Synthesis and luminescence properties of a nonsymmetrical ligand-bridged reI−reI chromophore
Xue, W. M.
Eichhorn, David M.
Orizondo, Peter L.
Rillema, D. Paul
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Xue, W.-M.; Goswami, N.; Eichhorn, David M.; Orizondo, Peter L.; Rillema, D. Paul. 2000. Synthesis and Luminescence Properties of a Nonsymmetrical Ligand-Bridged ReI−ReI Chromophore. Inorganic Chemistry, v.39 no.20 pp.4460-4467
The preparation and the physical and photophysical properties of three complexes containing the bridging ligand 5-(2-(4-pyridyl)ethyl)-2-(2-pyridyl)pyrimidine (pypm-py) are described. Two of the complexes are monometallic, [Re(pypm-py)(py)(CO)3]+ and [Re(phen)(py-pypm)(CO)3]+, and one is bimetallic, [(CO)3(py)Re(pypm-py)Re(phen)(CO)3]2+, where phen is 1,10-phenanthroline and py is pyridine. [Re(pypm-py)(py)(CO)3](CF3SO3) crystallized in the space group P21/n with a = 13.98 (1) Å, b = 12.704 (6) Å, c = 15.66 (1) Å, and Z = 4. The Re−N(pypm) bond distances for Re−N(py of pypm) = 2.167(9) Å and for Re−N(pm of pypm) = 2.202 (9) Å. The Re−N(py) bond distance is 2.203(9) Å. The complexes exhibit CO infrared-active bands in the 1900−2100 cm-1 region of the infrared spectrum; three bands were present for [Re(pypm-py)(py)(CO)3]+, but only two for the other complexes. Methylene protons for [Re(pypm-py)(py)(CO)3]+ are nonequivalent on the basis of NMR spectra analysis, but are equivalent for the other two complexes. Oxidation of the complexes occurs in the 1.83−1.87 V vs SSCE region and is attributed to the Re2+/+ redox couple; three to four reductions occur, the first of which is assigned to reduction of the coordinated diimine ligand, either the (pypm0/--py) or the (phen0/-) couple occurring at −1.05 and −1.23 V, respectively. The three complexes undergo electronic excitation in the 300−400 nm region assigned to dπ → π*(diimine) transitions and in the 200−300 nm region assigned to intraligand π → π* transitions. Strong emission occurs from the complexes in solution at room temperature. The emission bands are structureless, and the positions are solvent dependent, consistent with MLCT emitters. Quantum efficiencies and emission lifetimes in 4:1 ethanol/methanol at room temperature fall in the order [Re(phen)(py-pypm)(CO)3]+ (φem = 0.087, τ = 1.65 μs) > [(CO)3(py)Re(pypm-py)Re(phen)(CO)3]2+ (φem = 0.037, τ = 1.09 μs) > [Re(pypm-py)(py)(CO)3]+ (φem = 0.014, τ = 0.11 μs), indicating that energy transfer occurs between the Re(phen) chromophore and the Re(pypm) center in the bimetallic complex.
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