Preparation, properties, and crystal structure of Zr5Zn39, a vacancy variant of the Ce5Mg41-type, and structure refinement of ZrZn22

Well-developed crystals of Zr5Zn39 and ZrZn22 were obtained from binary alloys with an excess of zinc by dissolving the matrices in hydrochloric acid, which attacks the binary compounds at a slower rate. Both compounds are diamagnetic with susceptibility values of chi = -25(+/-15) x 10(-9) m(3)/mol for Zr5Zn39 and chi = -12(+/-2) x 10(-9) m(3)/mol for ZrZn22. Electrical conductivity measurements confirm the expected metallic conductivity of Zr5Zn39. The crystal structure of Zr5Zn39 was determined from single-crystal X-ray diffractometer data: C2/m, a = 1785.5(7) pm, b = 859.6(2) pm, c = 1254.6(4) pm, beta = 134.40(2)degrees, Z = 2, R = 0.035 for 1744 structure factors and 119 variable parameters. The previously reported structure of ZrZn22 is confirmed: Fd3m, a = 1410.5(1) pm, Z = 8, R = 0.026 for 248 F values and 18 variables. Both compounds show significant deviations from the full occupancy for one zinc site, resulting in the exact compositions Zr5Zn38.921(7) and ZrZn21.798(7). Both structures contain relatively large voids, which are suited for the accommodation of interstitial atoms. It is suggested that these voids are filled with nonbonding electrons of the zinc atoms. This is supported by the existence of the tetragonal Ce5Mg41 type structure, which may be regarded as a translationengleiche ''filled-up'' version of Zr5Zn39. (C) 1996 Academic Press, Inc.