Chiral Direction and Interconnection of Helical Three-Connected Networks in Metal-Organic Frameworks

The control of the interpenetration and chirality of a family of metal-organic frameworks is discussed. These systems
contain two- (A) and four-fold (B) interpenetration of helical three-connected networks generated by binding the
1,3,5-benzenetricarboxylate (btc) ligand to a metal center. These frameworks have the general formula Ni3(btc)2XmYn·solvent (where X = pyridine or 4-picoline, Y = ethylene glycol, 1,2-propanediol, 1,4-butanediol, meso-2,3-butanediol,
1,2,6-hexanetriol, glycerol). The structural and chemical effects of modifying the alcohol and aromatic amine ligands
bound to the metal center include controlling the thermal stability and the degree of interpenetration. Covalent
linking of the four interpenetrating networks in the A family and the switching of diol binding from mono- to bidentate
are demonstrated. Recognition of chiral diols by the hand of the network helices is investigated by binding an
alcohol ligand with two chiral centers of opposite sense to the same helix. This reveals the subtle nature of the
helix−ligand interaction.