Unusual structural phenomena in the reaction of copper and nickel dihalides with NH_3(g) at ambient conditions

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Solution/ammonolysis syntheses of unsupported and silica-supported copper(I) nitride nanostructures from oxidic precursors

Herein we describe an alternative strategy to achieve the preparation of nanoscale Cu3N. Copper(II) oxide/hydroxide nanopowder precursors were successfully fabricated by solution methods. Ammonolysis of the oxidic precursors can be achieved essentially pseudomorphically to produce either unsupported or supported nanoparticles of the nitride. Hence, Cu3N particles with diverse morphologies were synthesized from oxygen-containing precursors in two-step processes combining solvothermal and solid−gas ammonolysis stages. The single-phase hydroxochloride precursor, Cu2(OH)3Cl was prepared by solution-state synthesis from CuCl2·2H2O and urea, crystallising with the atacamite structure. Alternative precursors, CuO and Cu(OH)2, were obtained after subsequent treatment of Cu2(OH)3Cl with NaOH solution. Cu3N, in the form of micro- and nanorods, was the sole product formed from ammonolysis using either CuO or Cu(OH)2. Conversely, the ammonolysis of dicopper trihydroxide chloride resulted in two-phase mixtures of Cu3N and the monoamine, Cu(NH3)Cl under similar experimental conditions. Importantly, this pathway is applicable to afford composite materials by incorporating substrates or matrices that are resistant to ammoniation at relatively low temperatures (ca. 300 °C). We present preliminary evidence that Cu3N/SiO2 nanocomposites (up to ca. 5 wt.% Cu3N supported on SiO2) could be prepared from CuCl2·2H2O and urea starting materials following similar reaction steps. Evidence suggests that in this case Cu3N nanoparticles are confined within the porous SiO2 matrix

Photosynthesis of H-2 and its storage on the Bandgap Engineered Mesoporous (Ni2+/Ni3+)O @ TiO2 heterostructure

A noble-metal free and surface defect-induced mesoporous mixed valent NiO decorated TiO2 heterostructure with tuned bandgap has been successfully prepared. Its outstanding visible-light driven hydrogen evolution and its excellent H-2 storage ability have been examined and confirmed. The formation of oxygen vacancies by surface defect creates the Ni3+ and Ti3+ on the interface of the heterostructure induce the efficient H-2 evolution, benchmarked by 1200% enhancement in catalytic performance. The underlying chemistries include the near-unity occupancy of e(g) orbital (t(2g)(6) e(g)(1)) of Ni3+ which speeds up the electron transfer and significantly promote the excellent electron-hole separation efficiency, establishes the outstanding overall charge-transfer efficiency and long-term photocatalytic activity in the visible light spectrum. Multiple Ti3+ adsorption centers in the structure attract multiple intact H-2 molecules per each center via a sigma - pi bonding motif - namely the Kubas interaction - which leads to 480% higher H-2 adsorption capability against the performance of the pristine mesoporous TiO2. Not only the significant results, the study also provide an air-stable synthetic method on the basis of low-cost and abundant materials, which are strongly favoured for scaling up production.Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 11170414 ANID/FONDAP/1511001

Elastic coupling and anelastic relaxation associated with multiple phase transitions in para-chloroanilinium tetrachlorocuprate, [p-ClC6H4NH3]2CuCl4

The perovskite-like salt [p-ClC6H4NH3]2CuCl4 1 exhibits a wealth of magnetic and structural phase transitions which have been probed by variable temperature single crystal X-ray diffraction, SQUID magnetometry, resonant ultrasound spectroscopy (RUS), EPR spectroscopy, DSC measurements and DFT calculations. Single crystal X-ray diffraction studies between room temperature and 3 K reveal a rich tapestry of structural changes; at 298 K the structure conforms to a monoclinic setting but undergoes a first order phase transition upon cooling below ∼275 K to a higher symmetry orthorhombic cell. This is facilitated by a transition to an intermediate phase at ∼277 K. Whilst the intermediate phase has a limited stability window (∼2 K) and has not been structurally determined, the two discrete phase transitions at 275.5 K and 277 K have been clearly detected by differential scanning calorimetry, EPR spectroscopy and RUS studies. On further cooling a dynamic relaxation process is observed in RUS measurements, evidenced by a Debye-like peak in the dissipation at ∼140 K. Residual electron density maps from single crystal X-ray diffraction studies reveal that this may be associated with a freezing out of the NH3⋯Cl hydrogen-bonding between cation and anion frameworks upon cooling. The activation barrier for this order/disorder process was estimated to be at least 27 kJ mol−1 from the RUS data. Variable temperature dc SQUID data reveal that 1 is a 2D ferromagnet with antiferromagnetic interactions between layers below 9 K. Analysis of the temperature dependence of the magnetic susceptibility for T > 40 K reveals that 1 exhibits Curie–Weiss behaviour with θ = +22.8 K indicative of dominant ferromagnetic interactions. Good agreement is observed between the strength of the ferromagnetic interaction extracted from the Weiss constant (J/k = +22.8 K) and that calculated by DFT (J/k = +25 to +28 K) and from EPR studies (J/k = +17 K). The presence of short range ferromagnetic interactions is reflected in a marked temperature dependence of the g-factors determined from EPR spectroscopy below 20 K and possibly a small elastic anomaly in the RUS data. RUS studies indicate a very small elastic anomaly associated with the transition to long range order, implying weak or no magnetoelastic effect. At fields above ∼15 G a spin flip transition is induced and 1 displays metamagnetic behaviour, with a saturation magnetization of 0.96 μB