Hibbs Wendy, van Koningsbruggen Petra J, Arif Atta M, Shum William W, Miller Joel S
Department of Chemistry, University of Utah, 315 S. 1400 E. RM Dock, Salt Lake City, Utah 84112-0850, USA.
Inorg Chem. 2003 Sep 8;42(18):5645-53. doi: 10.1021/ic034226p.
The structure and spin-crossover magnetic behavior of [Fe(II)1(6)]BF(4) (1 = isoxazole) and [Fe(II)1(6)]ClO(4) have been studied. [Fe(II)1(6)]BF(4) undergoes two reversible spin-crossover transitions at 91 and 192 K, and is the first two-step spin transition to undergo a simultaneous crystallographic phase transition, but does not exhibit thermal hysteresis. The single-crystal structure determinations at 260 [space group P3, a = 17.4387(4) A, c = 7.6847(2) A] and at 130 K [space group P1, a = 17.0901(2) A, b = 16.7481(2) A, c = 7.5413(1) A, alpha = 90.5309(6) degrees, beta = 91.5231(6) degrees, gamma = 117.8195(8) degrees ] reveal two different iron sites, Fe1 and Fe2, in a 1:2 ratio. The room-temperature magnetic moment of 5.0 mu(B) is consistent with high-spin Fe(II). A plateau in mu(T) having a moment of 3.3 mu(B) centered at 130 K suggests a mixed spin system of some high-spin and some low-spin Fe(II) molecules. On the basis of the Fe-N bond distances at the two temperatures, and the molar fraction of high-spin molecules at the transition plateau, Fe1 and Fe2 can be assigned to the 91 and 192 K transitions, respectively. [Fe(II)1(6)]ClO(4) [space group P3, a = 17.5829(3) A, c = 7.8043(2) A, beta = 109.820 (3) degrees, T = 295 K] also possesses Fe1:Fe2 in a 1:2 ratio, and magnetic measurements show a single spin transition at 213 K, indicating that both Fe1 and Fe2 undergo a simultaneous spin transition. [Fe(II)1(6)]ClO(4) slowly decomposes in solutions containing acetic anhydride to form [Fe(III)(3)O(OAc)(6)1(3)][ClO(4)] [space group I2, a = 10.1547(7) A, b = 16.5497(11) A, c = 10.3205(9) A, beta = 109.820 (3) degrees, T = 200 K]. The isosceles Fe(3) unit contains two Fe.Fe distances of 3.2844(1) A and a third Fe.Fe distance of 3.2857(1) A. The magnetic data can be fit to a trinuclear model with H = -2J(S(1)xS(2) + S(2)xS(3)) - 2J(13)(S(1)xS(3)), where J = -27.1 and J(13) = -32.5 cm(-1).
对[Fe(II)1(6)][BF₄]₂（1 = 异恶唑）和[Fe(II)1(6)][ClO₄]₂的结构及自旋交叉磁行为进行了研究。[Fe(II)1(6)][BF₄]₂在91 K和192 K经历两个可逆的自旋交叉转变，是首个经历同时晶体学相变的两步自旋转变，但不表现出热滞现象。在260 K[空间群P3，a = 17.4387(4) Å，c = 7.6847(2) Å]和130 K[空间群P1，a = 17.0901(2) Å，b = 16.7481(2) Å，c = 7.5413(1) Å，α = 90.5309(6)°，β = 91.5231(6)°，γ = 117.8195(8)°]进行的单晶结构测定揭示了两种不同的铁位点，Fe1和Fe2，比例为1:2。室温下5.0 μB的磁矩与高自旋Fe(II)一致。在130 K处μ(T)出现一个以3.3 μB为中心的平台，表明存在一些高自旋和一些低自旋Fe(II)分子的混合自旋体系。基于两个温度下的Fe-N键距离以及转变平台处高自旋分子的摩尔分数，Fe1和Fe2可分别对应91 K和192 K的转变。[Fe(II)1(6)][ClO₄]₂[空间群P3，a = 17.5829(3) Å，c = 7.8043(2) Å，β = 109.820 (3)°，T = 295 K]也具有1:2比例中的Fe1:Fe2，磁测量显示在213 K有单一自旋转变，表明Fe1和Fe2同时发生自旋转变。[Fe(II)1(6)][ClO₄]₂在含有乙酸酐的溶液中缓慢分解形成[Fe(III)₃O(OAc)₆1₃][ClO₄][空间群I2，a = 10.1547(7) Å，b = 16.5497(11) Å，c = 10.3205(9) Å，β = 109.820 (3)°，T = 200 K]。等腰Fe₃单元包含两个3.2844(1) Å的Fe.Fe距离和第三个3.2857(1) Å的Fe.Fe距离。磁数据可拟合到一个三核模型H = -2J(S₁xS₂ + S₂xS₃) - 2J₁₃(S₁xS₃)，其中J = -27.1且J₁₃ = -32.5 cm⁻¹。
