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Schiff base complexes of new palladium(II) and nickel(II) are prepared through the treatment of symmetrical Schiff base ligand which are derivative of 4,5-dimethyl-o-phenylenediamine with Ni(OAc)2.4H2O and Pd(OAc)2 salts. Elemental analysis, as well as spectroscopic methods like FT-IR and 1H NMR, were employed to investigate the molecular structure of the produced ligand and its associated metal complexes. The crystal structure investigation confirms that the coordination environment of the nickel in the NiL complex is tetra-coordinate occupied by ONNO sets of the coordinated ligand in slightly distorted square planar geometry. A Hirshfeld surface investigation is carried out for further exploration and understanding of the intermolecular interactions and a comparative study with some relevant crystal structures. The DFT's theoretical calculations, which used the B3LYP/Def2-TZVP level of theory, showed that the theoretical conclusions corresponded to the actual findings.

Herein, two new cobalt and manganese-based polymers named as catena‑Poly[[diaquabis(4-nitrobenzoato-κO1)cobalt(II)]-µ-pyrazine-κ2N:Nʹ] (COPNO2) and catena‑Poly[[diaquabis(4-nitrobenzoato-κO1)manganese(II)]-µ-pyrazine–κ2N:Nʹ] (MNPNO2) were synthesized. The crystal structure of COPNO2 and MNPNO2 was determined and explored by X-rays diffraction method. O H ⋯ O, C H ⋯ π, N O ⋯ π, and π ⋯ π stacking interactions were the key aspects of the crystal packing of COPNO2, whereas for MNPNO2, O H ⋯ O, C H ⋯ π, and π ⋯ π stacking interactions were the key aspects of the crystal packing. The Hirshfeld surface (HS) studies were accomplished for further investigation of the intermolecular interactions. In addition to that, density functional theory (DFT) computations for COPNO2 and MNPNO2 had been carried out at M06 functional, to obtain optimized geometries and double-check the experimental results. Moreover, DFT calculations at the M06 level manifest excellent correlation with the experimental data, which validates the clarity of cobalt and manganese-based polymers. Frontier molecular orbital (FMO) findings were explored to describe nonlinear optical (NLO) properties. The energy gap of COPNO2 was 0.81 eV, while MNPNO2 was examined as 2.16 eV. The global reactivity parameters of COPNO2 and MNPNO2 were determined from the FMO energies. The global reactivity parameters showed that COPNO2 and MNPNO2 have the more donating ability. The NLO results of MNPNO2 (βtot = 1259.17178a.u.) were observed better than COPNO2 (βtot = 34,678.44833a.u.). We propose that this synergistic (experimental-computational) study of COPNO2 and MNPNO2 may deliver new ways for its exploitation as NLO material for hi-tech applications.

A novel dioxomolybdenum Schiff base complex, [MoO2(L)(H2O)], was synthesized by the reaction of MoO2(acac)2 and an ONO donor Schiff base ligand (H2L: (E)-4-amino-N'-(3-ethoxy-2-hydroxybenzylidene)benzohydrazide) derived by the condensation of 4-aminobenzohydrazide and 3-ethoxysalicylaldehyde. The synthesized ligand and complex were characterized by various spectroscopic techniques like FT-IR, 1H NMR, 13C NMR, and elemental analysis (CHN). The structure of the complex was confirmed by single crystal X-ray diffraction analysis (SC-XRD). The geometry around the central metal ion in the complex was distorted octahedral as revealed by the data collected from diffraction studies. Theoretical calculations of the synthesized compounds, carried out by DFT using B3LYP and PBE0 levels of theory at the Def2-TZVP basis set, indicated that the calculated results are in agreement with the experimental findings. Moreover, the catalytic efficiency of the complex was investigated by oxidizing the aryl and alkyl sulfides in the presence of 30 % aqueous H2O2 in ethanol.

A new iron(III) complex has been successfully prepared by the reaction of an ONO donor Schiff base, derived by condensing isoniazid and 3-ethoxysalicylaldehyde, with Fe(acac)3. The structure of the complex was explored spectroscopically through FT-IR, UV-Vis, PXRD and by elemental composition (CHN) through combustion analysis. The structure of the complex was explored by using single crystal X-ray crystallographic studies. It was revealed from the diffraction studies that both the keto and enol tautomeric forms of the ligand are present simultaneously in the Fe(III) complex. X-ray results showed that one of the ligands, due to keto-enol tautomerization, is doubly deprotonated and coordinated to the metal center through one nitrogen and two oxygen atoms, while the other ligand behaves as a monoanionic moiety and is coordinated via phenolic oxygen, iminic nitrogen, and oxygen of the carbonyl group. Furthermore, it was also investigated by diffraction studies that the Fe(III) centre adopts a distorted octahedral geometry. HSA, QTAIM, MEP, and NCI calculations were performed to explore the presence of different kinds of non-covalent interactions. NBO analysis was also used to show the donor-acceptor interactions between the HOMO and LUMO of the molecule. Theoretical calculations performed by DFT at the B3LYP/Def2-TZVP method show that the theoretically calculated results are in close association with the experimental outcomes.

