Tris(5-methylpyrazolyl)methane: Synthesis and Properties of Its Iron(II) Complex

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• 作者：Margaret A. Goodman ; Alexander Y. Nazarenko ; Barbara J. Casavant ; Zhanjie Li ; William W. Brennessel ; Michael J. DeMarco ; Gen Long ; M. Scott Goodman
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：January 16, 2012
• 年：2012
• 卷：51
• 期：2
• 页码：1084-1093
• 全文大小：398K
• 年卷期：v.51,no.2(January 16, 2012)
• ISSN：1520-510X

文摘

The new ligand, tris(5-methylpyrazolyl)methane (1), has been prepared by the reaction of n-butyl lithium with tris(pyrazolyl)methane followed by trimethylation of the tetralithiated species with methyl iodide. The BF₄^{鈥?/sup>, ClO₄鈥?/sup>, and BPh₃CN鈥?/sup> salts of the Fe(II) complex of this ligand were also synthesized. The X-ray crystal structure of the BF₄鈥?/sup> complex (2) at 100 K had Fe鈥揘 bond lengths of 1.976 脜, indicative of a low spin Fe(II) complex, while at room temperature, the structure of this complex had a Fe鈥揘 bond distance close to 2.07 脜, indicative of an admixture of approximately 50% low-spin and 50% high-spin. The solid-state structure of the complex with a ClO₄鈥?/sup> counterion was determined at 5 different temperatures between 173 and 293 K, which allowed the thermodynamic parameters for the spin-crossover to be estimated. M枚ssbauer spectra of the BF₄鈥?/sup> complex further support spin-state crossover in the solid state with a transition temperature near 300 K. UV鈥搗isible spectroscopy and 1H NMR studies of 2 show that the transition temperature in solution is closer to 400 K. No spin-crossover was observed for [Fe(1)₂]2+路2BPh₃CN鈥?/sup>. The results allow the separation of effects of groups in the 3-position from those in the 5-position on tpm ligands, and also point toward a small cooperative effect in the spin-crossover for the Fe(II) complex.}