MIL-100(Fe)-Based Composite Films for Food Packaging.

A biocompatible metal-organic framework MIL-100(Fe) loaded with the active compounds of tea tree essential oil was used to produce composite films based on κ-carrageenan and hydroxypropyl methylcellulose with the uniform distribution of the particles of this filler. The composite films featured great UV-blocking properties, good water vapor permeability, and modest antibacterial activity against both Gram-negative and Gram-positive bacteria. The use of metal-organic frameworks as containers of hydrophobic molecules of natural active compounds makes the composites made from naturally occurring hydrocolloids attractive materials for active packaging of food products.

Bis(2,6-pyrazolyl)pyridines as a New Scaffold for Coordination Polymers.

Two coordination polymers, Fe(L)(CHCOO)(CHCN)]•nCHCN and [Fe(L)AgNOBF•CHOH]•1.75nCHOH•nHO (L = 3,3'-(4-(4-cyanophenyl)pyridine-2,6-diyl)bis(1-(2,6-dichlorophenyl)-1H-pyrazol-5-olate)), were obtained via a PCET-assisted process that uses the hydroxy-pyrazolyl moiety of the ligand and the iron(II) ion as sources of proton and electron, respectively. Our attempts to produce heterometallic compounds under mild conditions of reactant diffusion resulted in the first coordination polymer of 2,6-bis(pyrazol-3-yl)pyridines to retain the core N(L)MN(L).

Synthesis, X-ray structure and magnetic properties of the apically functionalized monocapped cobalt(II) tris-pyridineoximates possessing SMM behaviour.

The title cobalt(II) pseudoclathrochelate complexes possess an intermediate trigonal prismatic-trigonal antiprismatic geometry. As follows from PPMS data, they exhibit an SMM behaviour with Orbach relaxation barriers of approximately 90 K. Paramagnetic NMR experiments confirmed a persistence of these magnetic characteristics in solution.

Parahydrogen-Induced Hyperpolarization of Unsaturated Phosphoric Acid Derivatives.

Parahydrogen-induced nuclear polarization offers a significant increase in the sensitivity of NMR spectroscopy to create new probes for medical diagnostics by magnetic resonance imaging. As precursors of the biocompatible hyperpolarized probes, unsaturated derivatives of phosphoric acid, propargyl and allyl phosphates, are proposed. The polarization transfer to H and P nuclei of the products of their hydrogenation by parahydrogen under the ALTADENA and PASADENA conditions, and by the PH-ECHO-INEPT+ pulse sequence of NMR spectroscopy, resulted in a very high signal amplification, which is among the largest for parahydrogen-induced nuclear polarization transfer to the P nucleus.

Universal Character of Breaking of Wormlike Surfactant Micelles by Additives of Different Hydrophobicity.

Wormlike surfactant micelles are widely used in various applications including fracturing technology in oil industry, template synthesis of different nanoobjects, micellar copolymerization of hydrophilic and hydrophobic monomers, and so forth. Most of those applications suggest the solubilization of different additives in the micelles. The present paper is aimed at the comparative study of the effect of the solubilization of hydrophobic (n-decane and 1-phenylhexane) and hydrophilic (N-isopropylacrylamide and acrylamide) substances on the rheological properties and structure of the micelles using several complementary techniques including rheometry, small angle neutron scattering, dynamic light scattering, and diffusion ordered NMR spectroscopy.

Selective Pathway toward Heteroleptic Spin-Crossover Iron(II) Complexes with Pyridine-Based -Donor Ligands.

A new synthetic pathway is devised to selectively produce previously elusive heteroleptic iron(II) complexes of terpyridine and ,'-disubstituted bis(pyrazol-3-yl)pyridines that stabilize the opposite spin states of the metal ion. Such a combination of the ligands in a series of the heteroleptic complexes induces the spin-crossover (SCO) not experienced by the homoleptic complexes of these ligands or shifts it to lower/higher temperatures respective to the SCO-active homoleptic complex. The midpoint temperatures of the resulting SCO span from ca.

Synthesis, crystal polymorphism and spin crossover behavior of adamantylboron-capped cobalt(II) hexachloroclathrochelate and its transformation into the CoCoCo-bis-macrobicyclic derivative.

