Exploring and expanding the three-dimensional structural diversity of supramolecular dendrimers with the aid of libraries of alkali metals of their AB3 minidendritic carboxylates

Abstract

The synthesis of the alkali metal salts of 3,4,5-tris(n-alkan-1-yloxy)-benzoic acid [(3,4,5)nG1-CO2M, where n is the number of methylenic units in the alkane group for n = 12, 14, 16, 18 and M = Li, Na, K, Rb, Cs] is described. The structural analysis of these AB3 molecules by a combination of methods which includes X-ray diffraction experiments was performed. These experiments have demonstrated that (3,4,5)nG1-CO2M self-assemble at low temperatures into supramolecular cylinders and at high temperatures into spheres which subsequently self-organize into two-dimensional c2mm rectangular columnar, p6mm hexagonal columnar, three-dimensional Pm3̄n and Im3̄m cubic lattices. In addition a novel unidentified liquid crystalline lattice was also discovered. The dependence between the symmetry of the lattice and the molecular structure of (3,4,5)nG1-CO2M was established. (3,4,5)nG1-CO2M represents one of the AB3 minidendrons (i.e., first-generation monodendron attached to the periphery of larger generation dendrons) that is responsible for the control of the three-dimensional structures created from libraries of larger generations of dendrimers. Therefore, the molecular structure-lattice dependence elaborated here will aid the rational design of the three-dimensional shapes from larger generations of supramolecular dendrimers and of their lattices. In addition, the temperature responsive shape change of these supramolecular objects may generate new supramolecular concepts and technological applications.