Crystal Structure of YB41Si1.2

Abstract The crystal structure of a new compound, YB 41 Si 1.2 , has been determined by single-crystal X-ray diffractometry. The crystal was grown by the floating-zone method. The intensity data were collected on a four-circle diffractometer using Cu K α radiation. The structure was solved by direct methods and refined with the aid of a full-matrix least-squares program to the R ( R w ) value of 0.034 (0.040); 2686 independent reflections were used for 232 variable parameters. The structure of YB 41 Si 1.2 belongs to the orthorhombic system (space group Pbam ), with lattice constants a =16.674(1) A, b =17.667(1) A, and c =9.5110(7) A, and is composed of B 12 icosahedra and a new B 12 Si 3 polyhedral unit. Three Si sites of the B 12 Si 3 unit are assumed to be fully occupied by both Si and B atoms, and the actual chemical composition of this unit is estimated to be B 12 Si 1.5 B 1.5 . The boron framework is thus proved to be of a new structure type which is made up of five crystallographically different five B 12 icosahedra and the B 12 Si 3 unit. The Y atom occupies a large hole outside the icosahedra and the B 12 Si 3 unit. Interstitial sites, one Si and seven B sites, are also found outside the polyhedral units, with various occupancies from 100% to 9%.