Electrochemical Generation of Cyano Ligated Molybdenum Sulphur Tetramer Cubane Core: Synthesis and Characterization

Abstract

For the first time the conversion of trimeric {M₃S₄}⁴⁺ to tetrameric (M₄S₄}⁴⁺ core has been made for molybdenum complex. The complex, K₅[Mo₃S₄(CN)₉] (1) on using with strong reducing agent transformed into K₈[Mo₄S₄(CN)₁₂] (2) in near quantitative yield. The diamagnetic complex (1) containing {Mo₃}⁶ core can accommodate two electrons in its non bonding molecular orbital 2a₁ under reducing environment to give a complex ion [Mo₃S₄(CN)₈]^7- with [Mo₃]⁸ electronic configuration. This reduced species undergoes re-oxidation by atmospheric air to give back the original compound with [Mo₃]⁶ core via a partially oxidized an intermediate species [Mo₃S₄(CN)₉]^6- with [Mo₃]⁷ core shows a characteristic EPR signal. However, under drastic reducing condition, the two electrons reduced species [Mo₃S₄(CN)₉]^7- with [Mo₃]⁸ core accommodate the next coming electron to its antibonding 2e orbital and thus achieve an unstable tri-nuclear [Mo₃(III)]⁹ core, where each metal centre has been reduced by one electron. The highly unstable and super reduced species [Mo₃S₄(CN)₉]^8- with [Mo₃(III)]⁹ configuration undergoes core transformation from cuboidal trinuclear [Mo₃(IV)S₄]⁴⁺ to the cubane type tetranuclear core [Mo₄(III)S₄]⁴⁺ of [Mo₄S₄(CN)₁₂]^8- complex ion. The corresponding tungsten-analogue though responses this reduction, but quickly oxidizes back to the starting material during work-up procedure.