Coupling of Bifunctional CoMn‐Layered Double Hydroxide@Graphitic C3N4 Nanohybrids towards Efficient Photoelectrochemical Overall Water Splitting

The development of durable, low‐cost, and efficient photo‐/electrolysis for the oxygen and hydrogen evolution reactions (OER and HER) is important to fulfill increasing energy requirements. Herein, highly efficient and active photo‐/electrochemical catalysts, that is, CoMn‐LDH@g‐C₃N₄ hybrids, have been synthesized successfully through a facile in situ co‐precipitation method at room temperature. The CoMn‐LDH@g‐C₃N₄ composite exhibits an obvious OER electrocatalytic performance with a current density of 40 mA cm^?2 at an overpotential of 350 mV for water oxidation, which is 2.5 times higher than pure CoMn‐LDH nanosheets. For HER, CoMn‐LDH@g‐C₃N₄ (η₅₀=?448 mV) requires a potential close to Pt/C (η₅₀=?416 mV) to reach a current density of 50 mA cm². Furthermore, under visible‐light irradiation, the photocurrent density of the CoMn‐LDH@g‐C₃N₄ composite is 0.227 mA cm^?2, which is 2.1 and 3.8 time higher than pristine CoMn‐LDH (0.108 mA cm^?2) and g‐C₃N₄ (0.061 mA cm^?2), respectively. The CoMn‐LDH@g‐C₃N₄ composite delivers a current density of 10 mA cm^?2 at 1.56 V and 100 mA cm^?2 at 1.82 V for the overall water‐splitting reaction. Therefore, this work establishes the first example of pure CoMn‐LDH and CoMn‐LDH@g‐C₃N₄ hybrids as electrochemical and photoelectrochemical water‐splitting systems for both OER and HER, which may open a pathway to develop and explore other LDH and g‐C₃N₄ nanosheets as efficient catalysts for renewable energy applications.     

Fluordiazadiphosphetidine, 17. Mitt.

The reactions of (CH₃NPF₃)₂ and F₃P(CH₃N)₂PF₂OCH₃ with lithium-1,1,1-trimethyl-N-(trimethylsilyl)-silanamide yield two new dispiro-compounds:XF₂P(CH₃N)₂PF(NSiCH₃)₂PF(CH₃N)₂PF₂ X withX=F, OCH₃. Synthesis, mass-spectra and X-ray structures are discussed.

Herrn Prof. Dr.K. L. Komarek zum 60. Geburtstag gewidmet.     

Modeling substrate- and inhibitor-bound forms of liver alcohol dehydrogenase: chemistry of mononuclear nitrogen/sulfur-ligated zinc alcohol,formamide, and sulfoxide complexes

Using a mixed nitrogen/sulfur ligand possessing a single internal hydrogen bond donor (N,N-bis-2-(methylthio)ethyl-N-(6-amino-2-pyridylmethyl)amine (bmapa)), we prepared and structurally and spectroscopically characterized a series of zinc complexes possessing a single alcohol ([(bmapa)Zn(MeOH)](ClO(4))(2) (1)), formamide ([(bmapa)Zn(DMF)](ClO(4))(2) (3), [(bmapa)Zn(NMF)](ClO(4))(2) (4)), or sulfoxide ([(bmapa)Zn(DMSO)](ClO(4))(2) (7), [(bmapa)Zn(TMSO)](ClO(4))(2) (8)) ligand. X-ray crystallographic characterization was obtained for 1.MeOH, 3, 4, 7.DMSO, and 8. To enable studies of the influence of the single hydrogen bond donor amino group of the bmapa ligand on the chemistry of zinc/neutral oxygen donor binding interactions, analogous alcohol ([(bmpa)Zn(MeOH)](ClO(4))(2) (2)), formamide ([(bmpa)Zn(DMF)](ClO(4))(2) (5), [(bmpa)Zn(NMF)](ClO(4))(2) (6)), and sulfoxide ([(bmpa)Zn(DMSO)](ClO(4))(2) (9), [(bmpa)Zn(TMSO)](ClO(4))(2) (10)) complexes of the bmpa (N,N-bis-2-(methylthio)ethyl-N-(2-pyridylmethyl)amine) ligand system were generated and characterized. Of these, 2, 5, 6, and 9.2DMSO were characterized by X-ray crystallography. Solution spectroscopic methods ((1)H and (13)C NMR, FTIR) were utilized to examine the formamide binding properties of 3-6 in CH(3)CN and CH(3)NO(2) solutions. Conclusions derived from this work include the following: (1) the increased donicity of formamide and sulfoxide donors (versus alcohols) makes these competitive ligands for a cationic N/S-ligated zinc center, even in alcohol solution, (2) the inclusion of a single internal hydrogen bond donor, characterized by a heteroatom distance of approximately 2.80-2.95 A, produces subtle structural perturbations in N/S-ligated zinc alcohol, formamide, or sulfoxide complexes, (3) the heteroatom distance of a secondary hydrogen-bonding interaction involving the oxygen atom of a zinc-coordinated alcohol, formamide, and sulfoxide ligand is reduced with increasing donicity of the exogenous ligand, and (4) formamide displacement on a N/S-ligated zinc center is rapid, regardless of the presence of an internal hydrogen bond donor. These results provide initial insight into the chemical factors governing the binding of a neutral oxygen donor to a N/S-ligated zinc center.     

