Quaternary Silicide Carbides AT2SiC ( A=Rare Earth Elements and Actinoids, T=Mn, Re, Ru, Os) with DyFe 2SiC-Type Structure

The 49 compounds AMn ₂SiC ( A=Y, Sm, Gd-Tm, Lu, Th, U), ARe ₂SiC ( A=Y, Ce-Nd, Sm, Gd-Tm, Th), ARu ₂SiC ( A=Y, Ce-Nd, Sm, Gd-Tm, Th), and AOs ₂SiC ( A=Y, La-Nd, Sm, Gd-Tm, Th, U) have been prepared for the first time. They crystallize with DyFe ₂SiC-type structure, which was refined for PrOs ₂SiC from single-crystal X-ray data: Cmcm, a=396.02(5) pm, b=1105.8(1) pm, c=717.2(1) pm, Z=4, R=0.030 for 320 structure factors Fand 18 variable parameters V. The refinement of the occupancy parameters revealed that the silicon site contains 2.0(3)% osmium. Mixed occupancy for this site resulted also from two structure refinements of the corresponding thorium compound, yielding the compositions ThOs _2.040(2)Si _0.960(2)C ( a=396.41(7) pm, b=1115.5(1) pm, c=717.0(1) pm, R=0.013, 245 F, 18 V) and ThOs _2.284(2)Si _0.716(2)C ( a=397.1(1) pm, b=1113.9(2) pm, c=724.5(1) pm, R=0.025, 483 F, 18 V). No such deviations from the ideal compositions were detected by the (less accurate) Rietveld refinements of the structures of TbRe ₂SiC, DyRu ₂SiC, and HoRu ₂SiC. Magnetic susceptibility measurements with a SQUID magnetometer indicate Pauli paramagnetism for YRu ₂SiC and YOs ₂SiC. Chemical bonding in the DyFe ₂SiC-type compounds is discussed. It is shown that an electron count of 18 can be achieved for most of the transition metal atoms.