Krzysztof Kruczała

Coordination polymers based on octacyanometalates(IV,V)(M = Mo, W) and aliphatic polyamine copper(II) tectons with [N3] donor atom sets

The cyano-bridged [CuII(tetrenH2)]2[WIV(CN)8]2·5H2O (tetren = tetraethylenepentaamine) (1), [CuII(tetrenH2)][CuII(tetrenH)][WV(CN)8][WIV(CN)8]·2.5H2O (2), [CuII(dien)]2[WIV(CN)8]·4H2O (dien = diethylenetriamine) (3) and its isomorphous molybdenum(IV) analogue (4) have been prepared and structurally characterised. 1 and 2 are built from the W2Cu2(μ-CN)4 squares extended into 1-D structure by cyano-bridges. 2-D 3 and 4 form a square grid pattern with tungsten atoms in the corners and –CN–Cu(dien)–NC– linkages on the edges of the squares. The magnetic behaviour of 1 and 3 indicates the presence of two isolated CuII spins S = 1/2 with a very weak antiferromagnetic coupling through the diamagnetic NC–WIV–CN bridges in the low temperatures. Assembly 2 exhibits a weak ferromagnetic interaction between CuII and WV isolated by diamagnetic [WIV(CN)8]4− spacer from another CuII centre within WV–CN–CuII–NC–WIV–CN–CuII unit and the antiferromagnetic interaction between the CuII2WVWIV units.

Heteropolyanion-doped polypyrrole as catalyst for ethyl alcohol conversion

Abstract Heteropolyanion-doped polypyrrole can serve as a catalyst for ethyl alcohol conversion. The insertion of 12-molybdophosphoric anions into the polymer matrix significantly changes the selectivity of the catalyst with respect to unsupported crystalline H 3 PMo 12 O 40 . For example catalytic conversion of ethyl alcohol carried out on polypyrrole containing 75.5 wt.% of 12-molybdophosphoric anions and standardized by heating in helium, gives acetaldehyde as the main product (51%). On the acid-base centers ethylene (45%) and small amounts of diethyl ether (3.5%) are formed. Standardization of the catalyst by heating in air leads to heavy crosslinking of the polymer with simultaneous restoration of acid molecules. As a result, the selectivity and activity of this catalyst are similar to those of unsupported H 3 PMo 12 O 40 .

Highly efficient rutile TiO2 photocatalysts with single Cu(II) and Fe(III) surface catalytic sites

Highly active photocatalysts were obtained by impregnation of nanocrystalline rutile TiO2 powders with small amounts of Cu(II) and Fe(III) ions, resulting in the enhancement of initial rates of photocatalytic degradation of 4-chlorophenol in water by factors of 7 and 4, compared to pristine rutile, respectively. Detailed structural analysis by EPR and X-ray absorption spectroscopy (EXAFS) revealed that Cu(II) and Fe(III) are present as single species on the rutile surface. The mechanism of the photoactivity enhancement was elucidated by a combination of DFT calculations and detailed experimental mechanistic studies including photoluminescence measurements, photocatalytic experiments using scavengers, OH radical detection, and photopotential transient measurements. The results demonstrate that the single Cu(II) and Fe(III) ions act as effective cocatalytic sites, enhancing the charge separation, catalyzing “dark” redox reactions at the interface, thus improving the normally very low quantum yields of UV light-activated TiO2 photocatalysts. The exact mechanism of the photoactivity enhancement differs depending on the nature of the cocatalyst. Cu(II)-decorated samples exhibit fast transfer of photogenerated electrons to Cu(II/I) sites, followed by enhanced catalysis of dioxygen reduction, resulting in improved charge separation and higher photocatalytic degradation rates. At Fe(III)-modified rutile the rate of dioxygen reduction is not improved and the photocatalytic enhancement is attributed to higher production of highly oxidizing hydroxyl radicals produced by alternative oxygen reduction pathways opened by the presence of catalytic Fe(III/II) sites. Importantly, it was demonstrated that excessive heat treatment (at 450 °C) of photocatalysts leads to loss of activity due to migration of Cu(II) and Fe(III) ions from TiO2 surface to the bulk, accompanied by formation of oxygen vacancies. The demonstrated variety of mechanisms of photoactivity enhancement at single site catalyst-modified photocatalysts holds promise for developing further tailored photocatalysts for various applications.

