Cesium Cation−π Interactions Stabilize Pyrogallol[4]arene Coordination Networks

Abstract

Pyrogallol[4]arene macrocycles represent versatile precursors for the rational design of a rapidly expanding range of coordination networks, metal−organic nanocapsules, hierarchical nanocapsular assemblies, and elegant nanostructures. In this work, the solvothermal reaction of C-alkylpyrogallol[4]arene (alkyl = methyl, ethyl) in cesiumcontaining N,N-dimethylformamide (DMF) afforded coordination networks having a composition of [Cs 2 (C-methylpyrogallol[4]arene)(DMF)]•(DMF) 2 and [Cs 2 (C-ethylpyrogallol[4]arene)(DMF) 3 ], respectively. These extended coordination networks each display a duplicity of cesium environments featuring both (i) a "pseudocrown ether" environment involving O-coordination between Cs + and the phenolic oxygens of four neighboring doubly deprotonated C-alkylpyrogallol[4]arenes, plus DMF ligation, and (ii) polyhapto η 6 -type coordination of a Cs + center by the four phenyl rings of a C-alkylpyrogallol[4]arene receptor. The presence of both an exo coordination mode in which the cesium cation is bound to the "hard" phenolic/phenoxide upper rim pyrogallol[4]arene oxygens plus an endo one corresponding to cesium cation−π bonding by the "soft" aromatic rings defining the pyrogallol[4]arene cavity is unique among pyrogallol [4]arene chemistry. This duality is pivotal to the cross-linking arrangement which yields an extended network and suggests that a number of interesting architectures might be identified by further study of alkali metal-incorporated C-alkylpyrogallol[4]arene systems.

Nanocapsules of unprecedented internal volume seamed by calcium ions

“…34,42 For instance, the magnesium nanocapsule was functionalized externally (altering the ligand to C-propan-3olpyrogallol [4]arene; PgC 3 OH from C-propylpyrogallol [4]arene; PgC 3 ) and internally (coordinating six proline molecules endohedrally). 42 Very recently, solvothermal methods were employed in synthesizing hierarchical self-assemblies from nanocapsules of Dy, 41 Gd, 41 and Pr, 37 advocating the use of solvothermal methods in obtaining diverse 43 and controlled self-assemblies.…”