Ordered vacancies in the commensurately modulated structure of SrPt1.833□0.167Sn2

The stannide SrPt1.833□0.167Sn2 was synthesized from the elements in a sealed niobium tube in a high-frequency furnace. Its structure was determined by and refined on the basis of single crystal X-ray diffraction data at 300 and 90 K. The refinement of 1177/1169 F2 values with 34/37 variables leads to residuals [I≥3σ(I)] RM=0.026 (375) and RS=0.075 (53)/RM=0.0211 (408) and RS=0.0503 (128) for the 300/90 K data sets, respectively. SrPt1.833□0.167Sn2 crystallizes with an orthorhombic (3+1)D structure with the supercentered superspace group Ccmme(0β0)s00 [β=1/3 b*, a=655.25(15), b=656.7(4), c=2062.3(5) pm]. It is related to the tetragonal CaBe2Ge2 type structure. The crystal chemistry is described and the structure solution is discussed based on (3+2)D-(3+1)D-3D group-subgroup relations in the Baernighausen formalism. 119Sn Moessbauer spectra at ambient temperature and 78 K revealed a single signal with isomer shifts of δ=1.78(1) and δ=1.83(1) mm s-1 with quadropole splitting of ΔEQ=0.71(1) and 0.86(1) mm s-1, respectively reflecting the low-symmetric site symmetry of the tin atoms. SrPt1.833□0.167Sn2 was classified as a Pauli-paramagnet by magnetic susceptibility measurements. Its specific heat capacity is Cpm=121.4(1) J mol-1K-1 at 300 K.