Distinction between light and heavy lanthanide(III) ions based on the 1H NMR spectra of heteroleptic triple-decker phthalocyaninato sandwich complexes

The H-1 NMR spectra of two series of heteroleptic triple-decker phthalocyaninato sandwich complexes of the rare earth(III) ions have been recorded. The ligands comprise unsubstituted phthalocyanine (Pc) and 2,3,9,10,16,17,23,24-octakis(1 ' -octyloxy)phthalocyanine (Pc*), and the complexes are of the form PcMPc*MPc (series 1) and PeMPc*MPc* (series 2), where M = Pr - Tm (except Pm, Gd). In some cases, the homoleptic complexes Pc*MPc*MPc* (series 3) were also available. The chemical shifts of five proton positions in series 1, and 10 positions in series 2 were compared with the shifts for the analogous complexes of the diamagnetic yttrium(III) ion. The experimental lanthanide-induced shifts,(LIS) were separated into the contact and dipolar contributions using the crystal-field dependent methods of Reilley and co-workers. This work represents the first analysis of LIS in triple-decker phthalocyaninato lanthanide complexes. The results showed a dominance of dipolar contributions but also revealed that contact influences cannot be ignored, even for protons located in the peripheral alkoxy substituents. Analysis by graphical and matrix methods indicates that there is a clear discontinuity in the data between terbium and dysprosium, whereby the metals Nd, Sm, Eu and Tb possess a positive hyperfine coupling term Fi, and the later metals Dy, Ho (limited data), Er and Tra require a negative contact term. This change is coincident with a near-halving of the dipolar term G(i).A(2)(0)<r(2)> for the later metals. The properties of praseodymium are anomalous, in that its complexes are readily demetalated, and its NMR behavior places it in the second group of metal ions, despite its early position in the lanthanide series. Use of crystal-field independent analysis shows that the discontinuity near the middle of the series is related to variation in both the hyperfine electron-nuclear coupling constant and the crystal-field properties of the metal ions, rather than to gross changes in geometry.