bis-(1H-Benzimidazol-2-yl)-methanone: New preparation method, crystal structure, vibrational spectroscopy and DFT calculations

Metaelectric multiphase transitions in a highly polarizable molecular crystal

Metaelectric transition, i.e. an abrupt increase in polarization with an electric field is just a phase change phenomenon in dielectrics and attracts increasing interest for practical applications such as electrical energy storage and highly deformable transducers. Here we demonstrate that both field-induced metaelectric transitions and temperature-induced phase transitions occur successively on a crystal of highly polarizable bis-(1H-benzimidazol-2-yl)-methane (BI2C) molecules. In each molecule, two switchable polar subunits are covalently linked with each other. By changing the NH hydrogen location, the low- and high-dipole states of each molecule can be interconverted, turning on and off the polarization of hydrogen-bonded molecular ribbons. In the low-temperature phase III, the tetragonal crystal lattice comprises orthogonally crossed arrays of polar ribbons made up of a ladder-like hydrogen-bond network of fully polarized molecules. The single-step metaelectric transition from this phase III corresponds to the forced alignment of antiparallel dipoles typical of antiferroelectrics. By the transition to the intermediate-temperature phase II, the polarity is turned off for half of the ribbons so that the nonpolar and polar ribbons are orthogonal to each other. Considering also the ferroelastic-like crystal twinning, the doubled steps of metaelectric transitions observed in the phase II can be explained by the additional switching at different critical fields, by which the nonpolar ribbons undergo "metadielectric" molecular transformation restoring the strong polarization. This mechanism inevitably brings about exotic phase change phenomena transforming the multi-domain state of a homogeneous phase into an inhomogeneous (phase mixture) state.

Heteroatom and solvent effects on molecular properties of formaldehyde and thioformaldehyde symmetrically disubstituted with heterocyclic groups C4H3Y (where Y = O-Po)

In this work several molecular properties of symmetrically disubstituted formaldehyde and thioformaldehyde have been studied using a quantum chemistry approach based on density functional theory. Five-membered heteroaromatic rings containing a single group 16 heteroatom were taken into account as the substituents (i.e., furan-2-yl, thiophen-2-yl, selenophen-2-yl, tellurophen-2-yl, and the experimentally as yet unknown polonophen-2-yl). For the resulting ten formaldehyde and thioformaldehyde derivatives, the geometry, energetics, frontier molecular orbitals, dipole moment and polarizability of their molecules were examined in order to establish the effect of ring heteroatom on these properties. Furthermore, these properties were also determined for the molecules in three solvents of low polarity (benzene, chloroform, and dichloromethane) in order to expand our study to include solvent effects. The dipole moment and polarizability of the investigated molecules show regular variations when the ring heteroatom descends through group 16 and the solvent polarity grows. The heteroatom and/or solvent effects on the part of the studied properties are, however, more complex. An attempt is made to rationalize the observed variations in the molecular properties. The conformational behavior of the investigated molecules was also explored and the conformationally weighted values of dipole moment and polarizability are presented.

Graphical abstract

A unique copper(ii)-assisted transformation of acetylacetone dioxime in acetone that leads to one-dimensional, quinoxaline-bridged coordination polymers

A novel Cu^II-assisted transformation of acetylacetone dioxime to coordinated quinoxaline has been discovered.

Circular serendipity: in situ ligand transformation for the self-assembly of an hexadecametallic [CuII16] wheel

A [Cu₁₆^II] wheel has been isolated serendipitously from the reaction of acetylacetone dioxime with Cu^II and Ln^III ions. The ligand has been transformed in situ to three different forms, all found within the [Cu₁₆], with the original ligand absent.

