Kershaw Cook Laurence J, Thorp-Greenwood Flora L, Comyn Tim P, Cespedes Oscar, Chastanet Guillaume, Halcrow Malcolm A
Inorg Chem. 2015 Jul 6;54(13):6319-30.
The synthesis of 4-methyl-2,6-di(pyrazol-1-yl)pyridine (L) and four salts of [FeL2]X2 (X– = BF(4)(–), 1; X– = ClO(4)(–), 2; X– = PF(6)(–), 3; X– = CF3SO(3)(–), 4) are reported. Powder samples of 1 and 2 both exhibit abrupt, hysteretic spin-state transitions on cooling, with T(1/2)↓ = 204 and T(1/2)↑ = 209 K (1), and T(1/2)↓ = 175 and T(1/2)↑ = 193 K (2). The 18 K thermal hysteresis loop for 2 is unusually wide for a complex of this type. Single crystal structures of 2 show it to exhibit a Jahn–Teller-distorted six-coordinate geometry in its high-spin state, which would normally inhibit spin-crossover. Bulk samples of 1 and 2 are isostructural by X-ray powder diffraction, and undergo a crystallographic phase change during their spin-transitions. At temperatures below T(1/2), exposing both compounds to 10(–5) Torr pressure inside the powder diffractometer causes a reversible transformation back to the high-temperature crystal phase. Consideration of thermodynamic data implies this cannot be accompanied by a low → high spin-state change, however. Both compounds also exhibit the LIESST effect, with 2 exhibiting an unusually high T(LIESST) of 112 K. The salts 3 and 4 are respectively high-spin and low-spin between 3 and 300 K, with crystalline 3 exhibiting a more pronounced version of the same Jahn–Teller distortion.
报道了4-甲基-2,6-二(吡唑-1-基)吡啶(L)的合成以及四种[FeL₂]X₂盐(X⁻ = BF₄⁻,1;X⁻ = ClO₄⁻,2;X⁻ = PF₆⁻,3;X⁻ = CF₃SO₃⁻,4)。1和2的粉末样品在冷却时均表现出突然的、滞后的自旋态转变,T(1/2)↓ = 204 K且T(1/2)↑ = 209 K(1),以及T(1/2)↓ = 175 K且T(1/2)↑ = 193 K(2)。对于这种类型的配合物,2的18 K热滞回线异常宽。2的单晶结构表明其在高自旋态呈现出 Jahn - Teller 畸变的六配位几何结构,这通常会抑制自旋交叉。1和2的块状样品通过X射线粉末衍射是同构的,并且在其自旋转变过程中经历晶体学相变。在低于T(1/2)的温度下,将这两种化合物置于粉末衍射仪内10⁻⁵ Torr压力下会导致可逆转变回高温晶相。然而,对热力学数据的考虑表明这不可能伴随着低自旋态到高自旋态的变化。这两种化合物还表现出LIESST效应,2表现出异常高的112 K的T(LIESST)。盐3和4在3到300 K之间分别为高自旋和低自旋,结晶态的3表现出相同Jahn - Teller畸变的更明显版本。