Solvent-Mediated Transformation from Achiral to Chiral Nickel(II) Metal-Organic Frameworks and Reassembly in Solution

摘要

Reactions of 5-nitroisophthalic acid (NO2-H(2)ip), 1,4-bis(imidazol-1-yl)butane (bimb), and Ni(NO3)(2)6H(2)O gave rise to four metal-organic frameworks (MOFs), [Ni-2(NO2-ip)(2)(bimb)(1.5)](n) (1), [Ni-4(NO2-ip)(3)(bimb)(2)(OH)(2)(H2O)](n) (CH3CH2OH)(0.5n) (2), [Ni(NO2-ip)(bimb)(1.5)(H2O)](n)(H2O)(n) (CH3CH2OH)(0.5n) (3), and [Ni(NO2-ip) (bimb)(-H2O)](n)(H2O)(n) (4). The metal/ligand ratio, pH value, and solvent exerted a subtle but crucial influence on the formation of complexes 1-4, which possess different visual color and crystal structures. Complex 1 exhibits a twofold interpenetrating 3D pillared bilayer framework composed of binuclear and mononuclear Ni-II units, whereas complex 2 is a 3D chiral network that consists of asymmetric tetranuclear Ni-II units. Complexes 3 and 4 are 3D layer-pillared frameworks that consist of mononuclear Ni-II ions and a 3D six-connected network of -water-bridged dinuclear Ni-II units, respectively. Interestingly, achiral 4 can be transformed into chiral 2 by using a solvent-mediated single-crystal-to-single-crystal process without any chiral auxiliary. Magnetic analyses of 2 and 4 show the occurrence of antiferromagnetic interactions. Complex 3 is difficult to obtain directly as a single solid phase, but it can be homogeneously formed by solvent-mediated transformations from 1, 2, and 4.