Copper(II) benzoate nitroxide dimers and chains: structure and magnetic studies

Copper(II) benzoate dimers and linear chains have been synthesized and exhibit very different magnetic behaviors. The benzoate dimers, 1a, show typical dimeric singlet-triplet transitions and strong antiferromagnetic coupling (JST = -206 K (-143 cm-1); H = -2JSTSa.Sb). The bromobenzoate dimer can be converted into linear chains of hydrogen-bonded monomers, showing 1-D ferromagnetic coupling (6a, theta = +9 K). Copper(II) sites can also be bridged by nitroxide-substituted benzoates, 1b and 1c, that is, 2-(4'-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (NNBA, 3a), with JST = -216 K (-150 cm-1), with comparable interactions between the nitroxide and triplet Cu(II) spins, theta T = -157 K. A 1-D chain similar to the bromobenzoate monomers can also be produced with NNBA, also exhibiting ferromagnetic coupling (6b, theta = +0.67 K), albeit much weaker. Other nitroxides have been introduced into the Cu(II) dimer system by capping copper(II) acetate with the polydentate 2-(4'-pyridyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PYNN, 3b), which exhibits almost no coupling to the copper centers when both ends of the dimer are capped (1d, theta = -5.8 K). In contrast, strong coupling is observed when only one PYNN is used (2, theta = -300 K), which is the result of direct coordination of the nitroxide to the copper centers, producing a chain of the dimer units.     

Ambidentate pyridyl-carboxylate ligands in the coordination-driven self-assembly of 2D Pt macrocycles: self-selection for a single isomer

The coordination-driven self-assembly of discrete 2D macrocyclic species from ambidentate pyridyl-carboxylate-based donor ligands and platinum-containing acceptors is presented. All these species are characterized by electrospray ionization mass spectrometry (ESIMS), multinuclear NMR, and in one example, X-ray crystallography. In each case only one isomeric assembly is selectively formed in high yield, despite the potential for more than one product as a consequence of differences in connectivity.     

NMR studies of mononuclear octahedral Ni(II) complexes supported by tris((2-pyridyl)methyl)amine-type ligands

The recent discovery of acireductone dioxygenase (ARD), a metalloenzyme containing a mononuclear octahedral Ni(II) center, necessitates the development of model systems for evaluating the role of the metal center in substrate oxidation chemistry. In this work, three Ni(II) complexes of an aryl-appended tris((2-pyridyl)methyl)amine ligand (6-Ph(2)TPA, N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine), [(6-Ph(2)TPA)Ni(CH(3)CN)(CH(3)OH)](ClO(4))(2) (1), [(6-Ph(2)TPA)Ni(ONHC(O)CH(3))]ClO(4) (3), and [(6-Ph(2)TPA)Ni-Cl(CH(3)CN)]ClO(4) (4), and one Ni(II) complex of tris((2-pyridyl)methyl)amine, [(TPA)Ni(CH(3)CN)(H(2)O)](ClO(4))(2) (2), have been characterized in acetonitrile solution using conductance methods and NMR spectroscopy. In acetonitrile solution, 1-4 have monomeric cations that exhibit isotropically shifted (1)H NMR resonances. Full assignment of these resonances was achieved using one- and two-dimensional (1)H NMR techniques and (2)H NMR of analogues having deuteration of the supporting chelate ligand. COSY cross peaks were observed for pyridyl protons of the 6-Ph(2)TPA ligand in 1 and 3. This study lays the groundwork for using NMR methods to examine chemical reactions of 1 and 2 with model substrates of relevance to ARD.     

L-malic acid biosensor for field-based evaluation of apple, potato and tomato horticultural produce

A screen-printed three-electrode amperometric biosensor incorporating malic enzyme for the measurement of L-malic acid in apple, potato and tomato horticultural samples has been developed. The working electrode contained 0.38 mU of immobilised enzyme and was fabricated using rhodinised carbon to facilitate NADPH oxidation at an operating potential of +300 mV vs. Ag/AgCl compared with > +600 mV for bare carbon. The linear range of the sensor was 0.028-0.7 mM L-malic acid with relative standard deviations of 3.3-13.3%. When testing with real apple, potato and tomato samples, the sensor accuracy was within 13.7% of a standard commercially available photometric test kit. The sensor approach is cheap, simple to perform and rapid (6 min), requiring only buffer-electrolyte and a small sample volume.     

