Azo-containing pyridine amide ligand. A six-coordinate nickel(II) complex and its one-electron oxidized species: Structure and properties |
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Authors: | Anuj Kumar Sharma |
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Affiliation: | Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India |
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Abstract: | A new potentially tridentate ligand HL11 consisting of 2-pyridinecarboxamide unit and azo functionality has been used, in its deprotonated form, to prepare a nickel(II) complex which has been structurally characterized. The ligand L11(−) affords a bis-complex [NiII(L11)2] (1). In 1, the two L11(−) ligands bind to the NiII center in a mer configuration. The relative orientations within the pairs of pyridyl-N, deprotonated amido-N, and azo-N atoms are cis, trans, and cis, respectively. The NiIIN2(pyridyl)N′2(amide)N″2(azo) coordination environment is severely distorted from ideal octahedral geometry. The Ni-Nam (am = amide) bond lengths are the shortest and the Ni-Nazo bond lengths are the longest. Complex 1 exhibits a quasireversible NiIII/NiII redox process. Moreover, the complex displays two ligand-centered (azo group) quasireversible redox processes. Spectroscopic (absorption and EPR) properties have been studied on coulometrically-generated nickel(III) species. To understand the nature of metal-ligand bonding interactions Density Functional Theory (DFT) calculations have been performed on 1 at the B3LYP level of theory. Calculations have also been done for closely related nickel(II) complexes of deprotonated pyridine amide ligands and comparative discussion has been made using observed results. |
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Keywords: | Azo group containing pyridine amide ligand Ni(II) complex Crystal structure Redox properties Electrochemically-generated nickel(III) EPR spectra |
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