Six New Metal−Organic Frameworks Based on Polycarboxylate Acids and V-shaped Imidazole-Based Synthon: Syntheses, Crystal Structures, and Properties

Solvothermal reactions of 4,4′-bis(imidazol-1-yl)diphenyl ether (BIDPE) with deprotonated 5-hydroxy-isophthalic acid (5-OH-H2bdc), and benzene-1,3,5-tricarboxylic acid (H3btc) in the presence of cadmium(II), zinc(II), cobalt(II), nickel(II), and manganese(II) salts in H2O or H2O/DMF produced six new complexes, namely, [Cd(BIDPE)(5-OH-bdc)·H2O]n (1), [Co(BIDPE)(5-OH-bdc)·H2O]n (2), [Zn3(BIDPE)3(5-OH-bdc)3·4H2O]n (3), [Ni(BIDPE)2(5-OH-bdc)(H2O)·3H2O]n (4), {[Mn2(BIDPE)2(5-OH-bdc)2]n (5), and [Ni(BIDPE)2(Hbtc)(H2O)]n (6). These complexes were characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. Compounds 1 and 2 reveal the same two-dimensional (2D) sheets with a 32-membered [(Cd/Co)2(BIDPE)2] metallocyclic ring constructed from BIDPE and 5-OH-H2bdc with Cd or Co salts. For compound 3, six identical 2D sheets are polycatenated in parallel to form a rare 2D → 2D framework; it displays ferroelectric behavior with a remnant electric polarization (Pr) of 0.033 μC/cm2 and an electric coercive field (Ec) of 11.15 kV/cm. In compounds 4 and 6, only one carboxyl group coordinated to the Ni atom from 5-OH-H2bdc or H3btc. Compound 5 exists as binuclear Mn clusters, which are linked by BIDPE and 5-OH-H2bdc to generate a 2D sheet and displays weak antiferromagnetic character. In addition, the thermal stabilities and photochemical properties of these new complexes have been studied.