THE CRYSTAL-STRUCTURE AND BONDING OF BIS(DIETHYLENETRIAMMONIUM) HEPTAMOLYBDATE(VI) TETRAHYDRATE

The title compound, (C4H16N3)2[Mo7O24] • 4H2O, crystallizes in the monoclinic system, space group C2/c, Z = 8, a = 20.949(8), b = 8.138(5), c = 39.009(11) Å, β= 103.40(3)°, V = 6470(3)Å3 Å3, Dx = 2.75, D0 = 2.74(1) Mg/m3, F(000) = 5184. The crystal structure has been refined to R = 0.039 and Rw =0.057 for 6636 independent observed reflexions with I 3σ(I). The asymmetric unit contains one discrete [M07O24]6 polyanion, two independent crystallographically diethylenetriammonium cations and four independent water molecules. The structure of diethyl enetriammonium heptamolybdate reported here is the first heptamolybdate structure containing a multifunctional organic cation in which three nitrogen atoms are protonated. The heptamolybdate anions consists of seven distorted MoO6 octahedra sharing edges and corners. Bond lengths and angles in the polyanion are similar as those in the analogous heptamolybdates. The cations and the water molecules are positioned so as to be able to form an extensive network of hydrogen bonds with either molybdate oxygen atoms or water oxygen atoms. Five different types of hydrogen contacts have been found: N — H O (mono and bifurcated), N —H …O (monofurcated), Ow-Hw … O (mono and bifurcated), Ow—Hw … Ow (mono and bifurcated) and C —H … O (mono and bifurcated). The proposed strong hydrogen-bonding interactions apparently stabilize the structure and explain its high thermal stability. © by R. Oldenbourg Verlag, München 1990