Thermometric nanosize NMR-sensors for temperature determination in weakly polar non-aqueous media on the base of ion pairs of paramagnetic complexes of lanthanides(III)

For temperature determination in solutions it is suggested that the temperature dependence of the paramagnetic lanthanide-induced shifts (LIS) in the NMR spectra on the ligand nuclei be used for [Ln(PTA)2(18-crown-6)]+[Ln(PTA)4]- complex ion pairs formed in CCl4, CDCl3, CD2Cl2, CD3C6D5, and C2D3N type low-polar solvents (Ln = La, Ce, Pr, Nd, Eu; PTA is the pivalyltrifluoroacetonate anion). It was found experimentally that the [Ln(PTA)2(18-crown-6)]+ complex cation molecules (Ln = Ce and Pr) proved most suitable for use as nanosized (∼1.1 nm) probes for temperature determinations in nonaqueous solutions. A linear dependence of the LIS on the 1H nuclei of different groups and the difference between the LIS corresponding to the CH2 groups of the 18-crown-6 molecules and the CH groups of the PTA anions on the reciprocal temperature (1/T) was found. The LIS of the individual signals of different groups in Ln paramagnetic complexes (relative to the signals of the diamagnetic analogs, e.g., La or Lu) may be used for temperature control in the sample, although the temperature measurement error is smaller (≤0.04 K) when the difference between the LIS of the CH2 and CH groups is used. Due to the high thermodynamic and kinetic stability combined with small sizes of [Ln(PTA)2(18-crown-6)]+[Ln(PTA)4]- molecules in nonaqueous solutions, these compounds may be used as thermometric NMR sensors directly in reaction media for in situ control over temperature