Complexation of Ln³⁺ with Pyridine-2,6-dicarboxamide: Formation of the 1:2 Complexes in Solution and Gas Phase

Abstract

Electrospray ionization of LnCl 3 and tetramethylpyridine-2,6-dicarboxamide (TMPDA) mixtures in methanol generated abundant tripositively charged Ln(TMPDA) 2 3+ions with an unprecedented 1:2 stoichiometry in the gas phase. Different from the very common 1:3 Ln(L) 3 3+ (L = TMGA, tetramethyl glutaramide; TMOGA, tetramethyl-3oxaglutaramide; TMTDA, tetramethyl-3-thiodiglycolamide) complexes, Ln 3+ is coordinated by four O carbonyl and two N pyridine atoms from two perpendicular TMPDA ligands based on the DFT calculations. The observation of 1:2 Ln(TMPDA) 2 3+ in the gas phase is due to the desolvation of Ln(TMPDA) 2 (MeOH) 2 3+ that is predominant in the methanol solution of LnCl 3 and TMPDA according to the extended X-ray absorption fine structure analysis, and the 1:3 Ln(TMOGA) 3 3+ and Ln(TMGA) 3 3+ complexes observed in the gas phase also parallel the speciation in relevant solutions. Such a difference in solution speciation is most likely a result of the unfavorable steric effect caused by the pyridine ring of TMPDA.

Strong Periodic Tendency of Trivalent Lanthanides Coordinated with a Phenanthroline-Based Ligand: Cascade Countercurrent Extraction, Spectroscopy, and Crystallography

“…To further investigate the complex species during the extraction, we employed mass spectrometry to study the complexes of La(III) and Ce(III) in 1-(trifluoromethyl)-3-nitrobenzene, in which the extracted organic phase was diluted with acetonitrile to guarantee a real extraction condition. 63 The concentration of metal ions was 2 mM in the aqueous phase, and the ligand concentration was 10 mM in the organic phase. Because of the relatively low distribution ratio of Pr(III) (Figure S3f), few complexes were formed, and it was difficult to detect in the mass spectrum.…”

HMNTA Complexes of Tetravalent Metal Ions: On the Roles of Carbonyl Oxygen and Amine Nitrogen in the Stabilization of Gas-Phase M(HMNTA)24+Complexes

“…In addition to the tetrapositive ions, most of the other peaks present in Figure are triply and doubly charged metal complexes where the ligands arise from deprotonated HMNTA as well as N amine –C methylene , C methylene –C carbonyl , and C carbonyl –N amide bond cleavages of HMNTA. All of these fragment ligands are analogous to those observed when mixtures of metal ions and diamide ligands were subjected to ESI. − ,− Compared with the species observed in the mass spectra of Zr­(ClO 4 ) 4 /Hf­(ClO 4 ) 4 /Th­(ClO 4 ) 4 :HMNTA, the ESI mass spectrum of U­(ClO 4 ) 4 :HMNTA exhibits greater diversity in speciation due to the presence of more common VI oxidation state of uranium, and a wide variety of U VI O 2 2+ complexes were also observed, which indicates that it is relatively facile for U­(IV) to be oxidized to U­(VI) during ESI as found in other experiments . In addition, zinc-containing species such as Zn­(HMNTA) 2+ were generated together with U­(HMNTA) 2 4+ since zinc was added into the UO 2 (ClO 4 ) 2 stock solution as a reducing agent to prepare U­(ClO 4 ) 4 .…”

Gas‐phase structure, bonding, and fragmentation chemistry of the An (IV)–TMPDCAM complexes studied using mass spectrometry and theoretical calculation (An = Th and U)

“…The neutral character of diamides enables them to form multiply charged complexes with lanthanide and actinide cations, and the structures and reactivities of such complexes can be conveniently investigated in the gas phase using electrospray ionization-mass spectrometry (ESI-MS) in conjunction with density functional theory (DFT) calculation. Various researches have revealed the gas-phase coordination structures and fragmentation chemistry of lanthanide- [12][13][14][15] and actinide-diamide [16][17][18][19][20] complexes by employing this method in recent years, which provides parallel results with their behaviors in the condensed phase. As the simplest representative of glutaramides, diglycolamides, thio-diglycolamides, or PDCAMs, TMGA…”