A Schiff-base bibracchial lariat ether selective receptor for lanthanide(III) ions

Abstract

The bibracchial lariat ether N, , in its di-deprotonated form, behaves as a selective receptor for lanthanide() ions. It only forms stable complexes with the three lightest members of the lanthanide series, lanthanum(), cerium() and praseodymium(). The X-ray crystal structures of these three complexes show the metal ion ten-coordinated and deeply buried in the cavity of the dianionic receptor. In all three structures the lariat ether presents a syn arrangement. However, the different size of the encapsulated metal ion modifies the conformation of the receptor, particularly in the fold of the crown, resulting in a very different coordination polyhedron for La() (distorted tetracapped trigonal prism) with respect to that of Ce() and Pr() (bicapped square antiprism). Spectrophotometric titration of the dianionic lariat ether with anhydrous La(ClO 4 ) 3 in acetonitrile allowed us to calculate log K[La(L Ϫ 2H)] = 4.65(4).

H4octapa: Highly Stable Complexation of Lanthanide(III) Ions and Copper(II)

“…17a, 33 The average values of the nine bond distances of the metal coordination environments plotted against the number of f electrons of the Ln 3+ ion give an excellent quadratic fit of the form y = a + bx + cx 2 with R 2 > 0.999 ( Figure S5 and Table S6 − complexes. Aiming to gain further insight into the reasons behind the stability trend observed for Ln 3+ complexes of octapa 4− across the 4f period, we performed an energy analysis using the following thermodynamic cycle.…”

Solid‐State and Solution Structure of Lanthanide(III) Complexes with a Flexible Py‐N6 Macrocyclic Ligand

“…[15] However, many of the Ln-N and Ln-O bond lengths are longer in the Pr III complex than in the Ce III one (N1, N4, N5, O1n, O7n, O8n), as previously observed for lanthanide complexes with a macrocyclic ligand. [16] These results are indicative of increasing steric crowding around the lanthanide ion for a 12-coordinate environment and anticipate the structural change observed along the lanthanide series between Pr and Nd. The La-N1 and Nd-N1 bond lengths are slightly longer than those observed for lanthanide complexes with an 18-membered Schiff base macrocyclic ligand containing pyridine head units.…”

Metal Ion Complementarity: Effect of Ring‐Size Variation on the Conformation and Stability of Lead(II) and Cadmium(II) Complexes with Pendant‐Armed Crowns

“…[14] Figure 5 and Figure S1, Supporting Information), which allows an easy interconversion between the two optical isomers (∆ and Λ) characteristic of the syn conformation. [24] When this interconversion is fast enough on the 1 H NMR time scale, an effective C s symmetry in solution is observed (Figure 6). (Figure 4b), reflecting a strong interaction between Pb II and the coordinated nitrogen pivot atoms of the receptor.…”

“…This result indicates a syn arrangement of the receptor in the complex. [24] The H8 protons appear as an AB spin system ( 2 J 8a,8b = 18.40 Hz) in the spectrum of 6, while a singlet is observed for the H8 protons in the Cd II analogue 5. These results are in agreement with a syn conformation of the Pb II complex with the pendant arms adopting a faceto-face conformation, as observed for [Cd(L 2 )] 2+ .…”