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Abstract

The title compounds were prepared from the elements by
reactions in sealed tantalum tubes in a water-cooled sample
chamber of a high-frequency furnace. They crystallize with the
ZrNiAl-type structure, space group P (6) over bar 2m. The
structures of the cerium compounds were refined from single-
crystal x-ray diffraction data: a = 767.3(1) pm, c = 410.37(4)
pm, wR2 = 0.0324, 521 F-2-values for CePdMg; a = 755.02(7) pm,
c = 413.82(4) pin, wR2 = 0.0393, 514 F-2-values for CePtMg; and
a = 774.1(3) pm, c = 421.6(1) pm, wR2 = 0.0355, 395 F-2-values
for CeAuMg, with 14 variables for each refinement. The
palladium compound shows a small homogeneity range: CePd1+xMg1-
x. The structures contain two crystallographically different
transition metal sites T1 and T2 which are located in tri-
capped trigonal prisms: [T1Mg(6)Ce(3)] and [T2Ce(6)Mg(3)].
Magnetic susceptibility and heat capacity measurements reveal
long-range magnetic ordering at 2.1(2) K for CePdMg, 3.6(2) K
for CePtMg, and 2.0(2) K for CeAuMg. Curie-Weiss behaviour at
higher temperatures shows that the cerium ions are in the 3+
oxidation state. The isotypic LaTMg compounds are Pauli
paramagnetic down to lowest temperatures (T = 0.3 K). All the
compounds, RETMg (RE = La, Ce; T = Pd, Pt, Au) show metallic
behaviour.