Abstract
Reaction of Fe(II) with the tris-(pyridin-2-yl)ethoxymethane (py3C-OEt) tripodal ligand in the presence of the pseudohalide ancillary NCSe− (E = S, Se, BH3) ligand leads to the mononuclear complex [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCSe)3]2·2CH3CN (3), which has been characterised as an isomorph of the two previously reported complexes, Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1), BH3 (2). X-ray powder diffraction of the three complexes (1–3), associated with the previously reported single crystal structures of 1–2, revealed a monomeric isomorph structure for 3, formed by the spin crossover (SCO) anionic [Fe(py3C-OEt)(NCSe)3]− complex, associated with the low spin (LS) [Fe(py3C-OEt)2]2+ cationic complex and two solvent acetonitrile molecules. In the [Fe(py3C-OEt)2]2+ complex, the metal ion environment involves two py3C-OEt tridentate ligands, while the [Fe(py3C-OEt)(NCSe)3]− anion displays a hexacoordinated environment involving three N-donor atoms of one py3C-OEt ligand and three nitrogen atoms arising from the three (NCSe)− coligands. The magnetic studies for 3 performed in the temperature range 300-5-400 K, indicated the presence of a two-step SCO transition centred around 170 and 298 K, while when the sample was heated at 400 K until its complete desolvation, the magnetic behaviour of the high temperature transition (T1/2 = 298 K) shifted to a lower temperature until the two-step behaviour merged with a gradual one-step transition at ca. 216 K.
Highlights
The spin crossover (SCO) materials are by far the most investigated molecular systems among switchable systems during the last decade due to their many possible applications for the development of new generations of electronic devices, such as displays [1,2,3,4], memory devices [4,5,6,7,8], and sensors [9,10,11,12,13,14]
(3), based on the [Fe(py3 C-OEt)2 ]2+ low spin (LS) cation and the SCO [Fe(py3 C-OEt)(NCSe)3 ]− anion, displays a reversible desolvation process that affects the SCO behaviour. This compound has been prepared as a polycrystalline powder and as single crystals using a similar protocol to that used previously for the syntheses of the two isomorphic complexes [Fe(py3 COEt)2 ][Fe(py3 C-OEt)(NCE)3 ]2 ·2CH3 CN (E = S (1), BH3 (2)) based on the two ancillary linear ligands NCS− and NCBH3 − [28]
thermogravimetric analysis (TGA) analyses performed on the single crystal samples of the three isomorphs revealed clearly that the two isomorphs 1 and 2, for which the corresponding single crystals are stable, retained their solvent molecules up to
Summary
The spin crossover (SCO) materials are by far the most investigated molecular systems among switchable systems during the last decade due to their many possible applications for the development of new generations of electronic devices, such as displays [1,2,3,4], memory devices [4,5,6,7,8], and sensors [9,10,11,12,13,14]. The SCO behaviour can be essentially observed in octahedral complexes based on metal ions allowing spin state changes between the low spin (LS) and high spin (HS) states under external stimulus, such as temperature, pressure, light irradiation, or magnetic field, those based on Fe(II) ion exhibiting d6 electronic configuration remain the most studied systems [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]. The second one consists of the trinuclear [FeII3(μ-L)6(H2O)6]6− com2 − ) [22], which displays a HS-HS-HS to HS-LS-HS transition around (Lplex roomwhich temperature involving the 4-(1,2,4-triazol-4-yl)ethanedisulfonate anion (L2−) [22], displays and a large hysteresis loop
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