title: Electrochemical, computational, and photophysical characterization of new luminescent dirhenium-pyridazine complexes containing bridging OR or SR anions.
abstract: A series of [Re(2)(μ-ER)(2)(CO)(6)(μ-pydz)] complexes have been synthesized (E = S, R = C(6)H(5), 2; E = O, R = C(6)F(5), 3; C(6)H(5), 4;  CH(3), and 5; H, 6), starting either from [Re(CO)(5)O(3)SCF(3)] (for 2 and 4), [Re(2)(μ-OR)(3)(CO)(6)](-) (for 3 and 5), or [Re(4)(μ(3)-OH)(4)(CO)(12)] (for 6). Single-crystal diffractometric analysis showed that the two μ-phenolato derivatives (3 and 4) possess an idealized C(2) symmetry, while the μ-benzenethiolato derivative (2) is asymmetrical, because of the different conformation adopted by the phenyl groups. A combined density functional and time-dependent density functional study of the geometry and electronic structure of the complexes showed that the lowest unoccupied molecular orbital (LUMO) and LUMO+1 are the two lowest-lying π* orbitals of pyridazine, whereas the highest occupied molecular orbitals (HOMOs) are mainly constituted by the "t(2g)" set of the Re atoms, with a strong Re-(μ-E) π* character. The absorption spectra have been satisfactorily simulated, by computing the lowest singlet excitation energies. All the complexes exhibit one reversible monoelectronic reduction centered on the pyridazine ligand (ranging from -1.35 V to -1.53 V vs Fc(+)|Fc). The benzenethiolato derivative 2 exhibits one reversible two-electron oxidation (at 0.47 V), whereas the OR derivatives show two close monoelectronic oxidation peaks (ranging from 0.85 V to 1.35 V for the first peak). The thioderivative 2 exhibits a very small electrochemical energy gap (1.9 eV, vs 2.38-2.70 eV for the OR derivatives), and it does not show any photoluminescence. The complexes containing OR ligands show from moderate to poor photoluminescence, in the range of 608-708 nm, with quantum yields decreasing (ranging from 5.5% to 0.07%) and lifetimes decreasing (ranging from 550 ns to 9 ns) (3 > 4 > 6 ≈ 5) with increasing emission wavelength. The best emitting properties, which are closely comparable to those of the dichloro complex (1), are exhibited by the pentafluorophenolato derivative (3).
authors.affiliation: Department of Inorganic, Metallorganic and Analytical Chemistry Lamberto Malatesta, Università degli Studi di Milano, and UdR INSTM of Milano, Via Venezian 21, 20133 Milano, Italy.
authors.forename: Alessio
authors.initials: A
authors.lastname: Raimondi
authors.forename: Monica
authors.initials: M
authors.lastname: Panigati
authors.forename: Daniela
authors.initials: D
authors.lastname: Maggioni
authors.forename: Laura
authors.initials: L
authors.lastname: D'Alfonso
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Mercandelli
authors.forename: Patrizia
authors.initials: P
authors.lastname: Mussini
authors.forename: Giuseppe
authors.initials: G
authors.lastname: D'Alfonso
mesh_terms: D000838:Anions / Q000737:chemistry; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D055664:Electrochemical Techniques; D049449:Luminescence; D049408:Luminescent Agents / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011724:Pyridazines / Q000138:chemical synthesis / Q000737:chemistry*; D012211:Rhenium / Q000737:chemistry*
chemical_list: D000838:Anions; D056831:Coordination Complexes; D049408:Luminescent Agents; D011724:Pyridazines; C062482:pyridazine; D012211:Rhenium