Volume 73, Issue 10

Catenanes are of considerable interest as potential building blocks for molecular machines. The simplest [2]catenanes, Hopf links, consist of two macrocycles that are mechanically interlocked. This unusual architecture cannot be opened without breaking at least one covalent bond. Based on these structural characteristics, unusual properties on Hirshfeld or electrostatic potential surfaces could be expected. For a comparison of their structural and electronic properties, the electron densities (EDs) of two [2]catenanes, coded H 2 2 and H 4 L7 in the original papers, were examined after application of the invariom formalism, relying on X-ray diffraction data collected earlier. The obtained electron density distributions were subjected to an analysis using the QTAIM formalism to yield bond and atomic properties. Moreover, molecular Hirshfeld surfaces and electrostatic potentials (ESP) were calculated. There are different types of intra- and intermolecular interactions in these two [2]catenanes. In addition to classical N–H···N and C–H···O hydrogen bonds, various types of π···π interactions in H 2 2 and in H 4 L7 exist. Most of them are verified by local ED concentrations visible on the corresponding Hirshfeld surfaces, except for the parallel π···π interactions in H 2 2 , which are either too weak or too diffuse to generate an ED signal on the Hirshfeld surface between the contributing aromatic rings. The electrostatic potentials (ESPs) were calculated and displayed on molecular surfaces. The interaction in the cavity of one macrocycle with the penetrated fragment of the second one was examined and it was found that corresponding to the above-mentioned contacts attractive and repulsive interactions exist. Additionally the ED was examined using results of density functional calculations, including non-covalent interaction index (NCI) and electron localizability indicator (ELI-D) surface analysis, complementing experimental findings.

The orthoamides of alkyne carboxylic acids 4 react with acetophenones 5 – catalyzed by trialkylborates – to give ketene aminals 6 , which can be transformed to 5-amino-5-hydrazino-penta-2,4-dien-1-ones 10 by treatment with 2,4-dinitro-phenylhydrazine. From acetophenone-phenylhydrazones 12 and orthoamides 4 1 H -1,2-diazepines 18 (fett) are formed at room temperature, whereas 4-dimethylamino-pyridines 22 are obtained at elevated temperatures. The diazepine 18a is degraded to the pyridine-derivative 22b upon heating. The N-unsubstituted acetophenone-hydrazone 25 reacts with 4c to give amidrazone 26 . The constitution of compounds 18a , 22a , 22b , 26 is established by crystal structure analyses.

An efficient, economic, and air-promoted metal-free method for direct arylation of benzoquinone with phenylhydrazines was developed. This approach leads to the formation of corresponding [1,1′-biphenyl]-2,5-dione derivatives as biological and pharmaceutical materials of interest in good yields, under mild reaction conditions, and at ambient temperature.

Triethanol ammonium acetate ([TEAH] + [OAc] − ) and triethanol ammonium formate ([TEAH] + [HCOO] − ) as multifunctional ionic liquids and catalysts were successfully applied for the preparation of tetrahydrobenzo[ b ]pyrans by the one-pot three-component condensation reaction of various aldehydes, dimedone and malononitrile under solvent-free conditions. These reactions were also tested using boric acid in water. In this catalytic system, by the reaction of water with boric acid, the hydronium ion caused by water separation can catalyze the reaction.

1-(2-Chlorophenyl)-3-methyl-4-propionyl-1 H -pyrazol-5(4 H )-one was synthesized and characterized by Fourier transform infrared (FT-IR) spectroscopy, 1 H nuclear magnetic resonance, and single-crystal X-ray analysis. Its Cu(II) complex was prepared and characterized by FT-IR, thermo gravimetric analysis-differential thermal analysis, ultraviolet-visible spectroscopy, cyclic voltammetry, and single-crystal X-ray structure determination. On the basis of analytical and spectroscopic techniques, a distorted square planar geometry of the complex has been found.

Lanthanum cobaltite, LaCoO 3 , finds applications as an oxidation and reduction catalyst in gas-sensing materials and in electrode materials for high-temperature fuel cells. The compound has been synthesized through several routes aimed at obtaining LaCoO 3 at lower temperatures. We propose a synthetic procedure based on the combined use of mechanical and thermal energy on mixtures of Co(II) oxalate dehydrate and La acetate sesquihydrate. We studied the reactions taking place by increasing the temperature. The study has been performed either on mixtures prepared by a simple physical mixing of the reactants or on the same mixtures after having been subjected to mechanical activation by high-energy milling. The products formed in the mixtures by annealing at different temperatures have been characterized by means of different experimental techniques (thermogravimetric analysis, XRPD, IR, scanning electron microscopy).

The crystal and molecular structures of N′ -(2-furylmethylidene)-3-(3-pyridyl)acrylohydrazide and N′ -(2-thienylmethylidene)-3-(3-pyridyl)acrylohydrazide are reported, and the influence of the type of the heteroatom on the aromaticity of the aromatic rings is discussed. Both molecules are nearly planar. The geometry of the acrylohydrazide arrangement is comparable to that of homologous compounds. Density functional theory (DFT) calculations were performed in order to analyze the changes in the geometry of the studied compounds in the crystalline state and for the isolated molecule. The most significant changes were observed in the values of the N–N and C–N bond lengths. The harmonic oscillator model of aromaticity index, calculated for the furan and thiophene rings, demonstrated a noticeable increase in aromaticity in comparison to isolated rings and their DFT-calculated structures. By contrast, the nucleus independent chemical shift index indicated a decrease in aromatic character of the rings containing heteroatoms.

A new modification of the homometallic silver(I) cluster [Ag 4 Br 4 (PPh 3 ) 4 ] has been prepared and characterized by elemental analysis, UV/Vis and IR spectroscopy, and X-ray crystallography. The tetramer shows a polycyclic structure with a chair conformation. The bromine atoms adopt μ 2 - and μ 3 -bridging modes. The shortest Ag–Ag distance in the cluster is 3.159(2) Å, which indicates significant Ag–Ag interactions. A supramolecular structure is arranged by hydrogen bonds (C–H···Br). Cyclic voltammograms of the cluster indicate a quasi-reversible Ag + /Ag couple. The fluorescence properties of the ligand and the Ag(I) cluster were studied in the solid state. The emission peaks of the Ag(I) cluster are attributed to ligand-centered luminescence.

The magnetocaloric effect (MCE) of the ferromagnetic compound GdAg 2 Mg [ T C =98.3(5) K] was investigated along with its electrical resistivity and the specific heat capacity. The magnetic entropy changes (–Δ S M ) as well as the changes in adiabatic temperature (Δ T ad ) have been calculated from these data. Furthermore, the magnetic susceptibility of the pseudo-quaternary Heusler phases GdAgAuMg, TbAgAuMg and DyAgAuMg [i.e. RE (Ag 0.5 Au 0.5 ) 2 Mg] were measured and compared to the data for the pure silver and gold compounds RE Ag 2 Mg and RE Au 2 Mg. The substitution of the transition metal at the crystallographic Wyckoff site 8 c influences the magnetic ground state of the trivalent rare earth metals and therefore drastically alters the Curie temperatures. The structure of GdAgAuMg was refined from single crystal X-ray diffraction data, revealing a small deviation from the equiatomic composition leading to the refined formula GdAg 0.92(6) Au 1.08(6) Mg [space group Fm 3̅ m , Z =4, a =695.03(10) pm, wR 2=0.0883, 55 F 2 values, six parameters]. The intermetallic compounds were synthesised in sealed niobium ampoules under high temperature conditions. They have reddish to brassy colour.