Intermetallic gold compounds REAuMg (RE = Y, La-Nd, Sm, Eu, Gd-Yb)

New intermetallic rare earth compounds REAuMg (RE = Y, La-Nd, Sm, Eu, Gd-Yb ) were synthesized by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. The compounds were investigated by X-ray diffract ion both on powders and single crystals. Some structures were refined on th e basis of single crystal data. The compounds with Y, La-Nd, Sm, and Gd-Tm adopt the ZrNiAl type structure with space group P (6) over bar 2m: a = 770 .8(2), c = 419.5(1) pm, wR2 = 0.0269, 261 F-2 values for PrAuMg, a = 750.9( 2), c = 407.7(1) pm, wR2 = 0.0561, 649 F-2 values for HoAuMg with 15 variab les for each refinement. Geometrical motifs in HoAuMg are two types of gold centered trigonal prisms: [Au1Mg(3)Ho(6)] and [Au2Mg(6)Ho(3)]. The gold an d magnesium atoms form a three-dimensional [AuMg] polyanion in which the ho lmium atoms fill distorted hexagonal channels. The magnesium positions show a small degree of magnesium/gold mixing resulting in the refined compositi ons PrAu1.012(2)Mg0.988(2) and HoAu1.026(3)Mg0.974(3) EuAuMg and YbAuMg con tain divalent europium and ytterbium, respectively. Both compounds crystall ize with the TiNiSi type structure, space group Pnma: a = 760.6(3), b = 448 .8(2), c = 875.8(2) pm, wR2 = 0.0491, 702 F-2 values, 22 variables for EuAu Mg, and a = 738.4(1), b = 436.2(1), c = 864.6(2)pm, wR2 = 0.0442, 451 F-2 v alues, and 20 variables for YbAuMg. The europium position shows a small deg ree of europium/magnesium mixing, and the magnesium site a slight magnesium /gold mixing leading to the refined composition Eu0.962(3)Au1.012(3)Mg1.026 (3). No mixed occupancies were found in YbAuMg where all sites are fully oc cupied. Tn these structures the europium(ytterbium) and magnesium atoms for m zig-zag chains of egde-sharing trigonal prisms which are centered by the gold atoms. As is typical for TiNiSi type compounds, also in EuAuMg and YbA uMg a three-dimensional [AuMg] polyanion occurs in which the europium(ytter bium) atoms are embedded. The degree of distortion of the two polpanions, h owever, is different.