Ivonne Chávez

Selective oxidants for organometallic compounds containing a stabilising anion of highly reactive cations: (3,5(CF3)2C6H3)4B−)Cp2Fe+ and (3,5(CF3)2C6H3)4B−)Cp*2Fe+

A major interest in ferrocenium compounds arises from their usefulness as selective oxidants to prepare mixed-valence metallocenic stable compounds. In this paper, Cp 2 FeBAr′ 4 =((3,5(CF 3 ) 2 C 6 H 3 ) 4 B − )Cp 2 Fe + ) ( a ), and Cp* 2 FeBAr′ 4 =((3,5(CF 3 ) 2 C 6 H 3 ) 4 B − ) Cp* 2 Fe + ) ( b ) are reported. These compounds have wide applications in the obtention of new organometallic salts with improved stability. The selective oxidation capacity of compounds a and b was investigated by the reaction of [Cp*Co II (C 8 H 6 )Fe II (C 8 H 7 )] with stoichiometric quantities of Cp 2 FeBAr′ 4 or Cp* 2 FeBAr′ 4 where [Cp*Co III (C 8 H 6 )Fe II (C 8 H 7 )]BAr′ 4 was exclusively obtained. All salts that have BAr′ 4 − as counterion showed an enhanced solubility in low-polarity solvents, especially in diethyl ether. This fact allowed us to perform non-conventional measurements like cyclic voltammetry in diethyl ether as solvent with NaBAr′ 4 as supporting electrolyte. Single-crystal structural determination of a and b was also achieved.

Synthesis, crystal structure and spectroelectrochemistry of [(C5Me5Ru)2-η6,η6-chrysene]2+(O3SCF3−)2. Form RuII)-η6η6 -chrysene]O3SCF3

Abstract The binuclear complex [(C 5 Me 5 Ru) 2 -η 6 ,η 6 chrysene](O 3 SCF 3 ) ( 1 ) was synthesized from [C 5 Me 5 Ru(CH 3 CN) 3 1 is reduced by sodium naphthalene to the mixed valence complex [(C 5 Me 5 Ru I [(C 5 Me 5 Ru II )-η 6 ,η 6 chrysene]O 3 SCF stable (coproportionation constant K c = 2.57 × 10 5 ). Complex 2 is also formed by electrochemical reduction, as established by cyclovo + e ⇌ 2 +. is reversible with E 1 = − 1.37 V ( vs. saturated calomel electrode), and at E 2 = − 1.69 V a second, ir 2 shows g 1 = 2.025, g 2 = 2.009 and g 3 = 1.998 ( g iso = 2.011). An intervalence absorption band is observed for 2 13 C-NMR data are reported for 1 . A dielectronic reduction of 1 ++ with two equivalents of sodium naphthalene affords the unstable diam η 5 -chrysene] ( 3 ) that probably has a cyclohexadienyl configuration configuration respect to the Ru II -chrysene bonds. An X-ray crystal str centrosymmetric doubly charged cation in 1 each of the two Ru atoms has a sandwich-type coordination between a C 5 Me 5 group and one of the t

Spectral, theoretical characterization and antifungal properties of two phenol derivative Schiff bases with an intramolecular hydrogen bond

Schiff bases show a wide variety of applications of great importance in medicinal research due to their range of biological activities. In this article we describe the electronic structure, optical, redox and wide antifungal properties of (E)-2-{[(2-aminopyridin-3-yl)imino]-methyl}-4,6-di-tert-butyl-phenol (L1) and (E)-2-{[(3-aminopyridin-4-yl)imino]-methyl}-4,6-di-tert-butyl-phenol (L2), two isomer phenol derivative Schiff bases exhibiting a strong intramolecular hydrogen bond (O–H⋯N). These compounds were characterized by their 1H, HHCOSY, 13C-NMR, FT-IR spectra, and by cyclic voltammetry. All the experimental results were complemented with theoretical calculations using density functional theory (DFT) and time-dependent DFT (TDDFT). The antimicrobial activity of the compounds described herein was assessed by determining the minimal inhibitory concentration (MIC) and by a modification of the Kirby–Bauer method. We tested Salmonella enterica serovar Typhi (S. Typhi, Gram-negative bacteria), Cryptococcus spp. (yeast), and Candida albicans (yeast). We found that neither L1 nor L2 showed antimicrobial activity against S. Typhi or Candida albicans. On the other hand, L2, in contrast to L1, exhibited antifungal activity against a clinical strain of Cryptococcus spp. (MIC: 4.468 μg ml−1) even better than ketoconazole antifungal medicaments. We mentioned above that L1 and L2 are isomer species, because the amino group is in the ortho-position in L1 and in the para-position in L2, however no significant differences were detectable by UV-vis, FT-IR, oxidation potentials and TDDFT calculations, but importantly, the antifungal activity was clearly discriminated between these two isomers.

