Synthesis,Structures, and Thermal Properties of Cobalt(II) Thiocyanate Coordination Compounds with 2,5‐Dimethylpyrazine

Reactions of Co(NCS)₂ with 2,5‐dimethylpyrazine lead to the formation of five compounds of compositions Co(NCS)₂(H₂O)₄ · 4(2,5‐dimethylpyrazine) ( 1 ), Co(NCS)₂(H₂O)₄ · 3(2,5‐dimethylpyrazine) ( 2 ), Co(NCS)₂(2,5‐dimethylpyrazine)(H₂O)₂ · 3(2,5‐dimethylpyrazine) ( 3 ), [Co(NCS)₂]₂(H₂O)₆ · 4(2,5‐dimethylpyrazine) · 4H₂O ( 4 ), and Co(NCS)₂(2,5‐dimethylpyrazine)(MeOH)₂ ( 5 ). 1 and 2 are simple aqua complexes, in which the Co cations are octahedrally coordinated by two thiocyanate anions and four water molecules, whereas in 3 the Co cations are linked by the 2,5‐dimethylpyrazine ligands into chains. In compound 4 Co(NCS)₂](H₂O)₆ dimers are observed, which are linked by bridging water molecules. In compound 5 the Co cations are connected into chains by the 2,5‐dimethylpyrazine co‐ligand and are additionally coordinated by terminal anionic ligands and methanol molecules. Thermogravimetric measurements of compounds 1 – 4 show several mass steps, in which the water and the co‐ligands and the water molecules are stepwise removed. Elemental analysis, XRPD investigations, and IR spectroscopic investigations indicate that all of these compounds decompose into new phases of composition Co(NCS)₂(2,5‐dimethylpyrazine)₂ ( 6 ) that on further heating decompose into [Co(NCS)₂]₃(2,5‐dimethylpyrazine) ( 8 ) via Co(NCS)₂(2,5‐dimethylpyrazine) ( 7 ) as intermediate. Compound 7 can be directly obtained by thermal removal of methanol from compound 5 .     

Crystal Structures and Selected Properties of CoII Containing Thiostannates prepared by a New Room Temperature Route

The room temperature reaction of Na₄Sn₂S₆ · 5H₂O with CoCl₂ · 6H₂O and 2-(aminomethyl)pyridine (2-AMP) or trans-1,2-diamino-cyclohexane (DACH) leads to crystallization of two compounds with the compositions [Co(2-(aminomethyl)pyridine)₃]₂ Sn₂S₆ · 10H₂O ( 1 ) and [Co(trans-1,2-diaminocyclohexane)₃]₂Sn₂S₆ · 8H₂O ( 2 ). In both compounds [Sn₂S₆]^4– anions are present that are charge balanced each by two Co²⁺ centered complexes. Each of the two Co^II cations are sixfold coordinated by six N atoms of three 2-AMP or DACH ligands within slightly distorted octahedra. In compound 1 , the two complexes are linked by one [Sn₂S₆]^4– anion via strong N–H ··· S hydrogen bonds into centrosymmetric charge neutral trimeric units, that are further linked by weak C–H ··· S and N–H ··· S hydrogen bonds into chains that are directed along the a axis. These chains are further joined by N–H ··· O and O–H ··· O hydrogen bonds into a 3D network, with the H₂O molecules forming chains along the b axis. The crystal structure of 2 is similar to that of 1 featuring trimeric units which are also linked into chains. Between the chains water molecules are embedded that link the chains into a 3D network. Upon heating 2 in a thermobalance the water and ligand molecules are removed in discrete steps, indicating that compounds with more condensed thiostannate networks will form.     

Crystal Structure of infin;2[Cu2I2(μ-4-4′-bipyridine)] and Investigations on the Thermal Decomposition of Cu X -4,4′-bipyridine Coordination Polymers

 The inorganic-organic coordination polymer _infin; ²[Cu₂I₂(μ-4-4′-bipyridine)] was prepared by the reaction of Cu(I)I and 4,4^′-bipyridine in acetonitrile. Its structure consists of staircase-like CuX double chains which are connected to sheets by the 4,4^′-bipyridine ligands. The thermal decomposition of the corresponding 1:1 copper(I) halide-4,4^′-bipyridine compounds _infin; ²[CuX(μ-4-4′-bipyridine)] (X = Cl, Br, I) was investigated using simultaneous difference thermal analysis and thermogravimetry (DTA-TG), thermomicroscopy, and temperature resolved X-ray powder diffraction in air or argon. Upon heating _infin; ²[CuX(μ-4-4′-bipyridine)], several changes in sample mass are observed which correspond to a stepwise loss of the organic ligands. Temperature-resolved X-ray powder diffraction proves that _infin; ²[CuX(μ-4-4′-bipyridine)] transforms to _infin; ²[Cu₂ X ₂(μ-4-4′-bipyridine)] during the decomposition; the latter looses the remaining ligands when heated further, forming the corresponding copper(I)halides. When the experiments were performed under an argon atmosphere, the 2:1 coordination polymers were obtained as phase-pure compounds.     

