Analysis Of Lanthanide-induced Shifts Research Articles

NMR Spectroscopy—A Versatile Tool for Studying the Structure and Magnetic Properties of Paramagnetic Lanthanide Complexes in Solutions (Review)

Coordination compounds of lanthanides attract increasing attention of researchers due to their unique physical and chemical properties, including interesting optical and magnetic behavior. Fine tuning of properties of functional materials based on them is possible by controlling the structure of complexes. This review describes the approach of applying NMR spectroscopy to solve the challenging problem of identification of paramagnetic lanthanide complexes, as well as to establish a correlation between the structure of the coordination sphere of lanthanide ions and the magnetic characteristics of the complexes. It has been shown how the analysis of lanthanide-induced shifts (LIS) and lanthanide-induced relaxation (LIR) in series of isostructural compounds contributes to the identification of spectral–structural correlations, which, in combination with X-ray diffraction and quantum-chemical data, make it possible not only to establish the structure of the compound in solution, but also to perform a primary assessment of the possibility of using lanthanides complexes as single molecule magnets.

Synthesis and structure of heteroleptic triple-decker neodymium, europium, holmium, erbium, and ytterbium crown phthalocyaninates

Two series of heteroleptic crown-substituted tris(phthalocyaninate) complexes (Pc)Ln[(15C5)4Pc]Ln(Pc) and [(15C5)4Pc]Ln[(15C5)4Pc]Ln(Pc), where 15C5 is 15-crown-5, (Pc2−) is the phthalocyaninate dianion, Ln = Nd, Eu, Ho, Er, and Yb, were prepared by the reaction of tetra-15-crown-5-phthalocyanine H2[(15C5)4Pc] with the corresponding lanthanide acetylacetonates and lanthanum bis(phthalocyaninate) La(Pc)2, which was used as a phthalocyaninate dianion donor. The composition and structure of the synthesized complexes were confirmed by MALDI TOF mass spectrometry, UV-Vis absorption spectroscopy, and 1H NMR. Complete assignment of the proton resonance signals of the paramagnetic lanthanide complexes was based on analysis of lanthanide-induced shifts.

An analysis of the Co2+-induced nuclear magnetic resonance perturbations of hen egg white lysozyme.

A general methodology is presented for analyzing dipolar shifts induced by paramagnetic ions in the nuclear magnetic resonance (NMR) spectra of ligand molecules. The method is applied to the shift perturbations induced by Co2+ in the spectrum of hen egg white lysozyme. A hypothesis testing scheme is employed to evaluate statistically the relative precision with which the axially symmetric and non-axially symmetric forms of the dipolar shift equation fit the observed data. The assumption of axial symmetry for the magnetic susceptibility tensor of Co2+ is rejected at the confidence level of 99%. Since the results presented here are similar to those reached in our analysis of lanthanide-induced shifts, we suggest that the assumption of axial symmetry may, in general, not hold. Similar conclusions have been reached by other investigators in studies of paramagnetic metal binding to model systems. We have included the three Co2+ coordinates in an eight-parameter fit of the Co2+ shift data. The Co2+ position obtained from this fit is in statistical agreement with the position inferred from x-ray data. Thus, the analysis of shift data may furnish a means for determining the site of metal complexation in macromolecules whose structure has been determined by x-ray crystallography.