Ruthenium complexes with asymmetric hydroxy- and methoxy-substituted bipyridine ligands

(2,2'-Bi-pyridine-κ2N,N')(4,4'-dimeth-oxy-2,2'-bipyridine-κ2N,N')palladium(II) bis-(tri-fluoro-meth-anesulfonate)

In the title complex salt, [Pd(C10H8N2)(C12H12N2O2)](CF3SO3)2, the palladium(II) atom is fourfold coordinated by two chelating ligands, 2,2'-bi-pyridine and 4,4'-dimeth-oxy-2,2'-bi-pyridine, in a distorted square-planar environment. In the crystal, weak π-π stacking inter-actions between the 2,2'-bi-pyridine rings [centroid-to-centroid distances = 3.8984 (19) Å] and between the 4,4'-dimeth-oxy-2,2'-bi-pyridine rings [centroid-to-centroid distances = 3.747 (18) Å] contribute to the alignment of the complex cations in columns parallel to the b-axis direction.

Accessing unsymmetrical Ru(II) bipyridine complexes: a versatile synthetic mechanism for fine tuning photophysical properties

Three novel unsymmetrical Ru(II) bipyridine complexes were generated via a convenient, modular, convergent synthetic route. An investigation of their photophysical properties revealed solvent-dependent excited state behaviour including altered absorption and emission wavelengths, emission lifetimes and quantum yields of phosphorescence.

Luminescent Iridium Complexes with a Sulfurated Bipyridine Ligand: PCET Thermochemistry of the Disulfide Unit and Photophysical Properties

Molecular systems combining light harvesting and charge storage are receiving great attention in the context of, for example, artificial photosynthesis and solar fuel generation. As part of ongoing efforts to develop new concepts for photoinduced proton-coupled electron transfer (PCET) reactivities, we report a cyclometallated iridium(III) complex [Ir(ppy)₂(^S-Sbpy)](PF₆) ([1]PF₆) equipped with our previously developed sulfurated bipyridine ligand ^S-Sbpy. A new one-step synthetic protocol for ^S-Sbpy is developed, starting from commercially available 2,2'-bipyridine, which significantly facilitates the use of this ligand. [1]⁺ features a two-electron reduction with potential inversion (|E₁| > |E₂|) at moderate potentials (E₁ = -1.12, E₂ = -1.11 V versus. Fc^+/0 at 253 K), leading to a dithiolate species [1]^-. Protonation with weak acids allows for determination of pK_a = 23.5 in MeCN for the S-H···S^- unit of [1H]. The driving forces for both the H atom and the hydride transfer are calculated to be ∼60 kcal mol^-1 and verified experimentally by reaction with a suitable H atom and a hydride acceptor, demonstrating the ability of [1]⁺ to serve as a versatile PCET reagent, albeit with limited thermal stability. In MeCN solution, an orange emission for [1]PF₆ from a triplet-excited state was found. Density functional calculations and ultrafast absorption spectroscopy are used to give insight into the excited-state dynamics of the complex and suggest a significantly stretched S-S bond for the lowest triplet-state T₁. The structural responsiveness of the disulfide unit is proposed to open an effective relaxation channel toward the ground state, explaining the unexpectedly short lifetime of [1]⁺. These insights as well as the quantitative ground-state thermochemistry data provide valuable information for the use of ^S-Sbpy-functionalized complexes and their disulfide-/dithiol-directed PCET reactivity.