Inductive detection of temperature-induced magnetization dynamics of molecular spin systems.

The development and technological applications of molecular spin systems require versatile experimental techniques to characterize and control their static and dynamic magnetic properties. In the latter case, bulk spectroscopic and magnetometric techniques, such as AC magnetometry and pulsed electron paramagnetic resonance, are usually employed, showing high sensitivity, wide dynamic range, and flexibility. They are based on creating a nonequilibrium state either by changing the magnetic field or by applying resonant microwave radiation. Another possible source of perturbation is a laser pulse that rapidly heats the sample. This approach has proven to be one of the most useful techniques for studying the kinetics and mechanism of chemical and biochemical reactions. Inspired by these works, we propose an inductive detection of temperature-induced magnetization dynamics as applied to the study of molecular spin systems and describe the general design and construction of a particular induction probehead, taking into account the constraints imposed by the cryostat and electromagnet. To evaluate the performance, several coordination compounds of VO2+, Co2+, and Dy3+ were investigated using low-energy pulses of a terahertz free electron laser of the Novosibirsk free electron laser facility as a heat source. All measured magnetization dynamics were qualitatively or quantitatively described using a proposed basic theoretical model and compared with the data obtained by alternating current magnetometry. Based on the results of the research, the possible scope of applications of inductive detection and its advantages and disadvantages in comparison with standard methods are discussed.

Field-Induced Slow Magnetic Relaxation in CoII Cyclopropane-1,1-dicarboxylates.

New CoII substituted malonate field-induced molecular magnets {[Rb6Co3(cpdc)6(H2O)12]∙6H2O}n (1) and [Cs2Co(cpdc)2(H2O)6]n (2) (where cpdc2- stands for cyclopropane-1,1-dicarboxylic acid dianions) were synthesized. Both compounds contain mononuclear bischelate fragments {CoII(cpdc)2(H2O)2}2- where the quasi-octahedral cobalt environment (CoO6) is complemented by water molecules in apical positions. The alkali metal atoms play the role of connectors between the bischelate fragments to form 3D and 2D polymeric structures for 1 and 2, respectively. Analysis of dc magnetic data using the parametric Griffith Hamiltonian for high-spin CoII supported by ab initio calculations revealed that both compounds have an easy axis of magnetic anisotropy. Compounds 1 and 2 exhibit slow magnetic relaxation under an external magnetic field (HDC = 1000 and 1500 Oe, respectively).

Removal of Acidic-Sulfur-Containing Components from Gasoline Fractions and Their Simulated Analogues Using Silica Gel Modified with Transition-Metal Carboxylates.

The removal of acidic sulfur-containing components [hydrogen sulfide (H2S) and alkanethiols or thiols (RSH)] from simulated mixtures and analogues of gasoline fractions with Zn(II), Cu(II), Co(II), and Ni(II) acetates, pivalates, and malonates applied on silica gel with various porosities under ultrasonic treatment in solution has been studied. The dependence of the adsorption of H2S and RSH on the surface of silica gel modified by metal complexes with organic ligands on various factors (the pore size of the silica gel, the time of ultrasonic treatment, and the nature of carboxylate complexes) is established. The best results for the removal of total sulfur from the model mixture and an analogue of the gasoline fraction were obtained using silica gel modified with zinc pivalate (96%) and cobalt pivalate (95%). A waste-free method to desulfurize fuel with zinc pivalate based on the production of practically useful ZnS is suggested.

Diastereoselective solid-state crossed photocycloaddition of olefins in a 3D Zn(ii) coordination polymer.

1,2-Bis(4-pyridyl)ethylene undergoes a photoinitiated [2+2] cross-cycloaddition reaction with allyl groups of allylmalonate in pores of a 3D metal-organic framework (MOF) [Zn2(H2O)2(Amal)2(bpe)] to produce a 3D MOF with a new topology.

Exploitation of knowledge databases in the synthesis of zinc(II) malonates with photo-sensitive and photo-insensitive N,N'-containing linkers.

Photoinitiated solid-state reactions are known to affect the physical properties of coordination polymers, such as fluorescence and sorption behaviour, and also afford extraordinary architectures (e.g. three-periodic structures with polyorganic ligands). However, the construction of novel photo-sensitive coordination polymers requires an understanding of the factors which govern the mutual disposition of reactive fragments. A series of zinc(II) malonate complexes with 1,2-bis(pyridin-4-yl)ethylene and its photo-insensitive analogues has been synthesized for the purpose of systematic analysis of their underlying nets and mutual disposition of N-donor ligands. The application of a big data-set analysis for the prediction of a variety of possible complex compositions, coordination environments and networks for a four-component system has been demonstrated for the first time. Seven of the nine compounds possess one of the highly probable topologies for their underlying nets; in addition, two novel closely related four-coordinated networks were obtained. Complexes containing 1,2-bis(pyridin-4-yl)ethylene and 1,2-bis(pyridin-4-yl)ethane form isoreticular compounds more readily than those with 4,4'-bipyridine and 1,2-bis(pyridin-4-yl)ethylene. The effects of the precursor, either zinc(II) nitrate or zinc(II) acetate, on the composition and dimensionality of the resulting architecture are discussed. For three of the four novel complexes containing 1,2-bis(pyridin-4-yl)ethylene, the single-crystal-to-single-crystal [2 + 2] cycloaddition reactions were carried out. UV irradiation of these crystals afforded either the 0D→1D or the 3D→3D transformations, with and without network changes. One of the two 3D→3D transformations was accompanied by solvent (H2O) cleavage.

Rational Synthesis and Investigation of Porous Metal-Organic Framework Materials from a Preorganized Heterometallic Carboxylate Building Block.

The tetranuclear heterometallic complex [Li2Zn2(piv)6(py)2] (1, where piv- = pivalate and py = pyridine) has been successfully employed as a presynthesized node for the construction of four porous metal-organic frameworks (MOFs) [Li2Zn2(R-bdc)3(bpy)]·solv (2-R, R-bdc2-; R = H, Br, NH2, NO2) by reaction with 4,4'-bipyridine (bpy) and terephthalate anionic linkers. The [Li2Zn2] node is retained in the products, representing a rare example of the rational step-by-step design of isoreticular MOFs based on complex heterometallic building units. The permanent porosity of the activated frameworks was confirmed by gas adsorption isotherm measurements (N2, CO2, CH4). Three compounds, 2-H, 2-Br, and 2-NH2 (but not 2-NO2), feature extensive hysteresis between the adsorption and desorption curves in the N2 isotherms at low pressures. The substituents R decorate the inner surface and also control the aperture of the channels, the volume of the micropores, and the overall surface area, thus affecting both the gas uptake and adsorption selectivity. The highest CO2 absorption at ambient conditions (105 cm3·g-1 or 21 wt % at 273 K and 1 bar for 2-NO2) is above the average values for microporous MOFs. The photoluminescent properties of the prototypic 2-H as well as the corresponding host-guest compounds with various aromatic molecules (benzene, toluene, anisole, and nitrobenzene) were systematically investigated. We discovered a rather complex pattern in the emission response of this material depending on the wavelength of excitation as well as the nature of the guest molecules. On the basis of the crystal structure of 2-H, a mechanism for these luminescent properties is proposed and discussed.