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 language | English (US) |
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Pages (from-to) | 74-80 |
Number of pages | 7 |
Journal | Inorganica Chimica Acta |
Volume | 387 |
DOIs | |
State | Published - May 30 2012 |
Externally published | Yes |
Keywords
- Aminopyridine ligand
- Crystal structure
- Electrochemistry
- Nickel(II) complex
- Thermochromism
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry