Synthesis and crystal structure of alkali metal oxo nitrido dimetallates(VI), A6[M2N4O3] (AK, Rb, Cs; MMo, W)

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Abstract

Mixtures of MMo3 with MMo, W react with an excess of alkali metal amides ANH2 (AK, Rb, Cs) in autoclaves at 600 °C to yield red and yellow crystals respectively, of oxo nitrido dimetallates(VI) of general composition A6[M2X7] embedded in alkali metal. The alkali metal is washed out by liquid ammonia at room temperature.

The structures were determined from X-ray single-crystal data. They are monoclinic with the K6[Co2O7] structure type, Z = 2, with the following unit cell parameters:

a (Å)b (Å)c (Å)β (deg)
K6[Mo2N4O3]6.721(3)9.490(6)9.582(4)92.07(4)
K6[W2N4O3]6.720(2)9.473(1)9.581(2)91.99(2)
Rb6[Mo2N4O3]6.960(2)9.766(2)9.827(2)92.02(2)
Rb6[W2N4O3]6.977(2)9.768(4)9.861(2)91.87(2)
Cs6[Mo2N4O3]7.305(2)10.108(7)10.204(4)91.53(3)
Cs6[W2N4O3]7.284(3)10.045(5)10.174(5)91.54(3)
The title compounds contain corner-sharing double tetrahedra units [M2X7]6−. The ligands XN, O are distributed statistically. The anions [M2X7]6− are stacked together following the motif of a distorted body-centred arrangement connected by alkali metal ions.

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Dedicated to Professor Hugo F. Franzeu on the occasion of his 60th birthday.

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