Synthesis, characterization, photophysics, and anion binding properties of platinum(ii) acetylide complexes with urea group

Abstract

A new class of platinum(II) acetylide complexes with urea group, [Pt(^tBu₃tpy)(CCC₆H₄-4-NHC(O)NHC₆H₄-4-R)](OTf) (^tBu₃tpy = 4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine; R = H (3a), Cl (3b), CF₃ (3c), and NO₂ (3d)), has been synthesized and characterized. The crystal structures of 3a, 3a·DMF·THF, 3b·CH₃CN, and 3c·CH₃CN have been determined by X-ray diffraction. Upon excitation at λ > 380 nm, the solid samples of complexes 3a–3d show orange light at 298 K. The anion binding properties of complexes 3a–3d have been studied by UV-vis titration experiments in CH₃CN and DMSO. In general, the log K values of 3a–3d with the same anion in CH₃CN depend on the substituent R on the acetylide ligand of 3a–3d and follow this order: R = NO₂ (3d) > CF₃ (3c) > Cl (3b) > H (3a). For the same complex with different anions, the log K values are in the following order: F⁻ > OAc⁻ > Cl⁻ > Br⁻ ≈ HSO₄⁻ ≈ NO₃⁻ > I⁻, which is in accordance with the decrease in the basicity of anions. Complex 3d with NO₂ group shows a dramatic colour change towards F⁻ in DMSO, allowing the naked eye detection of F⁻.