The development of chiral metallacrowns into anion recognition agents and porous materials

Chiral metallacrowns can be prepared by the reaction of resolved amino hydroxamic acids with divalent metal ions. The 15-metallacrown-5 structure is achieved by the reaction of α-amino hydroxamic acids (e.g. l -alanine hydroxamic acid, l -phenylalanine hydroxamic acid and l -tyrosine hydroxamic acid) with Cu(II) and a Ln(III) ion. If a resolved ligand is used, the structure obtained contains all sidechain functional groups on the same face of the metallamacrocycle. The metallacrowns made with l -phenylalanine hydroxamic acid and l -tyrosine hydroxamic acid dimerize in the solid state, forming cavities that selectively recognize anions. If one uses resolved β-aminohydroxamic acids (which have fused 5 and 6 membered chelate rings), chiral 12-MC-4 complexes can be realized. The resultant structure with β-phenylalanine hydroxamic acid and Cu(II) is remarkably similar in size and shape to Cu(II) tetraphenylporphyrin. These chiral units can be linked via Cu(II) paddle wheel dimers and nitrate to form microporous layered solids. Because the of the modular synthesis strategy, grams of solid with defined chiral centers can be prepared in excellent yield.