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

Reactions of 5‐nitroisophthalic acid (NO2‐H2ip), 1,4‐bis(imidazol‐1′‐yl)butane (bimb), and Ni(NO3)2⋅6 H2O gave rise to four metal–organic frameworks (MOFs), [Ni2(NO2‐ip)2(bimb)1.5]n (1), [Ni4(NO2‐ip)3(bimb)2(OH)2(H2O)]n ⋅(CH3CH2OH)0.5 n (2), [Ni(NO2‐ip)(bimb)1.5(H2O)]n⋅(H2O)n ⋅(CH3CH2OH)0.5 n (3), and [Ni(NO2‐ip) (bimb)(μ‐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 NiII units, whereas complex 2 is a 3D chiral network that consists of asymmetric tetranuclear NiII units. Complexes 3 and 4 are 3D layer‐pillared frameworks that consist of mononuclear NiII ions and a 3D six‐connected network of μ‐water‐bridged dinuclear NiII 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. Single‐crystal‐to‐single‐crystal: Different nickel(II) metal–organic frameworks (MOFs) have been constructed depending on the metal/ligand ratio, pH value, and solvent used (see figure). Examples are provided of an achiral MOF transformed into a chiral complex by using a single‐crystal‐to‐single‐crystal transformation without any chiral auxiliary and the solvent‐mediated reassembly of MOFs from other MOFs obtained under different reaction conditions.