Trigonal (-3) symmetry octahedral lanthanide(III) complexes of zwitterionic tripodal ligands: luminescence and magnetism
Creators: name: Janzen, Daron E.
name: Juchum, Michael
name: Presow, Shaun R.
name: Ronson, Tanya K.
name: Mohr, Wolfgang
name: Clérac, Rodolphe
name: Feltham, Humphrey L.C.
name: Brooker, Sally
Publisher: name: Taylor & Francis
Year: 2016
Subjects: subject: Biophysics
subject: Biochemistry
subject: 29999 Physical Sciences not elsewhere classified
subject: FOS: Physical sciences
subject: FOS: Physical sciences
subject: Medicine
subject: Molecular Biology
subject: Biotechnology
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: Cancer

description: Sandwich coordination complexes, [Ln<sup>III</sup>(H<sub>3</sub><b>L</b>)<sub>2</sub>]X<sub>3</sub>∙<i>solvents</i>, of Tb(III), Eu(III), Dy(III), Ho(III) and Er(III) were prepared with two new zwitterionic ester-substituted tripodal amine ligands, tris((2-hydroxy-5-<i>n</i>-butyl benzoate)aminoethyl)-amine (H<sub>3</sub><b>L</b><sup><b>1</b></sup>) and tris((2-hydroxy-5-methyl benzoate)aminoethyl)-amine (H<sub>3</sub><b>L</b><sup><b>2</b></sup>). These ligands were synthesised by condensation of the appropriately substituted salicylaldehyde with tris(2-aminoethyl)amine (tren) followed by <i>in situ</i> reduction of the tris-imine to tris-amine. Subsequent 2:1 reaction with lanthanide(III) ions yields [Ln<sup>III</sup>(H<sub>3</sub><b>L</b>)<sub>2</sub>]X<sub>3</sub>∙<i>solvents</i> (<b>L</b> = <b>L</b><sup><b>1</b></sup>, <b>L</b><sup><b>2</b></sup>; X = Cl<sup>−</sup>, NO<sub>3</sub><sup>−</sup>; <i>solvents</i> = MeOH or H<sub>2</sub>O). All complexes were characterised by microanalysis, infrared spectroscopy, high resolution mass spectrometry and solid-state photoluminescence measurements. The crystal structures of [Tb<sup>III</sup>(H<sub>3</sub><b>L</b><sup><b>1</b></sup>)<sub>2</sub>]Cl<sub>3</sub>·6MeOH, [Dy(H<sub>3</sub><b>L</b><sup><b>1</b></sup>)<sub>2</sub>]Cl<sub>3</sub>·6MeOH, [Eu<sup>III</sup>(H<sub>3</sub><b>L</b><sup><b>1</b></sup>)<sub>2</sub>]Cl<sub>3</sub>·6MeOH and [Tb<sup>III</sup>(H<sub>3</sub><b>L</b><sup><b>1</b></sup>)<sub>2</sub>](NO<sub>3</sub>)<sub>3</sub> reveal high-crystallographic −3 symmetry at the O<sub>6</sub>-coordinated octahedral lanthanide(III) ions and that the tripodal ligands are bound in zwitterionic form: the protons from the phenolic oxygens have migrated to the amino nitrogens. Photoluminescence measurements indicate various degrees of energy transfer of the ligand chromophore to the lanthanide ions, as both ligand and lanthanide emission features are observed. Despite the high-crystallographic symmetry and the likely small transverse magnetic anisotropy of the complexes, no evidence of slow relaxation of the magnetisation, characteristic of a single-molecule magnet, was observed for [Tb<sup>III</sup>(H<sub>3</sub><b>L</b><sup><b>1</b></sup>)<sub>2</sub>]Cl<sub>3</sub>·MeOH·3H<sub>2</sub>O, [Dy<sup>III</sup>(H<sub>3</sub><b>L</b><sup><b>1</b></sup>)<sub>2</sub>]Cl<sub>3</sub>·6H<sub>2</sub>O, [Ho<sup>III</sup>(H<sub>3</sub><b>L</b><sup><b>1</b></sup>)<sub>2</sub>](NO<sub>3</sub>)<sub>3</sub>·2H<sub>2</sub>O, [Er<sup>III</sup>(H<sub>3</sub><b>L</b><sup><b>1</b></sup>)<sub>2</sub>]·H<sub>2</sub>O and [Tb<sup>III</sup>(H<sub>3</sub><b>L</b><sup><b>1</b></sup>)<sub>2</sub>](NO<sub>3</sub>)<sub>3</sub> down to 2.0 K.