Rodion V. Belosludov

Highly controlled acetylene accommodation in a metal-organic microporous material.

Metal–organic microporous materials (MOMs) have attracted wide scientific attention owing to their unusual structure and properties, as well as commercial interest due to their potential applications in storage, separation and heterogeneous catalysis. One of the advantages of MOMs compared to other microporous materials, such as activated carbons, is their ability to exhibit a variety of pore surface properties such as hydrophilicity and chirality, as a result of the controlled incorporation of organic functional groups into the pore walls. This capability means that the pore surfaces of MOMs could be designed to adsorb specific molecules; but few design strategies for the adsorption of small molecules have been established so far. Here we report high levels of selective sorption of acetylene molecules as compared to a very similar molecule, carbon dioxide, onto the functionalized surface of a MOM. The acetylene molecules are held at a periodic distance from one another by hydrogen bonding between two non-coordinated oxygen atoms in the nanoscale pore wall of the MOM and the two hydrogen atoms of the acetylene molecule. This permits the stable storage of acetylene at a density 200 times the safe compression limit of free acetylene at room temperature.

Self-Accelerating CO Sorption in a Soft Nanoporous Crystal

Soft, Selective CO Sorption Many industrial processes produce CO, which could be used as a chemical feedstock, but separation of CO from other gases, especially N2, is too difficult to be economically viable. Sato et al. (p. 167, published online 12 December 2013) now report that a porous coordination polymer containing Cu2+ ions can selectivity bind CO through serial structural changes reminiscent of allosteric effects in proteins. The separation of CO-N2 mixtures can be achieved with a low input energy for CO desorption. A soft nanoporous crystalline solid exhibits self-accelerating, selective carbon monoxide adsorption. Carbon monoxide (CO) produced in many large-scale industrial oxidation processes is difficult to separate from nitrogen (N2), and afterward, CO is further oxidized to carbon dioxide. Here, we report a soft nanoporous crystalline material that selectively adsorbs CO with adaptable pores, and we present crystallographic evidence that CO molecules can coordinate with copper(II) ions. The unprecedented high selectivity was achieved by the synergetic effect of the local interaction between CO and accessible metal sites and a global transformation of the framework. This transformable crystalline material realized the separation of CO from mixtures with N2, a gas that is the most competitive to CO. The dynamic and efficient molecular trapping and releasing system is reminiscent of sophisticated biological systems such as heme proteins.

Designing Nanogadgetry for Nanoelectronic Devices with Nitrogen‐Doped Capped Carbon Nanotubes

A systematic analysis of electron transport characteristics for 1D heterojunctions with two nitrogen-doped (N-doped) capped carbon nanotubes (CNTs) facing one another at different conformations is presented considering the chirality of CNTs (armchair(5,5) and zigzag(9,0)) and spatial arrangement of N-dopants. The results show that the modification of the molecular orbitals by the N-dopants generates a conducting channel in the designed CNT junctions, inducing a negative differential resistance (NDR) behavior, which is a characteristic feature of the Esaki-like diode, that is, tunneling diode. The NDR behavior significantly depends on the N-doping site and the facing conformations of the N-doped capped CNT junctions. Furthermore, a clear interpretation is presented for the NDR behavior by a rigid shift model of the HOMO- and LUMO-filtered energy levels in the left and right electrodes under the applied biases. These results give an insight into the design and implementation of various electronic logic functions based on CNTs for applications in the field of nanoelectronics.

The mechanisms for pressure-induced amorphization of ice Ih

There has been considerable interest in the structure of liquid water at low temperatures and high pressure following the discovery of the high-density amorphous (HDA) phase of ice Ih (ref. 1). HDA ice forms at a pressure close to the extrapolated melting curve of ice, leading to the suggestion that it may have structure similar to that of dense water. On annealing, HDA ice transforms into a low-density amorphous (LDA) phase with a distinct phase boundary,. Extrapolation of thermodynamic data along the HDA–LDA coexistence line into the liquid region has led to the hypothesis that there might exist a second critical point for water and the speculation that liquid water is mixture of two distinct structures with different densities,. Here we critically examine this hypothesis. We use quasi-harmonic lattice-dynamics calculations to show that the amorphization mechanism in ice Ih changes from thermodynamic melting for T > 162 K to mechanical melting at lower temperatures. The vibrational spectra of ice Ih, LDA ice and quenched water also indicate a structure for LDA ice that differs from that of the liquid. These results call into question the validity of there being a thermodynamic connection between the amorphous and liquid phases of water.

THEORETICAL STUDY OF DONOR–SPACER–ACCEPTOR STRUCTURE MOLECULE FOR STABLE MOLECULAR RECTIFIER

Recently, field of molecular electronics has attracted strong attention as a “post-silicon technology” to enable future nanoscale electronic devices. To realize this molecular device, unimolecular rectifying function is one of the most fundamental requirements using nanotechnology. In the present study, the geometric and electronic structures of alkyl derivative C37H50N4O4 (PNX) molecule, (donor – spacer – acceptor), a candidate for a molecular rectifying device, has been investigated theoretically using ab initio quantum mechanical calculations. The results suggest that in such donor-acceptor molecular complexes, while the lowest unoccupied orbital concentrates on the acceptor subunit, the highest occupied molecular orbital is localized on the donor subunit. After the optimization of the structure by B3LYP/6-31(d), the approximate potential differences for the optimized PNX molecule have been estimated at the B3LYP/6-311++G(d,p) level of theory, which achieves quite good agreement with experimentally reported results.

