4 years ago

Solution and Solid-State Study of the Spin-Crossover [FeII(R-bik)3](BF4)2 complexes [R = Me, Et, Vinyl]

Rodrigue Lescouezec, Siddhartha DE, Goeffrey Gontard, Gopalan Rajaraman, Delphine Garnier, Yanling Li, Subrata Tewary, Alexandrine Flambard, Marie-Laure Boillot, Frank Breher, Laurent Lisnard
The magnetic properties of three spin-crossover complexes, [FeII(R-bik)3](BF4)2.nH2O (1-3), based on bis-imidazolyl-ketone ligands were investigated in solution and solid-state. Their properties were compared with those of the ketone-free analogue, [FeII(bim)3](OTf)2 (4). The alkyl and vinyl R groups have weak influence on the transition temperature, T1/2, in solution while stronger differences are observed in solid-state as different intermolecular interactions are observed in 1-3. The spin-state equilibria in solution were followed by SQUID magnetometry and Evans' NMR method. Interestingly, the equilibria can also be simply and efficiently probed by following the temperature dependence of an adequately chosen 1H chemical shift. Overall these experiments give coherent results with T1/2 located between 320 and 335 K, a narrow range in comparison to the solid-state. DFT calculations allowed rationalizing the differences in the magnetic differences. The molecular orbital and spin density calculations reveal that the presence of the C=O group between the imidazolyl units in the ligands of 1-3 leads to an extended aromatic system, an effective π-acceptor effect, stabilizing a LS state and reducing the LS-HS gap in comparison to 4.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/ejic.201701013

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