Fast crystallization of the monoclathrochelate cobalt(II) intracomplex [Co(ClGm)(BAd)] (where ClGm is a dichloroglyoxime dianion and BAd is an adamantylboron capping group, 1), initially obtained by the direct template condensation of the corresponding chelating α-dioximate and cross-linking ligand synthons on the Co ion as a matrix, from benzene or dichloromethane afforded its structural triclinic and hexagonal polymorphs. Its prolonged recrystallization from dichloromethane under air atmosphere and sunlight irradiation unexpectedly gave the crystals of the CoCoCo-trinuclear dodecachloro-bis-clathrochelate intracomplex [[Co(ClGm)(BAd)]Co] (2), the molecule of which consists of two macrobicyclic frameworks with encapsulated low-spin (LS) Co ions, which are cross-linked by a μ-bridging Co ion as a bifunctional Lewis-acidic center. The most plausible pathway of such a 1 → 2 transformation is based on the photoinitiated radical oxidation of dichloromethane with air oxygen giving the reactive species.

Fluoride Additive as a Simple Tool to Qualitatively Improve Performance of Nickel-Catalyzed Asymmetric Michael Addition of Malonates to Nitroolefins.

Nowadays, design of the new chiral ligands for organometallic catalysts is often based on the step-by-step increase in their complexity to improve efficiency. Herein we describe that simple in situ addition of the fluoride source to the asymmetric organometallic catalyst can improve not only activity but also enantioselectivity. Bromide-nickel diimine complexes were found to catalyze asymmetric Michael addition in low yields and ee, but activation with fluoride leads to a significant improvement in catalyst performance.

Molecular Compounds in Spintronic Devices: An Intricate Marriage of Chemistry and Physics.

Spintronics, a flourishing new field of microelectronics, uses the electron spin for reading and writing information in modern computers and other spintronic devices with a low power consumption and high reliability. In a quest to increase the productivity of such devices, the use of molecular materials as a spacer layer allowed them to perform equally well or even better than conventional all-inorganic heterostructures from metals, alloys, or inorganic semiconductors. In this review, we survey various classes of chemical compounds that have already been tested for this purpose─from organic compounds and coordination complexes to organic-inorganic hybrid materials─since the creation of the first molecule-based spintronic device in 2002.

Iron(IV) complexes with tetraazaadamantane-based ligands: synthesis, structure, applications in dioxygen activation and labeling of biomolecules.

4,6,10-Trihydroxy-1,4,6,10-tetraazaadamantane (TAAD) has been shown to form a stable Fe(IV) complex having a diamantane cage structure, in which the metal center is coordinated by three oxygen atoms of the deprotonated ligand. The complex was characterized by X-ray diffraction analysis, HRMS, NMR, FT-IR, Mössbauer spectroscopy and DFT calculations, which supported the d configuration of iron. The Fe(IV)-TAAD complex showed excellent performance in dioxygen activation under mild conditions serving as a mimetic of the thiol oxidase enzyme.

Analysis of reduced paramagnetic shifts as an effective tool in NMR spectroscopy.

A recently introduced concept of reduced paramagnetic shifts (RPS) in NMR spectroscopy is applied here to a series of paramagnetic complexes with different metal ions, such as iron(II), iron(III) and cobalt(II), in different coordination environments of N-donor ligands, including a unique trigonal-prismatic geometry that is behind some record single-molecule magnet behaviours. A simple, almost visual analysis of the chemical shifts as a function of temperature, which is at the core of this approach, allows for a correct signal assignment and evaluation of the anisotropy of the magnetic susceptibility, the key indicator of a good single molecule magnet, that often cannot be done using traditional techniques rooted in quantum chemistry and NMR spectroscopy. The proposed approach thus emerged as a powerful alternative in deciphering the NMR spectra of paramagnetic compounds for applications in data processing and storage, magnetic resonance imaging and structural biology.

Room-Temperature Spin Crossover in a Solution of Iron(II) Complexes with ,'-Disubstituted Bis(pyrazol-3-yl)pyridines.

