title: Highly emitting concomitant polymorphic crystals of a dinuclear rhenium complex.
abstract: The dinuclear complex [Re(2)(μ-Cl)(2)(CO)(6)(μ-4,5-(Me(3)Si)(2)pyridazine)] gives in the solid state two polymorphs (yellow, 1Y, and orange, 1O), which can be either concomitantly or separately obtained on varying the crystallization rate. Both crystal phases exhibit intense photoluminescence from the lowest lying triplet metal-to-ligand charge transfer state, much stronger than in solution (quantum yields 0.56 and 0.52, for 1O and 1Y respectively, vs 0.06 in toluene), likely due to the restricted rotation of the Me(3)Si groups in the solid state. A clean, irreversible 1O → 1Y single-crystal-to-single-crystal phase transition occurs at 443 K, as revealed by variable temperature X-ray diffraction analysis. In spite of the absence of any strong intermolecular interactions in both forms, 1O and 1Y show very different absorption and emission maxima (λ(abs) 370 and 393 nm, λ(em) 534 and 570 nm, for 1Y and 1O, respectively). This behavior highlights the importance of the local organization of molecular dipoles in perturbing the photophysical properties of the molecule in the crystal.
authors.affiliation: Dipartimento di Chimica Inorganica Metallorganica e Analitica Lamberto Malatesta, Università degli Studi di Milano, via Venezian 21, I-20133 Milano, Italy.
authors.forename: Elsa
authors.initials: E
authors.lastname: Quartapelle Procopio
authors.forename: Matteo
authors.initials: M
authors.lastname: Mauro
authors.forename: Monica
authors.initials: M
authors.lastname: Panigati
authors.forename: Daniela
authors.initials: D
authors.lastname: Donghi
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Mercandelli
authors.forename: Angelo
authors.initials: A
authors.lastname: Sironi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: D'Alfonso
authors.forename: Luisa
authors.initials: L
authors.lastname: De Cola