Abstract
Reactions of Fe(II) with the tripodal chelating ligand 1,1,1-tris(2-pyridyl)ethoxymethane (py3C-OEt) and (NCE)− co-ligands (E = S, Se, BH3) give a series of mononuclear complexes formulated as [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1) and BH3 (2). These compounds are the first Fe(II) spin cross-over (SCO) complexes based on the tripodal ligand tris(2-pyridyl)ethoxymethane and on the versatile co-ligands (NCS)− and (NCBH3)−. The crystal structure reveals discrete monomeric isomorph structures formed by a cationic [Fe(py3C-OEt)2]2+ complex and by two equivalent anionic [Fe(py3C-OEt)(NCE)3]− complexes. In the cations the Fe(II) is facially coordinated by two py3C-OEt tripodal ligands whereas in the anion the three nitrogen atoms of the tripodal ligand are facially coordinated and the N-donor atoms of the three (NCE)− co-ligands occupy the remaining three positions to complete the distorted octahedral environment of the Fe(II) centre. The magnetic studies show the presence of gradual SCO for both complexes: A one-step transition around 205 K for 1 and a two-step transition for compound 2, centered around 245 K and 380 K.
Highlights
In the last decade, spin cross-over (SCO) complexes are undoubtedly the most studied molecular systems among switchable materials thanks to their several potential applications, in particular, for the development of new generation electronic devices such as memories, molecular sensors and displays [1,2,3,4,5,6,7,8,9,10]
We report the syntheses, structural characterization, variable temperature infrared spectroscopy and magnetic properties of the two isomorph compounds: [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1) and BH3 (2) that are the first Fe(II) spin SCO systems involving the tripodal ligand tris(2-pyridyl)ethoxymethane and (NCS)− and (NCBH3)− as versatile co-ligands
The resulting solution was treated with one equivalent of 2,2 -dipyridyl ketone leading to a white powder which was characterized as tris(pyridin-2-yl)methanol after purification with a chemical yield of 88%, significantly higher than that reported in references 34–35 (See detailed synthesis and Figures S1–S3 in SI); (ii) the second step consists of a reaction in dimethylformamide under N2 atmosphere at 0 ◦C of tris(pyridin-2-yl)ethoxymethane in the presence of sodium hydride and iodoethane, leading to a white powder which was characterized as tris(pyridin-2-yl)ethoxymethane with a chemical yield of 85% (See detailed synthesis and Figures S4–S6)
Summary
Spin cross-over (SCO) complexes are undoubtedly the most studied molecular systems among switchable materials thanks to their several potential applications, in particular, for the development of new generation electronic devices such as memories, molecular sensors and displays [1,2,3,4,5,6,7,8,9,10] These complexes can be reversibly switched from high-spin (HS) state to the low-spin (LS) state by external physical stimuli such as temperature, pressure, or light irradiation. ((aa)) SSeelelecctetedd fufunncctitoionnaalilzizeedd trtirsis(2(2-p-pyyrrididyyl)l)mmeetthhaannee (p(pyy33CCRR)) lilgigaannddss aannddeexxaammpplelessoof f trtirdideenntatatetecocoordrdininataitoionnmmooddesesoobbsesrevrvededininananioinonicic(b(b) )ananddnneueutrtarla(lc()cF) eF(eI(II)Ic)ocmomplpelxeexse.s In addition to these SCO salts based on the anionic [Fe(py3C-R)(NCS)3]− complexes (Scheme 1b), other related systems with different structural features have been investigated.
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