Square planar Pd(ii)/oximate complexes as ‘metalloligands’ for the directional assembly of 4f-metal ions: a new family of {Ln2Pd} (Ln = lanthanide) clusters exhibiting slow magnetization relaxation

Abstract

A relatively unexplored approach in heterometallic chemistry of transition metals and lanthanides has been developed toward the controlled synthesis of a new family of linear heterotrinuclear Ln(III)–Pd(II)–Ln(III) complexes with the general formula [Ln₂Pd(pao)₂(NO₃)₆(MeOH)₂(H₂O)₂]·[Pd(pao)₂]₄, where Ln^III = Dy^III (2), Gd^III (3), Er^III (4) and Yb^III (5). This strategy was based on the diamagnetic ‘metalloligand’ [Pd(pao)₂] (1), where pao⁻ is the anion of 2-pyridinealdoxime, containing two dangling oximate O-atoms which were trans to each other and available for binding with oxophilic lanthanide ions. Because of their trans-configuration, the [Pd(pao)₂] ‘metalloligand’ was able to direct the binding of two {Ln(NO₃)₃(MeOH)(H₂O)} units on opposite sites, thus yielding the reported trinuclear {Ln–Pd–Ln} clusters. Complexes 2–5 constitute a new family of trinuclear heterometallic {Ln₂Pd} species, and they represent the first examples of a directional assembly approach towards the coordination of 4f-metal ions. Compounds 2 and 5 exhibit out-of-phase signals under applied dc fields of 300 and 2000 Oe, respectively, characteristics of the slow magnetization relaxation, albeit with very small energy barriers for the magnetization reversal. This was due to the combined onset of fast quantum tunneling and the weak crystal field effects induced by the coordinated ligands. The combined results highlight the potential of using the ‘metal complexes as ligands’ method to deliberately prepare heterometallic Pd^II–Ln^III complexes with unique structural and interesting physicochemical (magnetic, optical, catalytic) properties.