Nickel(II) complexes with tetradentate N₄ ligands: Synthesis, structure, electrochemistry and thermochromism in solution

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• 作者：Maria S. Kryatova^a ; Olga V. Makhlynets^a ; Alexander Y. Nazarenko^b ; Elena V. Rybak-Akimova^a ; ^{elena.rybak-akimova@tufts.edu}
• 关键词：Nickel(II) complex ; Aminopyridine ligand ; Crystal structure ; Thermochromism ; Electrochemistry
• 刊名：Inorganica Chimica Acta
• 出版年：2012
• 期刊代码：40_00201693
• 类别：ch
• 出版时间：30 May, 2012
• 卷：387
• 期：Complete
• 页码：74-80
• 文件大小：697 K

摘要

Complexes of nickel(II) chloride with homologous tetradentate aminopyridine ligands 1,8-bis(2-pyridyl)-3,6-dimethyl-3,6-diazaoctane (pdao) and 1,6-bis(2-pyridyl)-2,5-dimethyl-2,5-diazahexane (bpmen) were prepared in the crystalline state and characterized by elemental analysis and X-ray diffraction as [Ni(pdao)(H₂O)₂]Cl₂路H₂O (1) and [Ni(bpmen)Cl₂]路H₂O (2). In the solid state, both complexes are blue-green and contain octahedral Ni(II) with a cis-伪-coordinated tetramine. In aqueous solution, both complexes are strong electrolytes as follows from the measurements of electrical conductivity: complex 2 is hydrated and forms purple [Ni(bpmen)(H₂O)₂]²⁺(aq). Complex 1 displays thermochromic behavior in solution (it is blue-green at low temperatures and yellow at high temperatures) due to a temperature sensitive equilibrium [Ni(pdao)(H₂O)₂]²⁺(aq)  [Ni(pdao)]²⁺(aq) + 2H₂O(l), 螖H掳 = +30(1) kJ/mol and 螖S掳 = +80(3) J/mol K in 0.1 M NaClO₄(aq). Complex 1, but not 2, can be reversibly reduced to the Ni(I) species (E_1/2 = 鈭?.9 V versus SHE in aqueous solution and 鈭?.37 V versus Fc⁺/Fc in acetonitrile). The relative stabilization of nickel(I) by ligand pdao can be attributed to an optimal size of the ligand bite and to the presence of the pyridine and tertiary amine N-donors.