Effect of Heterocyclic Ring on LnIII Coordination, Luminescence and Extraction of Diamides of 2,2′-Bipyridyl-6,6′-Dicarboxylic Acid

Abstract

We have synthesized and examined several complexes of lanthanides with diamides of 2,2′-bipyridyl-6,6′-dicarboxylic acid bearing various hetaryl-based side chains for the elucidation of the effect of the heterocycle on the structure and properties of the ligands. The multigram scale methods for the preparation of various N-alkyl-hetaryls and their diamides were developed. The solid state structure of 6-methyl-2-pyridylamide of 2,2′-bipyridyl-6,6′-dicarboxylic acid possesses a flat structure where the conformation is completely different from that previously observed for N-alkylated 2,2′-bipyridyl-6,6′-dicarboxamides and 2,6-pyridinedicarboxamides. The complexes of new ligands were synthesized and NMR and X-Ray studied their structure in solution and solid state. The results demonstrate that complexes possess the same structures both in solid state and in solution. Stability constants of the complexes were less when comparing with dimethyl-substituted diamides, but higher than for unsubstituted dianilide. Contrarily, the extraction ability of 2-pyridyl-diamide is significantly lower than for corresponding anilide. Specific interaction of extractant with solvent molecules, which is not available for electron-sink pyridine amides, can explain this. The luminescence of new Eu complexes was significantly higher than for all previously 2,2′-bipyridyl-6,6′-dicarboxamides and QY reaches 18%. Asymmetry ratios of Eu complexes were 25% higher when compared other complexes with 2,2′-bipyridyl-6,6′-dicarboxamides, which indicates large deviation from the inversion center.

Solvent Extraction and Conformation Rigidity: Actinide(IV) and Actinide(VI) Come Together

“…The metal ions were in the middle of the straight line between the two amidic O atoms, and the An–O L and An–N L distance pairs were the same within errors for each complex. By contrast, significant differences in the Ln–O L and Ln–N L bond lengths were observed for all of the studied lanthanide complexes with bipyridyl-type ligands. ,, The ligands underwent significant distortion due to metal-ion coordination . Because of chelating-ring formation (An–OC–C Py –N Py ), the CO bond lengths increased from the typical value of 1.222–1.239 Å to 1.253–1.245 Å upon metal-ion coordination.…”

“…By contrast, significant differences in the Ln−O L and Ln−N L bond lengths were observed for all of the studied lanthanide complexes with bipyridyl-type ligands. 15,39,40 The ligands underwent significant distortion due to metal-ion coordination. 17 The structure of the rare dodecacoordinated Th complex (Figure 2) followed the coordination pattern of lanthanides with similar ligands: the metal ion was in the cavity of the ligand bonded with its four donor atoms and surrounded by chelating nitrate anions.…”

Formation of Complexes of f-Elements with Electron-Withdrawing N-Heterocyclic Diamides: Extraction and Solution Photophysics

“…The diamides 4Py, 2Py and 6Me2Py and their complexes were prepared according to methods presented earlier [27]. All other reagents and solvents were obtained from commercial sources: Merck, Acros Organics, ABCR and "P&M Invest" GmbH for fluorinated reagents.…”

Chelating Extractants for Metals

“…Using diamides, an attempt was made to separate europium(III) and americium(III) from concentrated nitric acid solutions. This was performed using N,N′-diethyl-N,N′-bis(6-methylpyridin-2-yl)-2,2′-bipyridine-6,6′-dicarboxamide 20 dissolved in nitrobenzene [29]. However, the separation factor proved to be lower than 1.…”

“…It should be noted that in the above-mentioned works [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34], separation of REEs from impurities of heavy and alkaline earth metals Fe (III), Pb (II), Ti (IV), Cu (II), Mg (II) and others as well as thorium Th (IV) contained in rare earth ores was not investigated.…”