Mirela-Fernanda Zaltariov

A new diamine containing disiloxane moiety and some derived Schiff bases: synthesis, structural characterisation and antimicrobial activity

A new siloxane diamine, 1,3-bis(amino-phenylene-ester-methylene)tetramethyldisiloxane (1), was obtained by a two-step procedure and used to prepare a series of Schiff bases (2–5), by reaction with different carbonylic compounds: salicylaldehyde, 3,5-dibromosalicylaldehyde, 5-chlorosalicylaldehyde and 3,5-di-tert-butyl-2-hydroxybenzaldehyde. All compounds, separated in crystalline form, were characterised by spectral (FTIR, UV–vis and NMR) analysis as well as by single-crystal X-ray diffraction. In these structures, different packing motifs occur depending on the different association degree determined by intra- and intermolecular π–π stacking interactions. Antimicrobial activity of the compounds was evaluated against three fungi and two bacteria, where the Schiff bases derived from salicylaldehyde and in special 5-chlorosalicylaldehyde showed remarkable activity.

Flexible linkers and dinuclear metallic nodes build up an original metal–organic framework

A Metal–Organic Framework (MOF) of formula [Cu2(μ3-tmds)2(imH)4]·H2tmds (imH = imidazole; H2tmds = 1,3-bis(3-carboxypropyl)tetramethyldisiloxane) 1 has been synthesized by successive additions of H2tmds and imidazole to a solution of copper(II) acetate. The crystal structure of compound 1 has been investigated by single-crystal X-ray diffraction. It crystallizes in the C2/c monoclinic space group. The crystals are composed of an extended coordination network welcoming H2tmds molecules. The network contains paddle-wheel dicopper(II) moieties where the two copper atoms are bridged by one of the carboxylate groups of two tmds2− anion. The basal plane of their coordination sphere is complemented by two imidazole molecules whereas the apical position is occupied by one oxygen atom of the second carboxylate group of a neighboring tmds2− anion leading to an overall square-pyramidal environment of the metal ions. These short and long bridging modes of the flexible tmds2− dianion build up a complex bidimensional coordination network where the nodes are dinuclear clusters rather than simple metal centres. H-bonds are found within the network with imidazole as a H-bond donor and tmds2− as a H-bond acceptor leading to a cis-oide conformation of the ligand. The coordination network is further H-bonded to H2tmds molecules leading to an overall three-dimensional supramolecular network mixing coordination and hydrogen bonds. Variable-temperature magnetic susceptibility measurements reveal antiferromagnetic interactions between the copper(II) ions within the paddle-wheel dinuclear units (J = −34.4(2) cm−1; H = −2JS1S2).

A silicon-containing polyazomethine and derived metal complexes: synthesis, characterization, and evaluation of the properties

A new dialdehyde-containing silicon was prepared by a reaction of Williamson-type and structurally characterized. By its subsequent condensation with 2,5-bis(p-aminophenyl)-1,3,4-oxadiazole, a multifunctional polyazomethine-containing imine, phenylene, oxadiazole, ether, and carbosilane groups within the chain was prepared. The complexes of this polymer with Co(II), Cu(II), and Zn(II) ions formed on the basis of electron-donor ability of the oxadiazole and azomethine groups were prepared in a one-step approach by mixing the two precursors of polyazomethine (dialdehyde and diamine) with corresponding metal salt. The ligand and metal complexes were characterized by spectral (Fourier transform infrared (FTIR), 1H, and 13C NMR) methods. The thermal, optical, electrochemical, and dielectric properties were studied and the effects of the metal insertion in dependence on its nature over these properties were evaluated. All compounds are soluble in common organic solvents and show low glass transitions due to the flexible ether and Si–C bonds, are fluorescent, mainly due to the oxadiazole ring, are redox active and have high dielectric constant due to the presence of oxadiazole, azomethine metal units.

Electroactive composites based on polydimethylsiloxane and some new metal complexes

Three different small molecule or polymeric well-determined complex structures containing siloxane moieties and 3d metals were incorporated into a polymeric matrix based on a polydimethylsiloxane of low molecular weight. After the incorporation of the complex, matrix crosslinking was performed with tetraethylorthosilicate, resulting in free-standing films. The films were investigated by scanning and transmission electron microscopy (SEM, TEM), dynamic vapour sorption (DVS) analysis, stress?strain measurements and dielectric spectroscopy. The presence of the siloxane moiety in the ligand (by its surface effect) improves the compatibility between the metal complex and the silicone matrix, which ensures good mechanical properties. Thus, modulus values between 0.10 and 0.50?MPa and elongations of 210?380% were obtained. Depending on the metal type and the complexation pattern, an increasing of the dielectric constant value up to 4.6 as compared with a value of 2.5 for the silicone matrix was obtained. The samples showed good electromechanical actuation behaviour even at small voltages.

