Cage compound Sc₅Pt₂₄B₁₂: a Pt-stuffed variant of filled skutterudite structure. Electronic and structural properties

The title compound was obtained from elements via arc melting and its crystal structure was determined from single-crystal X-ray diffraction data (space group Im , a = 10.2042(6) & Aring;). The refinement indicated the occupancy of icosahedral 2 a and cubooctahedral 8c sites solely by Sc atoms which lead to the composition Sc5Pt24B12 in contrast to the previously reported ternary stannides of Gd3Ni8Sn16 type (RE5- xM12 Sn24(+ x ) compounds). The compound is the first representative of borides crystallizing with a site exchange variant of this stannide structure type. The structural relationships of the boride structure and filled skutterudite LaFe4P12 vs. the Remeika phase of Yb3Rh Sn-4(13) -type are discussed . Analysis of chemical bonding classifies Sc5Pt24B12 as a cage compound exhibiting the ionic interaction of cationic scandium species in the cages of anionic framework, formed by covalently bonded B and Pt atoms. Electronic structure calculations show that the electronic states of atoms centered around the cubooctahedral 8c site, ie Sc2 3d-, Pt2 5d- and B 2p-states dominate the density of states (DOS) at the Fermi level E-F . Strong effect of spin-orbit coupling on the band structure at the gamma point has been found from density functional theory calculations. Sc5Pt24B12 exhibits superconductivity with a transition temperature of T-C = 2.45 K.