Unexpected Spin-Crossover and a Low-Pressure Phase Change in an Iron(II)/Dipyrazolylpyridine Complex Exhibiting a High-Spin Jahn-Teller Distortion
Unexpected Spin-Crossover and a Low-Pressure Phase Change in an Iron(II)/Dipyrazolylpyridine Complex Exhibiting a High-Spin Jahn-Teller Distortion
复制标题
DOI：
10.1021/acs.inorgchem.5b00614
复制
发表时间：
2015-07-06
影响因子：
4.6
通讯作者：
Halcrow, Malcolm A.
中科院分区：
文献类型：
--
作者：
Cook, Laurence J. Kershaw;Thorp-Greenwood, Flora L.;Halcrow, Malcolm A.
报道了4-甲基-2，6-二（吡唑-1-基）-吡啶（L）和四种[FeL 2]X-2（X- = BF 4-，1; X- = ClO 4-，2; X- = PF 6-，3; X- = CF 3SO 3-，4）盐的合成。1和2的粉末样品在冷却时都表现出突变的滞后自旋状态转变，其中T-1/2向下箭头= 204和T-1/2向上箭头= 209 K（1），以及T-1/2向下箭头= 175和T-1/2向上箭头= 193 K（2）。2的18 K热滞回线对于这种类型的复合物是异常宽的。2的单晶结构显示其在高自旋状态下表现出Jahn-Teller扭曲的六坐标几何结构，这通常会抑制自旋交叉。1和2的体样品通过X射线粉末衍射是同构的，并且在它们的自旋转变期间经历晶体学相变。在低于T-1/2的温度下，将两种化合物暴露于粉末衍射仪内的10（-5）吨压力下，会导致可逆转变回到高温晶相。然而，热力学数据的考虑意味着这不可能伴随着低->高自旋态的变化。这两种化合物也表现出LIESST效应，其中2表现出异常高的T（LIESST）112 K。盐3和4在3至300 K之间分别为高自旋和低自旋，其中晶体3表现出相同Jahn-Teller扭曲的更明显版本。
The synthesis of 4-methyl-2,6-di(pyrazol-l-yl)-pyridine (L) and four salts of [FeL2]X-2 (X- = BF4-, 1; X- = ClO4-, 2; X- = PF6-, 3; X- = CF3SO3-, 4) are reported. Powder samples of 1 and 2 both exhibit abrupt, hysteretic spin-state transitions on cooling, with T-1/2 down arrow = 204 and T-1/2 up arrow = 209 K (1), and T-1/2 down arrow, = 175 and T-1/2 up arrow = 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) Ton 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.