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Thermodynamic Parameters Governing the Self‐Assembly of Head–Head–Head Lanthanide Bimetallic Helicates
Author(s) -
Jensen Thomas B.,
Scopelliti Rosario,
Bünzli JeanClaude G.
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700468
Subject(s) - lanthanide , bimetallic strip , chemistry , ligand (biochemistry) , crystallography , metal , stacking , metal ions in aqueous solution , luminescence , ion , substituent , stereochemistry , materials science , organic chemistry , biochemistry , receptor , optoelectronics
The heterobitopic ligands L ABX (X=1, 2, 3, 4 or 5), differing only by a Cl or NEt 2 substituent, have been designed to complex with a pair of lanthanide ions to form triple‐stranded bimetallic helicates of overall composition [Ln 2 (L ABX ) 3 ] 6+ . The percentage of HHH (head–head–head) isomer, in which each of the three ligand strands coordinates to the same lanthanide ion with the same coordination unit, is deciding the ability of the ligands to selectively form heterobimetallic complexes containing one luminescent and one magnetic or two different luminescent ions. It deviates significantly from the statistical value of 25 % and ranges from 6–20 % for L AB2 complexes to 93–96 % for L AB4 complexes. The equilibrium between HHT (head–head–tail) and HHH isomers has been investigated in detail for homobimetallic helicates (Ln=Y, La, Ce, Pr, Nd, Sm, Eu, Lu) by means of variable temperature NMR and thermodynamic parameters have been determined. The equilibrium is characterized by small values of Δ H and Δ S , which vary in opposite direction along the lanthanide series for complexes with the same ligand in a way that keeps the value of Δ G almost constant. The results are interpreted in terms of differences in interstrand stacking, ion–dipole interactions and metal–metal repulsion.