Unique Use of Dibromo-L-Tyrosine Ligand in Building of Cu(II) Coordination Polymer-Experimental and Theoretical Investigations.

Although the crystals of coordination polymer {[CuCl(µ-O,O'-L-Br2Tyr)]}n (1) (L-Br2Tyr = 3,5-dibromo-L-tyrosine) were formed under basic conditions, crystallographic studies revealed that the OH group of the ligand remained protonated. Two adjacent [CuCl(L-Br2Tyr)] monomers, bridged by the carboxylate group of the ligand in the syn-anti bidentate bridging mode, are differently oriented to form a polymeric chain; this specific bridging was detected also by FT-IR and EPR spectroscopy. Each Cu(II) ion in polymeric compound 1 is coordinated in the xy plane by the amino nitrogen and carboxyl oxygen of the parent ligand and the oxygen of the carboxyl group from the symmetry related ligand of the adjacent [Cu(L-Br2Tyr)Cl] monomer, as well as an independent chlorine ion. In addition, the Cu(II) ion in the polymer chain participates in long-distance intermolecular contacts with the oxygen and bromine atoms of the ligands located in the adjacent chains; these intramolecular contacts were also supported by NCI and NBO quantum chemical calculations and Hirshfeld surface analysis. The resulting elongated octahedral geometry based on the [CuCl(L-Br2Tyr)] monomer has a lower than axial symmetry, which is also reflected in the symmetry of the calculated molecular EPR g tensor. Consequently, the components of the d-d band obtained by analysis of the NIR-VIS-UV spectrum were assigned to the corresponding electronic transitions.

Low pH constructed Co(ii) and Ni(ii) 1D coordination polymers based on Cα-substituted analogues of zoledronic acid: structural characterization, and spectroscopic and magnetic properties.

Three novel coordination compounds based on α,α-disubstituted analogues of zoledronic acid with a cyclopropane (cpp) or cyclobutane (cbt) ring on the Cα carbon, isomorphous [Co(H2cppZol)(H2O)]·H2O (1a), [Ni(H2cppZol)(H2O)]·H2O (1b) and [Co(H2cbtZol)(H2O)]·H2O (2a), were synthesized under hydrothermal conditions at low pH. Single-crystal X-ray diffraction analysis revealed that all the compounds had a 1D double zig-zag chain architecture with an 8 + 8 ring motif formed by alternately arranged symmetrical (-O-P-O-)2 bridges linking equivalent octahedral metal centres. Both the ligand coordination mode and chain architecture displayed by 1a, 1b and 2a are unique among 1D [M(H2L)(H2O) x ]·yH2O coordination polymers based on nitrogen-containing bisphosphonates reported so far. All the compounds exhibit similar decomposition pathways upon heating with thermal stabilities decreasing in the order 1b > 1a > 2a. The IR spectra revealed that lattice water release above 227, 178 and 97 °C, respectively, does not change the chain architecture leaving them intact up to ca. 320, 280 and 240 °C. Magnetic behaviour investigations indicated that 1a, 2a and 1b exhibit weak alternating antiferromagnetic-ferromagnetic exchange interactions propagated between the magnetic centres through double (-O-P-O-)2 bridges. The boundary between antiferro- and ferromagnetic couplings for the Co-O⋯O-Co angle in 1a and 2a was estimated to be ca. 80°. This value is also applicable for recently reported [M3(HL)2(H2O)6]·6H2O (M = Co, Ni) complexes based on α,α-disubstituted analogues of zoledronic acid and can be used to the explain magnetic behaviour of 1b.

Amphoteric Ion-Exchange Membranes with Significantly Improved Vanadium Barrier Properties for All-Vanadium Redox Flow Batteries.

