Matthias Eul

Octahedral Pd2+ coordination and ferromagnetic ordering in Pd(S2O7).

It is well known that square-planar coordination is typical for divalent palladium exhibiting an electronic d configuration. Only with ligands that cause a weak ligand field splitting might an octahedral coordination be stabilized. This situation has been shown especially for palladium fluorides, and in addition to both modifications of PdF2 [1–4] the polynary fluorides APdF3 (A = K, Rb), [2] PdZrF6, [5] CsPd2F5, [6] PdAu2F8, [7] LiPdGaF6, and RbPdAlF6 [8] show essentially undistorted [PdF6] octahedra. In contrast, with oxygen ligands, the typical square-planar palladium coordination is nearly always observed. The simplest example is the structure of PdO itself, that consists of vertex-connected [PdO4] polyhedra, at least in the bulk material. When the donor oxygen atoms of ligand molecules are considered, then the coordination chemistry of Pd is clearly dominated by a square-planar metal coordination environment. Nevertheless, it has been shown that octahedral oxygen coordination of Pd can be achieved if very rigid and stable frameworks are established, housing the Pd ions in octahedral voids. Two solid-state examples for this type of frameworks are known, namely Ca2PdWO6 [11] and PdAs2O6, [12] which are closely related to the structures of perovskite and aluminum trichloride, respectively. Two other highly interesting examples originate from polyoxometalate chemistry: In the anions [Pd13(AsPh)8O32] 6 and [Pd13Se8O32] 6 one of the thirteen Pd ions is in the center of a large cage providing octahedral or even cubic oxygen coordination. Finally, an oxalate framework has been described that clearly contains Pd in a distorted octahedral coordination environment, as demonstrated by powder diffraction and X-ray absorption (EXAFS) measurements. With respect to the efforts required to date to stabilize this uncommon coordination geometry, it is remarkable and unexpected that we now found an octahedral oxygen coordination environment for Pd in Pd(S2O7), a compound been obtained as highly moisture sensitive blue crystals from the reaction of elemental palladium with SO3 (Figure 1). It is the first time that this type of Pd coordination has been

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [Eu-II(Cp-BIG)(2)] (Cp-BIG=(4-nBu-C6H4)(5)-Cyclopentadienyl)

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24,270 cm(-1)) gives a symmetrical single band in the emission spectrum at 606 nm (νmax =16495 cm(-1), FWHM: 2090 cm(-1), Stokes-shift: 2140 cm(-1)), which is assigned to a 4f(6)5d(1) → 4f(7) transition of Eu(II). These remarkable values compare well to those for Eu(II)-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp(BIG))2] complex. Sharp emission signals, typical for Eu(III), are not visible.

Physical Properties of Superbulky Lanthanide Metallocenes: Synthesis and Extraordinary Luminescence of [Eu[superscript II](Cp[superscript BIG])[subscript 2]] (Cp[superscript BIG]=(4-nBu-C[subscript 6]H[subscript 4])[subscript 5]-Cyclopentadienyl)

The superbulky deca-aryleuropocene [Eu(Cp(BIG))2], Cp(BIG) = (4-nBu-C6H4)5-cyclopentadienyl, was prepared by reaction of [Eu(dmat)2(thf)2], DMAT = 2-Me2N-α-Me3Si-benzyl, with two equivalents of Cp(BIG)H. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp(BIG))2] (M = Sm, Yb, Ca, Ba) and shows the typical distortions that arise from Cp(BIG)⋅⋅⋅Cp(BIG) attraction as well as excessively large displacement parameter for the heavy Eu atom (U(eq) = 0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp(BIG))2] (M = Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp(BIG))2] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent (151)Eu Mössbauer effect spectroscopic examination of [Eu(Cp(BIG))2] was examined over the temperature range 93-215 K and the hyperfine and dynamical properties of the Eu(II) species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203 K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp(BIG))2]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp(BIG))2] (Ln = Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8 eV, for Sm, Eu, and Yb, respectively, lower than the Ln2O3 standards. No XANES temperature dependence was found from room temperature to 100 K. XANES also showed that the [Ln(Cp(BIG))2] complexes had less trivalent impurity than a [EuI2(thf)x] standard. The complex [Eu(Cp(BIG))2] shows already at room temperature strong orange photoluminescence (quantum yield: 45 %): excitation at 412 nm (24,270 cm(-1)) gives a symmetrical single band in the emission spectrum at 606 nm (νmax =16495 cm(-1), FWHM: 2090 cm(-1), Stokes-shift: 2140 cm(-1)), which is assigned to a 4f(6)5d(1) → 4f(7) transition of Eu(II). These remarkable values compare well to those for Eu(II)-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp(BIG))2] complex. Sharp emission signals, typical for Eu(III), are not visible.

