Similar structure observed between Cu(ii) and Ni(ii) based bis(pyridylimino)isoindole complexes, yet greatly different levels of catalytic activity.

Thin films of TiO2 and boron-nitrogen (B/N) co-doped TiO 2 on glass substrates have been prepared by a simple sol-gel dip coating route. Titanium (IV) isopropoxide, boric acid and urea have been used as titanium, boron and nitrogen sources, respectively. The films were characterized by X-ray diffraction, X-ray photo-electron spectroscopy, scanning electron microscopy, Raman spectroscopy and UV-vis spectroscopy. The TiO 2 thin films with co-doping of different B/N atomic ratios (0.27-20.89) showed better photo-catalytic degradation ability of methylene blue compared to that of bare-TiO2 under visible light. The TiO 2 film doped with the highest atomic concentration of N showed repeatedly the best photo-catalytic performance. The high activity of co-doped TiO2 thin films toward organic degradation can be related to the stronger absorption observed in the UV-vis region, red shift in adsorption edges and surface acidity induced by B/N doping. Furthermore, several atomic models for B/N doping have been used to investigate the effect of doping on electronic structure and density of states of TiO2 through ab-initio density functional theory calculations. The computational study suggested a significant narrowing of the band gap due to the formation of midgap states and the shift of Fermi-level for the interstitial N model supporting the experimental results. © 2013 Elsevier B.V

The unique redox cycle of NiII(dtc)2, where dtc– is N,N-diethyldithiocarbamate, in acetonitrile displays 2e– redox chemistry upon oxidation from NiII(dtc)2 → [NiIV(dtc)3]+ but 1e– redox chemistry upon reduction from [NiIV(dtc)3]+ → NiIII(dtc)3 → NiII(dtc)2. The underlying reasons for this cycle lie in the structural changes that occur between four-coordinate NiII(dtc)2 and six-coordinate [NiIV(dtc)3]+. Cyclic voltammetry (CV) experiments show that these 1e– and 2e– pathways can be controlled by the addition of pyridine-based ligands (L) to the electrolyte solution. Specifically, the addition of these ligands resulted in a 1e– ligand-coupled electron transfer (LCET) redox wave, which produced a mixture of pyridine-bound Ni­(III) complexes, [NiIII(dtc)2(L)]+, and [NiIII(dtc)2(L)2]+. Although the complexes could not be isolated, electron paramagnetic resonance (EPR) measurements using a chemical oxidant in the presence of 4-methoxypyridine confirmed the formation of trans-[NiIII(dtc)2(L)2]+. Density functional theory calculations were also used to support the formation of pyridine coordinated Ni­(III) complexes through structural optimization and calculation of EPR parameters. The reversibility of the LCET process was found to be dependent on both the basicity of the pyridine ligand and the scan rate of the CV experiment. For strongly basic pyridines (e.g., 4-methoxypyridine) and/or fast scan rates, high reversibility was achieved, allowing [NiIII(dtc)2(L) x ]+ to be reduced directly back to NiII(dtc)2 + xL. For weakly basic pyridines (e.g., 3-bromopyridine) and/or slow scan rates, [NiIII(dtc)2(L) x ]+ decayed irreversibly to form [NiIV(dtc)3]+. Detailed kinetics studies using CV reveal that [NiIII(dtc)2(L)]+ and [NiIII(dtc)2(L)2]+ decay by parallel pathways due to a small equilibrium between the two species. The rate constants for ligand dissociation ([NiIII(dtc)2(L)2]+ → [NiIII(dtc)2(L)]+ + L) along with decomposition of [NiIII(dtc)2(L)]+ and [NiIII(dtc)2(L)2]+ species were found to increase with the electron-withdrawing character of the pyridine ligand, indicating pyridine dissociation is likely the rate-limiting step for decomposition of these complexes. These studies establish a general trend for kinetically trapping 1e– intermediates along a 2e– oxidation path.

Energy storage is a vital aspect for the successful implementation of renewable energy resources on a global scale. Herein, we investigated the redox cycle of nickel(II) bis-(diethyldithiocarbamate), Ni II (dtc) 2 , for potential use as a multielectron storage catholyte in nonaqueous redox flow batteries (RFBs). Previous studies have shown that the unique redox cycle of Ni II (dtc) 2 offers 2e − chemistry upon oxidation from Ni II → Ni IV but 1e − chemistry upon reduction from Ni IV → Ni III → Ni II . Electrochemical experiments presented here show that the addition of as little as 10 mol % Zn II (ClO 4 ) 2 to the electrolyte consolidates the two 1e − reduction peaks into a single 2e − reduction where [Ni IV (dtc) 3 ] + is reduced directly to Ni II (dtc) 2 . This catalytic enhancement is believed to be due to Zn II removal of a dtc − ligand from a Ni III (dtc) 3 intermediate, resulting in more facile reduction to Ni II (dtc) 2 . The addition of Zn II also improves the 2e − oxidation, shifting the anodic peak negative and decreasing the 2e − peak separation. H-cell cycling experiments showed that 97% Coulombic efficiency and 98% charge storage efficiency was maintained for 50 cycles over 25 h using 0.1 M Zn II (ClO 4 ) 2 as the supporting electrolyte. If Zn II (ClO 4 ) 2 was replaced with TBAPF 6 in the electrolyte, the Coulombic efficiency fell to 78%. The use of Zn II to increase the reversibility of 2e − transfer is a promising result that points to the ability to use nickel dithiocarbonates for multielectron storage in RFBs.