J. Atwood, L. Barbour, M. Hardie
Nov 1, 2001
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Coordination Chemistry Reviews
Abstract
Abstract The main focus of this review is the self-assembly in aqueous solutions of bowl-shaped sodium p-sulfonatocalix[4,5]arenes with main group, transition metal and lanthanoid species, and with various organic molecules as additional supramolecular building components, for example 18-crown-6, and other macrocycles, pyridine N-oxide, amino-acids, and more. The versatility of building up new materials based on these components is demonstrated by the formation of a diverse range of complex inclusion structures assembled through π-stacking, hydrogen bonding and coordination interactions. There are up–down arrangements of calix[4]arenes in hydrophobic–hydrophobic bi-layer structures with the positively charged species and included molecules between the layers. A variant of this is prevalent in structures incorporating 18-crown-6 which, in essence, are built up of globular superanions or ionic capsules, for example {Na+⊂(18-crown-6)(H2O)n}⊂{(p-sulfonatocalix[4]arene4−)2}7−, n=0 or 2. These can crystallize, often selectively, polynuclear hydrolytic M(III) cations [M2(OH)2(H2O)8]4+, [M3(OH)4(H2O)10]5+, [M4(OH)6(H2O)12]6+, M=Cr or Rh, or [A113O4(OH)24(H2O)12]7+, depending on the pH and other synthetic parameters. Lanthanide(III) ions form a range of complexes at specific pH in the presence of the calixarene and crown ether, including complexes containing the capsule [{18-crown-6}⊂{(M(H2O)73+)1.33(p-sulfonatocalix[4]arene4−)}2], for the smaller lanthanides, or the Ferris-wheel type structure [{La3+⊂(18-crown-6)(OH2)3}⋂{(p-sulfonatocalix[4]arene4−+2H+)}]+, for the larger lanthanide. In the presence of pyridine N-oxide, at pH 4 where the calixarenes take on 5− charge, an up–up arrangement of sulfonated calixarenes results, either assembled in icosahedral spheres, or infinite chiral, helical nano-tubes.