Using supercritical CO2 in the preparation of metal-organic frameworks: Investigating effects on crystallisation

In this report, we explore the use of supercritical CO2 (scCO2) in the synthesis of well-known metal-organic frameworks (MOFs) including Zn-MOF-74 and UiO-66, as well as on the preparation of [Cu24(OH-mBDC)24]n metal-organic polyhedra (MOPs) and two new MOF structures {[Zn2(L1)(DPE)]∙4H2O}n and {[Zn3(L1)3(4,4’-azopy)]∙7.5H2O}n, where BTC = benzene-1,3,5-tricarboxylate, BDC = benzene-1,4-dicarboxylate, L1 = 4-carboxy-phenylene- methyleneamino-4-benzoate, DPE = 1,2-di(4-pyridyl)ethylene, 4.4’-azopy = 4,4’- azopyridine, and compare the results versus traditional solvothermal preparations at low temperatures (i.e., 40 °Ϲ). The objective of the work was to see if the same or different products would result from the ssCO2 route versus the solvothermal method. We were interested to see which method produced the highest yield, the cleanest product and what types of morphology resulted. While there was no evidence of additional meso- or macroporosity in these MOFs/MOPs nor any significant improvements in product yields through the addition of scCO2 to these systems, it was shown that the use of scCO2 can have an effect on crystallinity, crystal size and morphology

Pillared Two-Dimensional Metal–Organic Frameworks Based on a Lower-Rim Acid Appended Calix[4]arene

Solvothermal reactions of the lower-rim functionalized diacid calix[4]­arene 25,27-bis­(methoxycarboxylic, acid)-26,28-dihydroxy-4-<i>tert-</i>butylcalix­[4]­arene, (<b>L</b>H₂) with Zn­(NO₃)₂·6H₂O and the dipyridyl ligands 4,4′-bipyridyl (4,4′-bipy), 12-di­(4-pyridyl)­ethylene (DPE), or 4,4′-azopyridyl (4,4′-azopy) afforded a series of two-dimensional structures of the formulas {[Zn­(4,4′-bipy)­(<b>L</b>)]·2¹/₄DEF}_<i>n</i>, (<b>1</b>), {[Zn₂(<b>L</b>)­(DPE)]·DEF}_<i>n</i> (<b>2</b>), and {[Zn­(OH₂)₂(<b>L</b>)­(4,4′-azopy)]·DEF}_<i>n</i><i>,</i> (<b>3</b>) (DEF = diethylformamide)

Pillared MOFs: structure and ring opening polymerization of cyclic esters

The solvothermal reaction of Zn(NO3)2·6H2O with 5-aminoisophthalic acid and 4,4′-bipyridyl (4,4′-bipy) led to the self-assembly of the known 3-D hybrid H-bonded/covalent structure {[Zn(5-AIP)(4,4′-bipy)0.5]·DMF}n (1·DMF), but with DMF here (rather than H2O as previously): an analogous reaction using the related 4,4′-azopyridine (4,4′-azopy) in place of 4,4′-bipyridyl afforded the structurally related framework {[Zn(5-AIP)(4,4′-azopy)0.5]·0.75DMF}n (2·0.75DMF). Similar solvothermal reactions of Co(NO3)·6H2O, Mn(NO3)·4H2O and Cd(NO3)·4H2O with 5-aminoisophthalate and the potential linkers 4,4′-bipy, 2-di(4-pyridyl)ethylene (DPE), and 4,4′-azopy afforded the porous 3-D structures {[Co2(NO3)2(5-AIP)(4,4′-bipy)2]·2EtOH}n (3·2EtOH), {[Co(5-AIP)(DPE)]·2DMF}n (4·2DMF), {[Co(5-AIP)(4,4′-azopy)]·2DMA}n (5·2DMA), {[Mn(5-AIP)(4,4′-bipy)]·2DMA}n (6·2DMA), {[Mn(5-AIP)(DPE)]·6DMF}n (7·6DMF), {[Mn(5-AIP)(4,4′-azopy)]·2.5DMF}n (8·2.5DMF), the previously reported {[Cd(5-AIP)(4,4′-bipy)]·3DMF}n (9·3DMF), {[Cd(5-AIP)(DPE)]·DMF}n (10), and {Cd(5-AIP)(4,4′-azopy)(DMF)}n (11), with structures 4–10 bearing the same network topologies with metal atoms and 5-AIP ligands in sheets, bipy ligands acting as pillars, and solvent molecules of crystallisation located around the bipy ligands. The activated MOFs were employed as catalysts for the ring opening polymerization (ROP) of ε-caprolactone and δ-valerolactone. ROPs were conducted as melts, and under N2 only 1 with δ-VL (∼93% conversion) was active. In the case of ε-CL under air, all the systems were active with 1, 2, and 11 affording >90% conversion. Molecular weights (Mn) were in the range 3760–17 940 Da and the products formed were identified as both cyclic and linear PCL. For δ-VL, the catalysts performed somewhat better, with all systems (except 8) affording ∼90% conversion or more under air. Molecular weights (Mn) were in the range 2180–7940 and as for PCL, the products formed were identified as both cyclic and linear PCL.</p