A Highly Fluorescent Dinuclear Silver(I) Complex of Pyrazine Derivatives: Combined Experimental and DFT/TD-DFT Investigations

Abstract

A dinuclear neutral silver(I) complex, [Ag<inf>2</inf>(Hpyzdc) <inf>2</inf>(μ-dmpyz)] (1) (H<inf>2</inf>pydc = pyrazine-2,3-dicarboxylic acid, dmpyz = 2,3-dimethylpyrazine), has been synthesized and characterized by elemental analysis, IR spectroscopy, thermal analysis and single crystal X-ray diffraction. X-ray diffraction data have shown that the Hpydc ligands in 1 act as bidentate ligands via the pyrazine nitrogen and carboxylate oxygen atoms, and the further carboxylic group remains unbonded in the protonated form. Uncommon intermolecular interactions have been observed in the crystal structure, such as dihapto aromatic and intramolecular agostic interactions. DFT calculations have also supported the latterly mentioned agostic interaction. Complex 1 exhibits, in the solid state, strong fluorescence with two emission maxima in the visible region. TD-DFT calculations performed on the optimized structure in acetonitrile medium, modeled within PCM approach, have significantly quantified the experimental absorption profile and suggested that LLCT and MLLCT transitions are mainly responsible for the higher and lower energy fluorescences respectively. © 2013 Elsevier Ltd. All rights reserved.