Preparation and Crystal Structures of the Rare Earth Nitrido-Oxosilicates and Nitridosilicates with the General FormulaR6+x/3Si11N20+xO1−xand the Ideal CompositionsR6Si11N20O andR6.33Si11N21, Respectively (R=Y and Gd–Lu)

Abstract

The nine title compounds were prepared by reaction of multiple-phase rare earth silicide oxide powders with nitrogen. Single crystals of the erbium compound were isolated from a sample, which had been melted in a high-frequency furnace. Two slightly different trigonal crystal structures (P31c,Z=2) were established from single-crystal X-ray diffractometer data. Two fully occupied erbium sites were found for a crystal with the composition Er6Si11N20O:a=977.3(1) pm,c=1059.7(1) pm,R=0.021 for 1531 structure factors and 68 variable parameters. A third erbium site was refined with partial occupancy for another crystal with the composition Er6.254(3)Si11N20.762(9)O0.238(9):a=978.5(1) pm,c=1064.4(1) pm,R=0.023 for 884Fvalues and 71 variables. The presence and the location of the oxygen atoms in these transparent crystals are based on structure-chemical arguments. For a crystal without oxygen the third erbium site should have an occupancy of 33%, corresponding to the formula Er6.33Si11N21. The two fully occupied erbium sites are coordinated by six, the partially occupied erbium site is coordinated by seven nitrogen (oxygen) atoms. The silicon atoms have four nitrogen (oxygen) neighbors in tetrahedral arrangement. Some nitrogen atoms are bonded to only one silicon atom, but most are linking two SiN4tetrahedra via common corners. The compounds may therefore be considered essentially as framework nitridosilicates. In contrast to normal oxosilicates, where the oxygen atoms have one or two silicon neighbors, the structures of these nitridosilicates also contain nitrogen atoms which link three or even four SiN4tetrahedra.