Electrochemical fluorination on nickel anodes, also known as the Simons’ process, is an important fluorination method used on an industrial scale. Despite its success, the mechanism is still under ...debate. One of the proposed mechanisms involves higher valent nickel species formed on an anode acting as effective fluorinating agents. Here we report the first attempt to study fluorination by means of first principles investigation. We have identified a possible surface model from the simplest binary nickel fluoride (NiF2). A twice oxidized NiF2(F2) (001) surface exhibits higher valent nickel centers and a fluorination source that can be best characterized as an F2− like unit, readily available to aid fluorination. We have studied the adsorption of CH4 and the co-adsorption of CH4 and HF on this surface by means of periodic density functional theory. By the adsorption of CH4, we found two main outcomes on the surface. Unreactive physisorption of CH4 and dissociative chemisorption resulting in the formation of CH3F and HF. The co-adsorption with the HF gave rise to four main outcomes, namely the formation of CH3F, CH2F2, CH3 radical, and also physisorbed CH4.
The trifluorides of the two high field strength elements yttrium and holmium are studied by periodic density functional theory. As a lanthanide, holmium also belongs to the group of rare earth ...elements (REE). Due to their equivalent geochemical behavior, both elements form a geochemical twin pair and consequently, yttrium is generally associated with the REE as REE+Y. Interestingly, it has been found that DFT/DFT+U describe bulk HoF3 best, when the 4f-electrons are excluded from the valence region. An extensive surface stability analysis of YF3 (PBE) and HoF3 (PBE+Ud/3 eV/4f-in-core) using two-dimensional surface models (slabs) is performed. All seven low-lying Miller indices surfaces are considered with all possible stoichiometric or substoichiometric terminations with a maximal fluorine-deficit of two. This leads to a scope of 24 terminations per compound. The resulting Wulff plots consists of seven surfaces with 5–26% abundance for YF3 and six surfaces with 6–34% for HoF3. The stoichiometric (010) surface is dominating in both compounds. However, subtle differences have been found between these two geochemical twins.
Carbon-based materials doped with metal and nitrogen (M-N-Cs) have promising potential in electrocatalytic applications with the advantage of material sustainability. MN4 motifs incorporated into a ...carbon lattice are generally known to be responsible for the activity of these materials. While many computational studies assume the tetrapyridinic MN4 motifs, recent studies have elucidated the role of tetrapyrrolic MN4 motifs in electrocatalysis. Using density functional theory, we constructed and compared various structural models to study the incorporation of tetrapyrrolic and tetrapyridinic MN4 motifs in 2D carbon materials and analyzed the type of interactions between each metal species and the N4 site. We further quantified the relative affinity of various metal species to the two types of N4 site. Upon analysis of energies, bond lengths, electronic population and charges, we found that metals that exhibit highly ionic binding characters have a greater affinity towards tetrapyrrolic MN4 motifs compared to species that participate in covalent interactions with the π-system. Furthermore, the binding strength of each species in the N4 site depend on the electronegativity as well as the availability of orbitals for accepting electrons from the π-system.
Covalent functionalization tailors carbon nanotubes for a wide range of applications in varying environments. Its strength and stability of attachment come at the price of degrading the carbon ...nanotubes sp
network and destroying the tubes electronic and optoelectronic features. Here we present a non-destructive, covalent, gram-scale functionalization of single-walled carbon nanotubes by a new 2+1 cycloaddition. The reaction rebuilds the extended π-network, thereby retaining the outstanding quantum optoelectronic properties of carbon nanotubes, including bright light emission at high degree of functionalization (1 group per 25 carbon atoms). The conjugation method described here opens the way for advanced tailoring nanotubes as demonstrated for light-triggered reversible doping through photochromic molecular switches and nanoplasmonic gold-nanotube hybrids with enhanced infrared light emission.
Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon. We present here the first example of a plastically flexible one‐dimensional ...(1D) coordination polymer. The compound Zn(μ‐Cl)2(3,5‐dichloropyridine)2n is flexible over two crystallographic faces. Remarkably, the single crystal remains intact when bent to 180°. A combination of microscopy, diffraction, and spectroscopic studies have been used to probe the structural response of the crystal lattice to mechanical bending. Deformation of the covalent polymer chains does not appear to be responsible for the observed macroscopic bending. Instead, our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers. Moreover, our calculations propose a cause of the different mechanical properties of this compound and a structurally similar elastic material.
Bending the rules: The first example of a plastically flexible 1D coordination polymer is described. Zn(μ‐Cl)2(3,5‐Cl2Py)2n is flexible over two crystallographic faces and a single crystal remains intact when bent to 180°. Displacement rather than deformation of the coordination polymer chains appears to be responsible for the observed macroscopic bending.
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•The control of adiabatic attosecond charge migration in benzene using rationally designed pulses is demonstrated.•The analysis of transient angular electronic fluxes is performed ...using wave function based methods.•The electronic phase aquired during the laser preparation step has a marked influence on the charge migration mechanism.
We design four linearly x- and y-polarized as well as circularly right (+) and left (−) polarized, resonant π/2-laser pulses that prepare the model benzene molecule in four different degenerate superposition states. These consist of equal (0.5) populations of the electronic ground state S0(1A1g) plus one of four degenerate excited states, all of them accessible by dipole-allowed transitions. Specifically, for the molecule aligned in the xy-plane, these excited states include different complex-valued linear combinations of the 1E1u,x and 1E1u,y degenerate states. As a consequence, the laser pulses induce four different types of periodic adiabatic attosecond (as) charge migrations (AACM) in benzene, all with the same period, 504 as, but with four different types of angular fluxes. One of the characteristic differences of these fluxes are the two angles for zero fluxes, which appear as the instantaneous angular positions of the “source” and “sink” of two equivalent, or nearly equivalent branches of the fluxes which flow in pincer-type patterns from one molecular site (the “source”) to the opposite one (the “sink”). These angles of zero fluxes are either fixed at the positions of two opposite carbon nuclei in the yz-symmetry plane, or at the centers of two opposite carbon-carbon bonds in the xz-symmetry plane, or the angles of zero fluxes rotate in angular forward (+) or backward (−) directions, respectively. As a resume, our quantum model simulations demonstrate quantum control of the electronic fluxes during AACM in degenerate superposition states, in the attosecond time domain, with the laser polarization as the key knob for control.
In this Article, we explore the potential of triarylmethyl (TAM) oligomers as devices for organic molecular spintronic applications. We use the Landauer formalism to compute global spin transport and ...local current analysis to understand transport at finite bias voltages within the nonequilibrium Green’s function framework and using density functional theory calculations. Important variations of the total spin current are observed in chlorinated TAM dimers as a function of the electronic structure in the device. On the other hand, the spin-resolved local transport mechanism and the geometry of the nanodevice are found to depend weakly on the electronic structure, even at relatively high voltages. Such dimers could potentially be used in transistor applications. Further, devices based on chlorinated TAM monomers are shown to possess strong differential spin-transport properties at low bias voltage, a property that could be used for spin filtering.
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