Proton‐Switched Emission Behavior of Hexanuclear Molyb‐denum(II) Clusters Bearing Terminal Pyridine Carboxylate Ligands

Abstract

We designed and synthesized a new and novel octahedral hexamolybdenum(II) cluster bearing terminal pyridine‐3‐carboxylate ( 3L ) or pyridine‐4‐carboxylate ligands ( 4L ), [{Mo 6 Br 8 }( 3L ) 6 ] 2– ( 3 ) or [{Mo 6 Br 8 }( 4L ) 6 ] 2– ( 4 ), to demonstrate proton‐switched emission behaviour of the cluster. X‐ray crystal analysis of 4 demonstrated that the O‐atom in the carboxylate group of 4L coordinates to each Mo atom in the {Mo 6 Br 8 } 4+ ‐core, indicating that the N‐atom of 4L in 4 is open for protonation. Reflecting such structural characteristics of the cluster, both 3 and 4 showed proton‐switched emission behaviour owing to the changes in the electron‐donating abilities of the relevant terminal ligands upon protonation to the pyridine N atoms: blue shifts of the emission spectra and increases in the emission lifetimes of the clusters.