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

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Abstract
To understand the influence of the pH parameter on crystal growth, six compounds prepared at different pH values have been explored, namely {Cu(H2bptc)(bpa)(μ2-H2O)}n (1) {[Cu3(Hbptc)2(bpa)3(H2O)8]·4H2O}n (2), {[Cu2(bptc)(bpa)2(H2O)]·6.5H2O}n (3), {[Mn2(bptc)(bpa) (μ2-H2O)(H2O)5]·H2O}n (4), {[Co2(bptc)(bpe)(μ2-H2O)(H2O)5]·H2O}n (5) and {[Mn2(bptc)(bpe) (μ2-H2O)(H2O)5]·H2O}n (6) (H4bptc = 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 [Cu2(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 μ2-aqua bridge, respectively.

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