Li Ning, García-Rodríguez Raúl, Matthews Peter D, Luo He-Kuan, Wright Dominic S
Department of Chemistry, University of Cambridge, Lensfield Road, CB2 1EW, UK.
Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 2 Fusionopolis Way, 08-03, Innovis, Singapore138634, Singapore.
Dalton Trans. 2017 Mar 27;46(13):4287-4295. doi: 10.1039/c7dt00049a.
The influence of paramagnetic Ln ions on the NMR behaviour is investigated via a series of new isostructural lanthanide-containing cages with the general formula [LnTiO(OPr)(salicylate)] (Ln-1, Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er). Compared to conventional coordination compounds containing Ln ions, the peripheral ligands in Ln-1 are separated from the paramagnetic lanthanide centres by oxo-Ti linkages, and therefore experience a weaker paramagnetic influence. As a result, all of the H and C NMR signals of these Ln-1 cages (except for Gd-1) are observed and can be unambiguously assigned, which provides an excellent platform for the in-depth study of the NMR behaviour of paramagnetic Ln ions. Further analysis of the fully assigned paramagnetic signals suggests that the pseudo-contact component dominates the H NMR shifts, whereas both the pseudo-contact and Fermi-contact contributions affect the C shifts, although the majority of the resonance environments are at least four bonds distant from the central Ln ion. Our results also show that the use of Bleaney's factors to describe the pseudo-contact shift is inadequate for this Ln-1 cage series.
通过一系列通式为[LnTiO(OPr)(水杨酸盐)](Ln-1,Ln = La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho和Er)的新型同构含镧系元素笼状化合物,研究了顺磁性Ln离子对核磁共振行为的影响。与含有Ln离子的传统配位化合物相比,Ln-1中的外围配体通过氧代钛键与顺磁性镧系中心分离,因此受到的顺磁影响较弱。结果,观察到了这些Ln-1笼状化合物(除Gd-1外)的所有H和C核磁共振信号,并且可以明确归属,这为深入研究顺磁性Ln离子的核磁共振行为提供了一个极佳的平台。对完全归属的顺磁信号的进一步分析表明,赝接触分量主导了H核磁共振位移,而赝接触和费米接触贡献都影响C位移,尽管大多数共振环境与中心Ln离子至少相隔四个键。我们的结果还表明,使用布莱尼因子来描述赝接触位移对于这个Ln-1笼状化合物系列是不够的。