All-vanadium redox flow batteries (VRBs) have attracted considerable interest as promising energy-storage devices that can allow the efficient utilization of renewable energy sources. The membrane, which separates the porous electrodes in a redox flow cell, is one of the key components in VRBs. High rates of crossover of vanadium ions and water through the membrane impair the efficiency and capacity of a VRB. Thus, membranes with low permeation rate of vanadium species and water are required, also characterized by low resistance and stability in the VRB environment. Here, we present a new design concept for amphoteric ion-exchange membranes, based on radiation-induced grafting of vinylpyridine into an ethylene tetrafluoroethylene base film and a two-step functionalization to introduce cationic and anionic exchange sites, respectively. During long-term cycling, redox flow cells containing these membranes showed higher efficiency, less pronounced electrolyte imbalance, and significantly reduced capacity decay compared to the cells with the benchmark material Nafion 117.

Two isomorphous Co(ii) coordination polymers based on new α,α-disubstituted derivatives of zoledronic acid: synthesis, structures and properties.

Two novel α,α-disubstituted derivatives of zoledronic acid, namely 1-hydroxy-2-(1H-imidazol-1-yl)-2-methylpropylidene-1,1-diphosphonic acid (H4L1) and 1-hydroxy-2-[1-(1H-imidazol-1-yl)cyclopropyl]ethylidene-1,1-diphosphonic acid (H4L2) were synthesized and structurally characterized by single-crystal X-ray diffraction. The reaction of cobalt acetate with H4L1 and H4L2 carried out under hydrothermal conditions afforded two isomorphous Co3(HL1)2(H2O)6·6H2O (1a) and Co3(HL2)2(H2O)6·6H2O (2a) complexes. Both compounds are characterized by means of X-ray crystallography, IR and NIR-Vis-UV spectroscopic methods. Furthermore, their magnetic properties and thermal stabilities are reported. The crystals of 1a and 2a feature infinite 1D polymeric chains built from alternately arranged dinuclear [Co2(HL1/HL2)(H2O)2]2 units and {Co1O6} octahedra running along the [1[combining macron]10] crystallographic direction. In both compounds, crystallographically distinct Co1 and Co2 atoms are six-coordinated. As is reflected in T values (T - index of tetragonality), the coordination environment of Co1 generates a slightly elongated octahedron (T = 0.94), whereas a slightly compressed octahedron (T = 1.06 for 1a and 1.05 for 2a) is formed around Co2. An assumption that the d-d type absorption is mainly attributed to the inversion related Co2 centers, whose population is two times higher than that of Co1, afforded a good correlation between calculated transition energies and experimental NIR-Vis-UV spectra. The magnetic susceptibility measurements analyzed in terms of a spin-3/2 Heisenberg trimer chain revealed that Co1Co2 interactions within the trimer are antiferromagnetic whereas Co2Co2 intertrimer interactions are ferromagnetic.

Crystal structure of di-cyclo-hexyl-ammonium nitrate(V).

In the title mol-ecular salt, C12H24N(+)·NO3 (-), the cyclohexyl rings adopt chair conformations with the exocyclic C-N bonds in equatorial orientations. In the crystal, a bifurcated N-H⋯(O,O) hydrogen bond links the cation to the anion; the ion pairs are linked via C-H⋯O hydrogen bonds, forming layers in the ac plane.

Dicyclohexylammonium bromoacetate: a low molecular mass organogelator with a one-dimensional secondary ammonium monocarboxylate (SAM) synthon.

The asymmetric unit of the title salt, C12H24N(+)·C2H2BrO2(-), contains a dicyclohexylammonium cation connected to a bromoacetate anion by means of an N-H...O hydrogen bond. In the crystal, the ion pairs assemble via N-H...O interactions, forming zigzag infinite chains parallel to the c axis with the (...H-N-H...O-C-O...)n motif that is considered to be a prerequisite for ensuring gelation properties of secondary ammonium monocarboxylate salts. The title salt was characterized by FT-IR, X-ray powder diffraction (XRPD), TG-DTA and (1)H NMR spectroscopy in solution. Gelation experiments revealed that dicyclohexylammonium bromoacetate forms molecular gels with dimethylformamide and dimethyl sulfoxide. Scanning electron microscopy (SEM) was used to reveal morphological features of dried gels.