The investigation of transition metal dichalcogenide nanotubes is characterized by significant variability. The majority of experimental studies on these materials focus on the structural and optical properties of MoS2 and WS2 multi-walled nanotubes (MWNTs). In contrast, research on WSe2 nanotubes has received comparatively little attention. Only a limited number of studies have synthesized and explored the MWNTs based on HfS2 and HfSe2. Theoretical researches mainly include density functional theory (DFT) calculations for single-, double-, and triple-walled nanotubes with relatively small diameters. We propose new atomistic potentials designed to model the MWNTs based on W and Hf dichalcogenides, whose diameters approach the experimentally observed ones and are beyond the capabilities of ab initio methods. The developed force fields have been applied to the study of the structure and stability of achiral nanotubes, which are composed of 1-10 single-wall components. The properties of WX2-based nanotubes are compared with those of analogous HfX2-based nanotubes (X = S, Se). In particular, it has been shown that HfX2 multi-walled nanotubes are much more faceted than similar WX2 multi-walled nanotubes. The stability of multi-walled nanotubes with respect to single-wall components and nanolayers was investigated. For the first time, it has been found that the binding energy of achiral MWNTs is a linear function of the inverse wall number. The slope of the resulting line is related to the interwall adhesion energy.

Currently, multicage fullerene compounds (oligomers and polymers) with covalent bonds between the fullerene units attract great attention due to the possible applications whereby the proximate location of the fullerene cages plays crucial role. In contrast to most abundant C60 (Ih) fullerene, the oligomers and polymers of the C70 (D5h) are poorly studied but this fullerene must demonstrate wider diversity due to lower symmetry and diversified structural motifs. In the present theoretical work, we explore this diversity and use density-functional theory computations to scrutinize the polarizability, energy gaps and formation energies of 5 polymers constructed by the connection of the fullerene units via ab bonds. We compare their polarizabilities with the oligomers (C70)n (n up to 6) with the same structural motifs and provide the analytical expression that bridges the properties of oligomers and polymers, computed in terms of molecular and periodic paradigms, respectively.

A series of bis-diimine rhenium(I) complexes Re(NN1-OMe)-Re(NN3-OMe), containing neocuproine and methyl [2-(pyridin-2-yl)quinoline-4-carboxylate (NN1), methyl [2,2 '-biquinoline]-4-carboxylate (NN2), dimethyl [2,2 '-biquinoline]-4,4 '-dicarboxylate (NN3) was synthesized and characterized. Utilization of the asymmetric NN1 and NN2 ligands affords two types of structural isomers, which were isolated and structurally studied by X-ray diffraction analysis in the solid state. 1H-1H COSY and NOESY NMR experiments confirmed preservation of the structural patterns in liquid media for the complexes under study. Alkaline hydrolysis of the ester groups in the NN# diimine ligands was performed to give the Re(NN1-OK)-Re(NN3-OK) complexes exhibiting higher water solubility that made possible to use them in biological experiments. In MeOH and aqueous media, the complexes display NIR absorption with a long wavelength band at ca. 715 nm extended up to 850 nm in the case of both forms of Re(NN3)-OX. The Re(NN3-OK) complex demonstrated stable photoacoustic signal in oxygenated blood phantoms and showed no significant toxicity with the cell viability above 80% even at concentrations of 1 mM in cell experiments with CHO-K1 cell line.

