125 Te NMR provides evidence of autoassociation of organo-ditellurides in solution

The frequency of the resonance of ¹²⁵Te of two organo-ditellurides, R-Te-Te-R (R = 4-CH₃C₆H₄ and 2-(CH₃)₂NCH₂C₆H₄), in solution undergoes a low-field shift as the concentration of the sample increases. In sharp contrast, the resonance of a sterically hindered ditelluride (R = (C₆H₅(CH₃)₂Si)₃C) and telluric acid display the opposite effect. While the negative concentration coefficients can be explained by the change in magnetic susceptibility, the positive coefficients are consistent with autoassociation of the molecules through tellurium-centred supramolecular interactions. Although the corresponding equilibrium constants are small, the process is shown to be exothermic. However, the influence of autoassociation is much smaller than the effects of solvent polarity and the conformation of the ditelluride bond.