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?

The multimetallic complex [[(CO)3(phen)Re(l-Br)Re(phen)(CO)3][(CO)3Re(l-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 Re I centers are bridged by one or