Search

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]

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]

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]

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.