Heteroleptic bipyridine complex: Synthesis, spectral and structural analyses, and interconversion of its {Mo3S7} core to {Mo3S4} core

Abstract

Unsymmetrical substitution of the bromide ligands in [Et4N]2[Mo3(μ3-S)(μ-S2)3Br6] by the 2,2′-bipyridine(bpy) ligand affords neutral heteroleptic cluster Mo3(μ3-S)(μ-S2)3Br4(bpy). The single crystal analysis of the product shows that the cluster crystallizes in P-1 space group with a = 11.449(5), b = 12.842(5), c = 13.079(5); α=79.734(5), β=86.812(5), γ=66.222(5). The asymmetric unit contains one full cluster moiety, one Et4N+Br− salt and one acetonitrile solvent molecule. The free bromide ion (from Et4N+Br−) is responsible for strong halogen bonding interaction with three sulfur atoms of the cluster. The complex is formulated as [Et4N][Mo3(μ3-S)(μ-S2)3Br4(bpy).Br].CH3CN (1). Complex 1 contains a {Mo3S7} core and its treatment with excess triphenyl phosphine (PPh3) generates neutral complex 2 containing a {Mo3S4} core. Complex 2 (Mo3(μ3-S)(μ-S)3Br4(bpy)(PPh3)3) can reversibly transform to its parent compound 1 when treated with excess elemental sulfur. This transformation involves the interconversion of the disulfide bridges to sulfide bridges, while maintaining a triangular geometry with the three molybdenum centers through μ3-S bridging. The interconversion was examined by 31PNMR and FTIR spectroscopies. This interconversion is analogous to a molecular mimicry of the creation and refilling of desired sulfide vacancies. Complex 1 and complex 2 show strong emission bands at 350 and 345 nm, respectively, when their DMF solutions are excited at 300 nm. This suggests that these complexes have potential applications in photonic devices. © 2021 Elsevier B.V.