STRUCTURE REFINEMENT OF MONOCLINIC 12-LAYER TANI3 WITH BETA-NBPT3 TYPE - NEW CRYSTALLOGRAPHIC DESCRIPTIONS OF THIS TYPE AND OF THE NB3RH5 TYPE BASED ON SMALLER UNIT CELLS

The atom arrangements in the beta-NbPt3 and Nb3Rh5 [= (Nb0.75Rh0.25)Rh] structures can be described with unit cells having only one third of the original volumes. beta-NbPt3: mP16, P2(1)/m, a = 4.870, b = 5.537, c = 9.268 angstrom, beta = 100.62-degrees. Nb3Rh5: mP6, P2/m, a = 4.772, b = 2.806, c = 6.949 angstrom, beta = 103.76-degrees. According to the new description (Nb0.75Rh0.25)Rh is isotypic to LiSn. Structure refinement of 12-layer TaNi3 with beta-NbPt3 type, M(r) = 357.078, mP16, P2(1)/m - f2e4, a = 4.5319 (6), b = 5.1253 (8), c = 8.632 (1) angstrom, beta = 100.79 (1)degrees, V = 196.96 (4) angstrom 3, Z = 4, D(x) = 12.038 Mg m-3, lambda(Mo K-alpha) = 0.71073 angstrom, mu = 82.661 mm-1, F(000) = 628, T = 300 K, R = 0.068, wR = 0.062 for 309 contributing unique reflections. The new description of the structure type is confirmed.