Crystal engineering of zinc(II) metal–organic frameworks: role of steric bulk and angular disposition of coordinating sites of the ligands

Abstract

Three novel 2D and 3D coordination polymers, [Zn(TPA)(H₂MDP)]_n (1), [Zn(IPA)(H₂MDP)]_n (2) and [Zn(HTMA)(H₂MDP)]_n (3) (H₂MDP = methylenebis(3,5-dimethylpyrazole), H₂TPA = terephthalic acid, H₂IPA = isophthalic acid and H₃TMA = trimesic acid), have been synthesized under hydrothermal conditions and structurally characterized by single crystal X-ray diffraction. For all three structures, the zinc atoms show a coordination number of four and adopt tetrahedral geometry, and subsequently form a diamondoid, a (2,4) and a (4,4) network. The employment of sterically hindered H₂MDP ligand, on the other hand, successfully prohibits interpenetration among the 2D grids. The complex 1 features a metal–organic framework exhibiting a three-fold interpenetrated diamondoid network with linear dicarboxylate ligand (H₂TPA) as an auxiliary ligand. The bent dicarboxylate ligands (H₂IPA and H₃TMA), on the other hand, lead to 2D non interpenetrative grid networks for 2 and 3. A comparative study of 2 and 3 underpins the importance of the hydrogen bond and π–π interaction in the synthesis of coordination polymers.