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Molybdenum and tungsten cluster methoxides with bridging, terminal or mixed bridging-terminal methoxo groups: preparation and properties. Crystal structure of [Na(CH_3OH)_5]_2[Mo_6Br_8(OCH_3)_6]

New cluster methoxides of molibdenum or tungsten of the composition [(M_6X_8^i)X_2^a(OCH_3)_4/2^a-a]• 2CH_3OH (M = Mo, W ; X = Cl, Br), [Mo_6X_8^i(OCH_3)_2^a(OCH_3)_4/2^a-a]• CH_3OH (X = Cl, Br) and [Na(CH_3OH)_5]_2[Mo_6Br_8^i(OCH_3)_6^a] with bridging, mixed bridging-terminal or terminal methoxo groups, respectively, have been prepared. The preparation procedures, spetroscopic and physical properties, including X-ray photoelectron spectra have been correlated. The crystal structure has been solved for [Na(CH_3OH)_5]_2[Mo_6Br_8(OCH_3)_6]. The compound crystallizes in the triclinic crystal system. The structure is built of two [Na(CH_3OH)_5]^+ cations and the [Mo_6Br_8(OCH_3)_6]^2- anion. All six oxygen atoms from coordinated methoxo groups are acceptors of hydrogen of coordinated methanol molecules from the six neighbouring cations making a three-dimensional packing network.

Molybdenum clusters; Tungsten clusters; Bridging methoxides; bridging-terminal methixides

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