Organoamino Phosphonium Cations as Building Blocks for Hierarchical Supramolecular Assemblies

Organoamino phosphonium cations of formula [P(NHR)(4)](+) offer four hydrogen bonding sites that are arranged in tetrahedral fashion around the central phosphorus atom. This arrangement generates novel supramolecular building blocks that are distinct from the commonly planar NH donor systems, such as urea and guanidine. The supramolecular aggregation of these cations in the presence of chloride and several carboxylate anions is described. The carboxylate salts are obtained either by anion exchange reactions with phosphonium chlorides or by protonation reaction of the neutral phosphine imine P(NPh)-(NHPh)(3). X-ray structure analyses of the title compounds show that they form hierarchical structures ranging from 1D chains to 2D sheets and 3D networks. Control over the dimensionality of the supramolecular structure can be achieved by modulating the steric bulk of the phosphonium cation.