Interplay of Halogen and Hydrogen Bonding in a Series of Heteroleptic iron(III) Complexes

<div>The influence of the halogen substituent on crystal packing and redox properties is investigated in a series of heteroleptic complexes [Fe(qsal-X)(dipic)]MeOH (qsal-X = 4-halogen-2-[(8-quinolylimino)methyl]phenolate; dipic = 2,6-pyridinedicarboxylate; X = F 1, Cl 2, Br 3 and I 4).</div><div>Compounds 1 and 2 exhibit triclinic symmetry (P1̅), whereas 3 and 4 crystallise in monoclinic P21/n. The crystal packing shows self-sorting of the ligands with - interactions between the qsal-X ligands and overlap of the dipic ligands to form a 1D chain, that is supported by C-H···O interactions. In 1 and 2, the cross-section of the 1D chain is square, while for 3 and 4, it is rectangular. In the former, the dipic ligands interact through C=O··· interactions, while - interactions are found in 3 and 4. Neighbouring chains are connected via - interactions involving the quinoline rings, but their relative position is driven by the preference of 1 and 2, for C-H···X interactions, whereas 3 and 4 form O···X halogen bonds. The nature and topology of the electron density of these interactions have been investigated using molecular electrostatic potential (MEP) mapping, quantum theory of atoms in molecules (QTAIM) and ‘non-covalent interactions’ (NCI) analysis. UV-Visible experiments show MLCT bands associated with the qsal-X ligands, confirming the structure is stable in solution. Electrochemical studies reveal slight tuning of the Fe3+/Fe2+ redox couple showing a linear relationship between E° and the Hammett parameter σp.</div><div><br></div>

Interplay of Halogen and Hydrogen Bonding in a Series of Heteroleptic iron(III) Complexes

<div>The influence of the halogen substituent on crystal packing and redox properties is investigated in a series of heteroleptic complexes [Fe(qsal-X)(dipic)]MeOH (qsal-X = 4-halogen-2-[(8-quinolylimino)methyl]phenolate; dipic = 2,6-pyridinedicarboxylate; X = F 1, Cl 2, Br 3 and I 4).</div><div>Compounds 1 and 2 exhibit triclinic symmetry (P1̅), whereas 3 and 4 crystallise in monoclinic P21/n. The crystal packing shows self-sorting of the ligands with - interactions between the qsal-X ligands and overlap of the dipic ligands to form a 1D chain, that is supported by C-H···O interactions. In 1 and 2, the cross-section of the 1D chain is square, while for 3 and 4, it is rectangular. In the former, the dipic ligands interact through C=O··· interactions, while - interactions are found in 3 and 4. Neighbouring chains are connected via - interactions involving the quinoline rings, but their relative position is driven by the preference of 1 and 2, for C-H···X interactions, whereas 3 and 4 form O···X halogen bonds. The nature and topology of the electron density of these interactions have been investigated using molecular electrostatic potential (MEP) mapping, quantum theory of atoms in molecules (QTAIM) and ‘non-covalent interactions’ (NCI) analysis. UV-Visible experiments show MLCT bands associated with the qsal-X ligands, confirming the structure is stable in solution. Electrochemical studies reveal slight tuning of the Fe3+/Fe2+ redox couple showing a linear relationship between E° and the Hammett parameter σp.</div><div><br></div>

All about that base: investigating the role of ligand basicity in pyridyl complexes derived from a copper-Schiff base coordination polymer

Ligand pKa and Hammett parameter are key in rationalising the formation of complexes with a soluble copper(ii) Schiff base unit.

σ-Hammett parameter: a strategy to enhance both photo- and electro-luminescence features of heteroleptic copper(i) complexes

Hammett was also right for devices. This work directly links the enhancement of both the photoluminescence properties in solid-state and the electroluminescence features in light-emitting electrochemical cells (LECs) with a rational ligand design using the σ-Hammett parameter.

β-Tetrabromo-meso-tetrakis(4′-substituted phenyl)porphyrins: synthesis and electrochemical redox properties

A series of 2,3,12,13-tetrabromo-5,10,15,20-tetrakis(4′-substituted phenyl)porphyrins, H2 T(4′-R Ph) PBr4 ( R = OCH3 , t-butyl, H and CO2CH3 ) and their metal ( Co(II) , Cu(II) , and Zn(II) ) complexes were synthesized and their electrochemical redox properties were explored. The plot of E1/2vs. the Hammett parameter (σp) of the substituents (R) follow a fairly linear relationship for the ring centered redox potentials.

Phenolic Acids Ozonation: QSAR Analysis and pH Influence on the Selectivity of Ozone

Ozone reacts selectively with ortho-, meta- and para- substituted phenolic acids in aqueous solution. Analysis of second-order rate constants for correlations reveals quantitative structure-activity relationships (QSARs). The kinetic rate constants for oxidation of these phenolic acids were correlated to Hammett-substituent-electronic constant. The values of Hammett parameter ρ varying between -2.9 and -0.3 were found for different pH conditions. The pH influence on this parameter reveals the expected change in the ozonation mechanism due to the decomposition of ozone generating hydroxyl radicals. Contrarily, hydroxyl radicals are non-selective and the substituent-electronic effects are small. This Hammett’s study reflects the progressive change in the selectivity of the oxidation system when the pH increases from 2 up to 9.

Theoretical Investigation of Organic Amines as Hole Transporting Materials: Correlation to the Hammett Parameter of the Substituent, Ionization Potential, and Reorganization Energy Level

Theoretical calculations on organic amines widely used as hole-transporting materials (HTMs) in multilayer organic light-emitting diodes have been performed. The calculated Ip and the reorganization energy for hole transport (λ+) of triphenylamine (TPA), 9-phenyl-9H-carbazole (PC), and their derivatives, are found to be related to their Hammett parameter (σ). In this study, the density functional theory (DFT) calculation is used to optimize 82 TPA and PC derivatives. Electronic structures of these compounds in the neutral and the radical-cation states are obtained based on calculations on optimized geometrical structures. The Ip and λ+ values are derived from calculated heats of formation (or total energy) of the neutral and the radical-cation states. In particular, the calculated Ips for these derivatives correlate well with the experimental data. The substitution effect for the mono-substituted TPA and PC is displayed in that the Ips of the TPA and PC derivatives with electron-donating and -withdrawing substituents are lower and higher than those of TPA and PC, respectively. For the effect of substitution position, the para-substituted TPA derivatives have higher Ip and –EHOMO than those of meta-substituted TPAs. The substitution effects in di- and tri-substituted TPAs are more pronounced than that of mono-substituted ones. According to the results, the calculated Ips shows an excellent agreement with the experimental oxidation potentials (EP/2) in these TPA derivatives. Furthermore, these calculation results can be employed to predict electro-luminescent properties for new and improved HTMs.