Effect of Protonation and Interaction with Anions on a Lead(II) Complex with a Lateral Macrobicycle Containing a Phenol Schiff‐Base Spacer

Abstract

The macrobicycle receptor L 4 , derived from 1,10-diaza-15-crown-5 incorporating a phenol Schiff-base spacer, forms stable complexes with lead(II). In [Pb(L 4 )(ClO 4 )](ClO 4 )· CH 3 CN (1), the lead(II) ion is asymmetrically placed at the one end of the macrobicyclic cavity, because of the intramolecular hydrogen bonding interaction that occurs between an imine nitrogen atom and the phenol group. This asymmetric position of the metal ion inside the macrobicyclic cavity induces chirality in this system. Variable temperature 1 H NMR spectroscopic experiments indicate that the asymmetric coordination of the metal ion inside the macrocyclic cavity is maintained in acetonitrile solution, but a translocation of the Pb II ion from one end of the macrobicyclic cavity to the second one occurs. This dynamic behaviour, which corresponds to the interconversion between the two possible enantiomeric forms of the complex, is fast on the NMR timescale at 320 K but slow at low temperatures, and we have estimated

A merged experimental and theoretical conformational study on alkaline-earth complexes with lariat ethers derived from 4,13-diaza-18-crown-6

“…We have previously reported that reaction of L 1 and L 2 with dialdehydes leads to the formation of lateral macrobicyclic structures that are useful for the coordination of both cations and anions [27][28][29]. We have found that these macrobicycles cannot be prepared by direct reaction between the organic precursors due to the anti arrangement adopted by the diamines L 1 and L 2 , but Ba(II) can act as an effective template, thereby facilitating the formation of the desired macrobicycles in high yields [30].…”

New Insights into the Complexation of Lead(II) by 1,4,7,10‐Tetrakis(carbamoylmethyl)‐1,4,7,10‐tetraazacyclododecane (DOTAM): Structural, Thermodynamic, and Kinetic Studies

“…[14][15][16][17][18][19][20] Relying on the intermediate character of lead(II) in Pearson's HSAB classification, [21][22][23] mixed ligands that combine soft (e.g., sulfur) or intermediate bases (e.g., neutral carbonyl oxygen atoms) with a harder base like an amino nitrogen atom appear to be particularly adapted to sequester Pb 2+ . [21,[24][25][26] This rationale is found behind all currently approved drugs used in chelation therapy for treating chronic lead overloads. [27][28][29][30][31] From a stereochemical point of view, the Pb 2+ ion possesses an electronic lone pair (6s 2 ) that can be either stereochemically active, as a consequence of the hybridization of the 6s 2 with the unoccupied 6p 0 orbitals, or inactive according to the Valence Shell Electron Pair Repulsion (VSEPR) formalism.…”

Anion Coordination Effect on the Nuclearity of CoII, NiII, CuII, and ZnII Complexes with a Benzimidazole Pendant‐Armed Crown

“…The dynamic behavior observed in acetonitrile solution can be attributed to a translocation of the Zn II ion from one end of the macrocyclic cavity to the second one, as it was previously observed for a Pb II complex with a macrobicyclic ligand containing a 1,10-diaza-15-crown-5 moiety. [27] If it is assumed that the exchange process associated with this line broadening (before coalescence) is slow on the NMR timescale, then (6), or Cu (7) in good yield (42-63 %). The IR spectra (KBr disks) show a band at ca.…”