A hexanuclear coordination cage can increase the size of its cavity from nearly zero to more than 500 Å(3), which allows the encapsulation of two coronene molecules.

The ligands 4-7-H(2) were used in coordination studies with titanium(IV) and gallium(III) ions to obtain dimeric complexes Li(4)[(4-7)(6)Ti(2)] and Li(6)[(4/5a)(6)Ga(2)]. The X-ray crystal structures of Li(4)[(4)(6)Ti(2)], Li(4)[(5b)(6)Ti(2)], and Li(4)[(7a)(6)Ti(2)] could be obtained. While these complexes are triply lithium-bridged dimers in the solid state, a monomer/dimer equilibrium is observed in solution by NMR spectroscopy and ESI FT-ICR MS. The stability of the dimer is enhanced by high negative charges (Ti(IV) versus Ga(III)) of the monomers, when the carbonyl units are good donors (aldehydes versus ketones and esters), when the solvent does not efficiently solvate the bridging lithium ions (DMSO versus acetone), and when sterical hindrance is minimized (methyl versus primary and secondary carbon substituents). The dimer is thermodynamically favored by enthalpy as well as entropy. ESI FT-ICR mass spectrometry provides detailed insight into the mechanisms with which monomeric triscatecholate complexes as well as single catechol ligands exchange in the dimers. Tandem mass spectrometric experiments in the gas phase show the dimers to decompose either in a symmetric (Ti) or in an unsymmetric (Ga) fashion when collisionally activated. The differences between the Ti and Ga complexes can be attributed to different electronic properties and a charge-controlled reactivity of the ions in the gas phase. The complexes represent an excellent example for hierarchical self-assembly, in which two different noncovalent interactions of well balanced strengths bring together eleven individual components into one well-defined aggregate.

The solvent-induced structural rearrangement of synthetic supramolecular structures typically requires a pronounced change in solvent polarity. We describe a ruthenium-based coordination cage, whose geometry and topology can be altered dramatically by using two closely related solvents: chloroform and dichloromethane. In chloroform, we observe an octanuclear prismatic cage, whereas a tetranuclear complex is formed in dichloromethane. The basis of this unusual solvent-sensitivity is the incorporation of metallacrown recognition units into a flexible, kinetically labile nanostructure.

The onset of soluble complex formation between polycations and nonionic/anionic mixed micelles was found to occur at well-defined micelle surface charge density, σ c , which could be modulated via Y, the mole fraction of anionic surfactant in the mixed micelle. Critical values of Y were detected by precision turbidimetry for two polycations, each combined with any of the four mixed micelles formed from two anionic and two nonionic surfactants. The values of Y c observed for each of the resultant eight ternary polycation/ anionic−nonionic combinations were used as surrogates for polycation binding affinity: for a given polycation and a given value of Y, micelles with Y c < Y will bind, while those with Y c > Y will not. The polycation affinity of micelles correlated with their "zeta potentials" (ζ), measured by electrophoretic light scattering, and their average surface potentials (ψ 0 ), measured by potentiometric titration of a comicellized probe. For a given polycation at a fixed ionic strength, we found that the critical zeta potential (ζ c ) measured at Y c was independent of the surfactant pair chosen. This potential at the micelle "shear plane" is thus interpreted as the potential experienced by a bound polycation. The binding affinity was furthermore found to be stronger for polycations with higher linear charge density as well as for micelles with higher axial ratio, attributed respectively to an increase in the number of micelle-bound charged polycation repeat units and to the higher surface potential for micelles with lower surface curvature.