Ferromagnetism and Magnetocaloric Effect around 95 K in the Laves Phase EuRh_1.2Zn_0.8

Samples of the solid solution EuRh2−xZnx with x ≈ 1 were synthesized by high-frequency melting of the elements in sealed tantalum tubes. They crystallize with the structure of the cubic Laves phase MgCu2. The structure of one crystal was refined from single-crystal X-ray diffractometer data: space group Fd3̅m, a = 768.58(6) pm, wR2 = 0.0121, 99 F2 values, 6 variables. The rhodium and zinc atoms statistically occupy the 16d site of the three-dimensional tetrahedral network. The europium atoms have coordination number 16 by 12 Rh/Zn and 4 Eu neighbors. The sample with nominal composition EuRh1.2Zn0.8 was studied with respect to its physical properties. EuRh1.2Zn0.8 shows stable divalent europium (8.00 μB/Eu atom) and orders ferromagnetically at TC = 95 K. Magnetization isotherms characterize EuRh1.2Zn0.8 as a soft ferromagnet. 151Eu Mössbauer spectroscopic data confirm the europium valence state (δ = −7.44 mm/s at 77 K) and the magnetic ordering. According to magnetocaloric investigations, EuRh1.2Zn0.8 has a quite high normalized relative cooling power with 103 J K−1T−1 for ΔH = 5 T, which makes it an interesting cooling material

Sn₃I₈·2(18-crown-6): a Mixed-Valent Tin-Crown-Ether Complex

By reaction of SnI2, SnI4, and crown ether (18-crown-6) in the ionic liquid [NMe(n-Bu)3][N(Tf)2], Sn3I8·2(18-crown-6) is obtained in the form of black, plate-shaped crystals and crystallizes with a monoclinic lattice symmetry. In detail, Sn3I8·2(18-crown-6) is constituted of trigonal-bipyramidal [SnI5]−-anions and [Sn2I3(18-crown-6)2]+-cations. The cation exhibits an endocyclical coordination of Sn2+ by the crown ether. Both constituents are linked via long-ranging I−I contacts to form an infinite network. Besides crystal structure analysis, the mixed valence state of tin is evidenced by 119Sn-Mössbauer spectroscopy

Mixed Valence Europium Nitridosilicate Eu₂SiN₃

The mixed valence europium nitridosilicate Eu2SiN3 has been synthesized at 900 °C in welded tantalum ampules starting from europium and silicon diimide Si(NH)2 in a lithium flux. The structure of the black material has been determined by single-crystal X-ray diffraction analysis (Cmca (no. 64), a = 542.3(11) pm, b = 1061.0(2) pm, c = 1162.9(2) pm, Z = 8, 767 independent reflections, 37 parameters, R1 = 0.017, wR2 = 0.032). Eu2SiN3 is a chain-type silicate comprising one-dimensional infinite nonbranched zweier chains of corner-sharing SiN4 tetrahedra running parallel [100] with a maximum stretching factor fs = 1.0. The compound is isostructural with Ca2PN3 and Rb2TiO3, and it represents the first example of a nonbranched chain silicate in the class of nitridosilicates. There are two crystallographically distinct europium sites (at two different Wyckoff positions 8f) being occupied with Eu2+ and Eu3+, respectively. 151Eu Mössbauer spectroscopy of Eu2SiN3 differentiates unequivocally these two europium atoms and confirms their equiatomic multiplicity, showing static mixed valence with a constant ratio of the Eu2+ and Eu3+ signals over the whole temperature range. The Eu2+ site shows magnetic hyperfine field splitting at 4.2 K. Magnetic susceptibility measurements exhibit Curie−Weiss behavior above 24 K with an effective magnetic moment of 7.5 μB/f.u. and a small contribution of Eu3+, in accordance with Eu2+ and Eu3+ in equiatomic ratio. Ferromagnetic ordering at unusually high temperature is detected at TC = 24 K. DFT calculations of Eu2SiN3 reveal a band gap of ∼0.2 eV, which is in agreement with the black color of the compound. Both DFT calculations and lattice energetic calculations (MAPLE) corroborate the assignment of two crystallographically independent Eu sites to Eu2+ and Eu3+

Mixed Valence Europium Nitridosilicate Eu₂SiN₃

The mixed valence europium nitridosilicate Eu2SiN3 has been synthesized at 900 °C in welded tantalum ampules starting from europium and silicon diimide Si(NH)2 in a lithium flux. The structure of the black material has been determined by single-crystal X-ray diffraction analysis (Cmca (no. 64), a = 542.3(11) pm, b = 1061.0(2) pm, c = 1162.9(2) pm, Z = 8, 767 independent reflections, 37 parameters, R1 = 0.017, wR2 = 0.032). Eu2SiN3 is a chain-type silicate comprising one-dimensional infinite nonbranched zweier chains of corner-sharing SiN4 tetrahedra running parallel [100] with a maximum stretching factor fs = 1.0. The compound is isostructural with Ca2PN3 and Rb2TiO3, and it represents the first example of a nonbranched chain silicate in the class of nitridosilicates. There are two crystallographically distinct europium sites (at two different Wyckoff positions 8f) being occupied with Eu2+ and Eu3+, respectively. 151Eu Mössbauer spectroscopy of Eu2SiN3 differentiates unequivocally these two europium atoms and confirms their equiatomic multiplicity, showing static mixed valence with a constant ratio of the Eu2+ and Eu3+ signals over the whole temperature range. The Eu2+ site shows magnetic hyperfine field splitting at 4.2 K. Magnetic susceptibility measurements exhibit Curie−Weiss behavior above 24 K with an effective magnetic moment of 7.5 μB/f.u. and a small contribution of Eu3+, in accordance with Eu2+ and Eu3+ in equiatomic ratio. Ferromagnetic ordering at unusually high temperature is detected at TC = 24 K. DFT calculations of Eu2SiN3 reveal a band gap of ∼0.2 eV, which is in agreement with the black color of the compound. Both DFT calculations and lattice energetic calculations (MAPLE) corroborate the assignment of two crystallographically independent Eu sites to Eu2+ and Eu3+