High HOMO-LUMO Gap Research Articles

Prediction of a New Series of Thermodynamically Stable Actinide Encapsulated Fullerene Systems Fulfilling the 32-Electron Principle

Density functional theory (DFT) within the framework of zeroth order regular approximation has been used to predict a new class of stable clusters through encapsulation of an actinide or lanthanide atom/ion into the C26 cage. The electronic structures, bonding, stability, aromaticity and spectroscopic properties of these endohedral metallofullerenes, M@C26 (M = Pr–, Pa–, Nd, U, Pm+, Np+, Sm2+, Pu2+, Eu3+, Am3+, Gd4+, and Cm4+) have been investigated systematically using DFT and its time-dependent variant. On encapsulation of an f-block metal atom/ion with 6 valence electrons, the classical bare open shell C26 cage with D3h symmetry and ellipsoid shape is transformed to a more spherical closed shell D3h structures with high HOMO–LUMO gap (in the range of 2.44–3.99 eV for M@C26 clusters as compared to 1.62 eV for the bare C26 cage). Calculated binding energy values imply that all of the M@C26 clusters are stable with respect to dissociation into atomic fragments. Moreover, thermodynamic parameters indicate that the encapsulation process is highly favorable for all of the actinides and some of the lanthanides considered here. A higher stability and nearly spherical shape of M@C26 system is rationalized through the fulfillment of 32-electron principle corresponding to the fully occupied spdf atomic shells for the encapsulated central atom, where considerable amount of overlap between the metal and cage orbitals has been found. Thus, the calculated structural and energetic parameters strongly suggest the possible formation of M@C26 species under appropriate experimental conditions. Furthermore, the present work implies that the 32-electron principle might be important in designing of new materials involving lanthanides and actinides.

Density functional investigation on the structures and properties of Li atom doped Au20 cluster

Structures and properties of an Au20 cluster doped with two Li atoms, Au18Li2, have been investigated using relativistic density functional theory within the framework of the zeroth-order regular approximation. Various initial structures have been generated and employed for geometry optimization followed by vibration analysis to check the stability of the final optimized structures. We have calculated various properties like binding energy, ionization potential, electron affinity and the HOMO–LUMO gap of these structures. It has been found that two dopant Li atoms favour occupying two different surface positions of the pyramidal Au20 cluster. The binding energy of the surface-doped Au18Li2 cluster is 1.017 eV higher than that of the pure Au20 cluster and the HOMO–LUMO gap (1.742 eV) is as high as a pure Au20 cluster (1.786 eV). Interestingly, we observe that the HOMO–LUMO gap as well as the binding energy can be increased beyond those of the Au18Li2 cluster with the help of further Li atom doping. In fact, a doped tetrahedral Au16Li4 cluster, where all the dopants are at the surface sites, possesses a very high HOMO–LUMO gap of 2.117 eV. Geometric and energetic parameters indicate that the Au16Li4 cluster might be considered as a possible ‘superatom’ in the design of novel cluster-assembled materials.

Density Functional Theory Study of Gd<i><sub>n</sub></i>O<sub>3</sub> (<i>n</i>=1-5) Clusters

The geometries, stabilities, electronic and magnetic properties of small GdnO3(n=1-5) clusters have been systematically studied by using density functional theory with the generalized gradient approximation. We found that the Gd atoms and O atoms in GdnO3clusters prefer three and two coordination, respectively, which origin from the electronic configurations of Gd and O atoms. The results show that Gd2O3cluster is more stable than its respective neighbors, which is reflected from its high average binding energy and high HOMO-LUMO gap. In addition, we calculate the magnetic properties of GdnO3clusters. The local magnetic moments of the Gd atom in the GdnO3clusters exhibit a weak dependence on the O atoms, which are slightly enhanced with the increasing of the number of Gd atom.

