The Stannides EuPd2Sn2, EuPt2Sn2, EuAu2Sn2, and Eu5.4Sn5.6 – Structure and Magnetic Properties

Abstract

The europium stannides EuT2Sn2 (T = Pd, Pt, Au) and Eu3Ag5.4Sn5.6 were synthesized by highfrequency melting of the elements in sealed niobium ampoules in a water-cooled sample chamber. All samples were characterized by powder X-ray diffraction. The EuT2Sn2 (T = Pd, Pt, Au) stannides crystallize with the CaBe2Ge2-type structure, space group P4/nmm. The structure of EuPd2Sn2 was refined from single-crystal X-ray diffractometer data: a = 462.44(8), c = 1045.8(3) pm, wR = 0.0402, 237 F2 values and 15 refined variables. The palladium and tin atoms build up a threedimensional [Pd2Sn2] polyanionic network, exclusively with Pd-Sn interactions (261 - 269 pm). The Pd1 and Pd2 atoms have square-pyramidal and tetrahedral tin coordination, respectively. The europium atoms fill large voids within the network. They are coordinated to eight palladium and eight tin atoms. Temperature-dependent magnetic susceptibility studies confirm a stable divalent ground state of the europium atoms. The compounds become ordered antiferromagnetically below 6.3 (EuPd2Sn2), 6.1 (EuPt2Sn2) and 7.7 K (EuAu2Sn2). Eu3Ag5.4Sn5.6 adopts a partially ordered variant of the La3Al11 type, space group Immm, a = 471.33(8), b = 1382.5(4), c = 1032.4(2) pm, wR = 0.0449, 692 F2 values, 30 variables. The three-dimensional [Ag5.4Sn5.6] network shows one silver and one tin site besides two sites with substantial Ag/Sn mixing. The two crystallographically independent europium atoms fill larger and smaller cavities within the [Ag5.4Sn5.6] network. Eu3Ag5.4Sn5.6 also shows divalent europium and antiferromagnetic ordering at TN = 6:9 K. A 151Eu Mössbauer spectrum of Eu3Ag5.4Sn5.6 at 5.2 K shows an isomer shift of δ = −10.61 mms−1, typical for Eu(II) compounds, and a magnetic hyperfine field splitting of BHf = 5.9 T. 119Sn Mössbauer spectra of the four stannides show isomer shifts in the range of δ = 1.78 - 2.20 mms−1, usually observed for tin in intermetallic compounds.