Abstract
A novel mononuclear iron(II) complex with a linear hexadentate N6 ligand, containing two 1,2,3-triazole moieties, [Fe(L2-3-2Ph)](AsF6)2 (1), was synthesized (L2-3-2Ph = bis[N-(1-Phenyl-1H-1,2,3-triazol-4-yl)methylidene-2-aminoethyl]-1,3-propanediamine). Variable-temperature magnetic susceptibility measurements revealed a gradual one-step spin crossover (SCO) between the high-spin (HS, S = 2) and low-spin (LS, S = 0) states above room temperature (T1/2 = 468 K). The spin transition was further confirmed by differential scanning calorimetry (DSC). A single-crystal X-ray diffraction study showed that the complex was in the LS state (S = 0) at room temperature (296 K). In the crystal lattice, a three-dimensional (3D) supramolecular network was formed by intermolecular CH⋯ and – interactions of neighboring complex cations [Fe(L2-3-2Ph)]2+. AsF6− ions were located interstitially in the 3D network of complex cations, with no solvent-accessible voids. The crystal structure at 448 K (mixture of HS and LS species) was also successfully determined thanks to the thermal stability of the solvent-free crystal.
Highlights
Spin-crossover (SCO) compounds are one of the most attractive candidates for molecule-based memory, switching, and sensing devices for the generation
KAsF6 (0.456 g, 2 mmol) in 6 mL of a mixed solution of MeOH, and H2O (2/1 by volume) was added to a solution of FeIICl2·4H2O (0.199 g, 1 mmol) in MeOH (4 mL); the resulting mixture was stirred at room temperature (RT) for 40 min
differential scanning calorimetry (DSC) measurements were performed with a Rigaku (Tokyo, Japan) Thermo plus EVO2 DSC8231 instrument over the temperature range of 273–518 K, at a sweep rate of 5 K min−1 under a nitrogen atmosphere (50 mL min−1), using aluminum hermetic pans with an empty pan as reference
Summary
Spin-crossover (SCO) compounds are one of the most attractive candidates for molecule-based memory, switching, and sensing devices for the generation. While the spin transition temperature (T1/2) is essentially related to the ligand field strength, cooperativity between SCO metal sites, through intermolecular interactions and/or bridging ligands, has a key role in controlling T1/2 as well as abruptness of spin transition and width of hysteresis. The overall gradual SCO behavior, with no hysteresis of 1, presumably reflected weak cooperativity between SCO metal sites in the lattice, while the SCO-active cations constructed the 3D supramolecular network through intermolecular CH· · · π and π–π interactions. This may be due to the packing effect with counter anions, which tightly occupy the space of the 3D network. AAddjjaacceenntt ccoommpplleexxccaattiioonnss[F[Fee(L(L2-23-3--22PPhh))]]22++aarereccoonnnneecctteedd bbyy iinntteerrmmoolleeccuullaarr CCHH·⋯· ·ππ((ggrreeeennddootttteedd lliinnee)) aanndd ππ––ππ ((bbllaacckkddootttteeddlliinnee))iinntteerraaccttiioonnss,,ffoorrmmiinnggtthhee33DDnneettwwoorrkk..CCgg11== cceennttrrooiidd ooff tthhee CC11––CC66 rriinngg ((ttrraannssppaarreenntt rreedd)) aanndd CCgg22 ==cceenntrtrooididoof fththeeCC202–0C–C2525rinrigng(tr(atnrasnpsapreanretnbtlubelu).eS)y. mSymmetmryetorpyeorapteiorantsi:o(ni)s:− (xi), y−, 3x/,2y−, 3z/, 2(ii−) xz,,−(i1i)+xy, ,−z,1(i+ii)y,−zx, ,(i−ii1) −+ yx,,3−/21–+z,y(,i3v/),2–−x,z1, (–ivy),,–−z.xH, 1a−toym, s−azn.dHAastFo6m− isonans dhaAvseFb6−eeinonoms hitatvede bfoerencloamritiytt.ed for clarity
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