Structural and photophysical properties of [(CO)3(phen)Re(μ-Br)Re(phen)(CO)3]+[(CO)3Re(μ-Br)3Re(CO)3]−: Where does its luminescence come from?

Abstract

The multimetallic complex [[(CO)3(phen)Re(μ-Br)Re(phen)(CO)3][(CO)3Re(μ-Br)3Re(CO)3]]·CH2Cl2 was prepared by direct reaction of (Re(CO)3(THF)Br)2 (THF: tetrahydrofuran) and 1,10-phenanthroline in a 1:1 ratio, followed by recrystallization in dichloromethane. The compound is an ionic salt where both, cation and anion, are bimetallic complexes. Inside both of them the ReI centers are bridged by one or three bromides respectively. The compound has an absorption band centered at 375nm in CH2Cl2, which has been assigned to a MLCT band. Excitation at 375nm produces luminescent emission at 608nm. Comparison of these results with closely related rhenium complexes, in addition to Time Dependant-DFT analysis, allow us to propose the [(CO)3(phen)Re(μ-Br)Re(phen)(CO)3]+ cation as main responsible for luminescence. Luminescence lifetime and singlet oxygen formation quantum yield suggest also that the emissive excited state has a triplet character.