[Fe(3-OMe-salMen)2]2[Ni(mnt)2]•x CH3CN鐵三價 自旋交叉錯合物之合成、結構鑑定與磁性研究

Abstract

本研究為鐵三價自旋交叉 (spin crossover) 錯合物{[Fe(3-OMe-salMen)2]2 [Ni(mnt)2] • xCH3CN}(x=0, 2)合成、結構鑑定與磁性研究之相關探討。{[Fe(3-OMe-salMen)2]2 [Ni(mnt)2] • xCH3CN}有三種不同型態 (polymorph)：A含兩個結晶溶劑分子 (x = 2)，而B和C不含任何結晶溶劑 (x = 0)。其中A的空間群屬於triclinic Pī，晶格參數為a = 9.402(2)， b = 10.476(2)， c = 16.636(3) Å，α = 87.17(3)，β = 77.38(3)，γ = 75.21(3) º；B的空間群屬於triclinic Pī， 晶格參數為a = 10.519(2)，b = 10.797(2)，c = 13.698(3) Å，α = 100.16(3)，β = 100.48(3)，γ = 99.80(3) º；C的空間群屬於monoclinic P21/n，晶格參數為a = 9.5747(19)，b = 24.916(5)，c = 12.404(3) Å，α = 90，β = 102.52(3)，γ = 90 º。正一價錯合陽離子{[Fe(3-OMe-salMen)2]+}是由兩個三牙基 (3-OMe-salMen) 的兩個氮原子和一個氧原子與中心三價鐵離子以八面體 (N4O2) 形式配位成；而負二價錯合陰離子 {[Ni(mnt)2]2-} 是兩個雙牙基 (mnt；C2N2S2) 的兩個硫原子與中心鎳離子以平面四方配位而成。 A在溫度5至350 K範圍為低自旋狀態 (low spin, S = 1/2)，而B與C呈現緩漸 (gradual) 的自旋轉換現象，自旋轉換溫度 (T1/2) 分別為290 K與120 K。依據熱重分析、磁性測量的結果發現，在溫度超過360 K時，A中結晶溶劑 (CH3CN) 可被移除，轉變為B為高自旋狀態 (high spin, S = 5/2)，且A、B間的結晶溶劑吸脫附特性與磁性性質轉變為可逆反應，並且可進一步從X光粉末繞射結果證明。此外，當A在移除結晶溶劑時施以外加壓力，A會轉變為C，且其間的轉變過程不具可逆性。 A、B與C晶體結構的陽離子層與陰離子層交錯排列情形非常相似。A與B的相鄰陽離子間藉由配位基的苯環間π-π作用力形成二聚物 (dimer)，而C的陽離子則因相鄰配位基間的近作用力 (short contact) 而形成一維鏈狀結構。由A與B的晶體堆疊相似性可以進一步確認兩者間的可逆反應是容易進行的，而C的晶體堆疊與A的差異性大，推測其間轉變的不可逆特性亦與此有關，且不同的晶體排列亦伴隨著不同之磁性性質。

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.