Relevance of supramolecular interactions, texture and lattice occupancy in the designer iron(II) spin crossover complexes |
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Authors: | Anil D. Naik,Kai Muffler,Volker Schü nemann |
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Affiliation: | a Unité de Chimie des Matériaux Inorganiques et Organiques, Département de Chimie, Université Catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve, Belgium b Unité de Chimie Structurale et des Mécanismes Réactionnels, Département de Chimie, Université Catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve, Belgium c Technische Universität Kaiserslautern, Fachbereich Physik, Erwin-Schrödinger-Str. 56, 67663 Kaiserslautern, Germany |
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Abstract: | New FeII 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 T1/2=175 K and T1/2=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. |
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Keywords: | Spin crossover Crystal engineering Supramolecular chemistry DFT FeII mononuclear complexes Mö ssbauer spectroscopy |
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