Ligand-Directed and pH-Controlled Assembly of Chiral 3d-3d Heterometallic Metal-Organic Frameworks

Use of unsymmetric ligand 1,2,4-benzenetricarboxylic acid (1,2,4-H3BTC) and controlling the reaction pH value enabled isolation of two novel chiral 3d-3d heterometallic complexes [Zn2Co(tib)(3)(H2O)(5)][Zn-6(tib)(2)(1,2,4-BTC)(6)]center dot 12.7H(2)O (1) and [ZnCo(tib)(1,2,4-BTC)(H2O)(2)]Cl center dot 3H(2)O (2) [tib = 1,3,5-tris(1-imidazolyl)benzene]. Comparative study revealed that the use of symmetric ligand 1,3,5-benzenetricarboxylic acid (1,3,5-H3BTC) resulted one achiral 3d-3d heterometallic complex [ZnCo(tib)(1,3,5-BTC)Cl] (3) with 3D structure. Complex 1 is a 2D network with cationic and anionic layers arranged alternately, while 2 is a 3D framework with rare ID helical water chains. Furthermore, complex 1 displays ferroelectric behavior with a remnant electric polarization (P-r) of similar to 0.177 mu C/cm2 and an electric coercive field (E-c) of similar to 17.68 kV/cm.