Showing papers by "Oscar E. Piro published in 2021"

Photo-Induced Partially Aromatized Intramolecular Charge Transfer.

Abstract: Diverse models of intramolecular charge transfer (ICT) have been proposed for interpreting the origin of the charge-transfer (CT) state in donor-acceptor (D-A) dyes. However, a large variety of fused-heterocyclic dyes containing a pseudo-aromatic ring in the rigid structure have shown to be incompatible with them. To approximate a solution within the ICT concept, we reported a novel ICT model called partially aromatized intramolecular charge transfer (PAICT). PAICT involves the generation of a CT state from an ICT that occurred within a pre-excited D-A fused-heterocyclic structure possessing a pseudo-aromatic or unstable aromatic ring as the acceptor moiety. The model was proposed from the multiple-emissive mesomeric D-A N1-aryl-2-(trifluoromethyl)benzo[b][1,8]naphthyridin-4(1H)-one, whose excited mesomeric states, which are defined by the aromatic and pseudo-aromatic forms of the pyrindin-4(1H)-one ring, led to a common partial aromatized CT state upon excitation via PAICT. The latter was supported through theoretical calculations on the excited mesomeric states, one-dimensional (1D) and two-dimensional (2D) excitation-emission measurements in different solvents, and the detection of three excited states by lifetime measurements upon 370 nm excitation. The existence of mesomerism was supposed from: (i) two overlapping bands at 370-390 (or 400-420 nm) in UV-vis spectra, (ii) the direct interaction between the pyridinic nitrogen of one molecule and the carbonylic oxygen of the other found in the solid state and, (iii) the detection of three excited states by lifetime measurements. The PAICT opens new perspectives for interpreting the charge-transfer phenomenon in fused-heterocyclic dyes, in particular, those containing a pseudo-aromatic or unstable aromatic ring as an acceptor moiety.

Synthesis, Crystal Structure, Spectroscopic Characterization, DFT Calculations and Cytotoxicity Assays of a New Cu(II) Complex with an Acylhydrazone Ligand Derived from Thiophene

Abstract: A new Cu(II) complex is synthetized by the reaction of copper nitrate and a N-acylhydrazone ligand obtained from the condensation of o-vanillin and 2-thiophecarbohydrazide (H2L). The solid-state structure of [Cu(HL)(H2O)](NO3)·H2O, or CuHL for simplicity, was determined by X-ray diffraction. In the cationic complex, the copper center is in a nearly squared planar environment with the nitrate interacting as a counterion. CuHL was characterized by spectroscopic techniques, including solid-state FTIR, Raman, electron paramagnetic resonance (EPR) and diffuse reflectance and solution UV-Vis electronic spectroscopy. Calculations based on the density functional theory (DFT) assisted the interpretation and assignment of the spectroscopic data. The complex does not show relevant antioxidant activity evaluated by the radical cation of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) method, being even less active than the free ligand as a radical quencher. Cytotoxicity assays of CuHL against three human tumor cell lines, namely MG-63, A549 and HT-29, revealed an important enhancement of the effectiveness as compared with both the ligand and the free metal ion. Moreover, its cytotoxic effect was remarkably stronger than that of the reference metallodrug cisplatin in all cancer cell lines tested, a promissory result in the search for new metallodrugs of essential transition metals.

Role of hydrogen bonds and weak non-covalent interactions in the supramolecular assembly of 9-hydroxyeucaliptol: crystal structure, Hirshfeld surface analysis, and DFT calculations

Abstract: The compound 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octan-9-ol (9-hydroxyeucaliptol) has been prepared and characterized by single-crystal X-ray diffraction analysis, infrared, Raman, and UV-visible spectroscopies. The molecular geometry of the title compound was also investigated theoretically by density functional theory (DFT) calculations to compare with the experimental data. The substance crystallizes in the trigonal crystal system, space group P32 with Z = 9 molecules per unit cell. There are three independent molecules in the crystal asymmetric unit having the same chirality and showing some differences in the orientation of the H-atom of the hydroxyl group. The crystal structure of 9-hydroxyeucaliptol shows that the hydroxyl group presents an anti-conformation with respect to the O-atom of the ether group. The crystal packing of 9-hydroxyeucaliptol is stabilized by intermolecular O-H···O hydrogen bonds involving the hydroxyl groups of different molecules, which play a decisive role in the preferred conformation adopted in solid state. The intermolecular interactions observed in solid state were also studied through the Hirshfeld surface analysis and quantum theory of atoms in molecules (QTAIM) approaches. Energy framework calculations have also been carried out to analyze and visualize the topology of the supramolecular assembly, and the results indicate a significant contribution from electrostatic energy over the dispersion.