Series of MI[Co(bpy)3][Mo(CN)8]·nH2O (MI = Li (1), K (2), Rb (3), Cs (4); n = 7−8) Exhibiting Reversible Diamagnetic to Paramagnetic Transition Coupled with Dehydration−Rehydration Process

In this paper we report the synthesis and the structural and magnetic properties of the series of ionic compounds with general formula: M(I)[Co(bpy)(3)][Mo(CN)(8)] x nH(2)O (M(I) = Li, n = 8 (1), M(I) = K, n = 8 (2), M(I) = Rb, n = 8 (3), M(I) = Cs, n = 7.5 (4)). Solids 1-4 are characterized by the optical outer-sphere metal-to-metal charge transfer (MMCT) transition from Mo(IV) center to Co(III) center in the visible region and the Co(III)Mo(IV) <==> Co(II)Mo(V) spin equilibrium strongly dominated by the Co(III)Mo(IV) form. We show a gentle thermal treatment of diamagnetic compounds 1-4 leading to the dehydrated forms 1a-4a, which reveal a significant increase of paramagnetic contribution (from 0.5 to 2% to 30-40%). The rehydration allows to recover the diamagnetic phases 1b-4b of compositions and properties similar to those of 1-4. The irradiation of the dehydrated form 2a within the MMCT band in the Superconducting Quantum Interference Device (SQUID) cavity at T = 10 K causes further increase of the Co(II)Mo(V) contribution giving the metastable phase annealed back to the 2a phase after heating above T = 290 K. The IR, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) spectroscopic data along with the magnetic data are interpreted in terms of strong modification of the Co(III)Mo(IV) <==> Co(II)Mo(V) equilibrium occurring in these systems.

Metal–metal interactions in bent cyano-bridged trinuclear octacyanomolybdate(IV)–platinum(IV) complexes

Abstract The trinuclear cyano-bridged [(CN) 7 Mo IV –CN–Pt IV (L) 4 –NC–Mo IV (CN) 7 ] 4− species [L=NH 3 ( 1 ), 1/2en ( 2 )] have been synthesized by the inner-sphere redox reaction of [Mo(CN) 8 ] 3− with Pt(II) in aqueous solution. The complexes have been characterized in aqueous solution and in the solid state as localized-to-delocalized mixed-valence species with weak-to-moderate coupling between Pt and Mo centers. The remote Mo centers in electrochemically generated [(CN) 7 Mo V –CN–Pt IV (L) 4 –NC–Mo IV (CN) 7 ] 3− are strongly coupled through trans -CN–Pt(L) 4 –NC– linkage. The ground state delocalization Mo(IV)↔Pt(IV) in the solid state results in valence-trapped Mo(IV)/Mo(V) sites on the IR and ESR timescale. The structure of Cs 2 [Pt(en) 2 Cl 2 ][(CN) 7 Mo–CN–Pt(en) 2 –NC–Mo(CN) 7 ]·10H 2 O is characterized by significant bending of CN-bridges in the Pt(1)–N–C array. The network exhibits the large Cs + cations trapped within the ‘cage’ formed by Cl, N and O atoms of [Pt(en) 2 Cl 2 ] 2+ , terminal CN ligands and water molecules, indicating a crucial role of Cs + in stabilization of the structure.

Interactions of chromium ions with starch granules in an aqueous environment.

In this study, interactions of dichromate ions with potato starch granules in highly acidic aqueous solutions and at different temperatures were investigated. It was found that the process underwent a reduction of Cr(2)O(7)(2-) to Cr(3+) accompanied by the formation of intermediate Cr(5+) ions detected by electron paramagnetic resonance (EPR) spectroscopy. The reactions took place after the attachment of dichromate anions to the granules and resulted in a lowering of the Cr(2)O(7)(2-) initial content in the solution. The newly formed Cr(3+) ions were both accumulated by the granules or remained in the solution. It was observed for the first time that the quantity of such ions taken by the granules from the solution was noticeably higher than that delivered by trivalent chromium salt solution. It was revealed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) that the chromium ions were not only adsorbed on the granule surface but also introduced into the granule interior and evenly distributed there. An activation energy of the reduction reaction equal to 65 kJ·mol(-1) and the optimal parameters of the process were established. The proposed mechanism could be useful for the bioremediation of industrial effluents polluted by hexavalent chromium compounds.