Assessment of chemicals released in the marine environment by dielectric elastomers useful as active elements in wave energy harvesters

A series of elastomers, either natural or synthetic (some of them commercial, while others prepared in the laboratory), suitable for use as active elements in devices for wave energy harvesting, were evaluated concerning their behavior and effects on the marine environment. In this aim, the elastomer films, initially evaluated regarding their aspect, structure, surface wettability, and tolerance of microorganisms growth, were immersed in synthetic seawater (SSW) within six months for assessing compounds released. There were analyzed the changes occurred both in the elastomers and salt water in which they were immersed. For this, water samples taken at set time intervals were analyzed by using a sequence of sensitive spectral techniques: UV-vis, IR, and in relevant cases 1H NMR and electrospray ionization mass spectrometry (ESI-MS), able to detect and identify organic compounds, while after six months, they were also investigated from the point of view of aspect, presence of metal traces, pH, and biological activity. The changes in aspect, structure and morphology of the dielectric films at the end of the dipping period were also evaluated by visual inspection, IR spectroscopy by using spectral subtraction method, and SEM-EDX technique.

Metal–organic frameworks based on tri- and penta-nuclear manganese(II) secondary building units self-assembled by a V-shaped silicon-containing dicarboxylate

A bent V-shaped silicon-containing linker, bis(p-carboxyphenyl)diphenylsilane (H2cpdps), has been used to synthesize two coordination polymers, [Mn5(cpdps)(HCOO)2(H2O)2(DMF)4]·6DMF (1) (DMF – dimethylformamide) and [Mn3(μ-H2O)2(Hcpdps)2(cpdps)2(DMF)2]·2DMF·12H2O (2). The crystal structure of both compounds was determined by single-crystal X-ray diffraction. In complex 1, pentanuclear manganese(II) secondary building units (SBUs) are held together by cpdps2− ligands to form a 2D (4,4) coordination polymer. Crystal 2 is built of trinuclear manganese(II) SBUs that are held together by cpdps2− and Hcpdps− ligands within a 2D (4,4) coordination polymer. The magnetic susceptibility measurements revealed antiferromagnetic exchange interactions between the paramagnetic manganese(II) ions (d5). The exchange interactions are ranging between −0.6 and −2.25 cm−1. Thermal analysis consisting in simultaneous thermogravimetry and automated FTIR analysis of the evolved gases permitted to evaluate the stability of the compounds and identify the main processes underlying decomposition. The void volumes accessible for particular guest molecules (CO2, H2O, Ar, N2) were theoretical estimated on the basis of the crystallographic data. Water vapor sorption capacity was measured experimentally in dynamic regime at room temperature.

Crystal smectic E revisited for(E)-N-(biphenyl-4-ylmethylene)-4-butylaniline – mesomorphism, crystal structure and FTIR study

ABSTRACT This paper recalls the attention to an interesting compound having aromatic azomethine structure, namely: (E)-N-(biphenyl-4-ylmethylene)-4-butylaniline (PB4A). The molecular structure of PB4A was determined by X-ray single-crystal diffraction analysis. Besides the enantiotropic smectic B and nematic phases, this compound exhibits a monotropic crystal E phase. By polarising optical microscopy and differential scanning calorimetry, we confirmed the existence of these phases. FTIR measurements in attenuated total reflection configuration have been performed to investigate the evolution of significant absorption bands during phase transitions. Graphical Abstract

Coordination polymer of copper with a silicon-containing Schiff base Synthesis, structural characterization, and properties

A Schiff base was prepared by condensation reaction of 2,6-diformyl-4-methylphenol with trimethylsilyl-methyl-p-aminobenzoate and it was further used, without isolation, as a ligand for copper (Cu(II)) ions. The structure of the resulting coordination complex was evidenced by spectral techniques (Fourier transform infrared spectroscopy, nuclear magnetic resonance and ultraviolet-visible spectroscopy) and by single crystal X-ray diffraction, which revealed a covalent one-dimensional (1D) structure where neutral molecular units (Cu(II) coordination polymer [CuL2]) are linked through the bridging oxygen atoms. The 1D polymeric chains are associated by intermolecular C–H···O hydrogen bonding to form two-dimensional supramolecular layers. The polymeric nature of the compound was also supported by the presence of glass transition in differential scanning calorimetry trace. This coordination polymer forms spherical aggregates in a nonpolar medium (hexane) as was emphasized by transmission electron microscopy image taken on the film remained after solvent evaporation. The thermogravimetrical analysis indicates a good stability for the Cu(II) coordination polymer and the biological tests revealed good antibacterial and antifungal activities.