Syntheses and spectroscopic characterization of fac-[Re(CO)(3)(phen)(L)]PF6, L = trans- and cis-1,2-bis(4-pyridyl)ethylene

The complex fac-[Re(CO)(3)(phen)(t-bpe)]PF6 (t-bpe = trans-1,2-bis(4-pyridy l)ethylene, phen = 1,10-phenanthroline) was synthesized, purified and chara cterized by UV-Vis, H-1 NMR, Raman and IR spectroscopy. H-1 NMR resonance s pectrum of fac-[Re(CO)(3)(phen)(t-bpe)] reveals a clear electronic communic ation of the metal center across the coordinated t-bpe with upfield shift o f the ligand signals uyon complexation. The CO stretching frequencies are i n accord with facial geometry of the rhenium complex. The photochemical beh avior of free trans-1,2-bis(4-pyridyl)ethylene and of its protonated form i s also reported. The quantum yield for the trans --> cis photoinduced isome rization of free ligand in methanolic solutions at 313 nm irradiation is 0. 17 +/- 0.03. The average values for the photoisomerization of the protonate d ligand (pH 1.9) are 0.19 +/- 0.02 and 0.15 +/- 0.01, respectively at 313 and 334 nm excitation. The photoassisted trans --> cis isomerization of t-b pe in the fac-[Re(CO)(3)(phen)(t-bpe)](+) complex was achieved with higher quantum yields at lower energy irradiation by exploiting the red shifted ab sorption upon formation of the complex. The photoproducts cis-1,2-bis(4-pyr idyl)ethylene and fac-[Re(CO)(3)(phen)(c-bpe)]PF6 were synthesized and iden tified by UV-Vis, H-1 NMR and luminescence properties. (C) 2001 Elsevier Sc ience B.V. All rights reserved.