Diastereomeric dinickel(II) complexes with bis-octaazamacrocyclic 15-membered ligands [Ni(L1–3-L1–3)Ni] (4–6) have been prepared by oxidative dehydrogenation of nickel(II) complexes NiL1–3 (1–3) derived from 1,2- and 1,3-diketones and S-methylisothiocarbohydrazide. The compounds were...
Two 15-membered octaazamacrocyclic nickel(II) complexes are investigated by theoretical methods to shed light on their affinity forwards binding and reducing CO2. In the first complex 1[NiIIL]0, the octaazamacrocyclic ligand is grossly unsaturated (π-conjugated), while in the second 1[NiIILH]2+ one, the macrocycle is saturated with hydrogens. One and two-electron reductions are described using Mulliken population analysis, quantum theory of atoms in molecules, localized orbitals, and domain averaged fermi holes, including the characterization of the Ni-CCO2 bond and the oxidation state of the central Ni atom. It was found that in the [NiLH] complex, the central atom is reduced to Ni0 and/or NiI and is thus able to bind CO2 via a single σ bond. In addition, the two-electron reduced 3[NiL]2− species also shows an affinity forwards CO2.
The purpose of this review is to highlight how the antioxidant effectiveness (AE) of rubber additives can be quantitatively interpreted using results from quantum‐chemical calculations. The relationships between the AE of para‐phenylene diamines (PPD), evaluated through non‐isothermal differential scanning calorimetry measurements in styrene‐butadiene and polyisoprene rubber matrices, and various parameters obtained by quantum‐chemical calculations are reviewed. The N atom between both phenyl rings (A site) is more significant than the N atom between the phenyl ring and the alkyl chain (B site). The preferred formation of ketimine structures (instead of the quinonediimine ones) during dehydrogenation despite the higher stability of the NA‐centered radicals indicates a kinetic control of the antioxidant action. In most cases, the AE decreases with the strength of the NA–HA bond and increases with the chemical shifts of NA and HA. In hypothetical Cu(II) complexes, the AE rises with the affinity of NA to Cu, and the extent of electron density transfer from NA to Cu. Most deviations from linearity might be explained by steric hindrances. Reverse trends for the NA and NB chemical shifts are observed, despite the fact that similar reactions are supposed at both sites.
High-resolution X-ray diffraction experiments, theoretical calculations and atom-specific X-ray absorption experiments were used to investigate two nickel complexes, (MePh3P)2[NiII(bdtCl2)2]·2(CH3)2SO [complex (1)] and (MePh3P)[NiIII(bdtCl2)2] [complex (2)]. Combining the techniques of nickel K- and sulfur K-edge X-ray absorption spectroscopy with high-resolution X-ray charge density modeling, together with theoretical calculations, the actual oxidation states of the central Ni atoms in these two complexes are investigated. Ni ions in two complexes are clearly in different oxidation states: the Ni ion of complex (1) is formally NiII; that of complex (2) should be formally NiIII, yet it is best described as a combination of Ni2+ and Ni3+, due to the involvement of the non-innocent ligand in the Ni—L bond. A detailed description of Ni—S bond character (σ,π) is presented.
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