Theoretical Prediction of Icosahedral U@C20and Analogous Systems with High HOMO–LUMO Gap

The electronic structures, bonding, stability, aromaticity, and spectroscopic properties of the endohedral metallofullerenes, M@C20 (M = Pr–, Pa–, Nd, U, Pm+, Np+, Sm2+, Pu2+, Eu3+, Am3+, Gd4+, and Cm4+), have been investigated in a unified and systematic way using relativistic density functional theory (DFT) within the framework of zeroth-order regular approximation. The bare C20 cage with D3d point group transforms to highly symmetrical Ih structure through encapsulation of an f-block metal atom/ion with 6 valence electrons. The calculated values of HOMO–LUMO gap lie in the range of 2.5–4.9 eV (8.8–11.5 eV) at the B3LYP (HF) level. The stability of these metal encapsulated clusters can be attributed to the fulfillment of 26 valence electrons criteria corresponding to the fully occupied 2s2p1d atomic shells, where strong participation of the central metal atom orbitals in the ag, t1u, gu, and hg valence molecular orbitals have been observed.

Syntheses, crystal structures and properties of two novel imino-π-extended TTF derivatives

Abstract Two novel conjugated imino-π-extended tetrathiafulvalenes with p-iminobenzene, N,N′-bis(4,5-bis(methylthio)-1,3-dithiol-2-ylidene)benzene-1,4-diamine (1) and N,N′-bis(4,5-bis(ethylenedithio)-1,3-dithiolo-2-ylidene)benzene-1,4-diamine (2), have been synthesized and characterized by NMR, IR, MS and X-ray single-crystal diffraction. Both the two targets adopt chair-like conformation, and the central rings of p-iminobenzene moieties of the two molecules are severely twisted from the planarity of two dithiole rings, respectively. The UV–vis spectra of 1 and 2 show the lowest-energy absorption bands caused by the HOMO–LUMO one-electron promotion. Cyclic voltammetry (CV) measurements show only one, two-electron irreversible oxidation picks. These experimentally estimated energy levels of the frontier orbital of 1 and 2 (EHOMO 1: = −5.45, 2: −5.47 eV) are in good agreement with those obtained from DFT calculations (EHOMO 1: = −5.5, 2: = −5.3 eV). The high HOMO–LUMO gaps of 1 (4.05 eV) and 2 (4.00 eV) indicate high kinetic stability of the title compounds.

Tampering with Molecular Cohesion in Crystals of Hexaphenylbenzenes

Hexaphenylbenzene (HPB) and analogous compounds have properties of broad utility in science and technology, including conformationally well-defined molecular structures, high thermal stability, high HOMO-LUMO gaps, little self-association, inefficient packing, and high solubilities. Previous structural studies of HPB and its analogues have revealed persistent involvement of the central aromatic ring in strong C-H...pi interactions. These interactions can be blocked by adding simple ortho alkyl substituents to the peripheral phenyl groups. Comparison of the structures of HPB and a series of ortho-substituted derivatives has shown systematic changes in molecular cohesion and packing, as measured by packing indices, densities, solubilities, temperatures of sublimation, melting points, and ratios of H...H, C...H, and C...C contacts. These results illustrate how crystal engineering can guide the search for improved materials by identifying small but telling molecular alterations that thwart established patterns of association.

Novel bi‐transition metallic encapsulated naphthalene‐like Si20 prismatic cage: A DFT investigation

A theoretical investigation of stabilities and electronic properties of novel transition bimetallic atoms (BTMAs) encapsulated naphthalene-like Si(20) prismatic cage is being reported for the first time. The symmetry and electronic state of naphthalene-like TMA(2)@Si(20) is significantly affected by the type of encapsulated TMA from 3d, 4d to 5d series. Because of high binding energies, relative high HOMO-LUMO gaps, large charge-reverse transferring from naphthalene-like Si(20) cage to BTMAs at the centre of the 5d series, the most stable species of TMA(2)@Si(20) cage is favorable to form new 1D-TMA(n)@Si(m) nanotube, which is based on array of the novel naphthalene-like structure.

