Showing papers by "Gellert Mezei published in 2017"

Three-component 1D and 2D metal phosphonates: structural variability, topological analysis and catalytic hydrocarboxylation of alkanes

Abstract: Herein, we report the use of diphosphonate building blocks and chelating auxiliary N,N-ligands to generate novel polymeric architectures. Specifically, we report new 1D and 2D coordination polymers incorporating three components: transition metal ions (Co2+, Cu2+, Mn2+ or Zn2+), diphosphonate ligands (methane-diphosphonate, MDPA, or 1,2-ethanediphosphonate, EDPA) and N,N-heterocyclic chelators (1,10-phenanthroline, phen, or 2,2′-bipyridine, bpy). Six compounds were isolated under mild synthesis (ambient temperature) conditions: [Cu2(phen)2(EDPA)2(H2O)4]∞ (1), [Co(phen)(EDPA)(H2O)2]∞ (1a), {[Cu(phen)(MDPA)]·H2O]}∞ (2), [Mn(bpy)(EDPA)(H2O)2]∞ (3), [Zn(bpy)(EDPA)]∞ (4), and, lastly, a discrete Ni2+ molecular derivative [Ni(phen)(H2O)4](EDPA) (5). Synthetic details, crystal structures, and intermolecular interactions (π–π stacking and hydrogen bonding) in 1–5 are discussed. Topological analyses and classification of the underlying metal–organic networks in 1–4 were performed, revealing the uninodal 1D chains with the 2C1 topology in 1–3 and the binodal 2D layers with the 3,4L13 topology in 4. In 1–3 and 5, multiple hydrogen bonds lead to the extension of the structures to give 3D H-bonded nets with the seh-4,6-C2/c topology in 1 and 3, 2D H-bonded layers with the 3,5L52 topology in 2, and a 3D H-bonded net with the 6,6T1 topology in 5. The catalytic activity of compounds 1 and 1a was evaluated in a single-step hydrocarboxylation of cyclic and linear C5–C8 alkanes to furnish the carboxylic acids with one more carbon atom. These reactions proceed in the presence of CO, K2S2O8, and H2O at 60 °C in MeCN/H2O medium. Compound 1 showed higher activity than 1a and was studied in detail. Substrate scope was investigated, revealing that cyclohexane and n-pentane are the most reactive among the cyclic and linear C5–C8 alkanes, and resulting in the total yields of carboxylic acids (based on substrate) of up to 43 and 36%, respectively. In the case of cycloalkane substrates, only one cycloalkanecarboxylic acid is produced, whereas a series of isomeric monocarboxylic acids is generated when using linear alkanes; an increased regioselectivity at the C(2) position of the hydrocarbon chain was also observed.

Mapping the Intricate Reactivity of Nanojars toward Molecules of Varying Acidity and Their Conjugate Bases Leading To Exchange of Pyrazolate Ligands

Abstract: A comprehensive reactivity study of nanojars toward 18 different acidic compounds with varying pKa, including 12 different carboxylic acids (both aliphatic and aromatic mono- and dicarboxylic acids), p-toluenesulfonic acid, hydrogen sulfate, hydrogen carbonate, carbonic acid, 1-decanethiol, and methanol, as well as four different conjugate bases (formate, acetate, benzoate, 2-bromoethanesulfonate) is carried out with the aid of electrospray-ionization mass spectrometry. Thus, the effect on nanojar substitution and breakdown pattern of a number of variables, such as concentration of reagent (acid or conjugate base), acidity of reagent (pKa), effect of acid vs conjugate base, steric effects, aromaticity, incarcerated anion and size of the nanojar, is evaluated. Of the substitution and breakdown products identified by mass spectrometry, acetate-substituted nanojars (Bu4N)2[CO3⊂{Cu27(μ-OH)27(μ-pz)27–x(μ-CH3COO)x}] (x = 1 and 2), as well as dimeric complexes (Bu4N)2[Cu2(μ-pz)2A2] (A = CO32– and SO42–) have bee...

Reaction of Amines with Aldehydes and Ketones Revisited: Access To a Class of Non-Scorpionate Tris(pyrazolyl)methane and Related Ligands

Abstract: The reaction of amines with aldehydes and ketones has been exploited for over 150 years to produce Schiff bases, one of the most popular classes of compounds in both organic and coordination chemistry. In certain cases, however, compounds other than Schiff bases have been reported to result from such reactions. After conducting a representative reaction under various different conditions and identifying several reaction intermediates by NMR spectroscopy, mass spectrometry and X-ray crystallography, we now report a unified picture that explains the scattered and often inconsistent results obtained with 3(5)-aminopyrazole derivatives and other related molecules. Acid catalysis, which is often employed in Schiff base synthesis, radically changes the course of reaction and leads to bis(pyrazol-4-yl)methane derivatives instead of the expected Schiff base products. The stoichiometry of the reaction is also found to be crucial for obtaining quantitative conversions. A total of 31 new compounds have been isolated...

Dielectric response of branched copper phthalocyanine

Abstract: The dielectric constant of pressed pellets and thin films of branched copper phthalocyanine (CuPc) was investigated as a function of frequency from 0.1 kHz to 1 MHz and temperature from 20 °C to 100 °C. Surface morphology was studied using a scanning electron microscope. The high-frequency values of the dielectric constant of pellets and thin films are ~3.5 and ~5.8, respectively. The response was only weakly dependent on frequency and temperature. The branched structure of the CuPc molecules helped to cancel out the effects of low-frequency polarization mechanisms. A planar delocalized charge system with two-dimensional localization was found using time-resolved photoluminescence measurements.