Synthesis, characterization and computational studies of (E)-2-{[(2-aminopyridin-3-yl)imino]-methyl}-4,6-di-tert-butylphenol

(E)-2-{((2-Aminopyridin-3-yl)imino)-methyl}-4,6-di-tert-butyl-phenol (3), a ligand containing an intramolecular hydrogen bond, was prepared according to a previous literature report, with modifications, and was characterized by UV-vis, FTIR, 1H-NMR, 13C-NMR, HHCOSY, TOCSY and cyclic voltammetry. Computational analyses at the level of DFT and TD-DFT were performed to study its electronic and molecular structures. The results of these analyses elucidated the behaviors of the UV-vis and electrochemical data. Analysis of the transitions in the computed spectrum showed that the most important band is primarily composed of a HOMO→LUMO transition, designated as an intraligand (IL) charge transfer.

Experimental and theoretical studies of the ancillary ligand (E)-2-((3-amino-pyridin-4-ylimino)-methyl)-4,6-di-tert-butylphenol in the rhenium(I) core

The fac-[Re(CO)3(deeb)L]+ complex (C2) where L is the (E)-2-((3-amino-pyridin-4-ylimino)-methyl)-4,6-di-tert-butylphenol ancillary ligand, which presents an intramolecular hydrogen bond, has been synthesized and characterized using UV-vis, 1H-NMR, FT-IR, cyclic voltammetry and DFT calculations. The UV-vis absorption and emission properties have been studied at room temperature and the results were compared with TDDFT calculations including spin–orbit effects. We report an alternative synthesis route for the fac-Re(CO)3(deeb)Br (C1) complex where deeb = (4,4′-diethanoate)-2,2′-bpy. Besides, we have found that the C1 shows a red shift in the emission spectrum due to the nature of the ancillary electron donating ligand, while the C2 complex shows a blue shift in the emission spectrum suggesting that the ancillary ligand L has electron withdrawing ability and the importance of the intramolecular hydrogen bond. The calculations suggest that an experimental mixed absorption band at 361 nm could be assigned to MLCT and LLCT transitions. The electron withdrawing nature of the ancillary ligand in C2 explains the electrochemical behavior, which shows the oxidation of ReI at 1.83 V and the reduction of deeb at −0.77 V.

Theoretical and experimental characterization of a novel pyridine benzimidazole: suitability for fluorescence staining in cells and antimicrobial properties

Benzimidazoles presenting intramolecular hydrogen bonding interactions have been normally used to better understand the role of H-bonding in biological processes. Here, we present an experimental and theoretical study of a new compound [2,4-di-tert-butyl-6-(3H-imidazo[4,5-c]pyridine-2-yl)phenol]; (B2), a benzimidazole derivate, exhibiting an intramolecular hydrogen bond. B2 was synthesized and characterized by its 1H, HHCOSY, FT-IR and mass spectra (EI-MS 323 M+). The electronic and optical properties of B2 were studied with theoretical calculations using density functional theory (DFT) and time-dependent DFT (TDDFT). B2 showed luminescent emission at room temperature in different solvents, with a large Stokes shift (e.g.; λex = 335 nm; λem = 510 nm in acetonitrile). Also, the quantum yield (φ = 0.21) and theoretical band emission are reported. We found that B2 exhibited a fluorescence emission at around 500 nm in ethanol and in acetonitrile that could be quenched by aqueous solutions of Hg(NO3)2 in the range of micro molar concentrations. Cyclic voltammetry in acetonitrile showed a strong anodic response due to a quasireversible process, with reduction and oxidation waves at −1.28 and −0.47 V vs. SCE. Regarding the biological properties, we assessed the antimicrobial activity of B2 in Salmonella enterica (bacteria), Cryptococcus spp. (yeast), Candida albicans (yeast), Candida tropicalis (yeast) and Botrytis cinerea (mold). To this end, we determined the minimal inhibitory concentration (MIC) (for bacteria and yeasts), the growth inhibition halos (for yeasts), and the inhibition of mycelial growth (for the mold). We observed that B2 exerted an antifungal effect against Cryptococcus spp. and Botrytis cinerea. In addition, due to its fluorescence properties, B2 has proven to be a suitable marker to observe bacteria (Salmonella enterica and an Escherichia coli derivative), yeasts (Candida albicans), and even human cells (SKOV-3 and HEK-293) by confocal microscopy.