A series of diphosphine Re(I) complexes Re(PPh3)(P-bpy), Re(PPh3)(P-terpy), Re(P-OEG)(P-bpy) and Re(P-OEG)(P-terpy) have been designed via decoration the archetypal {Re(CO)2(NN-OEG)} core with the phosphine ligands bearing bipyridyl (P-bpy) and terpyridyl (P-terpy) functions, which are capable to bind Cu(I) and Cu(II) ions. The presence of the bipyridyl (NN-OEG) and the phosphine (P-OEG) ligands functionalized with oligo(ethylene glycol) fragments is sufficient to impart water-solubility to the target complexes Re(P-OEG)(P-bpy) and Re(P-OEG)(P-terpy) that makes possible to study their photophysical characteristics both in organic and aqueous media. The obtained complexes demonstrate phosphorescence from 3 MLCT excited state typical for this type of chromophores and display weak sensitivity to molecular oxygen in methanol, which becomes almost negligible in aqueous and model physiological media. Addition of copper ions (Cu+ and Cu2+) the solutions of Re(PPh3)(P-bpy), Re(PPh3)(P-terpy), Re(P-OEG)(P-bpy) and Re(P-OEG)(P-terpy) results in a dramatic decrease in their emission intensity accompanied by strong reduction of the excited state lifetime, while the other biologically relevant ions do not display a distinct effect onto the photophysical characteristics of the chromophores. The complexes response onto variations in the copper ions concentration was quantified by building up the lifetime concentration calibration curves. To gain a deeper understanding of the sensing processes, DFT calculations were performed, which showed the substantial involvement of the orbitals of {(P-bpy/terpy)Cu} fragment into formation of the emissive excited states. Cellular experiments with Chinese hamster ovary (CHO-K1) cells demonstrate cytoplasmic localization of the PPh3-containing Re(I) probes.

The experimentally observed dependencies of the average interwall distances on the number of walls and diameters of multi-walled WS2 2 nanotubes were reproduced in molecular mechanics simulations based on a recently developed force field. A common chiral angle was used for all walls inside each nanotube to ensure its onedimensional periodicity. The data obtained make it possible to determine the nature of changes in the diameters of single-wall components inside the nanotube and variations in the distances between the walls in its inner, middle and outer parts. The stability of multi-walled nanotubes with respect to WS2 2 nanolayers and free single-wall components was evaluated.

The polarizability exaltation (increase) is typical for oligomers (C-60)(n). It comprises the superadditive polarizability growth with n. This phenomenon was previously studied only for the molecular models of the (C-60)(n) oligomers. In the present work, we compare the DFT-computed polarizability, obtained for molecules (C-60)(n) and periodic model of quasi-1D covalently-bonded fullerene chains. We found that the increment of the (C-60)(n) mean polarizability growth (95.88 & Aring;(3) for n = 6) approaches the value, obtained for the periodic model, 97.49 & Aring;(3). According to the periodic computations, polymer (C-60)(n) should be a semiconductor with the direct band gap at the Gamma point (the computed energy gap value is 1.41 eV).

Quantum chemical calculations of ultrathin nanorods cut from two bulk selenium phases were performed. Two sets of nanorods with trigonal and hexagonal geometric shapes described by the rod symmetry groups p 3 1 and p 3 1 21, respectively, were constructed from the most stable Se-I ( P 3 1 21) phase. The ultrathin nanorods generated by the Se-I phase were found to be unstable with respect to spontaneous torsion deformations, which slightly shift the helical axis order away from its crystallographic integer value of 3. In order to describe their correct atomic structure, one should use the line symmetry groups and determine the exact order of the helical axis for each nanorod. As the nanorod thickness increases, the true order quickly approaches the crystallographic value, but is never equal to it. Nanorods with a square geometric shape were constructed from the Se-II′ ( I 4 1 / acd ) phase. Depending on their thickness, these nanorods are classified as either chiral or achiral, exhibiting p 4 1 22 or p 4 c 2 symmetries, respectively. It was shown that square nanorods represent a unique class of nanostructures that alternately exhibit chiral and achiral properties as their thickness increases. Chiral square nanorods are unstable with respect to spontaneous torsion deformations, which shift the helical axis order from the crystallographic integer value of 4 (similar to nanorods cut from the Se-I phase). At the same time, achiral square nanorods are stable with respect to spontaneous torsion deformations.

