New Zn2+ metal organic frameworks with unique network topologies from the combination of trimesic acid and amino-alcohols

Abstract

A series of new Zn 2+-trimesate (btc 3-) metal organic frameworks (MOFs) has been isolated in the presence of various amino-alcohols under solvothermal conditions. Thus, the reaction of ZnCl 2 with trimesic acid (H 3btc) and the amino-alcohols triethanolamine (teoa), 2-(hydroxymethyl)piperidine (hmpip), N-tert-butyldiethanolamine (tbdeoa), 1,4-bis(2-hydroxyethyl)piperazine (bhep), N-methyldiethanolamine (mdeoa), or 4-(2-hydroxyethyl)morpholine (hem) in a 1.6:1:5.6 molar ratio in DMF afforded compounds (teoaH) 2[Zn(btc) 1.33] (MOAAF-1) (MOAAF = metal organic amino-alcohol framework), (NH 2Me 2) 2(hmpipH)[Zn 3(btc) 3] (MOAAF-2), (NH 2Me 2)(tbdmaH) 2[Zn 3(btc) 3] (MOAAF-3) (tbdma = N-tert-butyl-dimethylamine), (NH 2Me 2)(bhepH 2)[Zn 3(btc) 3] (MOAAF-4), (NH 2Me 2)[Zn 4(btc) 3(mdeoa) 2] (MOAAF-5), and (NH 2Me 2)[Zn 4(btc) 3(hem) 2] (MOAAF-6), respectively. The compounds display 3D structures with relatively large cavities (4-10 Å) and high potential solvent-accessible areas (38-68% of the unit cell volumes). A number of novel structural features are revealed in the reported MOFs, such as unprecedented dinuclear [Zn 2(COO) 5] -1 secondary building units (SBUs) and unique network topologies (e.g., in compounds MOAAF-2, MOAAF-3, MOAAF-5, and MOAAF-6). The amino-alcohols employed played a key role for the appearance of such novel structural features in MOAAF 1-6 since they were found to act as bases responsible for the deprotonation of H 3btc, templates, and chelating ligands. Specifically, most of the compounds synthesized were shown to be templated by protonated amino-alcohols that are involved in hydrogen bonding interactions with the frameworks, whereas in two cases (compounds MOAAF-5 and MOAAF-6) the amino-alcohols acted as chelating ligands affecting significantly the underline topology of the MOFs. The thermal stability and photoluminescence properties of the MOFs are also discussed. This work represents the initial systematic investigation on the use of combination of amino-alcohols and polycarboxylate ligands for the synthesis of new MOFs, demonstrating it as a powerful synthetic strategy for the isolation of novel MOFs.