Paramagnetic Properties and Moderately RapidConformational Dynamics in the Cobalt(II) Calix[4]arene Complex by NMR

Abstract

1H NMR measurements are reported for the CD2Cl2/CDCl3 solutions of the Co(II) calix[4]arenetetraphosphineoxide complex (I). Temperature dependences of the 1H NMR spectra of 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. Conformational dynamics of the 2:1 Co(II) calix[4]arene complexes was conditioned by the pinched cone ↔pinched cone interconversion of I (with activation Gibbs energy ΔG≠(298K) = 40 ± 3 kJ/mol. Due to substantial temperature dependence of paramagnetic shifts, complex I can be used as model compound for designing an NMR thermosensor reagent for local temperature monitoring.

A case study using spectroscopy and computational modelling for Co speciation in a deep eutectic solvent

“…However, the extent of the peak shift to high ppm values for all the peaks, and the broader peaks from EG in the sulfate system compared to the chloride system, indicate a shorter average distance to the paramagnetic center (Co 2+ ) in the sulfate system. 70 For instance, in the sulfate system, the aliphatic protons (x) and hydroxyl protons (z) of EG show broader peaks overlapping the protons (b) and (a) of ChCl compared to the chloride system. Therefore, proton shifts in the sulfate system have been affected more by the paramagnetic properties of Co 2+ than in the chloride system, indicating a difference in the chemical environment between the two systems based on the type of Co salt.…”

“…In general, a broadening and shift to high ppm values of all the peaks were observed, consistent with the presence of a paramagnetic complex in the two Co containing systems compared to the neat EG : ChCl (4.5 : 1). [69][70][71] All the chemical shift values of protons in the neat solvent system and the two Co containing systems are given in Table 1.…”