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تسجيل مستخدم جديدChemical Bonds and Spin State Splittings in Spin Crossover Complexes. A DFT and QTAIM Analysis
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Density functional theory (DFT) calculations have been performed for the high-spin (HS) and low-spin (LS) isomers of a series of iron(II) spin crossover complexes with nitrogen ligands. The calculated charge densities have been analyzed in the framework of the quantum theory of atoms in molecules (QTAIM). For a number of iron(II) complexes with substituted tris(pyrazolyl) ligands the energy difference between HS and LS isomers, the spin state splitting, has been decomposed into atomic contributions in order to rationalize changes of the spin state splitting due to substituent effects.
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Density functional methods have been applied to calculate the quadrupole splitting of a series of iron(II) spin crossover complexes. Experimental and calculated values are in reasonable agreement. In one case spin-orbit coupling is necessary to expla
in the very small quadrupole splitting value of 0.77 mm/s at 293 K for a high-spin isomer.
Density functional theory (DFT) provides a theoretical framework for efficient and fairly accurate calculations of the electronic structure of molecules and crystals. The main features of density functional theory are described and DFT methods are co
mpared with wavefunction-based methods like the Hartree-Fock approach. Some recent applications of DFT to spin crossover complexes are reviewed, e.g., the calculation of Mossbauer parameters, of vibrational modes and of differences of entropy, vibrational energy, and total electronic energy between high-spin and low-spin isomers.
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Nuclear inelastic scattering (NIS) spectra were recorded for the spin-crossover complexes STP and ETP (STP = [Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methylg- ethane)](ClO4)2 and ETP = [Fe(1,1,1-trisf[N-(2-pyridylmethyl)-N-methylamino]methyl
g-butane)](ClO4)2) at 30 K and at room temperature and also at ambient pressure and applied pressure (up to 2.6 GPa). Spin transition from the high-spin (HS) to the low-spin (LS) state was observed by lowering temperature and also by applying pressure at room temperature and has been assigned to the hardening of iron-bond stretching modes due to the smaller volume in the LS isomer.
Iron complexes with a suitable ligand field undergo spin-crossover (SCO), which can be induced reversibly by temperature, pressure or even light. Therefore, these compounds are highly interesting candidates for optical information storage, for displa
y devices and pressure sensors. The SCO phenomenon can be conveniently studied by spectroscopic techniques like Raman and infrared spectroscopy as well as nuclear inelastic scattering, a technique which makes use of the Mossbauer effect. This review covers new developments which have evolved during the last years like, e.g. picosecond infrared spectroscopy and thin film studies but also gives an overviewon newtechniques for the theoretical calculation of spin transition phenomena and vibrational spectroscopic data of SCO complexes.
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