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

Unsymmetrical substitution of the bromide ligands in [Et4N](2)[Mo-3(mu(3)-S)(mu-S-2)(3)Br-6] by the 2,2'-bipyridine(bpy) ligand affords neutral heteroleptic cluster Mo-3(mu(3)-S)(mu-S-2)(3)Br-4(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); alpha=79.734(5), beta=86.812(5), gamma=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][Mo-3(mu(3)-S)(mu-S-2)(3)Br-4(bpy)center dot Br]center dot CH3CN (1). Complex 1 contains a [Mo 3 S 7 ) core and its treatment with excess triphenyl phosphine (PPh3) generates neutral complex 2 containing a [Mo3S4) core. Complex 2 (Mo-3(mu(3)-S)(mu-S)(3)Br-4(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 mu(3)-S bridging. The interconversion was examined by (PNMR)-P-31 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. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The text describes the synthesis and transformation process of a molybdenum-sulfur coordination cluster, forming different complexes through substitution of different ligands and reactions with excess triphenyl phosphine and elemental sulfur. The crystal structure and photoluminescent properties of the complexes are analyzed.