Connectivity-Dependent Conductance of 2,2'-Bipyridine-Based Metal Complexes.

The present work provides an insight into the effect of connectivity isomerization of metal-2,2'-bipyridine complexes. For that purpose, two new 2,2'-bipyridine (bpy) ligand systems, 4,4'-bis(4-(methylthio)phenyl)-2,2'-bipyridine (L meta ) and 5,5'-bis(3,3-dimethyl-2,3-dihydrobenzothiophen-5-yl)-2,2'-bipyridine (L para ) were synthesized and coordinated to rhenium and manganese to obtain the corresponding complexes MnL meta (CO) 3 Br, ReL meta (CO) 3 Br, MnL para (CO) 3 Br, MoL para (CO) 4 and ReL para (CO) 3 Br. The experimental and theoretical results revealed that coordination to the para system, i.e., the metal ion peripheral to the conductance path, gave a slightly increased conductance compared to the free ligand attributed to the reduced highest occupied molecular orbital (HOMO)-least unoccupied molecular orbital (LUMO) gap. The meta-based system formed a destructive quantum interference feature that reduced the conductance of a S···S contacted junction to below 10 -5.5 G o , reinforcing the importance of contact group connectivity for molecular wire conductance.