Kristof Van Hecke

Bio: Kristof Van Hecke is an academic researcher from Ghent University. The author has contributed to research in topics: Metal-organic framework & Supramolecular chemistry. The author has an hindex of 23, co-authored 164 publications receiving 2352 citations.

Synthesis, crystal structures, and luminescence properties of carboxylate based rare-earth coordination polymers.

Abstract: Rare-earth coordination polymers or lanthanide-organic frameworks with hitherto unreported crystal structures have been obtained on the basis of the "light" lanthanides Pr, Nd, Sm, and Eu in combination with terephthalic acid and using a slightly altered literature synthesis procedure. Rietveld refinement has shown that powder XRD patterns of such compounds are largely dominated by the positions of the heavy elements, pointing to isostructural networks for all four terephthalate-based materials. An in-depth luminescence study has been performed on the reported MOFs, showing rare praseodymium and samarium emission in the visible spectrum, aside from the strong europium luminescence and the near-infrared emission from both a terephthalate and 2,5-pyridinedicarboxylate based neodymium-MOF.

A series of d10 metal coordination polymers based on a flexible bis(2-methylbenzimidazole) ligand and different carboxylates: synthesis, structures, photoluminescence and catalytic properties

Abstract: To explore the influence of different aromatic polycarboxylates on the self-assembly and properties of d10 metal coordination frameworks, six coordination compounds containing a flexible bis(2-methylbenzimidazole) (pbmb) ligand, formulated as [Ag2(pbmb)(2,6-napdc)]n (1), {[Zn(pbmb)(tbta)]·H2O}n (2), {[Cd(pbmb)(tbta)]·H2O}n (3), [Zn2(pbmb)(btec)(H2O)]n (4), {[Zn2(OH)(pbmb)(bpdc)1.5]·H2O}n (5), and [Cd(pbmb)(3-npa)(H2O)]n (6), have been synthesized under hydrothermal conditions and characterized by physicochemical and spectroscopic methods as well as single-crystal X-ray diffraction analysis (2,6-H2napdc = 2,6-naphthalenedicarboxylic acid, H2tbta = tetrabromoterephthalic acid, H4btec = 1,2,4,5-benzenetetracarboxylic acid, H2bpdc = biphenyl-4,4′-dicarboxylic acid and H23-npa = 3-nitrophthalic acid). Complex 1 possesses an 8-connected 3D coordination framework with sqc3 topology based on rare tetranuclear Ag(I)-cluster secondary building units (SBUs). 2 and 3 possess 2D (4,4) grid structures. 4 shows a novel (3,4,5)-connected 2D network with the Schlafli symbol of {3·4·5}{3·42·52·6}{3·43·53·6·72}. 5 features a uninodal (4,4)-connected net containing binuclear {Zn2(OH)} SBUs and a 2-fold interpenetrating (3,6)-connected supramolecular framework with {42·6}{44·610·8}-3,6T24 topology that is formed via hydrogen bond interactions. Complex 6 is a 1D double-chain structure, which is finally extended to a 3D (4,5,5)-connected supramolecular network via hydrogen bonding interactions. Complexes 1–6 indicate high thermal stabilities and different photoluminescence behavior in the solid state. Moreover, all of these polymer materials manifest excellent photocatalytic activities for the degradation of methyl orange in the photo-Fenton-like process after 120 min (1: 99%, 2: 66%, 3: 91%, 4: 83%, 5: 91% and 6: 93%, respectively).

Four cobalt(II) coordination polymers with diverse topologies derived from flexible bis(benzimidazole) and aromatic dicarboxylic acids: syntheses, crystal structures and catalytic properties

Abstract: Four mixed ligand coordination polymers based on the flexible bis(5,6-dimethybenzimidazole) and aromatic dicarboxylic acids, namely, [Co(L1)(bpdc)]n (1), {[Co(L1)(npht)]·05H2O}n (2), [Co(L2)(bpdc)]n (3), and [Co(L3)(bpdc)(H2O)]n (4) (L1 = 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene, H2bpdc = 4,4′-biphenyldicarboxylic acid, L2 = 1,3-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene, H2npht = 3-nitrophthalic acid, L3 = 1,1′-bis(5,6-dimethylbenzimidazole)methane) have been hydrothermally synthesized and structurally characterized Polymer 1 features a 3D three-fold interpenetrating dia array with a 4-connected 66 network, while 2 exhibits a 3D noninterpenetrated 3-connected framework with a 103-ThSi2 architecture 3 and 4 have two-dimensional 3-connected (63) and 4-connected (4462) topologies, respectively Complex 4 ultimately is extended into an unusual 3D (3,5)-connected seh-3,5-P21/c supramolecular network via O–H⋯O hydrogen bonding interactions The fluorescence and catalytic properties of the complexes for the degradation of the Congo red azo dye in a Fenton-like process are reported

Rigid versus semi-rigid bis(imidazole) ligands in the assembly of two Co(ii) coordination polymers: structural variability, electrochemical properties and photocatalytic behavior

