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

Abstract

a b s t r a c tHerein, we report the synthesis and structural characterization of alkaline-earth complexes with the bibracchial lariat ethers N,N 0 -bis(2-aminobenzyl)-4,13-diaza-18-crown-6 (L 2 ) and N,N 0 -bis(benzimidazol-2ylmethyl)-4,13-diaza-18-crown-6 (L 4 ). The X-ray crystal structures of the Ca(II) and Sr(II) complexes of L 2 show the pendant arms of the ligand disposed on opposite sides of the macrocyclic mean plane, which results in an anti conformation in the solid state. A similar anti conformation is also observed for the Mg(II) complex of L 4 , whereas the Ca(II), Sr(II) and Ba(II) complexes of L 4 adopt a syn conformation in the solid state, with the two pendant arms pointing at the same side of the crown moiety. However, a different behavior is observed in solution. Indeed, 1 H and 13 C NMR spectroscopy, in combination with density functional theory (DFT) calculations performed at the B3LYP level, suggests that the [M(L 2 )] 2+ and [M(L 4 )] 2+ (M = Ca, Sr or Ba) complexes exist in solution as a mixture of syn and anti isomers involved in a dynamic equilibrium. Our results also show that the relative abundance of the syn conformation increases as the ionic radius of the metal ion increases and, furthermore, for a given metal ion the proportion of syn isomer is always higher for L 4 complexes than for L 2 ones.

Solid state and solution structures of alkaline-earth complexes with lariat ethers containing aniline and benzimidazole pendants

“…The 1 H NMR spectra of the complexes of L 3 and L 4 show essentially the same features than those of the L 1 and L 2 counterparts, but they show broader signals, particularly for L 3 complexes. A similar situation was observed previously when comparing the 1 H spectra of the complexes of L 5 and L 6 [24] . This indicates a more important degree of flexibility of the complexes containing aniline pendants in comparison to those with benzimidazole arms.…”

“…This in contrast with structures observed in the solid state for the Ca(II) and Sr(II) complexes of L 6 , which present an anti conformation of the ligand. Both the complexes of L 5 and L 6 exist in acetonitrile solution as a mixture of syn and anti conformers [24] . Table 8.…”

“…In previous papers we have reported the coordinative properties towards Mg(II), Ca(II), Sr(II) and Ba(II) of the bibracchial lariat ethers L 5 and L 6 (Scheme 1), which contain a 1,10-diaza-18-crown-6 platform and aniline or benzimidazole pendant arms [23,24] . As a continuation of these works, herein we report an structural study both in the solid state and solution of alkaline-earth complexes with the related receptors L 1 -L 4 (Scheme 1).…”

Spectrofluorimetric determination of magnesium ions in water, ampoule, and suspension samples using a fluorescent azothiazol‐benzenesulfonamide derivative

“…[26,27] Therefore, we aimed here to develop a novel fluorescent sensor that had high sensitivity and selectivity for Mg 2+ ion detection. In recent years, the details of several Mg 2+ selective fluorescent sensors have been published, such as crown ether derivatives, [28] imidazo-1,10-phenanthroline, [29] benzochromene, [30] diaza-18-crown-6, [31] and benzo-15-crown-5, [32] therefore the design of novel fluorescence sensors that have the advantages of high sensitivity and selectivity of Mg 2+ in different media remains an important task. Azothiazol-benzenesulfonamide derivatives containing thiazol and benzene sulfonamide associated with the azo group (ÀN=N-) are classified into three organic families: sulfonamide, azo, and pyrazole.…”

Tuning the Kinetic Inertness of Bi3+ Complexes: The Impact of Donor Atoms on Diaza-18-Crown-6 Ligands as Chelators for 213Bi Targeted Alpha Therapy

“…As such, we reasoned that the investigation of chelators with a reverse size-selectivity, a preference for large over small ions, would be a promising direction for the development of new BFCs for this radionuclide. In this context, ligands containing the 18-membered diaza-18-crown-6 macrocycle display this reverse size-selective property for metal ions. − Previously, we showed that macropa (Chart ) forms remarkably stable complexes with large medicinally relevant radiometals like 132/135 La, 223 Ra, and 225 Ac. ,, We further showed that alteration of the pendent donor arms and macrocyclic core rigidity changes the resulting selectivity for different metal ions. ,, On the basis of the reverse size-selectivity properties and tunability of this system, we sought to explore this class of ligands (Chart ) for chelating Bi 3+ for potential applications in TAT.…”