Structure and properties of Sr2Au3In4 and Eu2Au3In4

Sr2Au3In4 was synthesized by reacting the elements in glassy carbon crucibl es under an argon atmosphere in a high-frequency furnace. Eu2Au3In4 was obt ained in the same way but starting with EuAuIn as a precursor and admiring indium and gold. Both compounds were investigated by X-ray diffraction on p owders and single crystals: anti-Hf2Co4P3 type, P (6) over bar 2m, a = 1501 .6(9) pm, c = 457.9(2) pm, wR2 = 0.0734, 1030 F-2 values, 45 variables for Sr2Au2.85In4.15 and a = 1489.7(3)pm, c = 454.90(7) pm, wR2 = 0.1222, 1051 F -2 values, 45 variables for Eu,Au,In,. One gold site in the strontium compo und shows a mixed occupancy with indium atoms indicating a small homogeneit y range according to Sr2Au3-xIn4+x. Striking structural motifs of Sr2Au3In4 and Eu(2)A(2)In(4) are gold-centered trigonal prisms formed by the stronti um (europium) and indium atoms. All gold atoms have coordination number 9 i n the form of tricapped trigonal prisms. The indium atoms in Sr2Au3In4 and Eu2Au3In4 occupy the cobalt positions of the Hf2Co4P3 type and the more ele ctronegative gold atoms take the phosphorus positions, indicating that Sr2A u3In4 and Eu2Au3In4 may be considered as ternary aurides. The gold and indi um atoms form three-dimensional [Au3In4](4-) polyanions in which the divale nt strontium and europium atoms occupy distorted hexagonal tubes. Magnetic susceptibility measurements of Eu2Au3In4 show paramagnetic behavior above 5 0 K with an experimental magnetic moment of 7.88(5) mu(B)/Eu indicating Eu2 +. Antiferromagnetic ordering is detected at 9.5(5)K at low external fields . A metamagnetic transition is observed at 2 K at a critical field of 0.5(2 ) T. The experimental saturation moment at 2 K and 5.5 T is 5.95(5) mu(B)/E u. Electrical conductivity investigations exhibit metallic behavior with a room temperature value of 75 +/- 10 mu Omega cm for the specific resistivit y. Eu-151 Mossbauer spectroscopic measurements show a broadened line with a n isomer shift of -10.5(5) mm/s at 78 K in accordance with several sites of divalent europium. Below 10 K magnetic hyperfine field splitting is observ ed. (C) 1999 Academic Press.