ic4024585_si_003.cif (188.17 kB)
Rhodium Amidinate Dimers as Structural and Functional Hubs for Multimetallic Assemblies
dataset
posted on 2014-01-06, 00:00 authored by Daniel Chartrand, Garry S. HananThe
synthesis and characterization of multichromophore assemblies based
on a dirhodium tetra-N,N′-diphenylisonicotinamidinate
dimer are reported. The pyridyl moieties were used to coordinate up
to four positively charged rhenium(I) chromophores of the form fac-[Re(bpy)(CO)3L]PF6 (bpy = 2,2′-bipyridine, L = a pyridyl group
on the Rh2 dimer). The mono-, bis-, tris-, and tetrarhenium
assemblies were isolated by size-exclusion chromatography, and their
spectroscopic and electrochemical properties were studied and compared
with DFT and time-dependent (TD) DFT models of the original rhodium
dimer and the mono- and tetrarhenium assembly. The rhenium chromophores
modify the properties of the rhodium dimer: for example, the first
oxidation of the Rh2 dimer (Rh–Rh δ* orbital)
increased from the original 210 mV versus SCE in acetonitrile, by
45 mV per rhenium complex added, finishing at 390 mV for the tetrarhenium
complex. The rhodium dimers display solvatochromism with acetonitrile
(MeCN) due to the formation of an axial adduct and has an association
constant that increased by a factor of 3.8 when the dimer has four
rhenium chromophores. The absorption data clearly exhibited the cumulative
effect of the addition of rhenium chromophores in the 230 to 400 nm
range. The main visible band, a metal-dimer-to-ligand charge transfer
(1M2LCT) transition determined by TD-DFT, red-shifts
from 541 nm to 603 nm, while the main near-IR band, a 1Rh2(π*→σ*) transition, has a small
blue-shift (∼26 cm–1/Re), varying from 837
to 831 nm upon addition of the four Re(I) chromophores. This was observed
in TD-DFT also with a total shift of 105 cm–1 for
the tetrarhenium assembly. In terms of emission, the rhenium excited
state was completely quenched upon coordination to the dimer, suggesting
fast electron transfer of the rhodium dimer. All other aspects of
the rhenium chromophore are similar to the parent complex where L = pyridine, showing similar redox couples and additive spectral
characteristics.