Tuning the Charge Transport in Nickel Salicylaldimine Polymers by the Ligand Structure

Abstract

The conductivity of the polymeric energy storage materials is the key factor limiting their performance. Conductivity of polymeric NiSalen materials, a prospective class of energy storage materials, was found to depend strongly on the length of the bridge between the nitrogen atoms of the ligand. Polymers obtained from the complexes containing C3 alkyl and hydroxyalkyl bridges showed an electrical conductivity one order of magnitude lower than those derived from more common complexes with C2 alkyl bridges. The observed difference was studied by means of cyclic voltammetry on interdigitated electrodes and operando spectroelectrochemistry, combined with density functional theory (DFT) calculations.

Harmonizing Energies: The Interplay Between a Nonplanar SalEn‐Type Molecule and a TEMPO Moiety in a New Hybrid Energy‐Storing Redox‐Conducting Polymer

“…As seen from Figure S17a,b (Supporting Information), the polymer film consists of two domains: globular coral-structure formations and thin even polymer film between them. Such polymer layer's structure can be caused by the deviation from a square planar complex structure due to the presence of a triatomic imine bridge bearing an out-of-plane −OH group, [32] which is consistent with the DFT calculations mentioned above. A similar structure was also observed for another complex with a bulky imine fragment which influenced the morphology.…”

“…This pronounced nonplanarity was observed earlier for [NiSalP(OH)En] [ 32 ] by X‐ray crystal diffraction and is in stark contrast with many well‐known quasi‐planar nickel complexes with SalEn‐type ligands, such as NiSalEn, NiSaltmEn, NiSalPhen, and their derivatives, for which the corresponding calculated angles typically do not exceed 4° or 5° (Table S1, Supporting Information). It is also worth mentioning that a significantly smaller angle of 32° reported in [ 32 ] for [NiSalP(OH)En] was obtained using a different approach, namely, as the C–Ni–C plane angle, which is less informative than the criterion used in the present study.…”

“…This pronounced nonplanarity was observed earlier for [NiSalP(OH)En] [ 32 ] by X‐ray crystal diffraction and is in stark contrast with many well‐known quasi‐planar nickel complexes with SalEn‐type ligands, such as NiSalEn, NiSaltmEn, NiSalPhen, and their derivatives, for which the corresponding calculated angles typically do not exceed 4° or 5° (Table S1, Supporting Information). It is also worth mentioning that a significantly smaller angle of 32° reported in [ 32 ] for [NiSalP(OH)En] was obtained using a different approach, namely, as the C–Ni–C plane angle, which is less informative than the criterion used in the present study. For dimers and tetramers, the geometry of MTS units is largely preserved in neutral oligomers, though the Ph/Ph angle between the rings of the same unit does increase in [MTS] 2 and [MTS] 4 , as compared to the monomer complex.…”

“…The NiMeSalP(OH)En was synthesized using the same procedure described earlier for NiSalP(OH)En. [ 32 ] Attaching TEMPO to the monomeric NiMeSalP(OH)En for the MTS formation was performed using the following procedure described in the literature for 2,3‐dihydroxybenzaldehyde ( Figure ). [ 26 ]…”

“…[ 28,29 ] The deviation of the structure of the complex from the planar one may render the theoretical capacity maximum unattainable. [ 32 ]…”