Synthesis and structural, redox and photophysical properties of tris-(2,5-di(2-pyridyl)pyrrolide) lanthanide complexes

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 48; no. 25; pp. 9365 - 9375
• Main Authors: McPherson, James N, Abad Galan, Laura, Iranmanesh, Hasti, Massi, Massimiliano, Colbran, Stephen B
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 25.06.2019
• Subjects: Benzene; Coordination compounds; Crystallography; Diamagnetism; Gadolinium; Isomers; Ligands; Mass spectra; Near infrared radiation; NMR spectroscopy; Oxidation; Solid state; Spectrum analysis; Voltammetry; Ytterbium
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt01262a

A first series of lanthanide complexes of tris(dipyridyl)pyrrolide ligands has been prepared. The [Ln(dpp R 1 ,R 2 ) 3 ] complexes (Ln = La( iii ), Sm( iii ), Eu( iii ), Gd( iii ) and Yb( iii ); and dpp R 1 ,R 2 = 2,5-di(2-pyridyl-3-(R 1 )-4-(R 2 )) pyrrolide) have been isolated and their structures and photophysical and redox properties characterised, both in the solid-state and in solution. In the complexes, the three dpp − ligands form a distorted tricapped trigonal prismatic coordination geometry about the lanthanide ions, with the antiparallel isomer observed in the solid state for non-symmetric (dpp CO 2 Me,Me ) − . However, 1 H NMR spectroscopy of the diamagnetic and paramagnetic [Ln(dpp R 1 ,R 2 ) 3 ] complexes in d 6 -benzene solution reveal evidence for a statistical distribution of all possible isomers. Time-resolved luminescence studies suggest that the dpp − ligand (with triplet excited state T 1 energy at 18 622 cm −1 ) sensitises red emission from [Eu(dpp CO 2 Me,Me ) 3 ] and near-infrared emission from [Yb(dpp CO 2 Me,Me ) 3 ] through the antenna effect. Cyclic voltammetry reveals three consecutive, reversible, one-electron oxidation processes for each [Ln(dpp R 1 ,R 2 ) 3 ] complex, corresponding to oxidations of each dpp − ligand between 0.3-0.8 V vs. E 1/2 (Fc +/0 ), and for [Eu(dpp CO 2 Me,Me ) 3 ] the Eu III/II couple was −2.099 V vs . E 1/2 (Fc +/0 ). Nine-coordinate tris(dipyridylpyrrolide)lanthanide( iii ) complexes were readily obtained, and were investigated by X-ray crystallography, NMR spectroscopy, and photophysical and electrochemical studies.