Photoisomerization of 1,2-Di(4-pyridyl)ethylene According to NMR and UV Spectroscopy Data and Density Functional Modeling.

Photoisomerization of 1,2-di(4-pyridyl)ethylene under UV irradiation was studied by NMR and UV spectroscopy in solutions of acetone, acetonitrile and chloroform. It has been established that in the studied solutions under irradiation, geometric photoisomerization occurs: the trans-isomer transforms into the cis-isomer and then cyclization occurs. DFT modeling of the listed processes, states and UV absorption spectra of the sample in an acetonitrile solution was performed.

Effect of the chemical structure of a tetradentate equatorial ligand on the spin-crossover properties of the Fe (III) complexes chain structures: Electron paramagnetic resonance study.

The effect of the chemical structure of the equatorial ligand on the spin state of the Fe (III) ion in a series of 1-D chain complexes of the general formula [Fe(L)(tvp)]BPh4 ·nCH3 OH, where L = dianions of Schiff base containing a different number of aromatic groups: N,N'-ethylenebis (salicylaldimine) (salen) 1, N,N'-ethylenebis (acetylacetone)2,2'-imine (acen) 2, N,N'-ethylenebis (benzoylacetylacetone)2,2'-imine (bzacen) 3, and tvp = 1,2-di(4-pyridyl)ethylene, was studied by ultraviolet-visible (UV-vis) and electron paramagnetic resonance (EPR) methods. The values of exchange interactions, thermodynamic parameters of spin-crossover, and electronic structure features of the Fe (III) complexes were estimated from the EPR data. The substitution of a fragment of the equatorial ligand L in the series salen-acen-bzacen changes the local symmetry of the complex in the 1-D chain, thereby affecting the spin variable properties.

Spin crossover properties of Fe(III) complexes in [Fe (bzacen)(tvp)]BPh4 ·nSolv chain structures: EPR study.

Two types of Fe(III) polynuclear iron(III) 1D-chain coordination compounds of the general formula [Fe (L)(tvp)]BPh4 nSolv, where L = dianion of N,N'-ethylenebis (benzoylacetylacetone)2,2'-imine (bzacen), tvp = 1,2-di(4-pyridyl)ethylene were synthesized and studied by the electron paramagnetic resonance (EPR) and magnetic susceptibility methods in the temperature range (100-300) К. Two types of spin-variable complexes are formed depending on the time of precipitation of the complexes from the same solution leading to differently solvated species. They have different characteristics of the local ligand field and the spin transition behavior. The thermodynamic parameters of spin transitions were determined from the temperature dependence of the EPR signals integral intensity. The energy levels splitting values obtained by analyzing g-factors of low-spin Fe(III) centers evidenced not only on the crucial role of low-symmetry distortions on the principal possibility of spin-crossover processes, but also on the temperature peculiarities of spin transitions.