Abstract: The hydrothermal reactions of 1,2,4,5-cyclohexanetetracarboxylic acid (H4L) with CoCl2·2H2O and rigid or semi-rigid bis(imidazole) ligands were able to generate two Co(ii) coordination polymers (CPs), {[Co5(L)2(1,4-bimb)(μ3-OH)2(H2O)8]·2H2O}n (1), {[Co(L)0.5(1,4-bib)]·H2O}n (2) (1,4-bimb = 1,4-bis(imidazol-1-ylmethyl)benzene, 1,4-bib = 1,4-bis(1H-imidazol-1-yl)benzene). CPs 1 and 2 were structurally characterized by elemental analysis, IR spectroscopy, X-ray powder diffraction and single crystal X-ray diffraction. CP 1 features a 3D 3,3,4,4,5-connected framework with an unprecedented {42·8·102·12}{43·6·86}2{43}2{46}2{62·8}2 topology, which represents the first example of CPs with such a topology. CP 2 possesses a three-fold interpenetration 3D framework with mog topology. The distinct structures of the two CPs may result from diverse coordination modes of the (L)4- ligands and different structural characteristics of rigid or semi-rigid N-donor ligands. The thermal stabilities, photoluminescence properties and electrochemical behavior in the solid state for CPs 1 and 2 have been investigated. The photophysical studies indicated that CPs 1 and 2 are potential semiconductive materials. Moreover, both CPs 1 and 2 show high photocatalytic efficiency for the degradation of methylene blue (MB) under UV light irradiation and exhibit good stability and recyclability. A possible photocatalytic mechanism is speculated by introducing t-butyl alcohol (TBA) as a widely used ˙OH scavenger.

Lanthanide “Chameleon” Multistage Anti-Counterfeit Materials

Abstract: Hybrid materials displaying multistage security behavior, where a single material shows both wavelength- and temperature-dependent luminescence properties, are reported. The materials consist of mixed-lanthanide β-diketonate complexes grafted into the pores of a nanosized 2,2′-bipyridine-5,5′-dicarboxylate-acid MOF. A very specific choice of lanthanides and their ratios, as well as β-diketonate ligand, is crucial for obtaining the desired properties. The wavelength-dependent luminescence properties of the materials are very well matched with the excitation wavelengths of a standard UV lamp, and a clearly visible change in luminescence is observed in a narrow temperature range (slightly below and above room temperature), proving them to be excellent materials for use in anti-counterfeit technologies, which would be almost impossible to mimic.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Metal–organic framework-based materials: superior adsorbents for the capture of toxic and radioactive metal ions

Abstract: Highly efficient removal of metal ion pollutants, such as toxic and nuclear waste-related metal ions, remains a serious task from the biological and environmental standpoint because of their harmful effects on human health and the environment. Recently, highly porous metal–organic frameworks (MOFs), with excellent chemical stability and abundant functional groups, have represented a new addition to the area of capturing various types of hazardous metal ion pollutants. This review focuses on recent progress in reported MOFs and MOF-based composites as superior adsorbents for the efficient removal of toxic and nuclear waste-related metal ions. Aspects related to the interaction mechanisms between metal ions and MOF-based materials are systematically summarized, including macroscopic batch experiments, microscopic spectroscopy analysis, and theoretical calculations. The adsorption properties of various MOF-based materials are assessed and compared with those of other widely used adsorbents. Finally, we propose our personal insights into future research opportunities and challenges in the hope of stimulating more researchers to engage in this new field of MOF-based materials for environmental pollution management.

Catalysis and photocatalysis by metal organic frameworks

Abstract: Metal organic frameworks (MOFs) are a class of porous crystalline materials that feature a series of unique properties, such as large surface area and porosity, high content of transition metals, and possibility to be designed and modified after synthesis, that make these solids especially suitable as heterogeneous catalysts. The active sites can be coordinatively unsaturated metal ions, substituents at the organic linkers or guest species located inside the pores. The defects on the structure also create these open sites. The present review summarizes the current state of the art in the use of MOFs as solid catalysts according to the type of site, making special emphasis on the more recent strategies to increase the population of these active sites and tuning their activity, either by adapting the synthesis conditions or by post-synthetic modification. This review highlights those reports illustrating the synergy derived from the presence of more than one of these types of sites, leading to activation of a substrate by more than one site or to the simultaneous activation of different substrates by complementary sites. This synergy is frequently the main reason for the higher catalytic activity of MOFs compared to homogeneous catalysts or other alternative solid materials. Besides dark reactions, this review also summarizes the use of MOFs as photocatalysts emphasizing the uniqueness of these materials regarding adaptation of the linkers as light absorbers and metal exchange at the nodes to enhance photoinduced electron transfer, in comparison with conventional inorganic photocatalysts. This versatility and flexibility that is offered by MOFs to optimize their visible light photocatalytic activity explains the current interest in exploiting these materials for novel photocatalytic reactions, including hydrogen evolution and photocatalytic CO2 reduction.

Ionic Liquids-Based Extraction: A Promising Strategy for the Advanced Nuclear Fuel Cycle

Abstract: Ionic Liquids-Based Extraction: A Promising Strategy for theAdvanced Nuclear Fuel Cycle Xiaoqi Sun, Huimin Luo, and Sheng Dai* Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States Energy and Transportation Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37916, United States State Key Laboratory of Rare Earth Resource Utilization, Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China