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A series of pyridyl‐substituted nitronyl nitroxides was synthesized and structurally characterized. A comprehensive magnetochemical and quantum chemical study of extended raw of the nitroxides with different substituents R in the pyridine fragment was performed. It was shown, that temperature‐dependent magnetic properties are determined by the short contacts between nitroxide groups of adjacent molecules as well as between nitroxide group and methyl substituents in the pseudo axial positions of imidazoline fragments. Quantum chemistry allows to select the appropriate model of exchange cluster for analysis of experimental magnetic data and evaluation of the exchange interaction parameters. For NN–PyCl the "order‐disorder" transition was detected by means of low temperature XRD. The difference in the experimental and calculated exchange interaction energies may serve as an indicator of temperature‐induced structural rearrangements. For instance, for methyl substituted nitronyl nitroxide NN‐PyMe structural transformations and significant changes in exchange interaction energies were observed. [ABSTRACT FROM AUTHOR]

By the reaction of M(hfac)2 (M = Mn(II), Co(II), Cu(II), and Zn(II); hfac is the hexafluoroacetylacetonate anion) and ferrocenyl-substituted nitronyl nitroxide (L), we succeeded in the synthesis of stable heterospin complexes: mononuclear [Zn(hfac)2L], trinuclear {[Cu(hfac)2]3L2} and chain polymer [Mn(hfac)2L]n and [Co(hfac)2L]n. The specific steric bulkiness of the ferrocenyl substituent leads to the formation of trans-type coordination polyhedra in the [Mn(hfac)2L]n and [Co(hfac)2L]n chains. The introduction of the ferrocene substituent leads to an effective weakening of intermolecular or interchain magnetic exchange coupling. Ferrimagnetic ordering was observed for one-dimensional complexes [M(hfac)2L]n (M = Mn(II), Co(II)). [Co(hfac)2L]n exhibits features of single-chain magnet behaviour: slow relaxation of magnetization below 13 K is associated with a high coercive field (54 kOe at 2 K). [ABSTRACT FROM AUTHOR]

Bimolecular complexes [ML2(MeOH)2][ML2(EtOH)2], where M is CoII, NiII or Co II0.5 Ni II0.5 and L is a deprotonated enaminoketone 4-(3′,3,3′-trifluoro-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazolidin-1-oxyl, were found to be isolated in the solid phase from a solution containing MeOH and EtOH in the ratio 1 : 10. Their solids have a layered-polymer structure due to hydrogen bonds between the OH-groups of the coordinated ROH molecules and nitroxide groups of the neighboring [ML2(ROH)2] molecules. The peculiar crystal structures of [ML2(MeOH)2][ML2(EtOH)2] have ordered alternation of methanol- and ethanol-containing supramolecular layers. Detailed crystallochemical analysis showed that during the formation of [ML2(MeOH)2][ML2(EtOH)2] crystals, the MeOH containing layer is significantly deformed in comparison with the [ML2(MeOH)2] structure. This indicates that the ethanol-containing layer determines the crystal formation, while the {ML2(MeOH)2} layer "adjusts" to it. Magnetochemical study of the bimolecular complexes [ML2(MeOH)2][ML2(EtOH)2] revealed magnetic ordering at low temperatures. [ABSTRACT FROM AUTHOR]

Bimolecular complexes [ML2(MeOH)2][ML2(EtOH)2], where M is CoII, NiII or Co II0.5 Ni II0.5 and L is a deprotonated enaminoketone 4-(3′,3,3′-trifluoro-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazolidin-1-oxyl, were found to be isolated in the solid phase from a solution containing MeOH and EtOH in the ratio 1 : 10. Their solids have a layered-polymer structure due to hydrogen bonds between the OH-groups of the coordinated ROH molecules and nitroxide groups of the neighboring [ML2(ROH)2] molecules. The peculiar crystal structures of [ML2(MeOH)2][ML2(EtOH)2] have ordered alternation of methanol- and ethanol-containing supramolecular layers. Detailed crystallochemical analysis showed that during the formation of [ML2(MeOH)2][ML2(EtOH)2] crystals, the MeOH containing layer is significantly deformed in comparison with the [ML2(MeOH)2] structure. This indicates that the ethanol-containing layer determines the crystal formation, while the {ML2(MeOH)2} layer "adjusts" to it. Magnetochemical study of the bimolecular complexes [ML2(MeOH)2][ML2(EtOH)2] revealed magnetic ordering at low temperatures. [ABSTRACT FROM AUTHOR]

