ic300581a_si_001.pdf (487.96 kB)
Ferrocene–Dithiolene Hybrids: Control of Strong Donor–Acceptor Electronic Communication to Reverse the Charge Transfer Direction
journal contribution
posted on 2012-11-19, 00:00 authored by Tetsuro Kusamoto, Kenji Takada, Ryota Sakamoto, Shoko Kume, Hiroshi NishiharaWe prepared a novel class of ferrocene–dithiolene
hybrid
molecules, FcS4dt(Me)2 and FcS4dt[Pt(tBu2bpy)] (where FcS4dt indicates 2-(1,3-dithia[3]ferrocenophane-2-ylidene)-1,3-dithiole-4,5-dithiolate
and tBu2bpy indicates 4,4′-di-tert-butyl-2,2′-bipyridine), in which the ferrocene
moiety was bound to the planar conjugated dithiolene skeleton via
two sulfur atoms such that the cyclopentadienyl rings were perpendicular
to the dithiolene backbone. The physical properties and electronic
structures of the complexes and their oxidized species [FcS4dt(Me)2]•+ and [FcS4dt[Pt(tBu2bpy)]]•+ were
investigated by means of single-crystal X-ray diffraction (XRD) analysis,
cyclic voltammetry, electron paramagnetic resonance (EPR), and UV–vis
near infrared (UV–vis–NIR) spectroscopy. The electron
density distributions of the highest occupied molecular orbitals (HOMOs)
of FcS4dt(Me)2 and FcS4dt[Pt(tBu2bpy)] differed remarkably in
that the HOMO of the former was ferrocene-based whereas that of the
latter was dithiolene-based. The differences in the HOMO distributions
originated from the energy level of the dithiolene-based π-orbital
in each of the complexes, which was controlled by changing R in FcS4dt(R)2 (R = Me for FcS4dt(Me)2; 2R = Pt(tBu2bpy) for FcS4dt[Pt(tBu2bpy)]). We
succeeded in analyzing the crystal structure of [FcS4dt[Pt(tBu2bpy)]](F4TCNQ)·C6H14·CH2Cl2 (where F4TCNQ indicates 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane),
which provided a rare example of the crystal structure of a [Pt(diimine)(dithiolate)]•+ ion-based complex. A comparison of the bond lengths
in FcS4dt[Pt(tBu2bpy)] and [FcS4dt[Pt(tBu2bpy)]]•+ suggested that the latter complex
displayed a conjugated dithiolene-based π-radical character.
These considerations agreed well with the electronic structures calculated
using density functional theory (DFT) and time-dependent(TD)-DFT methods.
Significant electronic communication between the ferrocene and dithiolene
moieties was detected for both [FcS4dt(Me)2]•+ and [FcS4dt[Pt(tBu2bpy)]]•+ in the appearance
of an intramolecular charge transfer band, which was hardly observed
for previously reported ferrocene–dithiolene hybrid molecules.
The charge transfer direction was reversed between the two cations.
The electron coupling parameter HAB and
the potential energy curves of the oxidized complexes were estimated
based on the classical two-state Marcus–Hush theory. These
results suggest that FcS4dt-based metalladithiolenes can
exhibit controllable electronic structures expressed as double-minimum
potential energy curves.