Entangled metal-organic frameworks modulated by N-donor ligands of different conformations

Based on the aromatic dicarboxylic acid and N-donor ligands with different conformations, four Zn(II) metal-organic frameworks, namely [Zn(mfda)(L-1)](1), [Zn-2(mfda)(2)(L-2)]center dot DMF center dot H2O (2), [Zn-2(mfda)(2)(L-3)(H2O)]center dot DMF (3) and [Zn-2(mfda)(2)(L-4)] (4) have been synthesized (mfda = 9,9-dimethylfluorene-2,7-dicarboxylate anion, L-1 = 1,10-phenanthroline, L-2 = 4,4 '-bipyridine, L-3 = 2,5-bis(4-pyridyl)-1,3,4-ocadiazole and L-4 = 1,4-bis(imidazol-1-ylmethyl)benzene). Single-crystal X-ray diffraction has revealed that all compounds exhibit entangled structures. Compound 1 is composed of 1D zigzag chains that are entangled through the pi-pi stacking interactions to generate a three-fold interpenetrating diamond-like networks. 2 exhibits a two-fold interpenetrating (alpha-Po) net, which leaves 1D channels with high free volume. In 3, parallel mutual polythreadings of 2D layers are connected by hydrogen bonds into a self-penetrating framework with (4(4).6(10).7)(4.5.6)(4(6).5(2).6(16).7(3).9) topology. For 4, the interpenetrating 2D layers are connected into a self-interpenetrating net with (4(9).6(6)) topology. The potential of N-donor ligands to produce interesting metal-organic frameworks is investigated. Luminescent studies show that 1-4 exhibit strong blue fluorescent emissions.