529 research outputs found
Electrical Conductivity Criteria in Polyiodides Networks: Stunning Architectures in the Solid State
Network Formation via Anion Coordination: Crystal Structures Based on the Interplay of Non-Covalent Interactions
We describe the synthesis and the structural characterization of new H2L(CF3CO2)2 (1) and H2L(Ph2PO4)2 (2) compounds containing the diprotonated form (H2L2+) of the tetrazine-based molecule 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine. X-ray diffraction (XRD) analysis of single crystals of these compounds showed that H2L2+ displays similar binding properties toward both anions when salt bridge interactions are taken into account. Nevertheless, the different shapes, sizes and functionalities of trifluoroacetate and diphenyl phosphate anions define quite different organization patterns leading to the peculiar crystal lattices of 1 and 2. These three-dimensional (3D) architectures are self-assembled by a variety of non-covalent forces, among which prominent roles are played by fluorine–π (in 1) and anion–π (in 2) interactions
Ethyl (2E)-2-(hydroxyÂimino)propanoate
The molÂecule of the title compound, C5H9NO3, is essentially planar [the maximum deviation for a non-H atom from the mean plane is 0.021 (3) Å] due to the Ï€-conjugation of the hydroxyÂimino and carbonyl groups, which are trans to each other; ab initio calculations in vacuo at the DFT (B3LYP/6–311G**++) level of theory confirmed that E conformer is indeed the lowest in energy. The packing in crystal structure is influenced by strong interÂmolecular O—H⋯N hydrogen-bonding interÂactions between oxime groups and also by Ï€-stacking of the molÂecules due to the carbonyl and oxime group orbital overlap [interÂplanar distance between adjacent molÂecules = 3.143 (4) Å]. Jointly, these factors afford infinite 6.32 Å thick molÂecular sheets, where the plane of each molÂecule is perpendicular to the plane of the sheet. Seen from above, the molÂecules within the sheet are arranged in a herringbone pattern. Such sheets form a stack due to weak van der Waals interÂactions; the gap between adjacent sheets is 2.07 Å
Cation, anion and ion-pair complexes with a G-3 poly(ethylene imine) dendrimer in aqueous solution
The G-3 poly(ethylene imine) ligand L2 shows a multifaceted coordination ability, being able to bind metal cations, anions and ion-pairs. The equilibrium constants for the formation of metal (Cu2+, Zn2+), anion (SO42−) and ion-pair (Cu2+/SO42−) complexes were determined in 0.1 M Me4NCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric titrations. Thanks to its dendrimeric nature, L2 can form highly nucleated metal complexes, such as Cu5L210+ and Zn4L28+, in successive and well-defined complexation steps. Protonated forms of L2 give rise to relatively weak anion complexes with SO42−, but the addition of Cu2+ significantly enhances the binding ability of the ligand toward this anion below pH 9. In more alkaline solutions, an opposite trend is observed. The coordination properties of L2 are discussed with the support of modelling calculations. According to results, L2 is a promising molecule for the preparation of solid supported materials for the recovery of cations and anions from aqueous media and/or for applications in heterogeneous catalysis
Supramolecular forces and their interplay in stabilizing complexes of organic anions: tuning binding selectivity in water
Tales of the unexpected: The case of zirconium(IV) complexes with desferrioxamine
The Zr4+ complexes with desferrioxamine (H3DFO) and its derivatives are the only 89Zr-based imaging agents for proton emission tomography (PET) that have been used so far in clinical trials. Nevertheless, a complete speciation of the Zr4+/H3DFO system in solution has never been performed and the stability constants of the relevant complexes are still unknown. Here we report, for the first time, the speciation of this system in water, performed by potentiometric titrations, and the determination of the stability constants of all complexes formed in the pH range 2.5–11.5. Surprisingly, although desferrioxamine gives rise to very stable 1:1 complexes with Zr4+ (logK = 36.14 for Zr4+ + DFO3− = [ZrDFO]+), 2:2 and 2:3 ones are also formed in solution. Depending on the conditions, these binuclear complexes can be main species in solution. These results were corroborated by small-angle X-ray scattering (SAXS) and MALDI mass spectrometry analyses of complex solutions. Information on complex structures was obtained by means of density functional theory (DFT) calculations
Sensing Zn2+ in aqueous solution with a fluorescent scorpiand macrocyclic ligand decorated with an anthracene bearing tail
Synthesis of the new scorpiand ligand L composed of a [9]aneN3 macrocyclic ring bearing a CH2CH2NHCH2-anthracene tail is reported. L forms both cation (Zn2+) and anion (phosphate, benzoate) complexes. In addition, the zinc complexes of L bind these anions. The equilibrium constants for ligand protonation and complex formation were determined in 0.1 M NaCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric (pH-metric) titrations. pH Controlled coordination/detachment of the ligand tail to Zn2+ switch on and off the fluorescence emission from the anthracene fluorophore. Accordingly, L is able to sense Zn2+ in the pH range 6–10 down to nM concentrations of the metal ion. L can efficiently sense Zn2+ even in the presence of large excess of coordinating anions, such as cyanide, sulphide, phosphate and benzoate, despite their ability to bind the metal ion
Complexes of Organic Anions with Tetrazine-based Ligands in Water or How Multifaceted Equilibria Can Arise from Apparently Simple Systems
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