Novel silicide BaPt5Si12: Crystal structure and physical properties

BaPt5Si12 has been synthesized by argon arc melting the elements. The structure was solved by direct methods from Kappa CCD intensity data. The novel silicide crystallizes in a unique monoclinic structure type: space group C2/m; a = 0.61327(2) nm, b = 3.23481(8) nm, c = 0.61180(1) nm, β = 90.130(2)°. The structure of BaPt5Si12 is characterized by Pt atoms, which are all arranged in planes parallel x-z resulting in tetrahedral coordination for Si1, Si2, Si3 and Si4 atoms and more complex distorted polyhedra around Si5 and Si6 atoms. Three voids were encountered in the structure at the centres of an Achimedian antiprism and two cube-octahedra. These voids do not show any residual electron densities. BaPt5Si12 turns out to be metallic; no phase transitions are found within the temperature range from 300 mK to 300 K. The overall resistivity is rather large, presumably a consequence of the voids in the crystal structure. Additionally, the quite complex crystal structure gives rise to intricate phonon modes.