show that the dominant interaction occurs within the palladium-centred RE ₆ octahedra, while weaker bonding exists between them.     

Tin-rich Phases RE2Au3Sn6 with RE = La,Ce, Pr,Nd, Sm – Synthesis,Structure, Magnetic Properties,and 119Sn Mössbauer Spectra

The stannides RE₂Au₃Sn₆ (RE = La, Ce, Pr, Nd, Sm) were synthesized from the elements by arc-melting. Small single crystals were grown by annealing samples in sealed tantalum tubes in an induction furnace with a special annealing sequence. The polycrystalline phases were characterized through their X-ray powder diffraction pattern. The structures of Ce₂Au₃Sn₆, Pr₂Au₃Sn₆, and Nd₂Au₃Sn₆ were refined from single-crystal X-ray diffractometer data. The RE₂Au₃Sn₆ stannides crystallize with the orthorhombic La₂Zn₃Ge₆ type, space group Cmcm. The basic structural building units are Au1@Sn₄ tetrahedra and Au2@Sn₅ square pyramids. These units are condensed to layers and the structure can be described by a simple stacking of tetrahedral and pyramidal layers with the rare earth cations in between. Temperature dependent susceptibility studies indicate that all rare earth atoms are in the trivalent oxidation state, as their effective magnetic moments match the expected values of the free RE³⁺ ions. Pr₂Au₃Sn₆ and Nd₂Au₃Sn₆ exhibit antiferromagnetic ordering at T_N = 6.3(1) and 6.7(1) K. Investigations of the electrical resistivity of La₂Au₃Sn₆ and Ce₂Au₃Sn₆ confirmed that these compounds are metallic, for La₂Au₃Sn₆ a lower resistivity was observed, in line with the absence of screening unpaired electrons. ¹¹⁹Sn Mössbauer spectra for La₂Au₃Sn₆, Ce₂Au₃Sn₆, Pr₂Au₃Sn₆ and Nd₂Au₃Sn₆ show a complex superposition of three sub-spectra which can be differentiated through their distinctly different quadrupole splitting parameters. The isomer shifts (1.87 to 2.22 mm · s^–1) indicate significant s electron density at the tin nuclei.