Here, we report a combined study of the effects of two chemical modifications to an ,'-disubstituted bis(pyrazol-3-yl)pyridine (3-bpp) and of different solvents on the spin-crossover (SCO) behavior in otherwise high-spin iron(II) complexes by solution NMR spectroscopy. The observed stabilization of the low-spin state by electron-withdrawing substituents in the two positions of the ligand that induce opposite electronic effects in SCO-active iron(II) complexes of isomeric bis(pyrazol-1-yl)pyridines (1-bpp) was previously hidden by NH functionalities in 3-bpp precluding the molecular design of SCO compounds with this family of ligands. With the recent SCO-assisting substituent design, the uncovered trends converged toward the first iron(II) complex of ,'-disubstituted 3-bpp to undergo an almost complete SCO centered at room temperature in a less polar solvent of a high hydrogen-bond acceptor ability.

3D-Printed Porous Magnetic Carbon Materials Derived from Metal-Organic Frameworks.

Here we report new porous carbon materials obtained by 3D printing from photopolymer compositions with zinc- and nickel-based metal-organic frameworks, ZIF-8 and Ni-BTC, followed by high-temperature pyrolysis. The pyrolyzed materials that retain the shapes of complex objects contain pores, which were produced by boiling zinc and magnetic nickel particles. The two thus provided functionalities-large specific surface area and ferromagnetism-that pave the way towards creating heterogenous catalysts that can be easily removed from reaction mixtures in industrial catalytic processes.

Unravelling of a [High Spin-Low Spin] ↔ [Low Spin-High Spin] Equilibrium in Spin-Crossover Iron(II) Dinuclear Helicates Using Paramagnetic NMR Spectroscopy.

Spin-crossover between high-spin (HS) and low-spin (LS) states of selected transition metal ions in polynuclear and polymeric compounds is behind their use as multistep switchable materials in breakthrough electronic and spintronic devices. We report the first successful attempt to observe the dynamics of a rarely found broken-symmetry spin state in binuclear complexes, which mixes the states [HS-LS] and [LS-HS] on a millisecond timescale. The slow exchange between these two states, which was identified by paramagnetic NMR spectroscopy in solutions of two spin-crossover iron(II) binuclear helicates that are amenable to molecular design, opens a path to double quantum dot cellular automata for information storage and processing.

Transformations of wormlike surfactant micelles induced by a water-soluble monomer.

Hypothesis: Wormlike surfactant micelles (WLMs) are prospective as nanoreactors for micellar copolymerization of hydrophilic and hydrophobic monomers. Hydrophilic monomers can destroy WLMs. Large size and cylindrical shape of micelles can be preserved by high salt content favoring closer packing of surfactant heads.

Revealing the Structure of Transition Metal Complexes of Formaldoxime.

Aerobic reactions of iron(III), nickel(II), and manganese(II) chlorides with formaldoxime cyclotrimer (tfoH) and 1,4,7-triazacyclononane (tacn) produce indefinitely stable complexes of general formula [M(tacn)(tfo)]Cl. Although the formation of formaldoxime complexes has been known since the end of 19th century and applied in spectrophotometric determination of d-metals (formaldoxime method), the structure of these coordination compounds remained elusive until now. According to the X-ray analysis, [M(tacn)(tfo)] cation has a distorted adamantane-like structure with the metal ion being coordinated by three oxygen atoms of deprotonated tfoH ligand.

A Synergy and Struggle of EPR, Magnetometry and NMR: A Case Study of Magnetic Interaction Parameters in a Six-Coordinate Cobalt(II) Complex.

Herein, we combine for the first time SQUID magnetometry, cw-EPR, THz-EPR, and paramagnetic NMR spectroscopies to study the magnetic properties of a high-spin cobalt(II) heteroscorpionate complex. Complementary information provided by these methods allowed precise determination of the magnetic interaction parameters, thereby removing the ambiguity inherit to single-method studies. We systematically investigate the extent to which information about the magnetic interaction parameters can be deduced from reduced data sets.

Cucurbit[7]uril-driven modulation of ligand-DNA interactions by ternary assembly.

