Stepwise synthesis of heterotrimetallic FeII/PdII/AuI coordination cages

Abstract

The synthesis of heterotrimetallic molecular cages is reported. The assemblies contain three types of coordination compounds: Fe^II clathrochelate complexes, Au^I₃(pyrazolate)₃ complexes, and [Pd^II(pyridine)₄]²⁺ complexes. The cages were obtained in a stepwise fashion. A nanometer-sized metalloligand with three terminal 3-pyridyl donor groups was prepared by connection of three Fe^II clathrochelate complexes via a central Au₃(pyrazolate)₃ complex. A related strategy was employed for the synthesis of a ditopic N-donor ligand with two functionalized Fe^II clathrochelate complexes. Combining the tritopic ligand with [Pd(CH₃CN)₄](BF₄)₂ resulted in the clean formation of a spherical Pd^II₆Fe^II₂₄Au^I₂₄ coordination cage with a diameter of ∼4.1 nm and a molecular weight of 21 kDa. The ditopic metalloligand was used for the construction of a Pd^II₂Fe^II₈Au^I₁₂ cage.