Studies on Nickel(II) Complexes with Amide‐Based Ligands: Syntheses, Structures, Electrochemistry and Oxidation Chemistry

Abstract

The present work discusses the nickel chemistry in a set of amide-based open-chain ligands with subtle differences in the backbone or terminal amine substituents. The ligands coordinate to the Ni 2+ ion through the N amide and N amine atoms maintaining a square-planar geometry. Absorption spectra and NMR studies reveal that the solid-state square-planar geometry is retained in solution. The electrochemical results suggest that the Ni III /Ni II redox couple primarily depends on the N 4 donors, which is composed of two N amide and two N amine atoms and not on the peripheral substituents. All four ligands with variable backbone and substituents are equally

The Effect of Ligand Architecture on the Structure and Properties of Nickel and Copper Complexes of Amide‐Based Macrocycles

“…[14,15] Chemical oxidation of solutions containing the respective Ni complexes generated green to greenish-brown species, as observed electrochemically. A brown-colored species was generated in a similar fashion in the case of copper complexes.…”

“…Furthermore, the bathochromic shift in the ν C=O stretching frequency observed for all complexes with respect to the free ligand further confirms that the deprotonated N amide group is involved in coordination. [14][15][16] Different shifts were noticed in the position of the ν C=O stretches for the nickel (55 cm -1 ) and copper complexes (70 cm -1 ) with respect to the free ligand. This difference indicates different degrees of delocalization of the excess electron density on the deprotonated N amide atom into the NCO fragment for these complexes.…”

“…In this regard, an investigation to assess the possible role of non-innocent ligands derived from o-phenylenediamine in the stabilization of the high-valent nickel complexes has been initiated by us recently. [14,15] Our goal is to understand the factors that contribute towards the stability of metal ions in high oxidation states where both the metal center and the ligand can serve as electron reservoirs. The present study forms the basis of our earlier work on the coordination chemistry and redox investigation of nickel ions with amide-based macrocyclic ligands [14] and their open-chain analogues [15] (Scheme 1).…”

“…[14,15] Our goal is to understand the factors that contribute towards the stability of metal ions in high oxidation states where both the metal center and the ligand can serve as electron reservoirs. The present study forms the basis of our earlier work on the coordination chemistry and redox investigation of nickel ions with amide-based macrocyclic ligands [14] and their open-chain analogues [15] (Scheme 1). These macrocyclic ligands and their open-chain analogues have been shown to stabilize +2 as well as +3 (transiently) oxidation states of the nickel ion in a squareplanar geometry.…”

Synthesis, Structures, and Heterogeneous Catalytic Applications of {Co3+–Eu3+} and {Co3+–Tb3+} Heterodimetallic Coordination Polymers

“…[37][38][39][40][41] The ligand H 2 L 1 and complex Na[Co(L 1 ) 2 ] (1) were synthesized according to our earlier reports. [7,8] …”