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Syntheses and Characterization of Oxygen/Sulfur-Bridged Incomplete Cubane-Type Clusters, [Mo3S4Tp3]+ and [Mo3OS3Tp3]+, and a Mixed-Metal Cubane-Type Cluster, [Mo3FeS4ClTp3]. X-ray Structures of [Mo3S4Tp3]Cl, [Mo3OS3Tp3]PF6, and [Mo3FeS4ClTp3]

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posted on 2006-07-10, 00:00 authored by Tsutomu Yamauchi, Hideaki Takagi, Takashi Shibahara, Haruo Akashi
The reaction of [Mo3S4(H2O)9]4+ (1) with hydrotris(pyrazolyl)borate (Tp) ligands produced [Mo3S4Tp3]Cl·4H2O ([3]Cl·4H2O) in an excellent yield. An X-ray structure analysis of [3]Cl·4H2O revealed that each molybdenum atom bonded to the Tp ligand. We report four salts of 3, [3]Cl·4H2O, [3]tof·2H2O, [3]PF6·H2O, and [3]BF4·2H2O in this paper. The solubility and stability of the chloride salt in organic solvents differ completely from those of the other salts. We have also prepared a new compound, [Mo3OS3Tp3]PF6·H2O ([4]PF6·H2O), via the reaction of [Mo3OS3(H2O)9]4+ (2) with KTp in the presence of NH4PF6. All the molybdenum atoms bonded to Tp ligand. 1H NMR signals corresponding to nine protons bonded to three pyrazole rings in one Tp were observed in a spectrum (at 253 K) of [3]BF4·2H2O. It shows that cluster 3 has a 3-fold rotation axis in CD2Cl2 solution. Twenty-one 1H NMR signals corresponding to twenty-seven protons bonded to nine pyrazole rings in three Tp ligands were observed in a spectrum (at 233 K) of [4]PF6·H2O; obviously, 4 has no 3-fold rotation axis, in contrast to 3. The short CH···μ3S distance caused large upfield chemical shifts in the 1H NMR spectra of 3 and 4. The reaction of 3 with metallic iron in CH2Cl2 produced [Mo3FeS4XTp3] (X = Cl (5), Br (6)). X-ray structure analysis of 5 has revealed the existence of a cubane-type core Mo3FeS4. Complex 3 functions as a metal-complex ligand for preparing a novel mixed-metal complex even in nonaqueous solvents. The cyclic voltammogram of 5 shows two reversible one-electron couples (E1/2 = −1.40 and 0.52 V vs SCE) and two irreversible one-electron oxidation processes (Epc = 1.54 and 1.66 V vs SCE).

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