A first exploration of isostructurality in transition metal nitroprussides: X-ray analysis, magnetic properties and DFT calculations

Abstract: Five new transition metal nitroprussides with 1-methylimidazole (1-MeIm) have been synthesized and characterized by IR, XPS and UV-vis spectroscopy, thermal analysis, and powder and single-crystal X-ray diffraction. The structural analyses have revealed that the complexes Mn(1-MeIm)2[Fe(CN)5NO] (1), Fe(1-MeIm)2[Fe(CN)5NO] (2), Cu(1-MeIm)4[Fe(CN)5NO] (3), Zn(1-MeIm)2[Fe(CN)5NO] (4) and Cd(1-MeIm)2[Fe(CN)5NO] (5) are 2D coordination polymers. The supramolecular self-assembly of all the five complexes is governed by non-classical C–H⋯N hydrogen bonds and lone-pair(O)⋯π interactions. N⋯O chalcogen and π⋯π contacts are also present in the crystal packing of complexes 1, 2, 4 and 5. A detailed analysis of four geometric descriptors revealed the existence of a high degree of isostructurality for the molecular pair 1/2, and a moderate one for the pairs 1/5 and 2/5. The dissimilarity index was also calculated for molecular pairs in two series of related compounds, showing that the degree of similarity is lower than those found in the pairs 1/2, 1/5 and 2/5. The results herein discussed for first time in the literature may be useful to understand property/structure relationships in these types of complexes. By using DFT calculations at the PBE0-D3/def2-TZVP level of theory and discrete models of the coordination polymers, we have analyzed cooperative lp–π/π–π/π–lp assemblies that are observed in the solid state of these compounds. This interesting assembly has been further analyzed by a combination of QTAIM, NCIplot and MEP surface calculations. The magnetic measurements indicate that compounds 1–3 are paramagnetic at 300 K and the Curie–Weiss constants are negative, suggesting weak antiferromagnetic coupling between the metal centers, at very low temperatures.

Novel ‘main-part’ isostructuralism in metal complexes with 1-methylimidazole: crystal structures, energy calculations and magnetic properties

Abstract: Two new transition metal complexes with 1-methylimidazole (1-MeIm) and azide as ligands, namely, [Co(1-MeIm)4(N3)2] (1) and [Ni(1-MeIm)4(N3)2] (2), have been synthesized and characterized by IR, Raman, UV-Vis and XPS spectroscopy. Their crystal structures were solved by single-crystal X-ray diffraction. The supramolecular self-assembly of the two complexes is governed by non-classical C–H⋯N hydrogen bonds and C–H⋯π interactions. Lattice energies and intermolecular interaction energies for various molecular pairs are quantified using the PIXEL method. DFT computational studies to assess the binding energy through modern tools like non-covalent interaction (NCI plots) analysis and reduced density gradient (RDG) analysis have also been carried out. A detailed analysis of geometric descriptors revealed the existence of quasi-isostructural pairs or ‘main-part’ isostructuralism in a series formed by 1, 2, and a related cadmium complex, being more evident in the 1/2 pair. DFT studies using theoretical models have been used to disclose the relative importance of the H-bond and C–H⋯π noncovalent interactions. Magnetic measurements for compound 1 show weak ferrimagnetic coupling between adjacent M(II) centers, mediated by H-bonding and C–H⋯π non-covalent interactions.

The Bonding Interactions in Fluorinated Vinylogous Amides: A CF3‐Substituted Carbonyl‐β‐Aminoenone as a Case Study

Abstract: Fil: Espitia Cogollo, Edeimis. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Centro de Quimica Inorganica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Quimica Inorganica "Dr. Pedro J. Aymonino"; Argentina