The atomic structure, electronic, phonon, and optical properties of chalcogen helical chains (S, Se, Te) were studied using line symmetry groups and DFT calculations. The whole possible range of torsion deformations (from 0° to 180°), as well as the range of axial deformations (from 0.6 to 1.6) were considered. For the studied chains, the atomic and electronic structures at the energy minima were found. It was shown that for the considered chalcogen chains, the minimum of electronic energy is in the region of rotation angles ~103–107°. The electronic structure of all chains was considered in the helical Brillouin zone, which made it possible to trace its evolution up to the extreme torsional deformations: 0° (linear chain) and 180° (zigzag chain). A method for obtaining the dispersion of phonon states in the helical Brillouin zone has been developed based on the results of calculations by the CRYSTAL17 program. This allowed us to trace the evolution of phonon dispersion curves under torsion deformations up to their extreme values. Based on the known selection rules for helical polymers, the energies of optical, IR, and Raman transitions were obtained. This allows one to predict the optical properties of atomic chalcogen chains—both in a free state and inside carbon nanotubes.

In this contribution, we present an efficient synthetic method for obtaining Re(I) mixed-ligand bis-diimine dicarbonyl complexes of general formula [Re(NN1)(NNi)(CO)2]OTf (NN1 = neocuproine), starting from bis-acetonitrile rhenium(I) precursor [Re(NN1)(CO)2(NCMe)2]OTf. This method allows introduction of different diimine ligands, which contain fused moieties and electron-withdrawing functional groups. All complexes obtained demonstrate deep red to near-infrared (NIR) emission both in solution and in the solid state, achieving 845 nm. The 3MLCT character of the emissive excited state was confirmed by TD-DFT calculations of the electronic structures for the complexes considered.

Artificial metallopeptides hold immense potential to combine enzymatic activity with the versatility of organometallic catalysts. However, computational de novo design is largely limited to theozyme models that may neglect second-sphere atomic structure, overlook hydrogen-bonding networks, and ignore metal-induced conformational selection. We overcome these limitations for the case of helical metallopeptides and metal-containing helical motifs by proposing a DFT-based bottom-up methodology applied to the design of Pd-binding (Met-X)n sequences (X = Ala, Val, Ile). Line group symmetry theory is employed to accelerate the calculations by leveraging helical monoperiodicity for computational efficiency. The methodology (a) reproduces the geometric parameters of alpha-poly-Ala with near-experimental accuracy; (b) to the best of our knowledge, provides the first evidence that the alpha -> pi-transition may manifest as a first-order phase transition; (c) identifies (Met-Ala)n pi-helices as preferred matrices for canonical Pd(ii) Suzuki coupling intermediates. In contrast, Pd incorporation in the alpha-helical matrix poses significant challenges, as shown by relaxed potential energy scans. From the periodic pi-helix, we extract a cluster containing over 250 atoms and model it in aqueous solution at the omega B97X-V/def2-TZVP-gCP//B97-3c level to obtain reliable energetics for the free energy profile of the key oxidative addition step. The profile featured a low activation barrier and exergonic product formation, with reaction energy falling within the optimal window and barriers lower than those reported for bis-phosphine Pd(0) complexes. This methodology offers an efficient strategy for the de novo design of helical peptides and motifs and environmentally benign bioinorganic catalysts, from sequence to the reactivity of the metal center.

Group theoretical aspects of the three temperature-dependent and temperature-reversible experimentally observed phase transitions in the KNbO3 crystal (cubic-tetragonal, tetragonal-orthorhombic, orthorhombic-rhombohedral) in the framework of the group-subgroup relationship tree have been discussed. The ab initio DFT-HSE06 LCAO calculations of the electron and phonon properties, with optimisation of lattice parameters and atomic coordinates for all experimentally observed KNbO3 phases, are used for better understanding of the details of these phase transitions. Good agreement with the experimental data was found for the structural properties. Ab initio calculations of the phonon dispersion curves confirmed the existence of a stable phase only for the rhombohedral structure found experimentally for the lowest temperature of 263 K. For the remaining three higher temperature phases, imaginary frequencies appear, implying a nonstability of these phases. The only the cubic-tetragonal phase transition has been found to be symmetry allowed. The tetragonal-orthorhombic and orthorhombic-rhombohedral phases are not related to the group-subgroup relationship. An explanation is proposed based also on the results of ab initio calculations of the structure of the monoclinic phase, which we have chosen as a virtual one for the tetragonal-orthorhombic transition in the bulk.

