Diverse anion exchange of pliable [X2@Pd3L4]4+ double cages: a molecular ruler for recognition of polyatomic anions

Abstract

Reaction of Pd(BF₄)₂ with L (L = bis(pyridin-3-yl-propyl)pyridine-3,5-dicarboxylate) in the 1 : 2 mole ratio gives rise to a spiro-type [PdL₂]·(BF₄)₂·2C₆H₆·2CH₃CN, and further self-assembly of [PdL₂]·(BF₄)₂·2C₆H₆·2CH₃CN with Pd(NO₃)₂ in the 2 : 1 mole ratio in Me₂SO at 90 °C produces a uniquely pliable double cage of [(NO₃)₂(H₂O)₂@Pd₃L₄](BF₄)₄·6C₃H₇NO. Both the encapsulated NO₃⁻ and the outside BF₄⁻ anions are exchanged by X⁻ to form [(X)₂@Pd₃L₄](X′)₄ (X⁻ = PF₆⁻, ClO₄⁻, and/or NO₃⁻; X’⁻ = BF₄⁻, PF₆⁻, ClO₄⁻, and NO₃⁻) with all-inclusive pure or mixed anions. The pliable and characteristic properties of the double cages were confirmed by anion exchange of the nestled or outside anions in the present study. This system can be used as a ruler for recognition of ubiquitous polyatomic anions.