Heads or Tails? Sandwich-Type Metallocomplexes of Hexakis(2,3-di-O-methyl)-α-cyclodextrin

Abstract

Native and synthetically modified cyclodextrins (CDs) are useful building blocks in construction of large coordination complexes and porous materials with various applications. Sandwich-type complexes (STCs) are one of the important groups in this area. Usually, coordination of secondary hydroxyls or the “head” portal of native CD molecules to a notional multinuclear ring of metal cations leads to formation of head-to-head STCs. Our study introduces a new CD-ligand, hexakis(2,3-di-O-methyl)-α-cyclodextrin, which enables formation of intriguing head-to-head, but also novel tail-to-tail STCs. Homometallic silver-based head-to-head STCs, AgPF6-STC and AgClO4-STC, were obtained by coordination of ligand methoxy groups to six Ag+, while bulky counter-anions are located on the outside but also filling the inner space of infinite linear channels formed. In contrast, unique homometallic tail-to-tail RbF-STC was prepared by complexation of primary hydroxyls, “tails”, to twelve Rb+ tightly interconnected by twelve F- creating complex structure with accessible pores for potential gas adsorptions.