The crystal structures of m,o-Ce₃Pt₄Sn₆ and Ce_1-xPt₆Al_13+2x

The crystal structures of two novel ternary compounds, Ce₃Pt₄Sn₆ and Ce_1-xPt₆Al_13+2x (x = 0.207), have been derived by direct methods from X-ray single crystal data. Whereas Ce_1-xPt₆Al_13+2x is of a new structure type (a = 1.42224(2) nm, c = 0.87367(1) nm, space group P6¯2m), Ce₃Pt₄Sn₆ was found to crystallize in two different crystal modifications, (i) a monoclinic variant (a = 0.93682(2) nm, b = 0.46145(1) nm, c = 1.40434(3) nm, β = 99.635(1)°, space group P2₁/m), which is isotypic with the Y₃Pt₄Ge₆-type and (ii) an orthorhombic modification (a = 2.76394(4) nm, b = 0.460588(7) nm, c = 0.93530(1) nm, space group Pnma), which crystallizes with the ordered Pr₃Pt₄Ge₆-type. For the monoclinic arrangement m-Ce₃Pt₄Sn₆ an intrinsically defect growth pattern was found - it grows in two related motifs (opposite directions of pentagonal units) in the ratio of 90%: 10% ensuring a stoichiometric composition. TEM observation directly revealed intrinsic building defects detected by single crystal X-ray diffraction for m-Ce₃Pt₄Sn₆. Diffuse streaks in electron diffraction and inhomogeneous contrasts in a high resolution TEM image indicate the existence of a random stacking sequence between two related motifs.