Unexpected Self‐Sorting Self‐Assembly Formation of a [4:4] Sulfate:Ligand Cage from a Preorganized Tripodal Urea Ligand

Abstract

The design and synthesis of tripodal ligands 1-3 based upon the N-methyl-1,3,5-benzenetricarboxamide platform appended with three aryl urea arms is reported. This ligand platform gives rise to highly preorganized structures and is ideally suited for binding SO4 (2-) and H2 PO4 (-) ions through multiple hydrogen-bonding interactions. The solid-state crystal structures of 1-3 with SO4 (2-) show the encapsulation of a single anion within a cage structure, whereas the crystal structure of 1 with H2 PO4 (-) showed that two anions are encapsulated. We further demonstrate that ligand 4, based on the same platform but consisting of two bis-urea moieties and a single ammonium moiety, also recognizes SO4 (2-) to form a self-assembled capsule with [4:4] SO4 (2-) :4 stoichiometry in which the anions are clustered within a cavity formed by the four ligands. This is the first example of a self-sorting self-assembled capsule where four tetrahedrally arranged SO4 (2-) ions are embedded within a hydrophobic cavity.

Formation of Self‐Templated 2,6‐Bis(1,2,3‐triazol‐4‐yl)pyridine [2]Catenanes by Triazolyl Hydrogen Bonding: Selective Anion Hosts for Phosphate

“…We considered exploiting the unique btp – btp hydrogen‐bonding features of 3 for anion recognition: an area that we have been actively exploring . Although triazoles have not been widely exploited in catenane synthesis, they are often used in the synthesis of anion receptors owing to their hydrogen‐bond‐donor ability .…”

Anion Receptor Chemistry

“…Pandurangan et al 78 have recently reported an interesting example of self-sorting self-assembly of a 4:4 sulfate ligand cage. Proton NMR titrations were performed with SO 4 2À and revealed that 155-157 form both a 2:1 receptor-sulfate complex and, at higher anion concentrations, a 1:1 complex.…”

Supramolecular Chemistry of Anionic Dimers, Trimers, Tetramers, and Clusters

“…In 2015, Pandurangan et al 18 reported the design and synthesis of three tripodal receptors, 4 – 6 , based upon an N-methyl-1, 3, 5-benzenetricarboxamide platform bearing three appended aryl urea arms. The complexation and self-assembly of these three receptors with various anions (SO 4 2− , H 2 PO 4 − , AcO − , and Cl − ) was studied.…”