Computationally Designed Crystal Structures of the Supertetrahedral Ga4C and Ga4Si Solids

The structural, mechanical, electrical, and optical properties of new supertetrahedral structures cF-Ga₄X (X = C, Si) were studied by using a solid state DFT calculation. The crystal structures of cF-Ga₄X are built based on a diamond crystal lattice, in which pairs of adjacent carbon atoms are replaced by Ga₄X fragments, where Ga₄ is a tetrahedron of gallium atoms. Calculations have shown that new mixed-type supertetrahedral structures are dynamically stable, have densities of 3.49 g/cm³ (X = C) and 2.65 g/cm³ (X = Si), and are narrow band gap semiconductors. From the performed molecular dynamics calculations, it follows that the homogeneous melting temperature of the gallium-carbon structure is in the range from 600 to 700 K and that of the gallium-silicon structure is in the range from 400 to 500 K.

Titanium Germylidenes

Two novel 18-electron titanium germylene complexes, Cp₂ Ti(L)=Ge[Si₃ (SiMe^t Bu₂ )₄ ] 3 b (L=Me₃ P) and 3 c (L=XylNC), were synthesized, isolated, and structurally characterized. The length of the titanium-germanium bonds of 2.5387(3) Å and 2.5276(3) Å (in 3 b and 3 c, respectively) well match those expected for the double bond, which was further supported by the DFT study. Based on their structural characteristics, as well as their atomic charges calculations which revealed Ti(δ+)=Ge(δ-) bond polarization, both 3 b and 3 c are classified as the Schrock-type titanium germylidenes, as the germanium analogues of the widely known titanium alkylidenes. By contrast, germylene complexes of the group 6 metals 8 a (M=Mo) and 8 b (M=W) are better described as Fischer-type germylene complexes.

Stability, electronic, and optical properties of two-dimensional phosphoborane

The structure and properties of two-dimensional phosphoborane sheets were computationally investigated using Density Functional Theory calculations. The calculated phonon spectrum and band structure point to dynamic stability and allowed characterization of the predicted two-dimensional material as a direct-gap semiconductor with a band gap of ~1.5 eV. The calculation of the optical properties showed that the two-dimensional material has a relatively small absorptivity coefficient. The parameters of the mechanical properties characterize the two-dimensional phosphoborane as a relatively soft material, similar to the monolayer of MoS₂ . Assessment of thermal stability by the method of molecular dynamics indicates sufficient stability of the predicted material, which makes it possible to observe it experimentally.

Electronic structure and magnetic properties of the triangular nanographenes with radical substituents: a DFT study

DFT modeling of triangular polycyclic hydrocarbons bearing radicals provided insights into dependence of electronic ground states on their structural peculiarities

Superoctahedral two-dimensional metallic boron with peculiar magnetic properties

A novel two-dimensional ferromagnetic stable boron material has been predicted and exhaustively studied with DFT methods. Its magnetism can be described by the presence of two unpaired delocalized bonding elements inside each distorted octahedron.

Difluorophosphorane-Flattened Phosphorene through Difluorination

We computationally showed that by difluorination of phosphorene we can make a new material difluorphosphorane (DFP) with perfectly planar honeycomb structure out of phosphorus atoms with fluorine atoms attached to every phosphorus atom from above and below. The structure is dynamically stable. It is a semiconductor with a direct band gap of 4.51 eV and an indirect band gap of 3.88 eV. We hope that with the passivation this new DFP material if made could find many applications in nanoelectronics.

Metalcarbonyl analogues of annelated cyclooctatetraene and cyclodecapentaene derivatives with a planar core cycle: a quantum chemical study

With the help of DFT calculations the possibility of stabilizing non-standard flat conformations of cyclooctatetraene and cyclodecapentaene by equatorially located metalcarbonyl substituents has been predicted. Structures and stabilities of a new family of metalcarbonyl Cr(CO)5, Fe(CO)4, Ni(CO)3, Ti(CO)4, and Ni(CO)2 cyclooctatetraene and cyclodecapentaene derivatives have been studied. All cyclooctatetraene derivatives, except the Ti(CO)4 derivative, have planar structures and are characterized by the pronounced anti-aromaticity of the core cycle. In the case of cyclodecapentaene complexes, the planar structures are formed by only Fe(CO)4 and Ni(CO)3 derivatives. Stabilization of non-standard planar forms is caused by both sterically enforced flattening of the core cycles and their π-interactions with metalcarbonyl moieties.

