Quantum‐chemical study of the spin transition complex [Fe(bt)2(NCS)2] (bt=2,2′‐bithiazoline)

The spin crossover compound [Fe(bt)₂(NCS)₂] has been studied by several density functionals and basis sets. In the calculation, optimized geometries of the compound in the low‐, intermediate‐, and high‐spin states, the vibrational modes and IR spectra, spin splittings energies, excited states, and UV/vis absorption spectra were obtained. © 2012 Wiley Periodicals, Inc.     

Investigation of the Spin Crossover Complex [Fe（bapbpy）（NCS）_2 ] in Its Low-spin and Highspin State by DFT/TD-DFT/BS-DFT Calculations

The spin crossover（SCO） compound [Fe（bapbpy）（NCS）2],where bapbpy contains two fused N,N-bis（2-pyridyl）amines,has been studied by DFT/TD-DFT/BS-DFT methods.Several density functionals and basis sets were used in the calculation to obtain optimized geometries of the compound in the low-（LS） and high-spin（HS） states.The vibrational modes and IR spectra,spin splitting energies,excited states and UV/Vis absorption spectra were obtained.The structural parameters of the calculated isolated complex are in good agreement with the X-ray data.We investigate three dimers of [Fe（bapbpy）（NCS）2] complex for their magnetic properties.It has been found that the complex（1,3） has ferromagnetic character while the others are antiferromagnetic in nature by using a broken symmetry approach in the DFT framework（BS-DFT） with support from the coupling constant values（J） and spin density plots.     

Structure and Electronic Configuration of an Iron(II) Complex in a LIESST State: A Pump and Probe Method

Switchable molecules : The electronic configurations of the Fe center in trans‐[Fe(tzpy)₂(NCS)₂] in low‐spin, high‐spin, and LIESST states (LIESST=light‐induced excited spin‐state trapping) were confirmed by K‐ and L‐edge X‐ray absorption and magnetic measurements. The molecular structures at 40 K before and after irradiation are superimposed in the picture, which demonstrates a single‐crystal‐to‐single‐crystal transition by irradiation.

     

Relevance of supramolecular interactions, texture and lattice occupancy in the designer iron(II) spin crossover complexes

New Fe^II complexes of formula [Fe(3-Br-phen)₂(NCS)₂]·Solvent (Solvent=0.5 CH₃OH (1), 2 CH₂Cl₂ (2), desolvation of 2 (3), 0.5 CH₃COCH₃ (4) and 0 (5)) have been synthesized. ⁵⁷Fe Mössbauer and magnetic investigation reveal unique features atypical of classic [Fe(phen)₂(NCS)₂] polymorphs. Complex 1, prepared by precipitation in MeOH, undergoes upon cooling below room temperature an incomplete and gradual thermally induced spin conversion, while 4 prepared by an extraction method remains mostly in the low-spin state. The non solvated compounds 3 and 5, display a more abrupt spin crossover on cooling around T_1/2=175 K and T_1/2=198 K, respectively. Defects/soft lattice inclusion due to different methods of material synthesis, extent of aging, reaction medium and associated solvent molecules have enormous influence on the particle size and magnetic properties of these complexes. Scanning electron micrographs helps to establish a logical relationship among methods employed for synthesis, texture of materials and their effect on magnetic properties. The crystal structure of 2 determined in the monoclinic space group P2/c (100 K) reveals a mononuclear complex consisting of a distorted FeN₆ octahedron in the low-spin state, constructed from two 3-bromo-1, 10-phenanthroline and two isothiocyanato anions in cis position. Intermolecular interactions between mononuclear units of the S?Br, S?C(H) and π-π type afford a 2D supramolecular network. DFT calculations for the single molecule 2 reveals an energy difference between high-spin and low-spin isomers of 7 kJ/mol suggesting a slight destabilization of the low-spin state compared to [Fe(phen)₂(NCS)₂]. Normal co-ordinate analysis was also carried out for 3 and compared with experimental temperature dependent Raman spectra for 5.