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]

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 (E_1/2 = −1.40 and 0.52 V vs SCE) and two irreversible one-electron oxidation processes (E_pc = 1.54 and 1.66 V vs SCE).