43193-60-8

Pyrazine-2,3,5,6-tetracarboxylic acid (ptcH4) reacts with Cd(NO3)2·6H2O at room temperature in the presence of pyridine to form a 2D open framework built from alternating left- and right-handed helicates with the empirical formula, {[Cd2(ptc)·(py)5·H2O]·5H2O·py}n, 1. Lattice water and pyridine molecules form an intricate array of H-bonding with the 2D sheets leading to a 3D structure. This compound crystallizes in the monoclinic space group C2/c with the following lattice parameters-a=24.103(2), b=13.480(5), c=29.176(4) A?, β=109.427(3)°, V=8940(4) A?3, Z=8, R1=0.0513, wR2=0.1552, S=1.085.

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A dinuclear ruthenium complex bridged by 2,3,5,6-pyrazinetetracarboxylic acid (μ-LH22-) was synthesized and characterized by X-ray crystallography, cyclic voltammetry under ambient and elevated pressures, electron paramagnetic resonance (EPR) and UV/vis-NIR (NIR = near-infrared) spectroelectrochemistry, pulse radiolysis, and computational methods. We probed for the first time in the field of mixed-valency the use of high-pressure electrochemical methods. The investigations were directed toward the influence of the protonation state of the bridging ligand on the electronic communication between the ruthenium ions, since such behavior is interesting in terms of modulating redox chemistry by pH. Starting from the [RuII(μ-LH22-)RuII]0 configuration, which shows an intense metal-to-ligand charge transfer absorption band at 600 nm, cyclic voltammetry revealed a pH-independent, reversible one-electron reduction and a protonation-state-dependent (proton coupled electron transfer, PCET) reversible oxidation. Deeper insight into the electrode reactions was provided by pressure-dependent cyclic voltammetry up to 150 MPa, providing insight into the conformational changes, the protonation state, and the environment of the molecule during the redox processes. Spectroelectrochemical investigations (EPR, UV/vis-NIR) of the respective redox reactions suggest a ligand-centered radical anion [RuII(μ-LH2?3-)RuII]- upon reduction (EPR Δg = 0.042) and an ambiguous, EPR-silent one-electron oxidized state. In both cases, the absence of the otherwise typical broad intervalence charge transfer bands in the NIR region for mixed-valent complexes support the formulation as radical anionic bridged compound. However, on the basis of high-pressure electrochemical data and density functional theory calculations the one-electron oxidized form could be assigned as a charge-delocalized [RuII.5(μ-LH22-)RuII.5]+ valence tautomer rather than [RuIII(μ-LH2?3-)RuIII]+. Deprotonation of the bridging ligand causes a severe shift of the redox potential for the metal-based oxidation toward lower potentials, yielding the charge-localized [RuIII(μ-LH3-)RuII]0 complex. This PCET process is accompanied by large intrinsic volume changes. All findings are supported by computational methods (geometry optimization, spin population analysis). For all redox processes, valence alternatives are discussed.

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In contrast to the well documented role of charge- and resonance-assistance in very short hydrogen bonds, a very short O-Hacid···Owater hydrogen bond [O···O 2.4791(13) A] in the title acid is ascribed to the cumulative stabilisation from σ- and π-bond cooperativity.

A well-designed redox-active organic linker, pyrazine-2,3,5,6-tetracarboxylate (H4pztc) with brimming active sites for lithium ions storage was utilized to construct coordination polymers (CPs) via a facile hydrothermal reaction. Those two isostructural two-dimensional (2D) CPs, namely [M2(pztc)(H2O)6]n (M=Co for 1 and Ni for 2), delivered excellent reversible capacities and stable cycling performance as anodes in lithium ion batteries. As demonstrated in electrochemical studies, 1 and 2 can achieve highly reversible capacities of 815 and 536 mA h g?1 at 200 mA g?1 for 150 cycles, respectively, best performed for the reported 2D-CP-based anode materials. The electrochemical mechanism studies showed that the remarkable performances can be ascribed to the synergistic Li-storage redox reactions of metal centers and organic moieties. Our work highlights the opportunities of using a well-designed organic ligand to construct low-dimensional CPs as new type of electrode materials for advanced lithium ion batteries.

Disclosed are vanadyl complexes of Formula 1, Formula 2, and Formula 3, wherein Ri, R2, and R are defined as in the description. The pharmaceutical compositions containing these complexes and uses of the complexes for treatment of Diabetes Mellitus, such as Diabetes Mellitus Type 2, are also disclosed.

Two new 1D slide-fastener-like coordination polymers {[Mn2(pztc)(phen)2(H2O)2]·4H2O}n (1) and {[Mn2(pztc)(bpy)2(H2O)2]·2H2O}n (2) have been synthesized by the reactions of pyrazine-2,3,5,6-tetracarboxylic acid (pztcH4) and Mn(OAc)2·4H2O in the presence of 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy) under hydrothermal conditions and characterized by elemental analyses, FT-IR, TGA and X-ray diffraction. In complex 1 and 2, metal ions are bridged by pyrazine-2,3,5,6-tetracarboxylate, coordinating in a hexadentate manner, so forming 1D polymeric chains. The remaining coordination sites of the metal ions are occupied by one O atom of water molecule and two N atoms of the terminal ligand (phen or bpy). IR spectra and thermal analysis data are in agreement with the crystal structure.

Metal complexes of a hexameric network tetrapyrazineporpyrazine were synthesized by template polycyclotetramerization of pyrazine-2,3,5,6-tetracarboxamide in an urea melt in the presence of a corresponding metal acetate; irrespective of the metal, the polymerization degree of the polymeric ligand does not exceed six. A method for structural assessment of such compounds was proposed.

The occurrence of short hydrogen bonds in pyrazine di-, tri-, and tetracarboxylic acid dihydrates was analyzed. A very short O- H···O hydrogen bond was characterized in one of the tetracids. The synergy from resonance and polarization assistance in the finite, neutral array was found to be sufficient to result in short O-H···H hydrogen bonds when the carboxylic acid donor is activated. This synthon-assisted hydrogen-bond shortening phenomenon was postulated from the neutron-diffraction crystal structure.

A method of preparation and/or purification of acid anhydrides is disclosed. Dicarboxylic or polycarboxylic acids contained in the anhydrides to be treated, are dehydrated in an organic solvent in the presence of activated carbon.