The internal helical twist of ultrathin tellurium nanorods is explained using line symmetry groups theory. Continuous changes in the topology of the helical bands lead to qualitative changes in the band gap during torsion.

We propose a force field designed to model multi-walled WSe2 nanotubes whose size is beyond the capabilities of ab initio methods. The parameterization of interatomic potentials is successfully tested on single-walled and double-walled nanotubes, the structure of which is determined using non-empirical calculations. This force field has been used to model the structure and stability of chiral and achiral multi-walled WSe2 nanotubes with diameters approaching experimental values. The properties of WSe2-based nanotubes are compared with the properties of analogous WS2-based nanotubes calculated using the force field, which was published in the previous paper I of this series. The interwall distances obtained from the simulations are in good agreement with recent measurements of these parameters for existing WS2 and WSe2 nanotubes. It is found that the interwall interaction contributes to the stabilization of multi-walled nanotubes slightly more in the case of WSe2 than in the case of WS2. Analysis of the deviation of the nanotube shape from the cylindrical one showed a close similarity of the structure of the tubes of both compositions.

A technique for constructing force fields based on the use of genetic algorithms is proposed, which is aimed at parameterization of potentials intended for computer simulation of polyatomic nanosystems. To illustrate the proposed approach, a force field has been developed for modeling layered modifications of WS 2 , including multi-walled nanotubes, the dimensions of which are beyond the capabilities of ab initio methods. When determining the potential parameters, layered polytypes of bulk crystals, monolayers, bilayers, and nanotubes of small diameters were used as calibration systems. The parameterization found was successfully tested on double-walled nanotubes, the structure of which was determined using density functional calculations. The obtained force field was used for the first time to model the structure and stability of achiral multi-walled nanotubes based on WS 2 . The interwall distances obtained from the simulation are in good agreement with the results of recent measurements of these parameters for existing nanotubes.

A technique for constructing force fields based on the use of genetic algorithms is proposed. It is used to generate a force field designed to simulate multi-walled WS2 nanotubes, which is beyond the capabilities of ab initio methods. The resulting force field parameterization was successfully tested on single, double, and triple-walled nanotubes, which structure was determined using density functional calculations. The developed force field was applied to model the structure and stability of chiral and achiral multi-walled WS2 nanotubes. The interwall distances found by simulation are in good agreement with the results of recent measurements of these parameters for synthesized nanotubes. An analysis was made of the deviation of the shape of nanotubes from the cylindrical pattern.