Theoretical study of phthalocyanine–fullerene complex for a high efficiency photovoltaic device using ab initio electronic structure calculation

Abstract Many fullerene-based supramolecules have been proposed as potential organic photovoltaic devices, with their electrochemical and photo-electrochemical properties measured under light illumination. Phthalocyanine possesses good electron-donating properties due to its large easily ionised π-electron system, whereas fullerene is good π-electron acceptor which can be connected with other organic molecules. A phthalocyanine–fullerene-based supramolecular system is therefore a potential material candidate for a photovoltaic cell due to its large and flexible absorption combined with electrical properties similar to an inorganic semiconductor. We investigated the geometric and electronic structure of phthalocyanine–fullerene supramolecule using an ab initio quantum mechanical calculation. The results suggest that the lowest unoccupied molecular orbital (LUMO) state of this supramolecule localized on the fullerene and the highest occupied molecular orbital (HOMO) state is localized on half of the phthalocyanine. The energy difference of localized LUMO levels strongly depended on the functional group attached to the phthalocyanine and the structure of the supramolecule.

Theoretical study of phase transitions in Kr and Ar clathrate hydrates from structure II to structure I under pressure.

The theory developed in our earlier papers is extended to predict dynamical and thermodynamic properties of clathrate structures by accounting for the possibility of multiple filling of cavities by guest molecules. The method is applied to the thermodynamic properties of argon and krypton hydrates, considering both structures I (sI) and II (sII), in which the small cages can be singly occupied and large cages of sII can be singly or doubly occupied. It was confirmed that the structure of the clathrate hydrate is determined by two main factors: intermolecular interaction between guest and host molecules and the configurational entropy. It is shown that for guests weakly interacting with water molecules, such as argon or krypton, the free energy of host lattices without the contribution of entropy is the main structure-determining factor for clathrate hydrates, and it is a cause of hydrate sII formation at low pressure with these guests. Explicit account of the entropy contribution in the Gibbs free energy allows one to determine the stability of hydrate phases and to estimate the line of structural transition from sII to sI in P-T plane. The structural transition between sII and sI in argon and krypton hydrates at high pressure is shown to be the consequence of increasing intermolecular interaction and the degree of occupancy of the large cavities.

Combinatorial computational chemistry approach as a promising method for design of Fischer–Tropsch catalysts based on Fe and Co

Abstract The combinatorial computational chemistry approach was applied to design new types of catalysts, which can be used in the Fisher–Tropsh (FT) synthesis for the production of ecologically high-quality transportation fuels. For this purpose, the density functional theory (DFT) was used to investigate the CO adsorption on Fe- and Co-based multi-component catalysts. The energetic, electronic and structural properties of CO on the catalyst surfaces were calculated. It was found that Mn, Mo, and Zr could be used as additional elements in the Fe- and Co-based catalysts, since one cannot observe a degradation of the adsorption properties of the active sites as well as showing a high sulfur tolerance. For the Co-based catalyst, the same tendency is also found in the case of the Si promoter. The obtained results are in agreement with available experimental data that confirmed the validity of combinatorial computational chemistry approach.

First Excited State Properties and Static Hyperpolarizability of Ruthenium(II) Ammine Complexes.

First principles calculations were used to study the electronic excitation energies (E), transition dipole moments (μ), and difference of dipole moments between ground and excited states (Δμ) for low-lying singlets of the series of ruthenium(II) ammine complexes. Both cases of the gas phase and the acetonitrile solution were investigated in order to explain the discrepancy between the recent experimental and theoretical results and to develop the optimal way of estimation for the first static hyperpolarizability in the framework of a two-state model introduced by Oudar and Chemla. The present calculations reveal that the effect of solvent on the electronic properties of investigated compounds is not only the change of the excitation energy but also the increasing of ground-state molecular polarization and intensification of metal-to-ligand intramolecular charge transfer for electronic excitations. These effects lead to increasing of the values of Δμ and ground-state dipole moment μg in solution as compared with the gas-phase ones. The proposed theoretical approach gives good agreement with experiment and allows one to apply it for designing a new perspective nonlinear optical active organometallics.

Gate-induced switching and negative differential resistance in a single-molecule transistor: emergence of fixed and shifting states with molecular length.

The quantum transport of a gated polythiophene nanodevice is analyzed using density functional theory and nonequilibrium Greens function approach. For this typical molecular field effect transistor, we prove the existence of two main features of electronic components, i.e., negative differential resistance and good switching. Ab initio based explanations of these features are provided by distinguishing fixed and shifting conducting states, which are shown to arise from the interface and functional molecule, respectively. The results show that proper functional molecules can be used in conjunction with metallic electrodes to achieve basic electronics functionality at molecular length scales.