The structurally variable network of spin couplings and migrating paramagnetic centers in binuclear o-quinone CoII complexes with biradical acene linkers: a computational DFT study

A series of new magnetically-active coordination compounds comprising binuclear mixed-ligand complexes of cobalt bis-diketonates with acene linkers functionalized by two redox-active o-quinone moieties has been designed by means of density functional theory (DFT UB3LYP*/6-311++G(d,p)) calculations of their electronic structure, energy characteristics and magnetic properties. Two types of redox-active ligands include those with an acene linker bridging two o-benzoquinone fragments and the ligands containing an integrated π-conjugated system formed by annulation of o-quinone rings to the polycyclic core. The calculations reveal the dependence of spin density distribution in the compounds under study on the type of ligand. The considered binuclear CoII diketonate adducts manifest the capability of undergoing one- and two-step spin transitions induced by intramolecular electron transfers between the metal ions and the ligand system. An increase in the number of condensed rings of the acene linker promotes the stabilization of the biradicaloid state of the linker and enhances exchange interactions between all paramagnetic centers of the complexes giving rise to the formation of a flexible spin coupling network. The predicted unusual magnetic properties make the binuclear cobalt complexes with di-o-quinone ligand containing acene linker groups the promising building blocks for molecular electronic and spintronic devices.

Computational Assessment of an Elusive Aromatic N3P3 Molecule

We computationally proved that the planar aromatic hexagonal isomer N₃P₃ with the alteration of N and P is the second most stable structure for the N₃P₃ stoichiometry. We found that the aromatic isomer has high barriers for transition into the global minimum structure or into the three isolated NP molecules, making this structure kinetically stable. We showed that the sandwich N₃P₃CrN₃P₃ molecule corresponds to a minimum on the potential energy surface; thus, the aromatic N₃P₃ molecule has a potential to be a new ligand in chemistry.

Bis(stibahousene)

Strained hydrocarbons constitute one of the most prominent classes of organic compounds. Among them, bicyclo[2.1.0]pentene ("housene") derivatives represent a highly challenging and very attractive class. Although organic housenes have been known for more than five decades, there are still very few of them containing heavier main group elements. In this paper, we report on the two housene-type structures, novel monomeric stibahousene and dimeric bis(stibahousene). The bonding natures of both compounds were approached from both experimental and computational directions to reveal their peculiar structural features.

From Two- to Three-Dimensional Structures of a Supertetrahedral Boran Using Density Functional Calculations

With help of the DFT calculations and imposing of periodic boundary conditions the geometrical and electronic structures were investigated of two- and three-dimensional boron systems designed on the basis of graphane and diamond lattices in which carbons were replaced with boron tetrahedrons. The consequent studies of two- and three-layer systems resulted in the construction of a three-dimensional supertetrahedral borane crystal structure. The two-dimensional supertetrahedral borane structures with less than seven layers are dynamically unstable. At the same time the three-dimensional superborane systems were found to be dynamically stable. Lack of the forbidden electronic zone for the studied boron systems testifies that these structures can behave as good conductors. The low density of the supertetrahedral borane crystal structures (0.9 g cm-3 ) is close to that of water, which offers the perspective for their application as aerospace and cosmic materials.

Germanium, carbon-germanium, and silicon-germanium triangulenes

A series of germanium-containing triangular molecules have been studied by density functional theory (DFT) calculations. The triangulene topology of the compounds provides for their high-spin ground states and strong sign alternation of spin density and atomic charge distributions. High values of the exchange coupling constants witness ferromagnetic ordering of electronic structures of all studied triangulenes. The compounds bearing more electronegative atoms in a-positions of the triangular networks possess higher aromatic character and stronger ferromagnetic ordering.