Rhenium-pyridyl complex

The introduction of further metals into these systems can be achieved by placing pyridyl-functionalized alkynyl groups in the axial positions 91 and then coordinating rhenium bipyridine complexes 92. Again, electron delocalization was observed along the heterobimetallic axis. The inclusion of such donors in both axial positions allows a wide range of metal subunits to be introduced into these systems. 

Complexes of rhenium(I) tricarbonyl chloride with pyridyl ligands are often luminophores and hence in anion sensing have principally been used as reporter groups. In many cases this Re(I) fragment is compatible with the same bipyridyl receptor ligands that have been used in [Ru(bpy)3]2+ examples. 

Interestingly, the photoisomerizing styrylpyridine and l,2-di(4-pyridyl)-ethylene (dpe) rhenium complexes behave as luminescence switches [123-125], This phenomenon originates in the different nature of the lowest excited state of the trans and cis isomers, TI.(F) and MLCT, respectively. Near-UV irradiation converts the nonemissive trans isomer to the cis form, which shows strong phosphorescence from its 3MLCT state. Emission can be switched off by UV (254 rnn) light that induces a reverse cis—>trans isomerization. 

The use of Tapy (l-(2-pyridyl)-l,2,3-triazole) ligand bearing long allqrl chains demonstrates an impressive enhancement of the luminescent properties of the rhenium complexes in aqueous medium relative to the parent Pyta complex." ... 

Of course, sometimes the geometry of the spacer is not sufficient to fully control the behavior of the scaffold and the chromophores flexibility can be responsible for unusual behavior. For example. Hupp has reported the properties of two collapsed dimers showing a compact structures due to ethynyl-pyridyl side arms used for binding rhenium complexes that act as spacers (Fig ure 13.72)128,... 

The formation of bipyridines by C—C coupling between two pyridyl groups on the coordination sphere of group III complexes has been reported by Diaconescu et A difference with the rhenium tricarbonyl system... 

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