New linked di-germanocenes and di-stannocenes

Abstract New bridged di-germanocenes and di-stannocenes 2 have been synthesized from a reaction between (pentamethylcyclopentadienyl)metal chloride and the dilithium salts of the corresponding linked cyclopentadienyl ligands (spacer: phenylene, biphenylene, thiophene) in good yields. These di-metallocenes react easily with catechol giving preferentially the substitution reaction. With iodine or with metal 14 dichloride (M=Ge, Sn), the oxidative products are unstable and rapidly loose the linked cyclopentadienyl ligand. Starting from SnCl2, the ionic half-sandwich compound [Cp*Ge][SnCl3] 8, so obtained, was characterized by X-ray diffraction analysis which reveals a polymeric form in the solid state. The reaction of the di-germanocenes with o-quinone leads to the expected cycloadducts, stable in the case of permethylated compounds. An unusual single electron transfer reaction takes place with [Cp2Fe][BF4] and the transient cation radical rapidly gives [Cp*Ge][BF4]. Mass spectra measurements and electrochemistry study confirm the weak stability of this cationic species.

Toward the synthetic control of the HOMO-LUMO gap in binuclear systems: insights from density functional calculations.

Computational methods based on density functional theory have been applied to address the design of tailored HOMO-LUMO gap bimetallic complexes. We focus our attention on the [Cp*Fe-(L)-FeCp*] system, where two ferrocenyl units are linked through the dianion of fused ring ligands such as pentalene, s-indacene, dicyclopenta-[b,g]-naphthalene, dicyclopenta-[b,i]-anthracene and dicyclopenta-[b,l]-tetracene. Our DFT calculations on the title organometallic complexes suggest a controlled decrease in the HOMO-LUMO gap, which is desirable for studies on electron-transfer phenomena, as well as the design potential devices for molecular electronic purposes.

Synthesis and characterization of [Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*] and [Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*] BF4−

Abstract [Cp*Fe-dicyclopenta(a,f)naphthalene-FeCp*]n+ (Cp*=pentamethylciclopentadiene, n=0, 1), respectively named complexes V and VI, were synthesized and characterized. The X-ray structure has been solved and 1H-, 13C-NMR and elemental analysis were performed for the n=0 complex. Cyclic voltammetry showed a potential difference of 360 mV within the two redox peaks. An absorption band at 850 nm was assigned to an intervalence band. The Mossbauer investigations show a uniform Fe2+ environment for the neutral compound and two sites, assigned to Fe2+ and Fe3+ for the monoxidized compound. The information gathered by all the previously mentioned techniques indicates that the studied binuclear compound belongs to the mixed valence class II using Robin and Day classification.

Syntheses and Electrochemical Properties of [C5Me5Ru]+ Complexes with Polycyclic Arenes. Crystal Structure of[(C5Me5)Ru( μ6-chrysene)]PF6 · 0.5 Me2CO

Mononuclear and binuclear compounds [(C5Me5)Ru(η6-arene)PF6 and [(C5Me5Ru)2(η6,η6-arene)](PF6)2 were prepared by reacting (C5Me5)RuCl2, the arene and silver acetate with subsequent addition of NH4PF6, for arene = phenanthrene, chrysene, triphenylene, fluorene, bifluorene, biphenyl and 4,4′-biphenyl. The mononuclear compounds were also prepared for arene = naphthalene, anthracene, pyrene and coronene. The 1H and 13C NMR spectra are reported. By cyclic voltammetry all compounds show a first reduction potential that is considerably more positive compared with the free arene. The first cathodic wave is irreversible for a wide range of scanning speeds. However, the mononuclear coronene and the binuclear phenanthrene compounds show reversibility. The crystal structure of [(C5Me5)Ru(η6-chrysene)]PF6·0.5 Me2CO was determined by X-ray diffraction (3797 unique observed reflexions, R = 0.098). Crystal data: a = 1689.2(2), b = 1524.0(8), c = 2263.5(3) pm, β= 107.22(1)°, space group P21/n, Ζ = 8. Crystallographically independent, two cations [(C5Me5)Ru(η6-chrysene)]+ and two anions PF6- are present, but their structures are essentially equal. The [C5Me5Ru]+ unit is bonded to one of the terminal benzene rings of the chrysene in a sandwich manner; the rings bonded to Ru are nearly coplanar. The PF6- ions and the C5Me5 rings exhibit strong thermal vibrations.