Phosphide Oxides RE2AuP2O (RE = La, Ce, Pr, Nd): Synthesis, Structure, Chemical Bonding, Magnetism, and 31P and 139La Solid State NMR

Polycrystalline samples of the phosphide oxides RE(2)AuP(2)O (RE = La, Ce, Pr, Nd) were obtained from mixtures of the rare earth elements, binary rare earth oxides, gold powder, and red phosphorus in sealed silica tubes. Small single crystals were grown in NaCl/KCl fluxes. The samples were studied by powder X-ray diffraction, and the structures were refined from single crystal diffractometer data: La(2)AuP(2)O type, space group C2/m, a = 1515.2(4), b = 424.63(8), c = 999.2(2) pm, β = 130.90(2)°, wR2 = 0.0410, 1050 F(2) values for Ce(2)AuP(2)O, and a = 1503.6(4), b = 422.77(8), c = 993.0(2) pm, β = 130.88(2)°, wR2 = 0.0401, 1037 F(2) values for Pr(2)AuP(2)O, and a = 1501.87(5), b = 420.85(5), c = 990.3(3) pm, β = 131.12(1)°, wR2 = 0.0944, 1143 F(2) values for Nd(2)AuP(2)O with 38 variables per refinement. The structures are composed of [RE(2)O](4+) polycationic chains of cis-edge-sharing ORE(4/2) tetrahedra and polyanionic strands [AuP(2)](4-), which contain gold in almost trigonal-planar phosphorus coordination by P(3-) and P(2)(4-) entities. The isolated phosphorus atoms and the P(2) pairs in La(2)AuP(2)O could clearly be distinguished by (31)P solid state NMR spectroscopy and assigned on the basis of a double quantum NMR technique. Also, the two crystallographically inequivalent La sites could be distinguished by static (139)La NMR in conjunction with theoretical electric field gradient calculations. Temperature-dependent magnetic susceptibility measurements show diamagnetic behavior for La(2)AuP(2)O. Ce(2)AuP(2)O and Pr(2)AuP(2)O are Curie-Weiss paramagnets with experimental magnetic moments of 2.35 and 3.48 μ(B) per rare earth atom, respectively. Their solid state (31)P MAS NMR spectra are strongly influenced by paramagnetic interactions. Ce(2)AuP(2)O orders antiferromagnetically at 13.1(5) K and shows a metamagnetic transition at 11.5 kOe. Pr(2)AuP(2)O orders ferromagnetically at 7.0 K.

Structure and properties of Eu2Pt3Sn5

Abstract The new stannide Eu2Pt3Sn5 was synthesized by induction melting of the elements in a sealed tantalum tube in a water-cooled silica sample chamber. The structure was refined on the basis of single crystal X-ray diffractometer data: Y2Rh3Sn5 type, Cmc21, a = 453.30(9), b = 2662.9(8), c = 731.8(2) pm, wR2 = 0.0472, 1493 F2 values and 62 variables). The platinum and tin atoms build up a complex three-dimensional [Pt3Sn5] network with a broad range of Pt—Sn (264–293 pm) and Sn—Sn (308–373 pm) distances. The two crystallographically independent europium sites occupy large voids of coordination numbers 20 (Eu1) and 18 (Eu2) within the [Pt3Sn5] network. Eu2Pt3Sn5 shows Curie-Weiss behaviour in the temperature range 50–305 K with an experimental magnetic moment of 7.82(1) μB per Eu atom indicating purely divalent europium. Cp measurements show a broad anomaly with two maxima at 4.9(2) and 6.1(2) K. 151Eu Mössbauer spectra revealed both crystallographically independent europium sites to be divalent. At 4.2 K two rather different sizes of magnetic hyperfine field splittings are observed due to separate ordering of the two sites. The 119Sn Mössbauer spectrum shows complex superposition of the five signals in the paramagnetic range.

