Investigation of Chemical Bonding in In Situ Cryocrystallized Organometallic Liquids

Design, synthesis, DFT calculations, molecular docking and antimicrobial activities of novel cobalt, chromium metal complexes of heterocyclic moiety-based 1,3,4-oxadiazole derivatives

A Schiff base, 5-(4-methylphenyl)-4-[(pyridin-2-ylmethylidene)amino]-4H-1,2,4-oxadiazole as a bidentate ligand has been synthesized by the reaction between the 4-amino-5-(4-methylphenyl)-4H-1,3,4-oxadiazole and aromatic aldehyde. The Schiff base reacted with CoCl₃·6H₂O and CrCl₃·6H₂O in ethanol to yield 1,3,4-oxadiazole complexes. The structures of synthesized ligand and their complexes have been established on the basis of their IR, Mass and ¹H-NMR spectra. Electronic and geometric structures of both cobalt and chromium complexes were investigated by density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) calculations. DFT-based reactivity calculations estimated the studied system as strong electrophile and/or strong nucleophile in polar organic reactions. Moreover, most reactive sites were predicted theoretically based on the delocalized and localized indexes. The nature of Ligand-Metal chemical bonding is discussed in terms of the natural bond orbital (NBO) and QTAIM analysis. Accordingly, the metal ions such as cobalt and chromium are bidentate coordinated with the Schiff base by nitrogen atoms of imine function and pyridine, to form stable complexes. Furthermore, the chromium ions have an affinity superior to the cobalt ions towards Schiff base ligand. In addition, the results of the antibacterial activity in-vitro show that the metal complexation confers an increase in the antibacterial activity of the complexed ligand compared to the free ligand against both Gram-positive and Gram-negative bacteria with broad spectrum activity. In silico molecular docking studies of the ligands and their complexes were applied to describe the probable binding modes into the active site of Escherichia coli (E. coli) FabH and Salmonella typhimurium LT2 neuraminidase (STNA) receptors. The increase in biological activity could be attributed to the high stability of the complexes and strong affinities to bacterial enzyme receptors.Communicated by Ramaswamy H. Sarma.

Metal–ligand bonding in tricarbonyliron(0) complexes bearing thiochalcone ligands

Bonding interactions between iron and thiochalcones in a series of recently synthesized complexes were analyzed using various theoretical methods.

Overlap properties of chemical bonds in generic systems including unusual bonding situations

Chemical bond is a ubiquitous and fundamental concept in chemistry, in which the overlap plays a defining role. By using a new approach based on localized molecular orbitals, the overlap properties, e.g., polarizability [Formula: see text], population p_OP, intra [Formula: see text], and inter [Formula: see text] repulsions, and density ρ_OP, of polyatomic systems were calculated, analyzed, and correlated. Several trends are shown for these properties, which are rationalized by the balance of some well-known effects, such as, electron donor/withdrawing character and electronegativity. The overlap properties of unusual bonds are also analyzed, revealing an OZn₄(OOCH)₆ structure with four equivalent Zn-O chemical bonds with overlap properties like the O-O bond in H₂O₂, while in protonated methane [Formula: see text], it is observed that a CH₃⋯[Formula: see text] bond pattern at the equilibrium structure changes to a [Formula: see text]⋯H₂ pattern upon dissociation. Charge-shift resonance energies, atom-in-molecule properties, and the lone-pair-bond-weakening effects are related to the overlap properties, which can provide alternative views and insights into chemical bonds. Graphical abstract A chemical bond analysis approach based on its overlap properties is presented for the first time. The model was applied directly to 25 diatomics and for 28 bonds in polytomics employing localized molecular orbitals. Correlations of the overlap properties with the charge-shift resonance energies and with atom-in-molecule (AIM) properties were uncovered. In addition, it provided insights into the Zn-O bonds in the unusual OZn₄(OOCH)₆ system as well as in the bonding patterns of [Formula: see text] at equilibrium and upon dissociation.

Structural Properties and Reactive Site Selectivity of Some Transition Metal Complexes of 2,2'(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)dibenzoic Acid: DFT, Conceptual DFT, QTAIM, and MEP Studies

Herein is presented a density functional theory (DFT) study of reactivity and structural properties of transition metal complexes of the Schiff base ligand 2,2′(1E,1′E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)dibenzoic acid (hereafter denoted EDA2BB) with Cu(II), Mn(II), Ni(II), and Co(II). The quantum theory of atoms-in-molecules (QTAIM), conceptual DFT, natural population analysis (NPA), and molecular electrostatic potential (MEP) methods have been used. Results have revealed a distorted octahedral geometry around the central metal ion in each gas phase complex. In the DMSO solvent, a general axial elongation of metal-oxygen bonds involving ancillary water ligands has been observed, suggestive of loosely bound water molecules to the central metal ion that may be acting as solvent molecules. Weak, medium, and strong intramolecular hydrogen bonds along with hydrogen-hydrogen and van der Waals interactions have been elucidated in the complexes investigated via geometric and QTAIM analyses. From the chemical hardness values, the complex [Co(EDA2BB)(OH₂)₂] is the hardest, while [Cu(EDA2BB)(OH₂)₂] is the softest. Based on the global electrophilicity index, the complexes [Ni(EDA2BB)(OH₂)₂] and [Cu(EDA2BB)(OH₂)₂] are the strongest and weakest electrophiles, respectively, among the complexes studied. In conclusion, the reactivity of the complexes is improved vis-à-vis the ligand, and stable geometries of the complexes are identified, alongside their prominent electrophilic and nucleophilic sites.

Crystal packing analysis of in situ cryocrystallized 2,2,2-tri-fluoro-aceto-phenone

Crystals of the liquid compound 2,2,2-tri-fluoro-aceto-phenone (TFAP, C8H5F3O) were obtained using the state-of-art in situ cryocrystallization technique. TFAP crystallizes in the monoclinic space group C2/c, and its crystal structure is mainly stabilized by a set of C-H⋯F, C-H⋯O, F⋯F and F⋯O supra-molecular contacts. The overall mol-ecular arrangement shows the formation of mol-ecular sheets parallel to the bc plane, which are in turn stacked along the a-axis direction. The weak inter-actions have been studied thoroughly, performing both a Hirshfeld surface analysis and theoretical calculations, to obtain the inter-molecular inter-action energies. A structural comparison of this compound with the previously reported substituted analogs was also carried out, showing a qualitative difference in terms of packing behaviour.