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

Abstract

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.

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

“…Because the integral intensity of the EPR signal is proportional to the paramagnetic susceptibility, an analysis of the temperature dependence of the integral intensity can be used to estimate the changes in enthalpy and entropy that characterize the spin transition. The observed change in the integral intensity of signal A can be satisfactorily described by the equation [ 16 ] : where Δ Е is the energy interval between the ground (LS) and excited (HS) states of the system, I о is the normalizing factor, δ = hν is the interval between the levels involved in the formation of the EPR signal.…”

“…Polymeric coordination compounds [Fe(L)(tvp)]BPh 4 ·nCH 3 OH were prepared by the methods described earlier. [ 10,16 ] Elemental analysis data showed the presence of solvate molecules of in obtained complex.…”

“…[Fe (bzacen)(tvp)]BPh 4 ·CH 3 OH ( 3 ) was prepared by the method. [ 16 ] The product is dark green powder. Yield: 20%.…”

“…[ 13–15 ] Therefore, in addition to the described series of compounds, we obtained a complex with L = bzacen containing both aromatic and aliphatic groups. [ 16 ] It was shown that, depending on the time of crystallization from the solution, complexes with different solvate components are formed, which affects the SCO properties. This work is a continuation of previous studies in terms of the influence of the equatorial ligand L nature on the spin properties of Fe (III) complexes with bridging 1,2‐di(4‐pyridyl)ethylene in chain structures.…”

“…This work is a continuation of previous studies in terms of the influence of the equatorial ligand L nature on the spin properties of Fe (III) complexes with bridging 1,2‐di(4‐pyridyl)ethylene in chain structures. [ 8,16 ] For this purpose, a number of Fe (III) complexes with SB containing different amounts of aromatic groups, L = salen, acen, and bzacen (see Figure 1), have been synthesized, characterized, and investigated by ultraviolet–visible (UV–vis) and electron paramagnetic resonance (EPR) methods. EPR spectroscopy is a valuable tool for studying Fe (III) compounds.…”