Molecular structures of 2-arylaminomethyl-1H-benzimidazole: spectral, electrochemical, DFT and biological studies

In the present work, structural studies on (1H-benzimidazol-2-ylmethyl)-N-(4-chloro-phenyl)-amine (L(1)) and (1H-benzimidazol-2-ylmethyl)-N-(4-iodo-phenyl)-amine (L(2)) have been done extensively by a variety of physico-chemical techniques. Optimized geometrical structures, harmonic vibrational frequencies, natural bonding orbital (NBO) analysis, and Frontier molecular orbitals (FMO) were obtained by DFT/B3LYP method. TD-DFT calculations help to assign the electronic transitions. The polarizable continuum model (PCM) fails to describe the experimental chemical shift associated with the NH protons as calculated by applying Gauge-invariant atomic orbital (GIAO) method, but a very good correlation between the theoretical and experimental values was achieved by taking into account the specific solute-solvent interactions. DFT calculations showed a good agreement between the theoretical and observed results. These compounds exhibited a high biological activity through the inhibition of the metabolic growth of the investigated bacteria.

Molecular structure of 2-chloromethyl-1H-benzimidazole hydrochloride: single crystal, spectral, biological studies, and DFT calculations

In the present work, structural studies on 2-chloromethyl-1H-benzimidazole hydrochloride have been performed extensively by X-ray crystallography, (1)H NMR, FT-IR, UV/vis, and elemental analysis. The title compound crystallizes in a monoclinic space group P2(1)/c with a=7.1982 (3) Å, b=9.4513 (5) Å, c=14.0485 (7) Å and β=102.440 (3)° forming an infinite chain structure parallel to "b" axis through the intermolecular hydrogen bond. Optimized geometrical structure, harmonic vibrational frequencies, natural bonding orbital (NBO) and frontier molecular orbitals (FMO) were obtained by DFT/B3LYP method combined with 6-31G(d) basis set. TD-DFT calculations help to assign the electronic transitions. The (1)H NMR chemical shifts were computed at the B3LYP/6-311+G(2d,p) level of theory in different solvents by applying GIAO method using the polarizable continuum model (PCM). The title compound was screened for its antibacterial activity referring to Tetracycline as a standard antibacterial agent.

2-[(1H-benzimidazol-2-ylmethyl)-amino]-benzoic acid methyl ester: crystal structure, DFT calculations and biological activity evaluation

In the present study, structural properties of 2-[(1H-benzimidazol-2-ylmethyl)-amino]-benzoic acid methyl ester have been studied extensively by spectral methods and X-ray crystallography. Quantum mechanical calculations of energies, geometries, vibrational wavenumbers, NMR and electronic transitions were carried out by DFT using B3LYP functional combined with 6-31G(d) basis set. Natural bond orbitals (NBO) analysis and frontier molecular orbitals were performed at the same level of theory. DFT calculations showed good agreement between the theoretical and experimental values of optimized and X-ray structure as well as between the vibrational and NMR spectroscopy. The title compound was screened for its antibacterial activity referring to Tetracycline as standard antibacterial agent.

Structural and in vitro cytotoxicity studies on 1H-benzimidazol-2-ylmethyl-N-phenyl amine and its Pd(II) and Pt(II) complexes

[MLCl(2)]·zH(2)O (L = (1H-benzimidazol-2-ylmethyl)-N-phenyl amine; M = Pd, z = 0; M = Pt, z = 1) and [PdL(OH(2))(2)]·2X·zH(2)O (X = Br, I, NO(3), z = 0; X = SCN, z = 1) complexes were synthesized as potential anticancer compounds and characterized by elemental analysis, spectral and thermal methods. FT-IR and (1)H NMR studies revealed that the benzimidazole L is coordinated to the metal ions via the pyridine-type nitrogen (N(py)) of the benzimidazole ring and secondary amino group (NH(sec)). Quantum mechanical calculations of energies, geometries, vibrational wavenumbers, and (1)H NMR of the benzimidazole L and its complexes were carried out by density functional theory using B3LYP functional combined with 6-31G(d) and LANL2DZ basis sets. Natural bond orbitals (NBOs) and frontier molecular orbitals were performed at B3LYP/LANL2DZ level of theory. The synthesized ligand, in comparison to its metal complexes was screened for its antibacterial activity. The benzimidazole L is more toxic against the bacterium Staphylococcus aureus (MIC = 58 μg/mL) than the standard tetracycline (MIC = 82 μg/mL). The complexes showed cytotoxicity against breast cancer, Colon Carcinoma, and human heptacellular Carcinoma cells. The platinum complex (6) displays cytotoxicity (IC(50) = 12.4 μM) against breast cancer compared with that reported for cis-platin 9.91 μM.