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-H 3 BTC) and controlling the reaction pH value enabled isolation of two novel chiral 3d-3d heterometallic complexes [Zn 2 Co(tib) 3 (H 2 O) 5 ][Zn 6 (tib) 2 (1,2,4-BTC) 6 ]·12.7H 2 O ( 1 ) and [ZnCo(tib)(1,2,4-BTC)(H 2 O) 2 ]Cl·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-H 3 BTC) 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 1D helical water chains. Furthermore, complex 1 displays ferroelectric behavior with a remnant electric polarization ( P r ) of ∼0.177 μC/cm 2 and an electric coercive field ( E c ) of ∼17.68 kV/cm.