Structure and magnetic properties of an iron (III) spin crossover compound: [Fe(3-OMe-salMen)2]2[Ni(mnt)2]•x CH3CN
Date Issued
2008
Date
2008
Author(s)
Wei, Ching-Yi
Abstract
A cationic Fe(III) complex, [Fe(3-OMe-salMen)2]+, forms crystals with Ni(II) complex anion [Ni(mnt)2]2- in three forms in formula of [Fe(3-OMe-salMen)2]2 [Ni(mnt)2] • xCH3CN, (3-OMe-salMen = 2-({[2-(methyl-amino)ethyl]imino} methyl)-3-methoxyphenol; mnt = maleonitriledithiolate) where x =2 is designated as form A; x = 0 for other two forms (B and C). All three crystal structures are characterized by single crystal diffraction method. A belongs to triclinic space group, Pī, with cell parameters a = 9.402(2), b = 10.476(2), c = 16.636(3) Å, α = 87.17(3), β = 77.38(3) and γ = 75.21(3) º B also belongs to triclinic space group, Pī, with cell parameters a = 10.519(2), b = 10.797(2), c = 13.698(3) Å, α = 100.16(3), β = 100.48(3) and γ = 99.80(3) º C belongs to monoclinic space group, P21/n, with cell parameters a = 9.5747(19), b = 24.916(5), c = 12.404(3) Å, α = 90, β = 102.52(3) and γ = 90 º. The cation is an octahedrally coordinated (N4O2) iron(III) complex; the anion is a square planar nickel(II) complex. Iron(III) is coordinated by two tridentate ligands, 3-OMe-salMen. According to magnetic measurement, the iron(III) (d5) in A is at the low spin state (LS, S = 1/2) in the temperature range of 5~350 K, while B and C display a gradual spin transition between high spin (HS, S = 5/2) (6A1g) and low spin state (LS, 2T2g) with T1/2 ~ 290 K and 120 K, respectively. Based on the TGA, SQUID and in-situ powder XRD results, the solvent molecule CH3CN in A can be removed by heating at temperature higher than 360 K; meanwhile the spin state of iron(III) changes from LS to HS. B can be obtained from A by removing all the solvent molecules, CH3CN, from the lattice; however the process is completely reversible and accompanied with the structure change as evidenced by the in-situ X-ray powder diffraction. Furthermore, C can be obtained from A during the solvate extraction process with an external pressure. In contrary to the reversible transformation between A and B, the transformation from A to C is irreversible, and the phase transition from B to C is not found. The crystal packing of complex A, B and C are analogously arranged by alternate layers of complex cations and anions. The cations in complex A and B form dimer like pairs via π-π interaction of the phenyl rings of the ligands. As for C, such dimer like pairs no longer exist, the packing is quite different from those of A and B. It is plausible that the different molecular packing may cause the significant shift in magnetic transition temperature.
Subjects
Iron (III)
spin crossover
magnetic property
Type
thesis
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