Metallacrowns: A New Class of Metallamacrocycles

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This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports work by Professor Vencent L. Pecoraro at the University of Michigan to expand the breadth of metallacrown complexes with regard to the: 1) Preparation of peripherally adorned chiral metallacrowns. 2) Selective recognition of guests in molecular compartments 3) Modular synthesis of chiral solids, and 4) Development of new classes of single molecule magnets. The focus is on the synthesis of 12 and 15 membered metallamacrocycles that have made new chiral solids. These proposed 12-MC-4 and 15-MC-5 molecules may be prepared with a variety of metals, which will allow moderation of the physical properties of the compounds. Chiral 12-MC-4 structures will be prepared using beta-aminohydroxamic acids whereas 15-MC-5 structures will be produced when alpha-aminohydroxamic acids are used. The structure and properties of these metallacrowns can be drastically altered by modifying the sidechains of these aminohydroxamic acids. Sidechains such as benzyl (phenylalanine) or p-hydroxybenzyl (tyrosine) allow formation of metallamacrocyclic dimers in the solid state that can differentially recognize mono and dicarboxylic acids and chiral amino acids. Experiments aim to decorate these cavities with functionalities that will aid selective recognition of other molecules, including chiral carboxylates and alcohols. By changing heteroatom donors of the hydroxamic acids, it is proposed that modification of the metal composition of the metallacrown complexes will be possible. A modular synthetic approach for preparing layered, chiral solids is presented. The observation that metallamacrocycles molecules may act as magnets (single molecule magnetism or SMM) promises use in magnetic storage devices. Chiral recognition by metallacrowns may provide the basis of new methods for separations of chiral molecules using either selective crystallization or chromatographic methods. It may be possible to perform separations of amino acids, amino alcohols or hydroxy acids that are important starting materials for many organic and pharmaceutical syntheses. The modular approach for porous solid synthesis may provide a way to make new catalysts or storage materials.