Ordered vacancies in the commensurately modulated structure of SrPt1.833 square Sn-0.167(2)

The stannide SrPt1.833 square Sn-0.167(2) 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 90K. The refinement of 1177/1169 F-2 values with 34/37 variables leads to residuals [I >= 3 sigma(I)] R-M=0.026 (375) and R-S=0.075 (53)/R-M=0.0211 (408) and R-S=0.0503 (128) for the 300/90 K data sets, respectively. SrPt1.833 square Sn-0.167(2) crystallizes with an orthorhombic (3+1)D structure with the supercentered superspace group C(c)mme(O beta O)sOO [beta=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 Barnighausen formalism. Sn-119 Mossbauer spectra at ambient temperature and 78 K revealed a single signal with isomer shifts of delta=1.78(1) and delta=1.83(1) mm s(-1) with quadropole splitting of Delta E-Q=0.71(1) and 0.86(1) mm s(-1), respectively reflecting the low-symmetric site symmetry of the tin atoms. SrPt1.833 square Sn-0.167(2) was classified as a Pauliparamagnet by magnetic susceptibility measurements. Its specific heat capacity is C-pm=121.4(1) J mol(-1)K(-1) at 300 K.