Mononuclear and Dinuclear Complexes of Dibenzoeilatin:  Synthesis, Structure, and Electrochemical and Photophysical Properties

Abstract

This work describes a study of Ru(II) and Os(II) polypyridyl complexes of the symmetrical, fused-aromatic bridging ligand dibenzoeilatin (1). The synthesis, purification, and structural characterization by NMR of the mononuclear complexes [Ru(bpy)(2)(dbneil)](2+) (2), [Ru(tmbpy)(2)(dbneil)](2+) (3), and [Os(bpy)(2)(dbneil)](2+) (4), the homodinuclear complexes [[Ru(bpy)(2)](2)[micro-dbneil]](4+) (5), [[Ru(tmbpy)(2)](2)[micro-dbneil]](4+) (6), and [[Os(bpy)(2)](2)[micro-dbneil]](4+) (7), and the heterodinuclear complex [[Ru(bpy)(2)][micro-dbneil][Os(bpy)(2)]](4+) (8) are described, along with the crystal structures of 4, 6, and 7. Absorption spectra of the mononuclear complexes feature a low-lying MLCT band around 600 nm. The coordination of a second metal fragment results in a dramatic red shift of the MLCT band to beyond 700 nm. Cyclic and square wave voltammograms of the mononuclear complexes exhibit one reversible metal-based oxidation, as well as several ligand-based reduction waves. The first two reductions, attributed to reduction of the dibenzoeilatin ligand, are substantially anodically shifted compared to [M(bpy)(3)](2+) (M = Ru, Os), consistent with the low-lying pi orbital of dibenzoeilatin. The dinuclear complexes exhibit two reversible, well-resolved, metal-centered oxidation waves, despite the chemical equivalence of the two metal centers, indicating a significant metal-metal interaction mediated by the conjugated dibenzoeilatin ligand. Luminescence spectra, quantum yield, and lifetime measurements at room temperature in argon-purged acetonitrile have shown that the complexes exhibit (3)MLCT emission, which occurs in the IR-region between 950 and 1300 nm. The heterodinuclear complex 8 exhibits luminescence only from the Ru-based fragment, the intensity of which is less than 1% of that observed in the corresponding homodinuclear complex 5; no emission from the Os-based unit is observed, and an intramolecular quenching constant of k(q) > or = 3 x10(9) s(-)(1) is evaluated. The nature of the quenching process is briefly discussed.

Diastereoisomers as probes for solvent reorganizational effects on IVCT in dinuclear ruthenium complexes

“…4 and 5, respectively. The spectral features for the diastereoisomeric forms of the complexes are consistent with previous literature reports for [{Ru(bpy) 2 } 2 (l-bpm)] 4+ [30,[71][72][73][74]88] (as a diastereoisomeric mixture) and [{Ru(bpy) 2 } 2 (l-dbneil)] 4+ [68,69].…”

“…p*(BL) transitions. These assignments are supported by comparisons with the mononuclear complexes [Ru(bpy) 2 (bpm)] 2+ [72,73,80] and [Ru(bpy) 2 (dbneil)] 2+ [68] and the well-documented transitions in [Ru(bpy) 3 ] 2+ [89,90]. Table 2).…”

“…Separation of the mononuclear product from the crude mixture was achieved via a gradient elution procedure using aqueous 0.1-0.4 M NaCl as the eluent. The orange band of mononuclear material was precipitated as the PF À 6 salt by addition to the eluate of a saturated solution of aqueous KPF 6 [{Ru(Me 2 bpy) 2 } 2 (l-bpm)](PF 6 ) 4 was synthesized as described previously [48,49], and [{Ru(bpy) 2 } 2 (ldbneil)](PF 6 ) 4 was supplied by Prof. Moshe Kol [68]. Details of the separation of these complexes into their diastereoisomeric forms and the 1 H NMR characterization of the diastereoisomers have been reported previously [48,49,69].…”

“…The electrochemical characteristics of the diastereoisomers of [{Ru(bpy) 2 } 2 (l-dbneil)] 4+ have been discussed previously [68,69,84].…”

Probing the Transition between the Localised (Class II) and Localised‐to‐Delocalised (Class II–III) Regimes by Using Intervalence Charge‐Transfer Solvatochromism in a Series of Mixed‐Valence Dinuclear Ruthenium Complexes

“…[44][45][46][47][48][49][50] The present report represents one of only a handful of structures that have been obtained through selective diastereoisomer isolation prior to crystal growth. [13,19,[51][52][53] Electrochemical and UV/Vis/NIR spectral characterisation: …”