Properties of [Fe(Salten)Cl] Being a Precursor for Spin-Crossover Compounds in Polycrystals and Vitrified Acetonitrile Solutions

The complexes of precursor with pentadentate Salten ligand has been shown to have high-spin state (S = 5/2) in a single crystal and polycrystalline phase and contain both high-spin and low-spin (S = 1/2) fractions in vitrified acetonitrile solutions. A correlation between ESR spectrum shape and crystallinity degree has been tracked for polycrystalline phase. The majority of complexes in crystals has been found to form exchange-coupled clusters. The ESR spectra of vitrified solutions have shown several types of high-spin centers and two kinds of low-spin complexes with different g-factors. On the basis of quantum chemical calculations, conclusion was drawn for the most likely structural form of the precursor in single crystal and polycrystalline samples and possible supramolecular associates in frozen solutions.     

Lability of spin state of Fe(III) complexes with tetradentate Schiff’s bases

[FeLX₂]Y [L = N,N'-ethylenebis(salicylimine) (salen), N,N'-ethylenebis(acetylacetonylimine) (acen), or N,N'-ethylenebis(3-methyloxysalicylimine) (vanen); X = imidazole or N-methylimidazole; Y = BF₄, ClO₄, or BPh₄] compounds have been prepared and studied by means of EPR and magnetic susceptibility measurements at 5–300 K. It has been shown that the different electron-donating properties of acen and salen planar ligands result in different spin states of Fe(III) ions. Intermolecular π-interactions of the outer-sphere BPh₄ ion affect the complexes spin state as well.     

Study of liquid-crystalline copper(II) β-enaminoketonates by EPR

The structure of the chelate unit and magnetic properties of the homologous series of liquid-crystalline bis{1-[4-(4-alkoxybenzoyloxy)phenyl]-3-amyl-1-aminoprop-1-en-3-onate)copper(II) complexes was studied by EPR. The direction of the orientation of liquid crystal molecules in an external magnetic field in the mesophase state was determined. The complexes have a square-planar structure of the chelate unit determining their mesomorphic properties.     

EPR Features of Spin-Crossover in Tris(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dialkyl-Dithiocarbamato)Iron(III)

The temperature dependence of electron paramagnetic resonance (EPR) spectra of a series of dithiocarbamates Fe(RR′dtc)₃ was studied in the temperature range from 5 to 300 K. A small part of solvated complexes serving as spin probes in the EPR-silent matrix enabled the observation of EPR of the Fe(III) ion in the whole temperature range. The spin transition was revealed in the reduction of the integral intensity of the signal from the high-spin complexes and in the non-monotonous change of the line width with temperature decrease due to the effect of the low-spin complexes with short spin–lattice relaxation times. Below ca. 60 K, the ferromagnetic ordering of the magnetic moments in low-spin particles (“domains”) arising at the spin transition was observed.     

Thermo- and photoinduced properties of the Fe(III) complexes with the pentadentate ligand according to the EPR data

Compounds [Fe(Salten)L]BPh₄ (Salten = N,N-bis[(2-oxyphenyl)methylene]-4-azaheptane-1,7-diamine; L = Him (I) and Pic (II)) were studied by the EPR method in the temperature range from 5 to 300 K. The thermoinduced spin transition is observed in compound II. Its thermodynamic parameters and parameters of the ground electronic low-spin state were determined. The effect of decreasing the intensity of the stationary EPR signal upon laser pulse irradiation at λ = 532 nm was observed in the studied samples.     

Uniform convergence for the incompressible limit of a tumor growth model

We study a model introduced by Perthame and Vauchelet [19] that describes the growth of a tumor governed by Brinkman's Law, which takes into account friction between the tumor cells. We adopt the viscosity solution approach to establish an optimal uniform convergence result of the tumor density as well as the pressure in the incompressible limit. The system lacks standard maximum principle, and thus modification of the usual approach is necessary.     

Liquid crystal polymorphism of boron difluoride β-diketonates

Boron difluoride 2-alkyl-β-diketonates possessing liquid crystal polymorphism and luminescence properties were first obtained. Influence of the ligand structure on the liquid crystal properties of the boron difluoride complexes was demonstrated.     

The first mesogenic derivative of boron difluoride β-diketonate

Boron difluoride β-diketonate exhibiting liquid crystalline as well as photoluminescence properties was prepared for the first time. It is the promising material for creating supramolecular organized luminescent media.