Phenol Based‐Ligands with Two Adjacent N,N′,O‐Binding Pockets

The synthesis of three new ligands and their coordination behavior towards zinc ions with strongly coordinating anions and cobalt ions with weakly coordinating anions are reported. The ligands have two adjacent imidazolyl‐pyridinyl and pyrazolyl‐pyridinyl binding pockets, respectively, which are linked by a phenol unit. We also investigated the dynamic behavior of the ligand having the imidazolyl‐pyridiyl sidearm in solution. The reaction of the ligands and ZnCl₂ yielded complexes of the type [ L Zn₂Cl₃]. When we used Co^II salts with weakly coordinating anions, complexes of the general formula [ L ₂Co₂]²⁺ were formed.     

Poly­[[aqua­copper(I)-μ-bromo]-μ-(5-methyl­pyrazine-2-carboxyl­ato)-κ3N4:O,N1-[di­aqua­copper(II)]-μ-(5-methyl­pyrazine-2-carboxyl­ato)-κ3O,N1:N4-[aqua­copper(I)-μ-bromo]]

In the structure of the title compound, [Cu₃Br₂(C₆H₅N₂O₂)₂(H₂O)₄], both copper(I) and copper(II) cations are present. The copper(II) cations are located on centres of inversion and are coordinated by two N atoms and two carboxyl­ate O atoms from two symmetry-related 5-methyl­pyrazine-2-carboxyl­ate anions, with two water mol­ecules completing a distorted octahedron. The copper(I) cations are coordinated by the second N atom of the 5-methyl­pyrazine-2-carboxyl­ate anion, one water mol­ecule and two bromide anions within a distorted tetrahedron. Each of the bromide anions connects two symmetry-equivalent copper(I) cations to form zigzag-like CuBr chains. These chains are connected by the [di­aqua­bis(5-methyl­pyrazine-2-carboxyl­ato)]copper(II) complexes, forming corrugated sheets parallel to (100). The CuBr chains and the sheets are connected via O—H⋯O and O—H⋯Br hydrogen bonding.     

Low‐Molecular‐Weight Analogues of the Soluble Methane Monooxygenase (sMMO): From the Structural Mimicking of Resting States and Intermediates to Functional Models

The active centre of sMMO contains a diiron core ligated by histidine and glutamate residues, which is capable of catalysing a remarkable reaction: the oxidation of methane with O₂ yielding methanol. This review describes the results of efforts to prepare low‐molecular‐weight analogues of this active site directing towards 1) the assignment of the spectroscopic signatures identified for certain intermediates of the sMMO catalytic cycle to structural features and 2) the synthesis of molecular compounds that can mimic the reactivity. The historical development of the model chemistry, which is subdivided into structural and functional mimicking, is illustrated and achievements reached so far are highlighted.     

Anwendung biologischer Untersuchungsmethoden in der Nahrungsmittelchemie

Ohne Zusammenfassung     

Accumulation of Four Electrons on a Terphenyl (Bis)disulfide

The activation of N₂, CO₂ or H₂O to energy-rich products relies on multi-electron transfer reactions, and consequently it seems desirable to understand the basics of light-driven accumulation of multiple redox equivalents. Most of the previously reported molecular acceptors merely allow the storage of up to two electrons. We report on a terphenyl compound including two disulfide bridges, which undergoes four-electron reduction in two separate electrochemical steps, aided by a combination of potential compression and inversion. Under visible-light irradiation using the organic super-electron donor tetrakis(dimethylamino)ethylene, a cascade of light-induced reaction steps is observed, leading to the cleavage of both disulfide bonds. Whereas one of them undergoes extrusion of sulfur to result in a thiophene, the other disulfide is converted to a dithiolate. These insights seem relevant to enhance the current fundamental understanding of photochemical energy storage.     

Mechanism of an Elusive Solvent Effect in Organozinc Reagent Synthesis

Solvent effects are often difficult to understand in cases where reaction intermediates, and thus their differential behavior in different solvents, are not directly observable by traditional ensemble analytical techniques. Herein, the sensitivity of single-particle fluorescence microscopy uniquely enables direct observation of organozinc intermediates and solvent effects on their build-up and persistence. When combined with NMR spectroscopy, these imaging data pinpoint the previously elusive mechanistic origin of solvent effects in the synthesis of widely used organozinc reagents. These findings characterize the acceleration of oxidative addition of the starting organoiodide to the surface of zinc metal in DMSO relative to THF, but once formed, surface intermediates display similar persistence in either solvent. The current studies are the first demonstration of a highly sensitive, single-particle fluorescence microscopy technique to pinpoint otherwise elusive solvent effects in synthetic chemistry.