Replacement of 2,2'-Bipyridine by 1,4-Diazabutadiene Acceptor Ligands: Why the Bathochromic Shift for (NN̂)IrCl(C5Me5)+ Complexes but the Hypsochromic Shift for (NN̂)Ir(C5Me5)?

, , , , and .
Inorganic Chemistry, 42 (17): 5185--5191 (2003)
DOI: 10.1021/ic034464k


Replacement of 2,2'-bipyridine (bpy) by substituted 1,4-diazabutadiene (R-DAB) a-diimine ligands NN̂ leads to a substantial hypsochromic shift of $\sim$0.8 eV for the long-wavelength absorption band in (NN̂)Ir(C5Me5) but to a bathochromic absorption shift of $\sim$0.4 eV for (NN̂)IrCl(C5Me5)+. DFT calcns. on model complexes based on exptl. (R-DAB compds.) and geometry-optimized structures (bpy systems) reveal that the low-energy transitions of the cationic chloro complexes are largely of ligand-to-ligand charge-transfer character L'LCT (L = a-diimine, L' = Cl) whereas the neutral compds. exhibit p $\rightarrow$ p* transitions between the considerably mixed metal dp and a-diimine p* orbitals. The much more pronounced metal-ligand orbital interaction for the R-DAB complexes causes the qual. different shifts on replacing the stronger basic bpy by the better p-acceptors R-DAB. Only the LUMO of the neutral compds. is destabilized on replacement of bpy by R-DAB whereas the LUMO of (NN̂)IrCl(C5R'5)+ and both HOMOs are stabilized through this change. on SciFinder(R)



  • @b_schwederski
  • @huebleriac

Comments and Reviews