Safe-by-Design Ligand-Coated ZnO Nanocrystals Engineered by an Organometallic Approach: Unique Physicochemical Properties and Low Toxicity toward Lung Cells

The unique physicochemical properties and biocompatibility of zinc oxide nanocrystals (ZnO NCs) are strongly dependent on the nanocrystal/ligand interface, which is largely determined by synthetic procedures. Stable ZnO NCs coated with a densely packed shell of 2-(2-methoxyethoxy)acetate ligands, which act as miniPEG prototypes, with average core size and hydrodynamic diameter of 4-5 and about 12 nm, respectively, were prepared by an organometallic self-supporting approach, fully characterized, and used as a model system for biological studies. The ZnO NCs from the one-pot, self-supporting organometallic procedure exhibit unique physicochemical properties such as relatively high quantum yield (up to 28 %), ultralong photoluminescence decay (up to 2.1 μs), and EPR silence under standard conditions. The cytotoxicity of the resulting ZnO NCs toward normal (MRC-5) and cancer (A549) human lung cell lines was tested by MTT assay, which demonstrated that these brightly luminescent, quantum-sized ZnO NCs have a low negative impact on mammalian cell lines. These results substantiate that the self-supporting organometallic approach is a highly promising method to obtain high-quality, nontoxic, ligand-coated ZnO NCs with prospective biomedical applications.

Morphology and dispersion of nanostructured manganese–cobalt spinel on various carbon supports: the effect on the oxygen reduction reaction in alkaline media

In this work a model nanometric manganese–cobalt spinel was deposited on five selected carbon carriers (Vulcan XC-72, Printex85, multiwall carbon nanotubes (MWCNTs), mesoporous carbon CMK-1, and amorphous carbon C-am.) to examine their role in modifying the electrocatalytic properties of the supported active phase for the oxygen reduction reaction (ORR) in alkaline media. The synthesized materials were thoroughly characterized by scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), and Raman spectroscopy (RS). The results confirmed the formation of a highly crystalline nanometric manganese–cobalt spinel and allowed for assessment of an amorphous phase content in the carbon supports used. The composition of the obtained catalysts was investigated by thermogravimetric analysis (TGA) and X-ray fluorescence (XRF) measurements. The electrocatalytic properties of the supported spinels were determined by the rotating disk electrode (RDE) and the rotating ring disk electrode (RRDE) methods and compared with those of a commercial platinum catalyst (20 wt% Pt/Vulcan XC-72). STEM analysis revealed that the carbon support governs both the dispersion and the morphology of the deposited spinel. In the case of mesoporous and amorphous carbon supports, the spinel nanocrystals exhibit a polyhedral shape with almost equal abundance of the (111) and (100) facets. The shape of the spinel nanocrystals deposited on the Vulcan XC-72 and Printex85 supports is dominated by the (111) termination, whereas for the MWCNT support the (100) facet is the most abundant accompanied by the highest dispersion of the nanoparticles. Electrochemical studies of the ORR revealed that the amorphous phase fraction in the carbon support promotes 2e− reduction, leading to production of HO2−. This undesired pathway is inhibited by preferential exposition of the (100) facets. The superior performance of the MWCNT support in the 4e− reduction process results from three factors: lowest content of the amorphous component, best dispersion of the spinel active phase, and its ability to promote preferential (100) faceting of the nanocrystals.

All-natural bio-plastics using starch-betaglucan composites

Grain polysaccharides represent potential valuable raw materials for next-generation advanced and environmentally friendly plastics. Thermoplastic starch (TPS) is processed using conventional plastic technology, such as casting, extrusion, and molding. However, to adapt the starch to specific functionalities chemical modifications or blending with synthetic polymers, such as polycaprolactone are required (e.g. Mater-Bi). As an alternative, all-natural and compostable bio-plastics can be produced by blending starch with other polysaccharides. In this study, we used a maize starch (ST) and an oat β-glucan (BG) composite system to produce bio-plastic prototype films. To optimize performing conditions, we investigated the full range of ST:BG ratios for the casting (100:0, 75:25, 50:50, 25:75 and 0:100 BG). The plasticizer used was glycerol. Electron Paramagnetic Resonance (EPR), using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a spin probe, showed that the composite films with high BG content had a flexible chemical environment. They showed decreased brittleness and improved cohesiveness with high stress and strain values at the break. Wide-angle X-ray diffraction displayed a decrease in crystallinity at high BG content. Our data show that the blending of starch with other natural polysaccharides is a noteworthy path to improve the functionality of all-natural polysaccharide bio-plastics systems.

Chapter 12 ESR and ESR Imaging Methods for the Study of Oxidative Polymer Degradation

Publisher Summary Polymer degradation, which reflects changes in the properties of polymers due to chemical processes that occur as a function of a complex set of environmental conditions, is a challenging topic of great fundamental and technological importance. In recent years, analytical tools, such as microscopy, imaging, and computational techniques, have made possible the determination of structural and functional details of materials, some of which are hard to obtain by other methods. Electron spin resonance (ESR) spectroscopy, used in the direct detection or spin trapping modes, is a sensitive method for detecting polymer fragments and determining the degradation mechanism. Recent applications for the study of stability in ionomer membranes used as proton exchange membranes in fuel cells demonstrate the capability of ESR to detect details that cannot be obtained by other methods.