Anion-Solvent Dependence of Bistability in a Family of Meridional N-Donor-Ligand-Containing Iron(II) Spin Crossover Complexes
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- 作者：Ben A Leita ; Suzanne M. Neville ; Gregory J. Halder ; Boujemaa Moubaraki ; Cameron J. Kepert ; Jean-Franç ; ois Lé ; tard ; Keith S. Murray
- 刊名：Inorganic Chemistry
- 出版年：2007
- 出版时间：October 15, 2007
- 年：2007
- 卷：46
- 期：21
- 页码：8784 - 8795
- 全文大小：318K
- 年卷期：v.46,no.21(October 15, 2007)
- ISSN：1520-510X
文摘
Five mononuclear spin crossover iron(II) bis-meridional ligand complexes of the general formula [Fe(L)2](X)2·solvent,have been synthesized, where X = BF4- or ClO4-; L = 2-(1-pyridin-2-ylmethyl-1H-pyrazol-3-yl)-pyrazine (picpzpz)or 2-(3-(2-pyridyl)pyrazol-1-ylmethyl)pyridine) (picpypz); solvent = MeOH or EtOH. The magnetic and structuralconsequences of systematic variation of meridional ligand, solvent, and anion, including a desolvated species,have been investigated. The complex [Fe(picpzpz)2](BF4)2·MeOH, 1·MeOH, displays several unique propertiesincluding a two-step spin transition with a gradual higher-temperature step (1T1/2 = 197 K) and an abrupt low-temperature step with hysteresis (2T1/2 = 91/98 K) and a metastable intermediate spin state below 70 K withquench-cooling. Removal of the solvent methanol results in the loss of the abrupt step and associated hysteresis(T1/2 = 150 K). The complexes [Fe(picpzpz)2](BF4)2·EtOH (1·EtOH), [Fe(picpzpz)2](ClO4)2·MeOH (2·MeOH), [Fe(picpzpz)2](ClO4)2·EtOH (2·EtOH), and [Fe(picpypz)2](BF4)2·MeOH (3·MeOH) all show gradual one-step spintransitions with T1/2 values in the range 210-250 K. Photomagnetic LIESST measurements on 1·MeOH reveal anear-quantitative excitation of high-spin sites and a unique two-step relaxation process related to the two-stepthermal spin transition (1T(LIESST) = 49 K and 2T(LIESST) = 70 K). The structural consequences of the unusualspin transition displayed by 1·MeOH have been investigated by single-crystal X-ray diffraction structural analysesbetween 25 and 293 K. Detailed characterization of the unit cell parameter evolution vs temperature reflects boththe gradual high-temperature step and abrupt low-temperature step, including the thermal hysteresis, observedmagnetically.