Structure and properties of EuTSb (T = Cu, Pd, Ag, Pt, Au) and YbIrSb

Abstract The equiatomic antimonides EuTSb (T = Cu, Pd, Ag, Pt, Au) and YbIrSb were synthesized from the elements in sealed tantalum tubes in an induction furnace. The samples were investigated by powder X-ray diffraction and the structures were refined on the basis of single crystal X-ray diffractometer data: ZrBeSi type, P63/mmc, a = 450.7(5), c = 853.2(7) pm, wR2 = 0.032, 273 F2 values, 8 variables for EuCuSb, a = 474.9(1), c = 829.4(3) pm, wR2 = 0.028, 166 F2 values, 8 variables for EuAgSb, a = 467.1(2), c = 848.8(3) pm, wR2 = 0.042, 162 F2 valäues, 8 variables for EuAuSb, and TiNiSi type, space group Pnma, a = 762.5(3), b = 469.1(1), c = 792.1(1) pm, wR2 = 0.046, 670 F2 values, 20 variables for EuPdSb, and a = 700.7(1), b = 444.68(8), c = 781.3(1) pm, wR2 = 0.075, 592 F2 values, 20 variables for YbIrSb. The structures are ordered superstructure variants of the aristotype AlB2 with planar T3Sb3 hexagons in EuTSb (T = Cu, Ag, Au) and puckered T3Sb3 hexagons in EuTSb (T = Pd, Pt) and YbIrSb. TiNiSi type EuPtSb was characterized via powder data: a = 759.8(3), b = 465.4(3), c = 791.4(3) pm. Temperature dependent magnetic susceptibility measurements indicate antiferromagnetic ordering for all compounds. The samples were additionally characterized by 121Sb and 151Eu Mössbauer spectra.

Drastic change of the ferromagnetic properties of the ternary germanide GdTiGe through hydrogen insertion.

Hydrogen absorption of the CeFeSi- and CeScSi-type forms of GdTiGe was performed. Before hydrogenation they show an antiferromagnetic transition at around 412 K and a ferromagnetic transition at 376 K, respectively. Hydrogenation of both forms leads to formation of the same hydride GdTiGeH which crystallizes with a filled CeScSi-type structure where all the [Gd(4)] tetrahedra are filled by hydrogen. This hydride is paramagnetic in the temperature range 4-300 K. The slightly negative value of the paramagnetic Curie temperature θ(p) confirms that all ferromagnetic interactions were destroyed in the case of the CeScSi-type form. From first-principles calculations with the PAW GGA methodology, the localization of hydrogen within the [Gd(4)] tetrahedra was confirmed through energetic stabilization. It was also seen that the energy changes significantly with volume, indicating the itinerant (delocalized) role of the electrons in the magnetism.

An Extension of Pnictide Oxide Chemistry – Salt Flux Synthesis and Structure of La5Cu4As4O4Cl2

