| Summary: | <sup>1</sup>H NMR measurements are reported for the CD<sub>2</sub>Cl<sub>2</sub>/CDCl<sub>3</sub> solutions of the Co(II) calix[4]arenetetraphosphineoxide complex (<b>I</b>). Temperature dependences of the <sup>1</sup>H NMR spectra of <b>I</b> 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 <i>pinched cone</i> ↔<i>pinched cone</i> interconversion of <b>I</b> (with activation Gibbs energy Δ<i>G</i><b><sup>≠</sup></b>(298K) = 40 ± 3 kJ/mol. Due to substantial temperature dependence of paramagnetic shifts, complex <b>I</b> can be used as model compound for designing an NMR thermosensor reagent for local temperature monitoring.
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