Geometry and Stability of BenCm(n= 1−10;m= 1, 2, ..., to 11 −n) Clusters

Density functional theory B3PW91/6-31+G* calculations on BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters have been carried out to examine the effect of cluster size, relative composition, binding energy per atom, HOMO-LUMO gap, vertical ionization potential, and electron affinity on their relative stabilities. The most stable planar cyclic conformations of these clusters always show at least a set of two carbon atoms between two beryllium atoms, while structures where beryllium atoms cluster together, or allow the intercalation of one carbon atom between two of them, generally seem to be the least stable ones. Clusters containing 1, 2, and 3 beryllium atoms (Be2C8, Be3C6, Be2C6, BeC6, Be2C4, BeC4, Be2C2, and BeC2) are identified as clusters of "magic numbers" in terms of their high binding energy per atom, high HOMO-LUMO gap, vertical ionization potential, and second difference in energy per beryllium atom.

Cationic 16-electron half-sandwich ruthenium complexes containing asymmetric diamines: understanding the stability and reactivity of coordinatively unsaturated two-legged piano stool complexes

The cationic 16e complexes [RuCp*(η 2(N,N)-Me 2NCH 2CH 2N(CH 2CHMe 2) 2)] + ( 1) and [RuCp*(η 2(N,N)-Me 2NCH 2CH 2 NCH 2CH 2OCH 2C H 2] + ( 2) as well as the 18e complex [RuCp*(η 6-C 6H 5-N(Me)NCH 2CH 2NMe 2)] + ( 3) have been synthesized as the BAr′ 4 (Ar′=3,5-C 6H 3(CF 3) 2) salts in one-pot reactions starting from [RuCp*(Cl)] 4. For 1, the X-ray crystal structure has also been determined showing the absence of any agostic interactions between ruthenium and the C–H bonds of the diamine ligand, and only minor deviations from the planar geometry despite the bulky diamine ligand. Based on EH model calculations, the extraordinary kinetic inertness of the planar 16e [Cp*Ru(NN)] + structure is traced to a high HOMO–LUMO gap deriving from through-bond coupling through the intervening σ skeleton of the chelating diamine (NN) ligand (in contrast to the P analogs) and further to the high π donor strength of Cp* (relative to parent Cp). Possible ligand rearrangements to increase the chemical reactivity are analyzed.

More about boron-nitrogen B 12 + 3 nN 12 + 3 n fullerene-like cages. An ab initio and AM1 investigation of some [formula omitted] isomers

Full geometry optimizations have been carried out for B 12 + 3 n N 12 + 3 n H m at the 3-21G ab initio ( n = 0, p = 0; n = 0, p = 24; n = 1, p = 0) and AM1 ( n = 0, p = 24; n = 1–3, p = 0) levels, and good concordance between the results of the two type of calculations has been found. The high HOMO-LUMO gap for B 12N 12H 24 adds this cage to the list of possible (saturated) 4 6 heterofullerenes. The short B⋯B distance in the six four-membered rings of the cages with m = 0 and also in B 22N 22, slightly higher than in boranes,denotes transanular bonding interactions.

Chemical tuning of the electronic properties of poly(p-phenylenevinylene)-based copolymers

Molecular engineering has allowed the control of the HOMO-LUMO gap energy in a family of conjugated polymers based on poly(p-phenylenevinylene) (PPV). Random copolymerization of 1 and 6 afforded precursor polymers 10 with two different leaving groups. Treatment under thermal conditions led to a partially conjugated polymer 11 with regions of high and low HOMO-LUMO gap energy, showing a 30-fold improvement in electroluminescence efficiency compared with PPV, while treatment under acidic and thermal conditions gave more substantially conjugated polymers 12 with lower HOMO-LUMO gap energies. This chemistry enabled the formation of lithographically patterned polymers exhibiting electroluminescence. The scope of these copolymerizations was also explored with other copolymers, 19 and 22b,c.