Solvent, coordination and hydrogen-bond effects on the chromic luminescence of the cationic complex [(phen)(H2O)Re(CO)3]+

Abstract

The [(phen)(H₂O)Re(CO)₃]⁺(CF₃SO₃)⁻ salt, 1⁺(CF₃SO₃⁻), has been crystallized in the form of two new solvates, [(phen)(H₂O)Re(CO)₃]⁺(CF₃SO₃)⁻·(C₄H₈O)_0.5 and [(phen)(H₂O)Re(CO)₃]⁺(CF₃SO₃)⁻·CH₂Cl₂. The structures, as determined by single-crystal X-ray diffraction, show intense hydrogen bonding between the coordinated water molecule on 1⁺ and the triflate oxygen atoms, with O_water⋯O_triflate in the range from 2.608(13) to 2.972(13) Å. This feature, to the best of our knowledge, is preserved for each solvate of 1⁺(CF₃SO₃⁻). The spectroscopic characterization of 1⁺(CF₃SO₃⁻) in solution together with DFT and TD-DFT results suggest that its photophysical behavior depends on the solvent polarity, as normally found for MLCT, but additionally, on the coordinating and hydrogen bonding ability of the solvent. The results suggest that in low-polarity, non-coordinating and non-hydrogen bonding solvents, the intimate association observed in the solid between 1⁺(CF₃SO₃⁻) is preserved, in contrast to coordinating solvents that may replace the coordinated water. Finally, weakly coordinating but hydrogen bonding solvents may dissociate the ionic pair units. The sum of all these effects leads to an apparent unusual solvent dependency of the luminescence emission with hypsochromic or bathochromic shifts depending on the coordinating ability of the solvent.