Mononuclear and dinuclear complexes of isoeilatin

Sheba D. Bergman, Israel Goldberg, Andrea Barbieri, Moshe Kol*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

This work describes the synthesis and characterization of mononuclear and dinuclear Ru(II) and Os(II) complexes based on the symmetrical bridging ligand isoeilatin (1). The crystal structure of 1·[HCl]2 consists of layers of tightly π-stacked molecules of the biprotonated isoeilatin. The mononuclear complexes [Ru(bpy)2(ieil)]2+ (22+) and [Os(bpy)2(ieil)]2+ (32+) form discrete dimers in solution held together by face-selective π-stacking interactions via the isoeilatin ligand. Coordination of a second metal fragment does not hinder the π-stacking completely, as demonstrated by the concentration dependence of the 1H NMR spectra of the dinuclear complexes [{Ru(bpy)2}2{μ-ieil}]4+ (44+), [{Os(bpy)2}2{μ-ieil}]4+ (54+), and [{Ru(bpy)2}{μ-ieil}{Os(bpy)2}]4+ (6 4+) and supported by the solid-state structure of meso-4·[Cl]4. The bridging isoeilatin ligand conserves its planarity even upon coordination of a second metal fragment, as demonstrated in the solid-state structures of meso-4·[Cl]4, meso-4·[PF6]4, and meso-5·[PF 6]4. All of the dinuclear complexes exhibit a preference (3/2-3/1) for the formation of the heterochiral as opposed to the homochiral diastereoisomer. Absorption spectra of the mononuclear complexes feature a low-lying dπ(M) → π*-(ieil) MLCT band around 600 nm that shifts to beyond 700 nm upon coordination of a second metal fragment. Cyclic and square-wave voltammetry measurements of the complexes exhibit two isoeilatin-based reduction waves that are substantially anodically shifted compared to [M(bpy)3]2+ (M = Ru, Os). Luminescence spectra, quantum yields, and lifetime measurements at room temperature and at 77 K demonstrate that the complexes exhibit 3MLCT emission that occurs in the IR region between 950 and 1300 nm. Both the electrochemical and photophysical data are consistent with the low-lying π* orbital of the isoeilatin ligand. 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 bridging isoeilatin ligand.

Original languageEnglish
Pages (from-to)2513-2523
Number of pages11
JournalInorganic Chemistry
Volume44
Issue number7
DOIs
StatePublished - 7 Apr 2005

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