Metal sulfonatocalix[4,5]arene complexes: bi-layers, capsules, spheres, tubular arrays and beyond

(C) 2001 Elsevier Science B.V. All rights reserved.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 pi -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+ subset of (18-crown-6)(H2O)(n)} subset of {(p-sulfonatocalix[4]arene(4=))(2)}(7 -), n = 0 or 2. These can crystallize, often selectively, polynuclear hydrolytic M(III) cations [M-2(OH)(2)(H2O)(8)](4+), [M-3(OH)(4)(H2O)(10)](5+), [M4OH)(6)(H2O)(12)](6+), M = Cr or Rh, or [Al13O4(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} subset of {M(H2O)(7)(3+))(1.33)(p-sulfonatocalix[4]arene(4-))}(2)], for the smaller lanthanides, or the Ferris-wheel type structure [{La3+ subset of (18-crown-6)(OH2)(3)} boolean AND {(p-sulfonatocalix[4]arene(4=) + 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.