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-pyridyl)ethylene, phen=1,10-phenanthroline) was synthesized, purified and characterized by UV–Vis, 1H NMR, Raman and IR spectroscopy. 1H NMR resonance spectrum of fac-[Re(CO)3(phen)(t-bpe)]+ reveals a clear electronic communication of the metal center across the coordinated t-bpe with upfield shift of the ligand signals upon complexation. The CO stretching frequencies are in accord with facial geometry of the rhenium complex. The photochemical behavior of free trans-1,2-bis(4-pyridyl)ethylene and of its protonated form is also reported. The quantum yield for the trans→cis photoinduced isomerization of free ligand in methanolic solutions at 313 nm irradiation is 0.17±0.03. The average values for the photoisomerization of the protonated 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-bpe 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 absorption upon formation of the complex. The photoproducts cis-1,2-bis(4-pyridyl)ethylene and fac-[Re(CO)3(phen)(c-bpe)]PF6 were synthesized and identified by UV–Vis, 1H NMR and luminescence properties.