Dinuclear single-molecule magnets with porphyrin–phthalocyanine mixed triple-decker ligand systems giving SAP and SP coordination polyhedra

Abstract

Two terbium ions in a triple-decker complex (Pc)Tb(Pc)Tb(T(p-OMe)PP) (Pc = phthalocyaninato, T(p-OMe)PP = tetra-p-methoxyphenylporphyrinato) have shown sharply different magnetic behaviours depending on symmetry of the coordination polyhedron. The fast quantum tunnelling relaxation process in a square-prismatic site has been revealed to be hindered by magnetic-dipolar coupling between the f-electronic systems.

Single-molecule magnetism of tetrapyrrole lanthanide compounds with sandwich multiple-decker structures

“…By contrast, the effects of electron-donating substituents on homoleptic bis(phthalocyaninato) lanthanide double-decker compounds remain unclear [45,[48][49][50]56]. Compared with the Ln-Y or Y-Ln multiple-decker species, short-or long-range intramolecular f-f interactions in the bis-lanthanide multiple-decker compounds are usually beneficial for enhancing the energy barrier height of spin reversal and the blocking temperature (Scheme 3E) [60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76]. In general, the lanthanide magnetic anisotropy is closely related to the coordination geometry, oxidation state (the longitudinal contraction), lanthanide-organic radical (f-π) and…”

“…double-decker compound switches from non-SMM to typical SMM [53,54]. In addition, f-f interactions have significant effects when any lanthanide ion is located in an approximate SAP geometry [63]. However, if the coordination geometry of both paramagnetic lanthanide ions deviates largely from SAP in a di-lanthanide-involved sandwich tetarpyrrole multiple-decker compound, then the coordination geometry of the f-f interactions plays an important role in determining the SMM properties [64].…”

“…A c c e p t e d M a n u s c r i p t 63 great progress has been made in the past decade, novel sandwich tetrapyrrole lanthanide compounds with fixed molecular and electronic structures as well as improved magnetic properties are still highly desirable to address the theoretical and technical challenges in this field.…”

Molecular Design for Single-molecule Magnetism of Lanthanide Complexes

“…28,31 The SMM properties of phthalocyanine/porphyrin triple-decker complexes, [(Pc)Ln(Pc)-Ln¤(Por (Figures 7b and 7c). This implies that magnetic relaxation occurs separately in the two Tb III ions.…”

“…In an ideal SAP coordination site with D 4d local symmetry, the ligand field potential provides only diagonal matrix elements, where no mixing among the «J z ª states occurs. 28 When the symmetry is lowered from SAP, and finally to square prism (SP), off-diagonal matrix elements enter to admix particular pairs of «J z ª states, leading to faster magnetic relaxation. In fact, QTM cannot occur when the Kramers ground states are orthogonal to each other, except for the introduction of a perturbation Hamiltonian that allows mixing of the two states.…”