Temperature-induced assembly of MOF polymorphs: Syntheses, structures and physical properties

Four new coordination polymers, namely, [Co(BIPA)(titmb)]·H ₂O (1), [Co ₃(BIPA) ₃(titmb) ₂] ·0.73H ₂O (2), [Ni(SDBA)(bix)]·2H ₂O (3) and [Ni(SDBA)(bix)(H ₂O)]·0.38H ₂O (4) (H ₂BIPA = 5-bromoisophthalic acid, H ₂SDBA = 4,4′-dicarboxybiphenyl sulfone, titmb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-tri-methylbenzene, bix = 1,4-bis(imidazol-1-ylmethyl)benzene), were obtained under hydrothermal conditions. Four complexes were characterized by elemental analyses, IR spectra, thermogravimetric analyses and single-crystal X-ray diffraction. Complexes 1 and 2 are polymorphs formed from Co(II) cations, BIPA ^2- anions, titmb ligands and water molecules, showing a three-dimensional (3,5)-connected network with the topology of (6 ³)(6 ⁹.8) for 1 and a three-dimensional (3,4)-connected coordination framework with the topology of (4.6.8)(4.6 ².8 ³)(6.8 ⁵)(6 ².8 ³.10)(8 ³) for 2. Complexes 3 and 4 are also two polymorphs constructed from Ni(II) cations, SDBA ^2- anions, bix ligands and water molecules. Complex 3 exhibits a two-dimensional lamella structure with (4,4) topology, whereas complex 4 displays a two-dimensional 2-fold interpenetrating (6,3) network. It is shown that the reaction temperature plays a crucial role in the formation of the final products. Moreover, the nonlinear optical and ferroelectric properties of 1 have also been investigated.