The design of small organic molecules with a predictable and desirable DNA-binding mechanism is a topical research task for biomedicine application. Herein, we demonstrate an attractive supramolecular strategy for controlling the non-covalent ligand-DNA interaction by binding with cucurbituril as a synthetic receptor. With a combination of UV/vis, CD and NMR experiments, we demonstrate that the bis-styryl dye with two suitable binding sites can involve double stranded DNA and cucurbituril in the formation of the supramolecular triad.

Detailed electronic structure of a high-spin cobalt(ii) complex determined from NMR and THz-EPR spectroscopy.

Here we report a combined use of THz-EPR and NMR spectroscopy for obtaining a detailed electronic structure of a long-known high-spin complex, cobalt(ii) bis[tris(pyrazolyl)borate]. The lowest inter-Kramers transition was directly measured by THz-EPR spectroscopy, while the energies of higher Kramers doublets were estimated by a recently proposed NMR-based approach. Together, they produced magnetic parameters for a full model that explicitly includes spin-orbit coupling.

A Trigonal Prismatic Cobalt(II) Complex as a Single Molecule Magnet with a Reduced Contribution from Quantum Tunneling.

Herein, we report a new trigonal prismatic cobalt(II) complex that behaves as a single molecule magnet. The obtained zero-field splitting, which is also directly accessed by THz-EPR spectroscopy (-102.5 cm ), results in a large magnetization reversal barrier U of 205 cm .

Determination of Large Zero-Field Splitting in High-Spin Co(I) Clathrochelates.

Zero-field splitting (ZFS) of three high-spin Co(I) ( S = 1) clathrochelate complexes was determined by frequency-domain Fourier-transform THz-EPR (FD-FT THz-EPR). The following axial and rhombic ZFS values ( D and E, respectively) were determined: [N( n-Bu)]Co(GmCl)(BPh) (1, D/ hc = +16.43(1) cm, E/ hc = 0.

Very Large Magnetic Anisotropy of Cage Cobalt(II) Complexes with a Rigid Cholesteryl Substituent from Paramagnetic NMR Spectroscopy.

Variable-temperature NMR spectroscopy has recently emerged as a new alternative to the magnetometry methods for studying single molecule magnets. Its use is based on an accurate determination of magnetic susceptibility tensor anisotropy Δχ, which is not always achievable due to some contact contribution to NMR chemical shifts and possible conformational dynamics. Here, we applied this approach to cholesteryl-substituted cage cobalt(II) complexes featuring a very large magnetic anisotropy.

Synthesis and characterization of an Fe(i) cage complex with high stability towards strong H-acids.

The first synthesized and X-ray structurally characterized "classical" iron(i) dioximate showed an unrivaled stability towards strong acids, thus calling for a reassessment of the origins of the electrocatalytic activity of similar low-valent cobalt and iron cage complexes with electron-withdrawing ribbed substituents, shown previously to be effective electrocatalysts of the HER.

Probing Spin Crossover in a Solution by Paramagnetic NMR Spectroscopy.

Spin transitions in spin-crossover compounds are now routinely studied in the solid state by magnetometry; however, only a few methods exist for studies in solution. The currently used Evans method, which relies on NMR spectroscopy to measure the magnetic susceptibility, requires the availability of a very pure sample of the paramagnetic compound and its exact concentration. To overcome these limitations, we propose an alternative NMR-based technique for evaluating spin-state populations by only using the chemical shifts of a spin-crossover compound; those can be routinely obtained for a solution that contains unknown impurities and paramagnetic admixtures or is contaminated otherwise.

A New Series of Cobalt and Iron Clathrochelates with Perfluorinated Ribbed Substituents.

The study tackles one of the challenges in developing platinum-free molecular electrocatalysts for hydrogen evolution, which is to seek for new possibilities to ensure large turnover numbers by stabilizing electrocatalytic intermediates. These species are often much more reactive than the initial electrocatalysts, and if not properly stabilized by a suitable choice of functionalizing substituents, they have a limited long-time activity. Here, we describe new iron and cobalt(II) cage complexes (clathrochelates) that in contrast to many previously reported complexes of this type do not act as electrocatalysts for hydrogen evolution.