Zn(II) and Cd(II) Metal–Organic Frameworks with Azine-Functionalized Pores: Crystal Structures, Photoluminescence, Solvent Exchange, and Molecular Simulations of Carbon Dioxide Binding Sites
Vasile Lozovan, Victor Kravtsov, Yurii Chumakov, Natalia V. Costriucova, Nikita Siminel, Oleg Petuhov, Titus Vlase, Gabriela Vlase, Alic Barbă, Marina S. Fonarı
Abstract
Four neutral metal–organic frameworks (MOFs) {[Zn(bpdc)(3-bpmhz)]·1.5(dmf)} n MRT-1 ( 1 ), {[Zn(bpdc)(3-bpmhz)]·(dmf)·0.5(Py)} n MRT-2 ( 2 ), {[Zn(bpdc)(4-bpmhz)](MeOH)·0.5(H 2 O)} n MRT-3 ( 3 ), and {[Cd(bpdc)(bda4bPy)]·2.5(dmf)} n MRT-4 ( 4 ) (where MRT stands for the Moldova Research Team), along with a one-dimensional coordination polymer {[Zn(Hbpdc) 2 (3-bphz)(MeOH) 2 ]·2(dmf)} n ( 5 ), a binuclear complex [Cd 2 (bpdc) 2 (3-bpmhz)(H 2 O) 6 ] ( 6 ), and a two-dimensional coordination polymer {[Cd(bpdc)(dmso)(H 2 O)]·0.25(H 2 bpdc)} n ( 7 ), were obtained from blends of 4,4′-biphenyldicarboxylic acid (H 2 bpdc) with 1,2-bis(1-(pyridin-3-yl)ethylidene)hydrazine (3-bpmhz), 1,2-bis(pyridin-3-ylmethylene)hydrazine (3-bphz), 1,2-bis(1-(pyridin-4-yl)ethylidene)hydrazine (4-bpmhz), or N 1, N 4 -bis(pyridin-4-ylmethylene)-benzene-1,4-diamine (bda4bPy). MOFs 1 and 2 are supramolecular isomers. MOF 1 is built on a single tetrahedral Zn(II) atom giving rise to a diamondoid ( dia ) coordination network with threefold interpenetration. MOFs 2–4 represent a reticular series of primitive cubic ( pcu ) networks that originated from [M 2 (CO 2 ) 4 ] (M = Zn and Cd) secondary building units where the metal-carboxylate coordination layers are interlinked by azine double pillars. MOFs 2 and 4 reveal the twofold interpenetrations, while MOF 3 reveals threefold interpenetration. Thermal analysis of MOFs 1–4 carried out in the air and nitrogen atmospheres indicated their thermal stability. MOFs 1 and 4 had the solvent-accessible volumes of 30.1 and 43.7%, respectively. MOF 4 demonstrated an efficient solvent exchange with the nitrobenzene (nb) capture registered by spectroscopic methods and confirmed by X-ray single-crystal studies for the crystal {[Cd(bpdc)(bda4bPy)]·1.5(nb)} n ( 4-nb ). All compounds reveal ligand-based photoluminescence properties registered in the blue and green regions of the visible spectrum for 1–3 and 5–7 . The most porous MOF 4 emitted very near to the standard white light and in the orange region when loaded with nb. The symmetry-adapted perturbation theory showed advantages of azine-functionalized pores in the studied MOFs for efficient capture of CO 2 molecules on the pores’ walls.