A periodic mesoporous organosilica (PMO) that contains ethylene bridges was functionalized to obtain a series of cooperative acid–base catalysts. A straightforward, single-step procedure was devised to immobilize cysteine and cysteamine on the support material by means of a photoinitiated thiol-ene click reaction. Likewise, PMO materials capped with hexamethyldisilazane (HMDS) were used to support both compounds. This resulted in different materials in which the amine site was promoted by carboxylic acid groups, surface silanol groups, or both. The catalysts were tested in the aldol reaction of 4-nitrobenzaldehyde and acetone. It was found that silanol groups have a stronger promoting effect on the amine than the carboxylic acid group. The highest turnover frequency (TOF) was obtained for an amine-functionalized material that contained only silanol promoting sites. The loading of the active sites also had a significant effect on the activity of the catalysts, which was rationalized on the basis of a computational study.

The epoxidation of cyclohexene has been investigated on a metal–organic framework MIL-47 containing saturated V^+IV sites linked with functionalized terephthalate linkers (MIL-47-X, X=OH, F, Cl, Br, CH₃, NH₂). Experimental catalytic tests have been performed on the MIL-47-X materials to elucidate the effect of linker substitution on the conversion. Notwithstanding the fact that these substituted materials are prone to leaching in the performed catalytic tests, the initial catalytic activity of these materials correlates with the Hammett substituent constants. In general, substituents led to an increased activity relative to the parent MIL-47. To rationalize the experimental findings, first-principles kinetic calculations were performed on periodic models of MIL-47 to determine the most important active sites by creating defect structures in the interior of the crystalline material. In a next step these defect structures were used to propose extended cluster models, which are able to reproduce in an adequate way the direct environment of the active metal site. An alkylperoxo species V^+VO(OOtBu) was identified as the most abundant and therefore the most active epoxidation site. The structure of the most active site was a starting basis for the construction of extended cluster models including substituents. They were used for quantifying the effect of functionalization of the linkers on the catalytic performance of the heterogeneous catalyst MIL-47-X. Electron-withdrawing as well as electron-donating groups have been considered. The epoxidation activity of the functionalized models has been compared with the measured experimental conversion of cyclohexene. The agreement is fairly good. This combined experimental–theoretical study makes it possible to elucidate the structure of the most active site and to quantify the electronic modulating effects of linker substituents on the catalytic activity.

A general synthetic strategy has been developed, which can be used for the preparation of all the known as well as five new functionalised UiO-66-X compounds [X = H, F, F₂, Cl, Cl₂, Br, Br₂, I, CH₃, (CH₃)₂, CF₃, (CF₃)₂, NO₂, NH₂, OH, (OH)₂, OCH₃, (CO₂H)₂, SO₃H, C₆H₄]. Starting from a reaction mixture of ZrOCl₂·8H₂O, H₂BDC-X (BDC: 1,4-benzenedicarboxylate), formic acid and N,N-dimethylacetamide (DMA) having a molar ratio of 1:1:100:104.44, all the UiO-66-X compounds, except UiO-66-CO₂H, were obtained under solvothermal conditions (150 °C, 24 h). The phase purity of all the compounds was ascertained by X-ray powder diffraction (XRPD) analysis, DRIFT spectroscopy and elemental analysis. Determination of lattice parameters from the XRPD patterns of the new thermally activated UiO-66-X {X = CF₃ (1-CF₃), (CO₂H)₂ [2-(CO₂H)₂], F₂ (3-F₂), Cl₂ (4-Cl₂), Br₂ (5-Br₂)} compounds revealed their structural similarity with the unfunctionalised UiO-66. Thermogravimetric analyses (TGA) indicate that the five new compounds are stable in the range 290–390 °C in air. Except for 3-F₂, the new compounds maintain their structural integrity in water, acetic acid and 1 M HCl, as verified by XRPD analysis of the samples recovered after suspending them in the respective liquids. As confirmed by N₂ and CO₂ sorption analyses, all of the new thermally activated compounds exhibit significant microporosity values (S_Langmuir = 217–836 m² g^–1), which are lower than that of the parent UiO-66. Comparative CO₂ sorption studies reveal that the UiO-66-X compounds with X = NO₂, NH₂, OH, CH₃ and (CH₃)₂ show enhanced CO₂ uptake compared to that of the parent compound at 1 bar and 0 °C.

