Ca5Ni17Ge8 - A Complex Intermetallic Compound Combining Various Structure Motifs of Alkaline-Earth Nickel Germanides.

The intermetallic compound Ca5Ni17Ge8 was prepared by arc melting mixtures of the elements and subsequent annealing under argon atmosphere. The compound crystallizes in a new structure type with the space group Amm2, Z = 2, a = 4.0255(2) Å, b = 25.226(2) Å, c = 8.9861(6) Å and wR2 = 0.083 (all data).Ca5Ni17Ge8 consists of a $\rm^{3}_{\infty}$[Ni17Ge8] network in whose cavities the calcium atoms are situated. The three-dimensional network comprises a unusual large diversity of structural motifs that are known from other compounds of the systems Ae/Ni/Ge ( Ae: Ca, Sr, Ba), such as the coordination environments of the calcium atoms reminiscent to those in Ca7Ni49Ge22 and Ca15Ni68Ge37 as well as various Ni-Ge structural motifs which occur similarly in Ca2Ni3Ge2, BaNi2Ge, SrNi2Ge, Ni3Sn2 and Ni3Sn. [ABSTRACT FROM AUTHOR]