Binuclear transition-metal complexes based on conjugated systems containing coordinating functions are potentially suitable for a wide range of applications, including light-emitting materials, sensors, light-harvesting systems, photocatalysts, etc., due to energy-transfer processes between chromophore centers. Herein we report on the synthesis, characterization, photophysical, and theoretical studies of relatively rare rhenium(I) and rhenium(I)-iridium(III) dyads prepared by using the nonsymmetrical polytopic ligands (NN2 and NN3) with the strongly conjugated phenanthroline and imidazole-quinoline/pyridine coordinating fragments. Availability of these different diimine chelating functions and targeted synthetic procedures allowed one to obtain a series of mononuclear (Re and Ir) and binuclear (Re-Re and Re-Ir) metal complexes with various modes of {Re(CO)3Cl} and {Ir(NC)2} metal fragment coordination. The obtained compounds were characterized by 1D 1H and 2D (COSY and NOESY) NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction crystallography. The photophysical study of the complexes (absorption, excitation and emission spectra, quantum yields, and excited-state lifetimes) showed that their emission parameters display strong dependence on the manner of metal center coordination to the diimine bidentate functions. The mononuclear complexes with an unoccupied imidazole-quinoline/pyridine fragment [Re(NN2), Re(NN3), and Ir(NC2)2(NN2)] or those containing a coordinated {Ir(NC)2} fragment in this position [Ir(NC2)2(NN1) and Re(NN2)Ir(NC1)2-Re(NN2)Ir(NC4)2] exhibit moderate-to-intense phosphorescence (quantum yields vary from 3% to 56% in a degassed solution), whereas the complexes containing a {Re(CO)3Cl} moiety in the imidazole-quinoline/pyridine position [Re2(NN2), Re2(NN3), and Ir(NC2)2(NN2)Re] demonstrate a strong reduction in the phosphorescence efficiency with a quantum yield of ≪0.1%. Quenching of the phosphorescence in the latter types of emitters is discussed in terms of a strong decrease in the radiative rate constants for these complexes compared to their analogues mentioned above, while the nonradiative constants remain nearly unchanged. Theoretical density functional theory (DFT) and time-dependent DFT (TD DFT) calculations, including evaluation of the radiative rate constants for the couple of structurally analogous complexes with and without a {Re(CO)3Cl} moiety coordinated to the imidazole-quinoline/pyridine chelating function, confirmed the observed trend in the variation of the emission intensity.

The work presents a comparison of the structural, mechanical, electronic and magnetic properties of armchair and zigzag terminated nanohelicenes, using the first principles density functional calculations. It was found that these nanohelicenes are metals in their most symmetric state, but undergo a spontaneous symmetry breaking which results in a metal-insulator transition (MIT). It was shown that the edge termination (armchair or zigzag) determines the type of the MIT in the global energy minima. The armchair terminated nanohelicene undergoes a Peierls MIT and it is a diamagnetic semiconductor. The zigzag terminated nanohelicenes is an antiferromagnetic semiconductor due to a Mott-Hubbard MIT. It was shown that the edge terminations and MIT type influence on helical electronic bands. Analysis of non-covalent interactions demonstrates that the van der Waals forces between coils are stronger in the case of zigzag termination.

The first-principles simulations were performed to investigate the structure and properties of single-wall nanotubes constructed from the binary MX and mixed M2XY, MLX2 or MLXY (M, L = Ga, In, M =/ L; X, Y= S, Se, Te, X =/ Y) monolayers. Different types of parent monolayers, chirality and diameters of nanotubes have been considered. The simulation of Janus nanotubes based on post-transition metal chalcogenides has been performed for the first time. The stability of nanotubes was analyzed both with respect to bulk phases and with respect to monolayers. It is found that the monolayers of monoclinic phase may be preferable for folding of nanotubes in the case of GaTe. On the other hand, the Janus nanotubes possess the lower formation energy than their binary (pristine) counterparts if the heaver chalcogen atom is located on the external nanotube surface. The calculation of the electronic properties also indicates the promise of Janus nanotubes for photocatalytic applications. Young's and shear moduli, as well as Poisson ratios have been estimated for binary and mixed gallium chalcogenide nanotubes for the first time. Analysis of elastic properties of nanotubes based on gallium chalcogenides shows that they have lower rigidity than nanotubes based on transition metal chalcogenides.

In this study, the influence of torsional deformations on the properties of chiral WS2-based nanotubes was investigated. All calculations presented in this study were performed using the density functional theory (DFT) and atomic gaussian type orbitals basis set. Nanotubes with chirality indices (8, 2), (12, 3), (24, 6) and (36, 9) corresponding to diameters of 10.68 Å, 14.90 Å, 28.26 Å and 41.90 Å, respectively, are examined. Our results reveal that for nanotubes with smaller diameters, the structure obtained through rolling from a slab is not optimal and undergoes spontaneous deformation. Furthermore, this study demonstrates that the nanotube torsion deformation leads to a reduction in the band gap. This observation suggests the potential for utilizing such torsional deformations to enhance the photocatalytic activity of the nanotubes.