Chemistry of a binuclear cadmium(II) hydroxide complex: formation from water,CO(2) reactivity,and comparison to a zinc analog

Treatment of the bmnpa (N,N-bis-2-(methylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine) ligand with equimolar amounts of Cd(ClO(4))(2).5H(2)O and Me(4)NOH.5H(2)O in CH(3)CN yielded the binuclear cadmium hydroxide complex [((bmnpa)Cd)(2)(mu-OH)(2)](ClO(4))(2).CH(3)CN (1). Complex 1 may also be prepared (a) by treatment of a CH(3)CN solution of (bmnpa)Cd(ClO(4))(2) (2) with 1 equiv of n-BuLi, followed by treatment with water or (b) from 2 in the presence of 1 equiv each of water and NEt(3). The hydroxide derivative 1 is not produced from 2 and water in the absence of an added base. Complex 1 possesses a binuclear structure in the solid state with hydrogen-bonding and CH/pi interactions involving the bmnpa ligand. The overall structural features of 1 differ from the halide derivative [((bmnpa)Cd)(2)(mu-Cl)(2)](ClO(4))(2) (3), particularly in that the Cd(2)(mu-OH)(2) core of 1 is symmetric whereas the Cd(2)(mu-Cl)(2) core of 3 is asymmetric. In acetonitrile solution, 1 behaves as a 1:2 electrolyte and retains a binuclear structure and secondary hydrogen-bonding and CH/pi interactions, whereas 3 is a 1:1 electrolyte, indicating formation of a mononuclear [(bmnpa)CdCl]ClO(4) species in solution. Treatment of 1 with CO(2) in anhydrous CH(3)CN yields the bridging carbonate complex [((bmnpa)Cd)(2)(mu-CO(3))](ClO(4))(2).CH(3)CN (4). Treatment of a chemically similar zinc hydroxide complex, [((benpa)Zn)(2)(mu-OH)(2)](ClO(4))(2) (benpa = N,N-bis-2-(ethylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine, with CO(2) also results in the formation of a carbonate derivative, [((benpa)Zn)(2)(mu-CO(3))](ClO(4))(2) (5), albeit the coordination mode of the bridging carbonate moiety is different. Treatment of 4 with added water results in no reaction, whereas 5 under identical conditions will undergo reaction to yield the zinc hydroxide complex [((benpa)Zn)(2)(mu-OH)(2)](ClO(4))(2).     

Chemical reduction of 2,4,6-tricyano-1,3,5-triazine and 1,3,5-tricyanobenzene. Formation of novel 4,4',6,6'-Tetracyano-2,2'-bitriazine and its radical anion

Chemical reduction of 2,4,6-tricyano-1,3,5-triazine, TCT, results in the formation of an unstable radical anion that undergoes immediate dimerization at a ring carbon to form [C(12)N(12)](2-), [TCT](2)(2-), characterized by a long 1.570 (4) A central C[bond]C. [TCT](2)(2-) can decompose into the radical anion of 4,4',6,6'-tetracyano-2,2'-bitriazine, [TCBT]*-, the one-electron reduced form of planar (D(2h)) TCBT, which is also structurally characterized as the [TMPD][TCBT] charge-transfer complex (TMPD = N,N,N',N'-tetramethyl-p-phenylenediamine) with a 1.492 (2) A central sp(2)[bond]sp(2) C[bond]C. Although crystals could not be obtained for the radical anion [TCBT]*-, the electrochemistry (E degrees = +0.03 V), EPR (g = 2.003, (2)A((14)N) = 3.347 G, and (4)A((14)N) = 0.765 G and a line width of 0.24 G), and theoretical calculations support the formation of [TCBT]*-. In addition, thermolysis of [TCT](2)(2-) yields [TCBT]*-. Chemical reduction of 2,4,6-tricyanobenzene, TCB, forms an unstable radical anion that immediately undergoes dimerization at a ring carbon to form [C(12)H(6)N(6)](2-), [TCB](2)(2-), which has a long 1.560 (5) A central C[bond]C. Reaction of TCT with tetrathiafulvalene (TTF) forms structurally characterized [TTF][TCT], and in the presence of water, TCT hydrolyzes to 2,4-dicyano-6-hydroxy-s-triazine, DCTOH. In contrast, the reaction of TCT with TMPD forms [TMPD][TCT], which in the presence of water forms structurally characterized [HTMPD](+)[DCTO](-).     

Amide hydrolysis reactivity of a N4O-ligated zinc complex: comparison of kinetic and themodynamic parameters with those of the corresponding amide methanolysis reaction

Treatment of the mononuclear amide-appended zinc complex [(ppbpa)Zn](ClO4)2 (1(ClO4)2) with Me4NOH.5H2O in CD3CN/D2O (3:1) results in the formation of the deprotonated amide species [(ppbpa-)Zn]ClO4 (2). Upon heating in CD3CN/D2O, this complex undergoes amide hydrolysis to produce a zinc carboxylate product, [(ambpa)Zn(O2CC(CH3)3)]ClO4 (3). X-ray crystallography, 1H and 13C NMR, IR, and elemental analysis were used to characterize 3. The hydrolysis reaction of 1(ClO4)2 exhibits saturation kinetic behavior with respect to the concentration of D2O. Variable-temperature kinetic studies of the amide hydrolysis reaction yielded DeltaH++ = 18.0(5) kcal/mol and DeltaS++ = -22(2) eu. These activation parameters are compared to those of the corresponding amide methanolysis reaction of 1(ClO4)2.