La3Pd4Zn4 and La3Pt4Zn4 with a different coloring of the Gd3Cu4Ge4-type structure

Abstract

The intermetallic zinc compounds La3Pd4Zn4 and La3Pt4Zn4 were synthesized by induction melting of the elements in sealed tantalum tubes. The structures were refined from X-ray single-crystal diffractometer data: Gd3Cu4Ge4 type, Immm, a = 1,440.7(5), b = 743.6(2), c = 419.5(2) pm, wR 2 = 0.0511, 353 F 2 for La3Pd4Zn4; and a = 1,439.9(2), b = 748.1(1), c = 415.66(6) pm, wR 2 = 0.0558, 471 F 2 for La3Pt4Zn4 with 23 variables per refinement. The palladium (platinum) and zinc atoms build up a three-dimensional polyanionic [Pd4Zn4] (260–281 pm Pd–Zn) and [Pt4Zn4] (260–279 pm Pt–Zn) network in which the lanthanum atoms fill cavities of CN 14 (6 Pd/Pt + 8 Zn for La1) and CN 12 (6 Pd/Pt + 6 Zn for La2), respectively. The copper position of the Gd3Cu4Ge4 type is occupied by zinc and the two crystallographically independent germanium sites by palladium (platinum), a new coloring pattern for this structure type. Within the [Pd4Zn4] and [Pt4Zn4] the Pd2 and Pt2 atoms form Pd2–Pd2 (291 pm) and Pt2–Pt2 (296 pm) dumbbells. The structures of La3Pd4Zn4 and La3Pt4Zn4 are discussed with respect to the prototype Gd3Cu4Ge4 and the Zintl phase Sr3Li4Sb4. Temperature-dependent magnetic susceptibility measurements indicate diamagnetism for La3Pt4Zn4 and Pauli paramagnetism for La3Pd4Zn4.