A series of intriguing metal-organic frameworks with 3,3 ',4,4 '-benzophenonetetracarboxylic acid: structural adjustment and pH-dependence

To understand the influence of the pH parameter on crystal growth, six compounds prepared at different pH values have been explored, namely {Cu(H(2)bptc)(bpa)(mu(2)-H2O)}(n) (1) {[Cu-3(Hbptc)(2)(bpa)(3)(H2O)(8)]center dot 4H(2)O}(n) (2), {[Cu-2(bptc)(bpa)(2)(H2O)]center dot 6.5H(2)O}(n) (3), {[Mn-2(bptc)(bpa) (mu(2)-H2O)(H2O)(5)]center dot H2O}(n) (4), {[Co-2(bptc)(bpe)(mu(2)-H2O)(H2O)(5)]center dot H2O}(n) (5) and {[Mn-2(bptc)(bpe) (mu(2)-H2O)(H2O)(5)]center dot H2O}(n) (6) (H(4)bptc = 3,3',4,4'-benzophenonetetracarboxylic acid, bpa = 1,2-bis(4-pyridy) ethane and bpe = 1,2-bis(4-pyridy)ethene). The structure of 1 displays a 3D open rhombic framework based on an infinite metal-aqua chain. Compound 2 contains two different motifs: a cationic 1D chain of [Cu(bpa)(H2O)(4)](2+), and an anionic 2D network of [Cu-2(Hbptc)(2)(bpa)(2)(H2O)(4)](2-). Compound 3, a microporous open-framework structure, presents an uncommon 3D, trinodal, 4-connected self- penetrating network. Compounds 4, 5 and 6 present the same arrangement with 4,6-connected 3D networks. Comparing the experimental results, it is clear that the pH value plays a crucial role in the formation of the resulting structures. The thermal stabilities of compounds 1-6 are discussed. The magnetic properties for 2 and 4 are also studied and they both exhibit a weak antiferromagnetic coupling through the O2C-C-C-CO2 bridge and mu(2)-aqua bridge, respectively.