A series of coordination polymers based on varied polycarboxylates and different imidazole-containing ligands: syntheses, crystal structures and physical properties

Abstract

To investigate the effect of organic ligands on the coordination frameworks, seven new nickel complexes with formulae Ni(BDC) (titmb)·3H₂O (1), Ni₂(BDC)₂(bimb)₂(H₂O)₂·3H₂O (2), NiZn(BTC)(titmb)Br (3), Ni(TBDC)(titmb)(H₂O) (4), Ni(TBDC)(bix)·H₂O (5), Ni(TBDC)(mbix)(H₂O)·H₂O (6) and Ni(TBDC)(obix)(H₂O) (7) (titmb = 1,3,5-tris(1-imidazol-1-ylmethyl)-2,4,6-tri-methylbenzene, bimb = 4,4′-bis(imidazol-1-ylmethyl)biphenyl, bix = 1,4-bis(imidazol-1-ylmethyl)benzene, mbix = 1,3-bis(imidazol-1-ylmethyl)benzene, obix = 1,2-bis(imidazol-1-ylmethyl)benzene, H₃BTC = 1,3,5-benzenetricarboxylic acid, H₂BDC = isophthalic acid, H₂TBDC = 5-(tertbutyl)isophthalic acid), have been synthesized and characterized by elemental analyses, infrared spectra (IR), thermogravimetric analysis (TGA) and single-crystal X-ray diffraction. Single crystal structure analysis shows that complex 1 has a three-dimensional (3D) (3,5)-connected network with a topology of (6³)(6⁹·8). Complexes 2 and 6 have similar two-dimensional (2D) lamella structures with (4,4) topology. Complex 3 exhibits an interesting 3D (3,6)-connected framework by self-penetration of two sets of (10,3)-a nets. Complex 4 presents an unusual 2D (3,5)-connected framework with a topology of (3·5²)(3²·5³·6⁴·7). Complex 5 features a 3D two-fold interpenetrating framework with (4⁶·6⁴)-bnn hexagonal BN topology, whereas Complex 7 possesses an interesting one-dimensional (1D) independent single-wall metal–organic nanotube. The various dimensions and structural features of seven complexes may be attributed to the different species of functional groups, the number and position of the carboxylic groups in the carboxylates as well as the auxiliary ligands playing a significant role in promoting the diversity of the observed structural motifs. The SHG properties of 1, 3 and 4 as well as the ferroelectric properties for 1 have also been investigated.