om049443s_si_001.pdf (60.04 kB)
Spectroscopic and Computational Investigations of the Temperature-Dependent Emission Behavior of [Re(CNx)5Cl] and [Re(CNx)6]+ Complexes
journal contribution
posted on 2005-01-31, 00:00 authored by John M. Villegas, Stanislav R. Stoyanov, Joseph H. Reibenspies, D. Paul Rillema[Re(CNx)5Cl] and [Re(CNx)6](PF6) complexes form with the isocyanide ligand, 2,6-dimethylphenylisocyanide (CNx). [Re(CNx)5Cl] crystallizes in the space group P(2)1/c with
a Re−Cl bond length of 2.5278(16) Å, a Re−C bond length trans to Cl of 1.937(6) Å, and
Re−C bond lengths in the equatorial plane ranging from 1.998(6) to 2.034(6) Å. The complexes
are highly emissive at 77 K with emission lifetimes of 5.1 and 4.6 μs, respectively, but are
nonemissive at room temperature. Density functional theory (DFT) geometry optimizations
of the ground and the triplet metal-ligand-to-ligand charge transfer (3MLLCT) states of the
complexes in the gas phase place the energy of the 3MLLCT state for [Re(CNx)5Cl] 200 cm-1
higher than the experimental emission peak at 77 K. The energies of the singlet excited
states of the two complexes calculated in ethanol using time-dependent density functional
theory (TDDFT) and conductor-like polarizable continuum model (CPCM) deviate by less
than 600 cm-1 from the corresponding UV−vis peaks in the same solvent. The TDDFT/CPCM calculation confirms the existence of 3d−d states that provide a nonradiative relaxation
pathway accounting for loss of emission from the emitting state at room temperature.
Calculations also reveal a singlet to triplet excitation at 35 700 cm-1 near the absorption of
the CNx ligand at 35 200 cm-1 and a 3π→π* state of CNx 200 cm-1 higher than the
experimental phosphorescence energy.