A gallium 2,2′-bipyridine-5,5′-dicarboxylate metal–organic framework (MOF), denoted as COMOC-4, has been synthesized by solvothermal synthesis. This MOF exhibits the same topology as MOF-253. CuCl₂ was incorporated into COMOC-4 by a post-synthetic modification (PSM). The spectroscopic absorption properties of the MOF framework before and after PSM were compared with theoretical data obtained by employing molecular dynamics combined with time-dependent DFT calculations on both the as-synthesized and functionalized linker. The catalytic behavior of the resulting Cu²⁺@COMOC-4 material was evaluated in the aerobic oxidation of cyclohexene with isobutyraldehyde as a co-oxidant. In addition, the catalytic performance of Cu²⁺@COMOC-4 was compared with that of the commercially available Cu-BTC (BTC=benzene-1,3,5-tricarboxylate) MOF. Cu²⁺@COMOC-4 exhibits a good cyclohexene conversion and an excellent selectivity towards cyclohexene oxide in comparison to the Cu-based reference catalyst. Furthermore, no leaching of the active Cu sites was observed during at least four consecutive runs.

A vanadium 2,6-naphthalenedicarboxylate, V^III(OH)(O₂C–C₁₀H₆–CO₂)·H₂O, denoted as COMOC-3as (COMOC = Center for Ordered Materials, Organometallics and Catalysis, Ghent University), has been synthesized under hydrothermal conditions by means of both a solvothermal and a microwave synthesis procedure. The structure shows the topology of an aluminium 2,6-naphthalenedicarboxylate, the so-called MIL-69 (MIL = Materials of the Institute Lavoisier). After calcination at 250 °C in air, the V^III center was oxidized to V^IV with the structure of V^IVO(O₂C–C₁₀H₆–CO₂) (COMOC-3). The oxidation process was verified by cyclic voltammetry and EPR spectroscopy. The crystallinity was investigated by variable-temperature XRD. The title compound is stable against air and moisture. The catalytic performance of COMOC-3 was examined in the liquid-phase oxidation of cyclohexene. COMOC-3 exhibited similar catalytic performance to MIL-47 [VO(O₂C–C₆H₄–CO₂)]. The compound is reusable and maintains its catalytic activity through several runs.

Syntheses, characterization, and gas sorption properties of two new vanadium-based metal–organic frameworks [V₃OCl(DMF)₂(BDC)₃]·3.1DMF·10H₂O·0.1BDC (V–MIL-101 or 1) and [V₃OCl(DMF)₂(BDC–NH₂)₃]·2.8DMF·H₂O·0.1BDC–NH₂ (V–MIL-101–NH₂ or 2) (DMF = N,N′-dimethylformamide; BDC = terephthalate; BDC–NH₂ = 2-aminoterephthalate) having MIL-101 topology are presented. Compounds 1 and 2 were prepared under similar solvothermal conditions (150 °C, 24 h) in DMF by using VCl₃ and H₂BDC or H₂BDC–NH₂, respectively. Determination of lattice parameters from X-ray powder diffraction (XRPD) patterns of thermally activated compounds revealed their structural similarity with chromium-, iron-, and aluminum-based solids having two types of mesoporous cages and accessible metal sites. The phase purity of the compounds was ascertained by XRPD analysis, diffuse reflectance Fourier transform (DRIFT) spectroscopy, and elemental analysis. Thermogravimetric analyses (TGA) and temperature-dependent XRPD (TDXRPD) experiments indicate that the compounds are stable up to 320 and 240 °C, respectively, under an argon atmosphere. Removal of the guest DMF molecules by thermal activation enables the compounds to adsorb significant amounts of N₂ (690 and 555 cm³ g^–1 at p/p₀ = 1 for 1 and 2, respectively) and CO₂ (9.0 and 4.3 mmol g^–1 at 24.5 and 22.8 bar for 1 and 2, respectively).