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
(Lmeta) and 5,5′-bis(3,3-dimethyl-2,3-dihydrobenzothiophen-5-yl)-2,2′-bipyridine
(Lpara) were synthesized and coordinated to rhenium and
manganese to obtain the corresponding complexes MnLmeta(CO)3Br, ReLmeta(CO)3Br, MnLpara(CO)3Br, MoLpara(CO)4 and
ReLpara(CO)3Br. 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 Go, reinforcing the importance of contact group connectivity
for molecular wire conductance.