Unexpectedly Large Contribution of Oxygen to Charge Compensation Triggered by Structural Disordering: Detailed Experimental and Theoretical Study on a Li3NbO4-NiO Binary System.

Dependence on lithium-ion batteries for automobile applications is rapidly increasing. The emerging use of anionic redox can boost the energy density of batteries, but the fundamental origin of anionic redox is still under debate. Moreover, to realize anionic redox, many reported electrode materials rely on manganese ions through π-type interactions with oxygen. Here, through a systematic experimental and theoretical study on a binary system of Li3NbO4-NiO, we demonstrate for the first time the unexpectedly large contribution of oxygen to charge compensation for electrochemical oxidation in Ni-based materials. In general, for Ni-based materials, e.g., LiNiO2, charge compensation is achieved mainly by Ni oxidation, with a lower contribution from oxygen. In contrast, for Li3NbO4-NiO, oxygen-based charge compensation is triggered by structural disordering and σ-type interactions with nickel ions, which are associated with a unique environment for oxygen, i.e., a linear Ni-O-Ni configuration in the disordered system. Reversible anionic redox with a small hysteretic behavior was achieved for LiNi2/3Nb1/3O2 with a cation-disordered Li/Ni arrangement. Further Li enrichment in the structure destabilizes anionic redox and leads to irreversible oxygen loss due to the disappearance of the linear Ni-O-Ni configuration and the formation of unstable Ni ions with high oxidation states. On the basis of these results, we discuss the possibility of using σ-type interactions for anionic redox to design advanced electrode materials for high-energy lithium-ion batteries.

P2-type Na(2/3)Ni(1/3)Mn(2/3-x)Ti(x)O2 as a new positive electrode for higher energy Na-ion batteries.

New electrode materials of layered oxides, Na2/3Ni1/3Mn2/3-xTixO2 (0 ≤ x ≤ 2/3), are successfully synthesized, and their electrochemical performance is examined in aprotic Na cells. A Na//Na2/3Ni1/3Mn1/2Ti1/6O2 cell delivers 127 mA h g(-1) of reversible capacity and the average voltage reaches 3.7 V at first discharge with good capacity retention.

Structure-directing forces in intercluster compounds of cationic [Ag(14)(C[triple bond]CtBu)(12)Cl](+) building blocks and polyoxometalates: long-range versus short-range bonding interactions.

Crystallization of [Ag(14)(C[triple bond]CtBu)(12)Cl][BF(4)] and different polyoxometalates in organic solvents yields a series of new intercluster compounds: [Ag(14)(C[triple bond]CtBu)(12)Cl(CH(3)CN)](2)[W(6)O(19)] (1), (nBu(4)N)[Ag(14)(C[triple bond]CtBu)(12)Cl(CH(3)CN)](2)[PW(12)O(40)] (2), and [Ag(14)(C[triple bond]CtBu)(12)Cl](2)[Ag(14)(C[triple bond]CtBu)(12)Cl(CH(3)CN)](2)[SiMo(12)O(40)] (3). Applying the same technique to a system starting from polymeric {[Ag(3)(C[triple bond]CtBu)(2)][BF(4)]0.6 H(2)O}(n) and the polyoxometalate (nBu(4)N)(2)[W(6)O(19)] results in the formation of [Ag(14)(C[triple bond]CtBu)(12)(CH(3)CN)(2)][W(6)O(19)] (4). Here, the Ag(14) cluster is generated from polymeric {[Ag(3)(C[triple bond]CtBu)(2)][BF(4)]0.6 H(2)O}(n) during crystallization. In a similar way, [Ag(15)(C[triple bond]CtBu)(12)(CH(3)CN)(5)][PW(12)O(40)] (5) has been obtained from {[Ag(3)(C[triple bond]CtBu)(2)][BF(4)]0.6 H(2)O}(n) and (nBu(4)N)(3)[PW(12)O(40)]. The use of charged building blocks was intentional, because at these conditions the contribution of long-range Coulomb interactions would benefit most from full periodicity of the intercluster compound, thus favoring formation of well-crystalline materials. The latter has been achieved, indeed. However, as a most conspicuous feature, equally charged species aggregate, which demonstrates that the short-range interactions between the "surfaces" of the clusters represent the more powerful structure direction forces than the long-range Coulomb bonding. This observation is of significant importance for understanding the mechanisms underlying self-organization of monodisperse and structurally well-defined particles of nanometer size.

Structure-directing effects in the supramolecular intercluster compound [Au9(PPh3)8]2[V10O28H3]2: long-range versus short-range bonding interactions.

Although being composed of trivalent ions, the crystal structure of the supramolecular intercluster compound [Au9(PPh3)8]2[V10O28H3]2 is dominated by short-range intermolecular interactions, i.e., hydrogen bonds, and C-H/pi interactions, avoiding a simple AB-type packing.

Surfactant-free synthesis and functionalization of gold nanoparticles.

A new, facile and generally applicable synthesis of functionalized gold nanoparticles is presented. It is based on the surfactant-free generation of weakly stabilized nanoparticles by the reduction of HAuCl4 with sodium naphthalenide in diglyme. These nanoparticles were found to lack long-term stability. However, stabilization in both unpolar and polar solvents could straightforwardly be achieved by subsequent addition of various capping ligands. The resulting ligand-capped gold nanoparticles were investigated by TEM microscopy, UV-vis, and FT-IR spectroscopy. Particle core size can be tuned by the amount of reduction agent. The strict separation of the reduction step and the functionalization step in this one-pot synthesis offers an easy and fast access to highly functionalized gold nanoparticles.

Determining the geometry of hydrogen bonds in solids with picometer accuracy by quantum-chemical calculations and NMR spectroscopy.

The structure of multiply hydrogen-bonded systems is determined with picometer accuracy by a combined solid-state NMR and quantum-chemical approach. On the experimental side, advanced 1H-15N dipolar recoupling NMR techniques are capable of providing proton-nitrogen distances of up to about 250 pm with an accuracy level of +/-1 pm for short distances (i.e., around 100 pm) and +/-5 pm for longer ones (i.e., 180 to 250 pm). The experiments were performed under fast magic-angle spinning, which ensures sufficient dipolar decoupling and spectral resolution of the 1H resonance lines. On the quantum-chemical side, the structures of the hydrogen-bonded systems were computationally optimised, yielding complete sets of nitrogen-proton and proton-proton distances, which are essential for correctly interpreting the experimental NMR data. In this way, nitrogen-proton distances were determined with picometer accuracy, so that vibrational averaging effects on dipole-dipole couplings need to be considered. The obtained structures were finally confirmed by the complete agreement of computed and experimental 'H and '5N chemical shifts. This demonstrates that solid-state NMR and quantum-chemical methods ideally complement each other and, in a combined manner, represent a powerful approach for reliable, high-precision structure determination whenever scattering techniques are inapplicable.