Secondary-Sphere Chlorolanthanide(III) Complexes with a 1,3,5-Triazine-Based Ligand Supported by Anion−π, π–π, and Hydrogen-Bonding Interactions

Abstract

Dipicolylamine-functionalized 1,3,5-triazine (dpat) was isolated. When reacted with LaCl 3 , compound [(LaCl 6 )(H 3 dpat)][H 2 O] 2 (1) formed, which crystallized in the monoclinic P2 1 /n space group with parameters a = 11.47 Å, b = 19.22 Å, c = 20.98 Å, V = 4652.02 Å, and β = 90.53°. When reacted with NdCl 3 , the complex [NdCl 3 (H 2 O) 4 (H 3 dpat)][Cl] 3 (MeOH) 2 (2) crystallized in the monoclinic P2 1 /n space group with unit cell parameters a = 20.05 Å, b = 12.81 Å, c = 20.64 Å, V = 5004.40 Å, and β = 110.20°.In both cases, the dpat ligand forms a bowl-shaped cavity that partially envelops the Ln III -containing central unit, which is anionic in 1 and neutral in 2. The formation of these outer-sphere complexes is supported by secondary interactions, including π−π stacking, hydrogen bonding, and anion−π between the chlorolanthanide-(III) fragment and the electron-deficient 1,3,5-triazine ring. Evidence of protonation of the pyridine rings in dpat was substantiated through the isolation of [H 2 dpat][Cl] 2 (3). This compound crystallized in the monoclinic C2/c space group with parameters a = 11.93 Å, b = 20.22 Å, c = 15.28 Å, V = 3664.97 Å, and β = 94.35°. Four pyridine rings are pairwise protonated in 3. dpat showed a moderate ability to extract La III from an aqueous to an organic phase, indicating its potential, through judicious manipulation of secondary-sphere interactions, as the starting point for efficient extractants for Ln III ions.

Selective separation of light rare-earth elements by supramolecular encapsulation and precipitation

“…Nevertheless, pre-organised receptors can provide supramolecular host environments for these complex anion guests. A tripodal hexapyridyl triazine was reacted with RE chlorides and nitrates to form host:guest complexes of RE chlorido- and nitratometalates; a 1:1 bowl-shaped environment for chloride was reported whereas a completely encapsulated 1:2 complex formed with nitrate 22 , 23 . Supramolecular π-anion interactions were evident along with electrostatic interactions due to protonation of the receptor, but poor extraction and negligible selectivity was seen from aqueous nitric acid.…”

Spectroscopic Study into Lanthanide Speciation in Deep Eutectic Solvents

“…Based on a literature survey, it seems that the fitted Ln–Cl distances for Nd and Eu correlate quite well with CN’s of six and five, respectively (Table S13). − This is much lower than the fitted CN of 10 for both lanthanides. Homoleptic Nd 3+ - and Eu 3+ -chloro complexes tend to be six-coordinate octahedra, with average Ln–Cl distances of 2.73 and 2.69 Å, respectively.…”

Noncovalent Interactions at Lanthanide Complexes

“…properties. Like the cation‐π interactions, the lone pair‐π, π–π and anion‐π interactions are also emergent noncovalent interactions whose occurrence has already been recognized in the coordination chemistry of lanthanides [62–66] . For instance, the molecular conformation of an europium complex ( 5 ) is found to be stabilized through intermolecular lone pair‐π (3.194 Å) and π–π (3.371 Å) interactions, and the cooperative action of these noncovalent interactions lead to a 1D chain (Scheme 2a) [62] .…”

“…Like the cation-π interactions, the lone pair-π, π-π and anion-π interactions are also emergent noncovalent interactions whose occurrence has already been recognized in the coordination chemistry of lanthanides. [62][63][64][65][66] Scheme 1. Hydrogen, [57] halogen [59] and chalcogen [60] bonds, as well as cation-π interactions, [58] in lanthanide complexes.…”