Nickel(II) complexes with tetradentate N 4 ligands: Synthesis, structure, electrochemistry and thermochromism in solution

Maria S. Kryatova, Olga Makhylnets, Alexander Y. Nazarenko, Elena V. Rybak-Akimova

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Abstract

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)(H 2O) 2]Cl 2·H 2O (1) and [Ni(bpmen)Cl 2]·H 2O (2). In the solid state, both complexes are blue-green and contain octahedral Ni(II) with a cis-α-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)(H 2O) 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)(H 2O) 2] 2+(aq) [Ni(pdao)] 2+(aq) + 2H 2O(l), ΔH° = +30(1) kJ/mol and ΔS° = +80(3) J/mol K in 0.1 M NaClO 4(aq). Complex 1, but not 2, can be reversibly reduced to the Ni(I) species (E 1/2 = -0.9 V versus SHE in aqueous solution and -1.37 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.

Original languageEnglish (US)
Pages (from-to)74-80
Number of pages7
JournalInorganica Chimica Acta
Volume387
DOIs
StatePublished - May 30 2012
Externally publishedYes

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Keywords

  • Aminopyridine ligand
  • Crystal structure
  • Electrochemistry
  • Nickel(II) complex
  • Thermochromism

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

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