THE CRYSTAL-STRUCTURES OF THE ISOTYPIC AL KALINE EARTH-NITRIDOTUNGSTATE(VI)-NITRIDE-OXIDES CA-51[WN4](12)N8O3 AND SR-51[WN4](12)N8O3

Yellow single crystals of the isotypic phases Ca-51[WN4](12)N8O3 and S r-51[WN4](12)N8O3 (triclinic, P (1) over bar (#2); a = 1056.4(3)/1113. 1(5) pm, b = 1239.7(3)/1304.4(5) pm, c = 1598.2(3) / 1679.4(9) pm, alp ha = 102.78(1)/102.47(2)degrees, beta = 95.15(1)/95.43(3)degrees, gamm a = 109.89(1)/109.77(2)degrees; Z = 1) were grown in a Tl-flux (Ca:Tl, molar ratio 5:1, W-crucible; T-max 1273K reaction with N-2, 1 atm, 36 h) or from pellets (Sr2N + W, molar ratio 6:1; T-max 1023K; reaction with N-2, 1 atm, 36 h). The crystal structures contain tetrahedral ani ons [WN4](6-) in addition to isolated nitride and isolated oxide ions, which are octahedrally coordinated by Ca and Sr, respectively.