SYNTHESIS AND CRYSTAL-STRUCTURE OF ALKALI-METAL OXO NITRIDO DIMETALLATES(VI), A(6)[M(2)N(4)O(3)] (A=K, RB, CS, M=MO, W)

Mixtures of M-MO(3) with M=Mo, W react with an excess of alkali metal amides ANH(2) (A=K, Rb, Cs) in autoclaves at 600 degrees C to yield re d and yellow crystals respectively, of oxo nitrido dimetallates(VI) of general composition A(6)[M(2)X(7)] embedded in alkali metal. The alka li metal is washed out by liquid ammonia at room temperature. The stru ctures were determined from X-ray single-crystal data. They are monocl inic with the K-6[Co2O7] structure type, Z=2, with the following unit cell parameters: [GRAPHICS] The title compounds contain corner-sharing double tetrahedra units [M(2)X(7)](6-). The ligands X=N, O are distri buted statistically. The anions [M(2)X(7)](6-) are stacked together fo llowing the motif of a distorted body-centred arrangement connected by alkali metal ions.