La5Cu4As4O4Cl2 was prepared from a cold-pressed pellet of lanthanum filings, ground arsenic, Cu2O and LaOCl in the ideal 3 : 4 : 2 : 2 ratio. The pellet was annealed in an evacuated silica tube at 1473 K for two days and then cooled down to room temperature. LaOCl was always observed as a by-product. La5Cu4As4O4Cl2 crystallizes with a new structure type: I4/mmm, a = 413.46(7), c = 4144(1) pm, wR2 = 0.0763, 328 F2 values, 26 parameters. The new quaternary arsenide oxide La3Cu4As4O2 with La3Cu4P4O2-type structure (I4/mmm) was obtained in polycrystalline form: a = 413.0(1), c = 2748.6(1) pm. The structure of La5Cu4As4O4Cl2 is an intergrowth of structural slabs of LaOCl (PbFCl type), ZrCuSiAs- and La3Cu4P4O2-related slabs. The copper atoms have tetrahedral arsenic coordination, and all oxygen atoms fill lanthanum tetrahedra. In the LaOCl slab we observe a van der Waals gap built up by the chloride anions. Half of the arsenic atoms within the La3Cu4P4O2-related slab form As24− dumb-bells at an As-As distance of 249 pm. Electronic band structure calculations reveal La5Cu4As4O4Cl2 as a strongly anisotropic hybride material, composed of covalently bonded metallic CuAs4/4 layers, sandwiched between ionic insulating oxide and chloride blocks Graphical Abstract An Extension of Pnictide Oxide Chemistry – Salt Flux Synthesis and Structure of La5Cu4As4O4Cl2

P22− and P3− Units in the [Rh8P9]δ− Polyanion of La4Rh8P9

The phosphide La(4)Rh(8)P(9) was synthesized from the elements in a bismuth flux. The structure was refined from single crystal diffractometer data: space group Cmcm, a = 1303.1(2), b = 1893.2(2), c = 576.70(6) pm, wR2 = 0.0277, 1380 F(2) values, 65 variables. The rhodium and phosphorus atoms build up a three-dimensional [Rh(8)P(9)] polyanion which leaves larger cages for the three crystallographically independent lanthanum sites. The rhodium atoms have between four and six phosphorus neighbors at Rh-P distance ranging from 229 to 254 pm. Three of the four crystallographically independent phosphorus atoms are isolated (P(3-) units), while the P4 atoms form dimers with double bond character (208 pm P-P). The P(2)(2-) diphosphenide units bond side-on to a Rh3 and end-on to four Rh5 atoms. (31)P magic angle spinning (MAS) NMR spectroscopy is able to resolve three of the four crystallographically distinct phosphorus sites. The doubly bonded phosphorus site P4 is characterized by an axially symmetric shielding tensor of moderate anisotropy Δσ = σ(33) - σ(iso) = 257 ppm. Electronic band structure calculations prove the metallic character and reveal the significant difference between the isolated P(3-) and the phosphorus atoms of the P(2)(2-) units. Magnetic susceptibility measurement reveals Pauli paramagnetism.

The solid solution Gd2NixCu2−xMg: Large reversible magnetocaloric effect and a drastic change of the magnetism by substitution

Various samples of the solid solution Gd2NixCu2-xMg were synthesized from the elements in sealed tantalum ampoules in an induction furnace. All members crystallize with the tetragonal Mo2FeB2 type structure, space group P4/mbm, and they were characterized on the basis of Guinier powder patterns and energy dispersive X-rays analyses. The lattice parameters decrease with increasing nickel content in a Vegard-like manner. The Gd2NixCu2-xMg samples show Curie Weiss behavior with slightly higher magnetic moment values than the theoretical one for a free Gd3+ ion. The substitution of copper by nickel has a drastic influence on the magnetism and magnetic ordering temperature. For Gd2Ni0.5Cu1.5Mg a temperature induced FM -> AFM order-to-order transition was observed, whereas Gd2Ni1.0Cu1.0Mg is a metamagnet with H-Cr of about 8 kOe at 5 K. For both compounds, a large reversible magnetocaloric effect (MCE) near their ordering temperatures occurs. The values of the maximum magnetic entropy change -Delta S-M(max) reach 9.5 and 11.4 J kg(-1) K-1 for the field change of 5 T with no obvious hysteresis loss around 65 K for Gd2Ni0.5Cu1.5Mg and Gd2Ni1.0Cu1.0Mg, respectively. The corresponding relative cooling power with 688 and 630 J kg(-1) is relatively high as compared to other MCE materials in that temperature range. These results indicate that Gd2NixCu2-xMg could be a promising system for magnetic refrigeration at temperatures below liquid N-2