Quaternary Silicide CarbidesAT2SiC (A=Rare Earth Elements and Actinoids,T=Mn, Re, Ru, Os) with DyFe2SiCType Structure

The 49 compoundsAMn2SiC (A=Y, Sm, Gd–Tm, Lu, Th, U),ARe2SiC (A=Y, Ce–Nd, Sm, Gd–Tm, Th),ARu2SiC (A=Y, Ce–Nd, Sm, Gd–Tm, Th), andAOs2SiC (A=Y, La–Nd, Sm, Gd–Tm, Th, U) have been prepared for the first time. They crystallize with DyFe2SiC-type structure, which was refined for PrOs2SiC 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 factorsFand 18 variable parametersV. 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 ThOs2.040(2) Si0.960(2)C (a=396.41(7) pm,b=1115.5(1) pm,c=717.0(1) pm,R=0.013, 245F, 18V) and ThOs2.284(2)Si0.716(2)C (a=397.1 A(1) pm,b=1113.9(2) pm,c=724.5(1) pm,R=0.025, 483F, 18V). No such deviations from the ideal compositions were detected by the (less accurate) Rietveld refinements of the structures of TbRe2SiC, DyRu2SiC, and HoRu2SiC. Magnetic susceptibility measurements with a SQUID magnetometer indicate Pauli paramagnetism for YRu2SiC and YOs2SiC. Chemical bonding in the DyFe2SiC-type compounds is discussed. It is shown that an electron count of 18 can be achieved for most of the transition metal atoms.