Oxygen deficiency (O-vacancy) contributes to the photoefficiency of TiO₂ semiconductors by generating electron rich active sites. In this paper, the dispersion of O-vacancies in both bulk and surface of anatase and rutile phases was computationally investigated. The results showed that the O-vacancies dispersed in single- and double-cluster forms in the anatase and rutile phases, respectively, in both bulk and surface. The distribution of the O-vacancies was (roughly) homogeneous in anatase, and heterogenous in rutile bulk. The O-vacancy formation energy, width of defect band, and charge distribution indicated the overlap of the defect states in the rutile phase and thus eased the formation of clusters. Removal of the first and the second oxygen atoms from the rutile surface took less energy than the anatase one, which resulted in a higher deficiency concentration on the rutile surface. However, these deficiencies formed one active site per unit cell of rutile. On the other hand, the first O-vacancy formed on the surface and the second one formed in the subsurface of anatase (per unit cell). Supported by previous studies, we argue that this distribution of O-vacancies in anatase (surface and subsurface) could potentially create more active sites on its surface.

New zinc(II) Schiff base complexes (Z1 and Z2) were prepared through the treatment of ONNO tetradentate Schiff base ligands (H₂L¹ and H₂L²) with zinc acetylacetonate. Elemental analysis (C, H and N) and other spectroscopic techniques such as FT-IR and ¹H NMR were used to characterize the produced ligands and their associated Zn(II) complexes. The structure of Z1 was explored by single crystal X-ray diffraction analysis. The structural investigations of Z1 demonstrate that it exists in the form of a centrosymmetric dimer in which penta coordinated Zn(II) ions are inter connected via µ-phenoxo bridges from one of the phenolic oxygen atoms of each tetradentate Schiff base ligand to the opposite zinc(II) ions. The theoretical calculations, performed by DFT using the B3LYP/Def2-TZVP level of theory, directed that the intended outcomes are in compliance with the actual consequences. The nature and types of non-covalent interactions present among the sample molecules were also investigated by using QTAIM and NCI calculations. Furthermore, antimicrobial activities of the synthesized Schiff base ligands and their respective zinc(II) complexes were also examined against two Gram-positive (Staphylococcus aureus and Bacillus cereus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria, and two fungal species (Aspergillus brasiliensis and Candida albicans). The agar well diffusion method and poisoned media technique were used for the study of biological properties of bacterial and fungi species, respectively. According to assessments of inhibitory zones, metal chelates are found to be somewhat more efficient than free ligands. Graphical Abstract

In the current work, a symmetrical tetradentate Schiff base ligand (H₂L) derived by the condensation of methoxy-salicylaldehyde with substituted phenylenediamine is used to prepare nickel (II) and palladium (II) complexes. The chemical structures of the synthesized compounds were investigated with the help of combustion analysis and spectrophotometrically using FT-IR and ¹H NMR. H₂L and its nickel (II) complex were obtained in pure crystalline form, and hence, these compounds were characterized by diffraction analysis. It was evident from single-crystal X-ray diffraction analysis (SC-XRD) that the ligand was doubly deprotonated (L⁻²) and coordinated with the Ni(II) ion via ONNO-donor sites, and a distorted square planar geometry was achieved. Interestingly, the complex also attaches a solvent molecule (DMF) through its electronegative O atom with the H atom of DMF through hydrogen bonding. The molecular structure of the synthesized compounds was further validated with the help of density functional theory (DFT) using the B3LYP/Def2-TZVP level of theory. Furthermore, the Pd(II) complex was tested for Suzuki–Miyaura cross-coupling reactions and the results showed better catalytic activity in mild conditions concerning the traditionally available catalysts. Graphical Abstract

A new ONO-tridentate Schiff base ligand (H₂L) derived by the condensation of nicotinic hydrazide with 5-chlorosalicylaldehyde has been prepared and characterized by combustion analysis (CHN), FT-IR and multinuclear (¹H and ¹³C) NMR spectroscopy. The crystalline nature and molecular structure of the ligand were confirmed by single-crystal X-ray diffraction analysis. Furthermore, the optimized structural parameters of the four possible configurations of the ligand including Z and E stereoisomers each containing two tautomeric forms (enol and keto) have also been investigated. The theoretical parameters were calculated by performing the DFT method using the B3LYP/Def2-TZVP level of theory. In addition to this, dioxomolybdenum(VI) (MoO₂L) and oxovanadium(V) (VOL) complexes with the entitled Schiff base ligand have also been prepared and characterized by different techniques. Then, the catalytic efficiencies of synthesized VOL and MoO₂L complexes were also explored for the oxidation of sulfides using 30% aqueous H₂O₂ as a source of oxygen. These homogeneous catalysts showed excellent catalytic activities in the oxidation of both aromatic and aliphatic sulfides. GRAPHICAL ABSTRACT