title: Spin crossover in tetranuclear Fe(II) complexes, {[(tpma)Fe(μ-CN)]4}X4 (X = ClO4(-), BF4(-)).
abstract: Two Fe(II) complexes, {[(tpma)Fe(μ-CN)]4}X4 (X = ClO4(-) (1a), BF4(-) (1b); tpma = tris(2-pyridylmethyl)amine), were prepared by reacting the {Fe(tpma)}(2+) building block with (Bu4N)CN. The crystal structures of 1a and 1b feature a tetranuclear cation composed of cyanide-bridged Fe(II) ions, each capped with a tetradentate tpma ligand. The Fe4(μ-CN)4 core of the complex is strongly distorted, assuming a butterfly-like geometry. Both complexes exhibit gradual temperature-driven spin crossover (SCO) associated with the high-spin (HS) ↔ low-spin (LS) transition at two out of four metal centers. The evolution of HS and LS Fe(II) ions with temperature was followed by a combination of X-ray crystallography, magnetic measurements, and Mössbauer spectroscopy. Only the Fe(II) ions surrounded by six N atoms undergo the SCO. A comparison of the temperature-dependent SCO curves for the samples stored under solvent and the dried samples shows that the former exhibit a much more abrupt SCO. This finding was interpreted in terms of the increased structural disorder and decreased crystallinity caused by the loss of the interstitial solvent molecules in the dried samples.
authors.affiliation: Department of Chemistry and Biochemistry, Florida State University , 95 Chieftan Way, Tallahassee, Florida 32306, United States.
authors.forename: Oleksandr
authors.initials: O
authors.lastname: Hietsoi
authors.forename: Paul W
authors.initials: PW
authors.lastname: Dunk
authors.forename: Heather D
authors.initials: HD
authors.lastname: Stout
authors.forename: Alejandra
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authors.lastname: Arroyave
authors.forename: Kirill
authors.initials: K
authors.lastname: Kovnir
authors.forename: Raechel E
authors.initials: RE
authors.lastname: Irons
authors.forename: Nazira
authors.initials: N
authors.lastname: Kassenova
authors.forename: Rakhmetulla
authors.initials: R
authors.lastname: Erkasov
authors.forename: Catalina
authors.initials: C
authors.lastname: Achim
authors.forename: Michael
authors.initials: M
authors.lastname: Shatruk