Entangled metal-organic frameworks of m-phenylenediacrylate modulated by bis(pyridyl) ligands

Solvothermal reactions of m-phenylenediacrylic acid (H ₂mpda) and zinc(II) salts in the presence of different bis(pyridyl) ancillary ligands afforded a series of supramolecular interpenetrated coordination architectures with formula [Zn(mpda)(bpee)] _n (1), [Zn(mpda)(bpea)] _n (2), and [Zn(mpda)(bpp)] _n•2.5H ₂O (3) (bpee = 1,2-bis(4-pyridyl)ethylene, bpea = 1,2-bis(4-pyridyl)ethane, bpp = 1,3-bis(4-pyridyl)propane). X-ray analyses revealed that all of the compounds feature tetrahedral-based coordination geometry around Zn(II), two-dimensional (2D) 4 ⁴ coordination networks with different linkers, and parallel 2D→2D interpenetration, which is stabilized by interlayer hydrogen-bonding interactions. The arc-shaped mpda ligand collaborates with quasi-linear bpee or bpea to generate 2D achiral networks with chair-shape windows in 1 and 2, but with two different arc-shaped ligands (mpda and bpp); the single network in 3 is homochiral and has boat-shaped windows. The different shapes of the networks result in different interpenetration modes. Both networks of 1 and 2 exhibit 3-fold parallel interpenetration and give trilayers. Differently, two layers of the same handedness in 3 interpenetrate to give a homochiral bilayer featuring double helical motifs, and the alternating stacking of oppositely handed bilayers renders the compound racemic. The interpenetration mode and the formation of the double helices in 3 benefit not only from the arc shape of the two bridging ligands but also from the match of the two ligands in length.