Piezo-enhanced activation of dinitrogen for room temperature production of ammonia.

The catalytic conversion of nitrogen to ammonia remains an energy-intensive process, demanding advanced concepts for nitrogen fixation. The major obstacle of nitrogen fixation lies in the intrinsically high bond energy (941 kJ mol-1) of the N≡N molecule and the absence of a permanent dipole in N2. This kinetic barrier is addressed in this study by an efficient piezo-enhanced gold catalysis as demonstrated by the room temperature reduction of dinitrogen into ammonia. Au nanostructures were immobilized on thin film piezoelectric support of potassium sodium niobate (K0.5Na0.5NbO3, KNN) by chemical vapor deposition of a new Au(III) precursor [Me2Au(PyTFP)(H2O)]1(PyTFP = (Z)-3,3,3-trifluoro-1-(pyridin-2-yl)-prop-1-en-2-olate) that exhibited high volatility (60 °C, 10-3mbar) and clean decomposition mechanism to produce well adherent elemental gold films on KNN and Ti substrates. The gold-functionalized KNN films served as an efficient catalytic system for ammonia production with a Faradaic efficiency of 18.9% achieved upon ultrasonic actuation. Our results show that the spontaneous polarization of piezoelectric materials under external electrical fields augments the sluggish electron transfer kinetics by creating instant dipoles in adsorbed N2molecules to deliver a piezo-enhanced catalytic system promising for sustained activation of dinitrogen molecules.

Ergothioneine and related histidine derivatives in the gas phase: tautomer structures determined by IRMPD spectroscopy and theory.

l-Ergothioneine (ET) is a sulfur-containing derivative of the amino acid histidine that offers unique antioxidant properties. The enzyme independent redox-chemistry of ET relies on the availability of the thiol tautomer to allow oxidative formation of disulfide bridges, i.e., the tautomeric equilibrium. To study the intrinsic properties of ET the tautomeric equilibrium is studied in the gas-phase by infrared multiphoton dissociation (IRMPD) spectroscopy. The IR ion spectra of isolated molecular ions of ET and of the biosynthetic precursors of ET, i.e., hercynine and Nε-methyl-hercynine are acquired. The analyte structures are independently investigated by density functional theory (DFT) and computed linear IR-spectra of tautomer ion structures are compared with the gas-phase spectra for identification. For the molecular ion of ET the simulated IR spectra of thione and thiol structures match the recorded IRMPD spectrum and that prevents an individual structure assignment. On the other hand, theory suggests that ET adopts a thione tautomer in MeOH solution which could be carried over from the condensed phase to gas phase and could be kinetically trapped after effective electrospray phase transfer and desolvation. Such a non-thermal behavior is also found for the molecular ions of protonated hercynine and Nε-methyl-hercynine. Contrary to that, the sodium complex ions of ET, hercynine and Nε-methyl-hercynine adopt the respective ground structures predicted by theory, which are reliably identified spectroscopically. For ET the thione tautomer is by far the most stable isomer in the sodium complex molecular ion.

Temperature and pressure variations of d-d luminescence band maxima of bis(pyridylalkenolato)palladium(II) complexes with different ligand substituents: opposite-signed trends.

Luminescence spectra of two d(8)-configured bis(pyridylalkenolato)palladium(ii) complexes, [Pd{PyCHC(C3F7)O}2] and [Pd{PyCHC(CH3)O}2], are presented at variable temperature and pressure. Bands are assigned as d-d transitions. The heptafluoropropyl and methyl substituents on the ligands have different steric demands, influencing luminescence spectra. Broad bands with maxima at approximately 12 700 cm(-1) (790 nm) for ligands with heptafluoropropyl substituents and 12,100 cm(-1) (830 nm) for ligands with methyl substituents and widths of approximately 2100 cm(-1) for both complexes are observed at 80 K. Quenching of the luminescence is observed as temperature increases. The maxima of [Pd{PyCHC(C3F7)O}2] show a shift of -0.9 ± 0.1 cm(-1) K(-1) due to broadening of the spectra to lower energy. The luminescence maxima of [Pd{PyCHC(CH3)O}2] shift in the opposite direction by +7.2 ± 0.7 cm(-1) K(-1). Shifts with different signs are also obtained from variable-pressure luminescence spectra, with values of +13 ± 2 cm(-1) kbar(-1) and -15 ± 7 cm(-1) kbar(-1) for [Pd{PyCHC(C3F7)O}2] and [Pd{PyCHC(CH3)O}2], respectively. The pressure-induced decrease is unusual and likely caused by intermolecular interactions involving the palladium(ii) center and a vinylic proton of a neighboring complex.

Ligand-modulated chemical and structural implications in four-, five-, and six-fold coordinated aluminum heteroaryl alkenolates.

Synthesis and characterization (gas phase, solution, and solid-state) of a series of four-, five- and six-fold coordinated heteroaryl-alkenolato aluminum complexes were performed to demonstrate the delicate interplay of structural and chemical influences of ligands in the design of new precursors for chemical vapor deposition. We are investigating the properties of heteroaryl alkenols as O^N chelating ligands [where O^N is 3,3,3-trifluoro(pyridin-2-yl)propen-2-ol (H-PyTFP), 3,3,3-trifluoro(1,3-benzimidazol-2-yl)propen-2-ol (H-BITFP), 3,3,3-trifluoro(dimethyl-1,3-oxazol-2-yl)propen-2-ol (H-DMOTFP), 3,3,3-trifluoro(1,3-benzoxazol-2-yl)propen-2-ol (H-BOTFP), 3,3,3-trifluoro(1,3-benzthiazol-2-yl)propen-2-ol (H-BTTFP), and 3,3,3-trifluoro(dimethyl-1,3-thiazol-2-yl)propen-2-ol (H-DMTTFP)] to prepare volatile and air-stable compounds. All three methyl groups in highly reactive AlMe3 could be replaced by H-PyTFP, H-BITFP, H-DMOTFP, and H-BOTFP yielding octahedral complexes of the type Al(O^N)3; under similar conditions H-BTTFP and H-DMTTFP produced heteroleptic MeAl(O^N)2 compounds with five-fold coordinated aluminum centers. Various attempts to obtain tris-alkenolato derivatives by choosing higher temperatures and prolonged reaction times were not successful. The reaction of H-PyTFP with [Al(O(t)Bu)3]2 produced the dimeric heteroleptic [Al(PyTFP)(O(t)Bu)2]2 complex with Al atoms present in both octahedral (Oh) and tetrahedral (Td) coordination in a single molecular unit. The introduction of the chelating ligand H-PyTFP in the dimeric framework of [Al(O(t)Bu)3]2 enhanced the stability against hydrolyses significantly. The tendency of Al(III) centers to preferably coordinate in Td or Oh environment was elucidated by hydrolysis studies of monomeric Al(PyTFP)3, Al(BOTFP)3, and MeAl(BTTFP)2 that produced hydroxo-bridged dimers to retain the octahedral environment for Al atoms. Surprisingly, hydrolysis of monomeric MeAl(DMTTFP)2 yielded an oxo-bridged dimer with two five-fold coordinated aluminum centers. The structural features of all new complexes were investigated in solution, vapor, and solid state by multinuclear NMR spectroscopy, EI-MS spectrometry, and single-crystal X-ray diffraction analyses, respectively.