A novel Nb<inf>2</inf>S<inf>4</inf> complex with a dithiophosphinate ligand: Synthesis, structure and redox properties

Abstract

© 2018 Elsevier Ltd A new diisobutyldithiophosphinate complex, [Nb2S4(S2PiBu2)4] (1), was obtained by a ligand substitution reaction using (Bu4N)4[Nb2S4(NCS)8] and NaS2PiBu2·3H2O. Its crystal structure has been determined. The Nb–Nb distance is 2.9034(7) Å. The cyclic voltammogram (CV) of 1 in dichloromethane exhibits two successive chemically reversible one-electron oxidation waves at +0.55 and +1.10 V (versus Ag/AgCl) attributed to the NbIV/NbV couple. This is the first {Nb2S4} cluster that shows two reversible oxidations. The paramagnetic mixed-valence Nb(IV/V) product of the one-electron oxidation, [Nb2S4(S2PiBu2)4]+ (1+), was generated in situ. The EPR spectrum of 1+ in acetonitrile reveals a 19-line signal arising from the hyperfine interaction between the unpaired electron and two equivalent 93Nb nuclei with I = 9/2, indicating complete delocalization of the unpaired electron over both metal centers. DFT calculations have been performed for the complexes [Nb2S4(S2PMe2)4], [Nb2S4(S2P(OMe)2)4], [Nb2S4(S2CNMe2)4] and [Nb2S4(S2COMe)4] and their single and double oxidized species in order to explain the peculiarities of their redox behavior. The results show that the HOMOs responsible for oxidation have a predominantly metallic character in all cases, but they are significantly more high-lying for the dithiophosphinate and dithiocarbamate complexes, which explains their ability to be oxidized.