Intermetallic Cadmium Compounds M5T2Cd (M = Ca, Yb, Eu; T = Cu, Ag, Au) with Mo5B2Si-type Structure

The intermetallic compounds M5T2Cd (M = Ca, Yb, Eu; T = Cu, Ag, Au) and Yb5Cu2Zn were synthesized by melting the elements in sealed tantalum tubes followed by annealing at 923 K. All phases were characterized on the basis of powder and single-crystal X-ray diffraction data: Mo5B2Si type, 14/mcm, Z = 4, a = 828.7(1), c = 1528.1(3) pm, wR2 = 0.030, 440 F-2 values, 16 variables for Eu5Cu2Cd, a = 788.2(1), c = 1459.3(5) pm, wR2 = 0.053, 378 F-2 values, 16 variables for Yb5Cu2Cd, and a = 797.2(1), c = 1438.8(3) pm, wR2 = 0.036, 386 F-2 values, 17 variables for Yb5Au2.19Cd0.81, which shows a small degree of Au/Cd mixing. The M5T2Cd structures are intergrowth variants of slightly distorted CuAl2- and U3Si2-related slabs. Striking coordination motifs (exemplary for Eu5Cu2Cd) are square antiprisms of the Eu atoms around Cd, Eu-8 square prisms around Eu, and trigonal Eu-6 prisms around Cu within the AlB2-related slab. Temperature-dependent magnetic susceptibility measurements showed Pauli paramagnetism for Yb5Cu2Zn, indicating purely divalent ytterbium. Eu5Au2Cd exhibits Curie-Weiss behavior above 100 K with an experimental magnetic moment of 8.14 mu(B) per Eu atom and a Weiss constant of 56 K. Antiferromagnetic ordering of the Eu-II magnetic moments is evident at 36 K, and a metamagnetic transition is observed at 25 K and 13 kOe.