A new dioxomolybdenum(VI) complex has been successfully prepared by the reaction of an ONO donor Schiff base, derived by condensing 4-amino-2-hydroxybenzohydrazide and 3-ethoxysalicylaldehyde, with MoO2(acac)2. The structures of synthesized products were explored spectroscopically through FT-IR, 1H & 13C NMR and by elemental composition (CHN) through combustion analysis. The tridentate Schiff base ligand is bonded to the central metal through its deprotonated enolic and phenolic oxygen atoms and by the nitrogen of the azomethine group. The interpretation of the data obtained through diffraction analysis validates the distorted octahedral geometry for the prepared metal complex. Furthermore, the catalytic potential of the molybdenum complex was explored for the selective oxidation of the aryl and alkyl sulfides to the corresponding sulfones in the presence of 30% aqueous H2O2 in ethanol. The main edge of the present catalytic work is the accomplishment of reaction in a short period of time, high percentage yield and easy work-up procedure.

A rapid and efficient preparation of a new series of the Schiff bases (Pn) by the reaction of 2-aminopyridine derivatives with 3-ethoxysalicylaldehyde under ultrasonic irradiation is reported. Sono-chemical synthesis is the safest and greener method for the preparation of Schiff bases in the shorter period of time with higher yield as compared to traditional methods. The synthesized compounds have been characterized by 1H NMR spectroscopic technique and elemental analyses. Furthermore, the crystal structures of two compounds (P0 and P6) were determined by single crystal X-ray diffraction studies. Hirshfeld surface analysis showed that H…H interatomic contact is the most significant contributor in crystal packing of both compounds with percentage contribution of 53.7% and 57.7% for P0 and P6, respectively. Theoretical calculations of the synthesized compounds were carried out by DFT using B3LYP method with the help of Def2-TZVP basis set, indicating that the results of calculation are in accordance with the experimental findings.

A novel titanium(IV) complex (Ti(L)2) with tridentate ONO-donor Schiff base ligand (H2L (E)-4-amino-N'-(3-ethoxy-2-hydroxybenzylidene)benzohydrazide) was synthesized. The synthesized H2L ligand and Ti(L)2 complex were characterized by various spectroscopic techniques like FT-IR, 1H NMR, 13C NMR and elemental analysis (CHN). The single crystal X-ray diffraction (SC-XRD) was also accomplished to ensure the exact molecular structure of the complex. The geometry around the central metal ion in the complex was distorted octahedral as revealed by the data collected from diffraction studies. Hirshfeld surface analysis, QTAIM, MEP and NCI calculations were carried out to explore deeply into the nature and types of the non-covalent interactions. Moreover, theoretical calculations of the Schiff base complex were carried out by DFT at B3LYP/Def2-TZVP level of theory, which showed good correlation with the experimental findings.

In the present study, a series of mononuclear Ni(II), Cu(II) and Zn(II) complexes with ONNO donor salen-type Schiff base ligands, derived from different 3,5-dihalosalicylaldehyde with polymethylenediamines of varying chain length, have been prepared. All the synthesized compounds were characterized by using various spectroscopic (FT-IR and 1H NMR) and analytical (CHN etc.) techniques. Furthermore, three complexes (ZnL1, NiL3 and NiL4) were successfully characterized by single crystal X-ray diffraction. The data revealed that the geometry around Zn(II) was distorted square pyramidal for ZnL1, while NiL3 and NiL4 complexes adapted slightly distorted octahedral geometries around Ni(II). The antibacterial activities of the synthesized ligands and their respective complexes were elaborated by screening them against two strains of Gram positive (Staphylococcus aureus and Bacillus cereus) and two strains of Gram negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. It was found from the measurements of zones of inhibition that metal chelates are marginally more effective than free ligands.

The present work is related to the rapid and efficient preparation of Schiff bases (1 and 2) by reaction of 2-aminopyridine derivatives with 3-ethoxysalicylaldehyde under ultrasonic irradiation. The advantages, of using ultrasonic irradiation, are short reaction time, high yield and the ability to carry out large scale reactions. After characterization by NMR spectroscopic technique and elemental analyses, the crystal structures of compounds were confirmed by single crystal X-ray analysis (SC-XRD). For further elaboration of non-covalent interactions in the stabilization of packing of molecules, Hirshfeld surface (HS) inspection was accomplished by using crystal explorer software. B3LYP/Def2-TZVP level of theory was used to calculate electronic and structural parameters of synthesized compounds. Optimized structures and calculated data showed good correlation with experimental ones. In addition, two models of keto and phenol tautomerism were studied by calculating thermodynamic parameters and molecular electrostatic potential. Results showed that there are both nucleophilic and electrophilic centers in keto form, while only nucleophilic center is present in phenol form.