Synthesis, crystal structure and NMR-study new mononuclear paramagnetic Er (III) complex based on imine derivatives of thiacalix[4]arene

The synthesis, crystal structure and NMR-study of new paramagnetic Er (III) complex based on imine derivatives of thiacalix[4]arene was carried out. Temperature dependences of the 1H NMR spectra of complex Er(III) and calix[4]arene with N-contained substituents (I) have been analyzed using the line shape analysis, taking into account the temperature variation of paramagnetic chemical shifts, within the frame of the dynamic NMR method. Two kinds of molecular dynamics in I are reported for the CDCl3 solution. The first one conformational dynamics is conditioned by the pinched cone A ↔ pinched cone B interconversion with activation free energy ΔG≠(298 K) = 40 ± 3 kJ/mol (observed at low temperature). The second one dynamics is connected with rearrangements in coordination environment (with ΔG≠(298 K) = 58 ± 3 kJ/mol). Due to substantial temperature dependence of paramagnetic shifts, the complex I can be considered as NMR thermosensor reagent for local temperature monitoring. Owing to the large magnetic moments typical for many Ln-ions and especially high value of magnetic anisotropy for Er cation (III) adopting capped trigonal prismatic geometry of coordination sphere one may expect that 1-Er can potentially exhibit SMM behavior.