Benzo[1,2-b;4,5-b′]dithiophene-bridged bimetal complexes with different redox-active terminals: Syntheses, characterization and charge delocalization studied by spectro-electrochemical and DFT methods

Benzo[1,2-b;4,5-b']dithiophene have been used as bridge ligand to build up binuclear iron ethynylene complex 1 and ruthenuim vinylene complex 2, and their electronic and optical properties were investigated by electrochemistry, IR and UV-vis-NIR spectroelectrochemistry and theoretical calculations. These properties of two complexes 1 and 2, for comparison, of the previously reported ruthenium ethynylene complex 3 was analyzed. Complexes 1-3 exhibit obvious different redox characteristics. The highest anodic potentials and the largest Delta E value were found in ruthenium vinylene complex 2. IR spectroelcetrochemistry results show that two intense v(C C) bands of monocation 1(+) feature more larger v(C C) separation (73 cm(-1)) than that of 3(+) (36 cm(-1)), and v(C 0) band in 2 exhibit little changes upon electrolytic experiments. The NIR broad absorptions of different strength and energy were found in singly-oxidized 1(+)-3(+), which may be assigned to MLCT and proved further by DFT-TDDFT calculations. Similar to 3(+), different conformations from the relative position difference between metal terminal groups and bridge ligands may be attributable to broad NIR absorptions of 1(+). (C) 2017 Elsevier B.V. All rights reserved.