Study of 1H NMR spectra of dinuclear complexes of heavy lanthanides with phthalocyanines based on separation of the effects of two paramagnetic centers

Experimental and theoretical study of nuclear magnetic resonance (NMR) spectra of dinuclear complexes of paramagnetic trivalent Tb, Dy, Ho, Er, Tm, or Yb ions with phthalocyanine ligands is presented. The H-1 NMR paramagnetic shifts of the dinuclear Pc triple-decker complexes PcLnPcLnPc* (abbreviated as [Ln, Ln]; Pc is the dianion of phthalocyanine and Pc* is the dianion of 2,3,9,10,16,17,23,24-octabutoxyphthalo-cyanine) were measured in CDCl3 solution at 303 K. These values are analyzed using the corresponding data of two series of heterodinuclear complexes with a single paramagnetic ion, namely PcYPcLnPc* ([Y, Ln]) and PcLnPcYPc* ([Ln, Y]). The paramagnetic shifts in [Y, Ln] and [Ln, Y] were reproduced solely by the magnetic dipolar (pseudo-contact) term, using a geometric structure that was obtained by a density functional theory (DFT) calculation with a moderate modification. Each paramagnetic shift value of [Ln, Ln] is shown to be sum of those of [Y, Ln] and [Ln, Y]. The independence of the paramagnetic shift contributions of the two Ln ions is explained by the small interaction between f-electronic systems in [Ln, Ln]. The shifts in an [Ln, Ln] complex have the same sign, because all the protons are positioned in the same region of the contour map of the dipolar contributions of the two paramagnetic sites.