Using single crystal XRD, it was proved that the cyclocondensation of 3,4-diaminofurazan with diethyl-2-oxosuccinate gives two products belonging to different heterocyclic systems, being structural isomers -derivatives of furazano[3,4-b]pyrazin-6-one (2) and furazano[3,4-b][1,4]diazepin-7-one (6). The simultaneous formation of compounds 2 and 6 in this reaction provokes also the generation of a third solid product, an unusual co-crystal (2)0.40(6)0.60. This is a rare example of co-crystallization of two isomers, the molecules of which occupy the same position in the crystal structure, despite the differences of the heterocyclic systems. [ABSTRACT FROM AUTHOR]

Copper(II)–nitroxide based Cu(hfac)2LR compounds exhibit unusual magnetic behavior that can be induced by various stimuli. In many aspects, the magnetic phenomena observed in Cu(hfac)2LR are similar to classical spin-crossover behavior. However, these phenomena originate from polynuclear exchange-coupled spin clusters Cu2+–O˙–N< or >N–˙O–Cu2+–O˙–N<. Such peculiarities may result in additional multifunctionality of Cu(hfac)2LR compounds, making them promising materials for spintronic applications. Herein, we investigate the Cu(hfac)2LMeMe material, which demonstrates a three-step temperature-induced magnetostructural transition between high-temperature, low-temperature, and intermediate states, as revealed by magnetometry. Two main steps were resolved using variable-temperature Fourier-transform infrared and Q-band electron paramagnetic resonance (EPR) spectroscopies. The intermediate-temperature states (∼40–90 K) are characterized by the coexistence of two types of copper(II)–nitroxide clusters, corresponding to the low-temperature and high-temperature phases. High-field EPR experiments revealed the effect of partial alignment of Cu(hfac)2LMeMe microcrystals in a strong (>20 T) magnetic field. This effect was used to unveil the structural features of the low-temperature phase of Cu(hfac)2LMeMe, which were inaccessible using single-crystal X-ray diffraction (XRD) technique. In particular, high-field EPR allowed us to determine the relative direction of the Jahn–Teller axes in CuO6 and CuO4N2 units. [ABSTRACT FROM AUTHOR]

The 2-imidazoline nitroxide derivatives of cymantrene—2-(η5-cyclopentadienyl)tricarbonylmanganese(I)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (NNMn) and 2-(η5-cyclopentadienyl)tricarbonylmanganese(I)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl (INMn) were synthesized. It was shown that NNMn and INMn exhibit a sufficiently high kinetic stability both in solids and in solutions under normal conditions. Their structural characteristics, magnetic properties and electrochemical behavior are close to Re(I) analogs. This opens the prospect of using paramagnetic cymantrenes as prototypes in the design of Re(I) half-sandwiched derivatives for theranostics, where therapy is combined with diagnostics by magnetic resonance imaging due to the contrast properties of nitroxide radicals. [ABSTRACT FROM AUTHOR]

A model based on the spin-Peierls transitions in chains of exchange clusters is used to study the magnetostructural phase transitions in polymeric heterospin complexes. The intercluster elasticity of the chain is the main factor that determines the phase transitions.

Electron paramagnetic resonance (EPR) spectroscopy is used for studying the thermally induced spin transitions in a family of heterospin polymer chain complexes of [Cu.sup.2} hexafluoroacetylacetonate with two pyrazole-substituted nitronyl nitroxides. The studies have shown an efficient tool for characterizing the spin transitions and for understanding the temperature-dependent sign and value of the exchange interaction in strongly coupled spin triads.

The synthesis, X-ray crystal structure and magnetic studies of an example of organic/inorganic spin hybrid clusters extended in infinite ladder-type chain [[Cu[([C.sub.5][F.sub.6]H[O.sub.2]).sub.2]].sub.7][([C.sub.35][H.sub.35][N.sub.5][O.sub.4]).sub.2] formed by the reaction of a high spin nitronylnitroxide biradical [C.sub.35][H.sub.35][N.sub.5][O.sub.4] and bis(hexafluroacetylacetonate)copper(II) are described. The analysis has highlighted the importance of considering unexpected and complex regiospecific interactions due to the structural novelty.

The possibilities for synthesis of highly dimensional heterospin structures from Cu(hfac)2 complexes are examined with 1-alkylpyrazol-4-yl-substituted nitronyl nitroxides. 2D and 3D structures are obtained for this purpose.

The kinetic and thermodynamic properties of the regioselective addition of bifunctional hydroxylaminooxime-type HO-nucleophiles to form Pt-complexed nitriles are described. The results of the synthetic, kinetic and theoretical studies have shown that the high regioselectivity of the reactions of the 1,2-hydroxylaminooximes with ligated nitriles is both kinetically and thermodynamically controlled.