Synthesis, structure, and properties of molybdenum and tungsten cyano complexes with cuboidal M4(μ3-E)4 (M = Mo, W; E = S, Se, Te) cores

Four new tungsten and molybdenum cyano complexes of formula KCs5[W4S4(CN)(12)]. CH3OH . 2H(2)O (1), K-6[W-4- Se-4(CN)(12)]. 6H(2)O (2), K-6[W4Te4(CN)(12)]. 5H(2)O (3), and K-7[Mo4Te4(CN)(12)]. 12H(2)O (5) have been prepared by high-temperature 430-450 degrees C reaction of the polymeric chain compounds {W3S7Br4}(x), {W3Se7Br4}(x), {Mo3Te7I4}(x) and solid-state WTe2 with KCN, and crystallization from aqueous solutions. In addition Cs-6[Mo4Te4(CN)(12)]. 2H(2)O (4) has been prepared by oxidation of 5 with bromine water. The molecular structures have been investigated by X-ray crystallography. Mixed-valence (3.5) compounds 1-4 are diamagnetic. Mixed-valence (3.25) compound 5 is paramagnetic (mu = 2.03 mu(B) at 77 K). In addition to the structural data for these complexes IR and UV-vis spectroscopy have been used to characterize the complexes. Cyclic-voltammetry data have shown that M4E4n+ (M = Mo, W; E = S, Se, Te) cubes are capable of existing in three oxidation states ranging from the most oxidized (n = 6; 10 electrons) to the most reduced electron-precise (n = 4; 12 electrons). The Se-77, Te-125, and W-183 NMR spectra of the cubes (1-3) demonstrate unambiguously the unaltered environments of the W and E atoms in aqueous solution.