Spin-polarized transport properties in some transition metal dithiolene complexes.

Spin filtering materials are of great current interest in part due to their applications in molecular electronics. In this study, we carried out a theoretical investigation on the charge transport properties of transition metal (TM) dithiolene complexes with TM = Ni, Fe and Mn by using non-equilibrium Green's function/density functional theory (NEGF-DFT) methods. The characteristics of current-voltage and spin-resolved transmission spectra pointed out that Ni complexes are non-polarized, while Fe and Mn complexes exhibit high polarization and can be regarded as excellent candidates for spin-filtering materials with high spin-filtering efficiency. These differences were rationalized on the basis of electron delocalization over the molecular junction of the partial distribution of α- and ß-spin molecular projected self-consistent Hamiltonian (MPSH) orbitals, and also the first eigenchannels of molecular junctions.

Correction: Aromatic cages B42°/⁺: unprecedented existence of octagonal holes in boron clusters.

Correction for 'Aromatic cages B42(0/+): unprecedented existence of octagonal holes in boron clusters' by Truong Ba Tai et al., Phys. Chem. Chem. Phys., 2016, DOI: 10.1039/c5cp07342a.

Electronic Structure and Thermochemical Parameters of the Silicon-Doped Boron Clusters BnSi, with n = 8-14, and Their Anions.

We performed a systematic investigation on silicon-doped boron clusters BnSi (n = 8-14) in both neutral and anionic states using quantum chemical methods. Thermochemical properties of the lowest-lying isomers of BnSi(0/-) clusters such as total atomization energies, heats of formation at 0 and 298 K, average binding energies, dissociation energies, etc. were evaluated by using the composite G4 method. The growth pattern for BnSi(0/-) with n = 8-14 is established as follows: (i) BnSi(0/-) clusters tend to be constructed by substituting B atom by Si-atom or adding one Si-impurity into the parent Bn clusters with n to be even number, and (ii) Si favors an external position of the Bn frameworks. Our theoretical results reveal that B8Si, B9Si(-), B10Si and B13Si(-) are systems with enhanced stability due to having high average binding energies, second-order difference in energies and dissociation energies. Especially, by analyzing the MOs, ELF, and ring current maps, the enhanced stability of B8Si can be rationalized in terms of a triple aromaticity.

Aromatic cages B: unprecedented existence of octagonal holes in boron clusters.

The cage-like structures containing octagonal holes are located as the lowest-lying isomers for the B. The presence of octagonal holes, which have been found for the first time, not only gives us new insight into the bonding motif, but also marks a breakthrough in the structural characteristics of boron clusters since they were never expected to be stable units for elemental clusters. These cages are composed of both delocalized σ and π electron systems that consequently make them aromatic and thermodynamically stable.

A theoretical study on charge transport of dithiolene nickel complexes.

Organic semiconducting materials play an important role in the fabrication of high performance organic electronic devices. In the present work, we theoretically designed a series of organic semiconductors based on nickel complexes. Their characteristics of charge transport were investigated using DFT computational approaches. Based on the computed results, all compounds designed are found to be excellent candidates for ambipolar organic semiconductors with low reorganization energies for both holes and electrons. The (I-V) characteristics and transmission spectra of materials show that the replacement of benzene rings by thiophene rings results in an increase of their HOMO and LUMO energy levels. HOMOs of compounds containing thiophene end-groups are likely dominant for their conductance, while LUMOs of compounds containing benzene end-groups mainly affect their conductance. The electron distribution in these frontier MOs is identified as the main reason which makes the conductance of the compounds in the first series higher than those in the later series.

A new chiral boron cluster B44 containing nonagonal holes.

The B44 cluster has a cage-like structure containing two hexagonal, two heptagonal and two nonagonal holes. The presence of nonagonal holes is a new and remarkable finding since they have never been reported before in clusters. The present work does not only identify the new chiral members, but also provide more insight into the growth motif of large-sized boron clusters.

Electronic structure and photoelectron spectra of Bn with n = 26-29: an overview of structural characteristics and growth mechanism of boron clusters.

Boron clusters have been of great interest over the last few decades due to their unique chemical and physical properties. In the present work, we performed a theoretical study of geometrical and electronic structures of boron clusters Bn with n = 26-29 in both neutral and anionic states using DFT and MO computational methods. The photoelectron spectra of anionic species were simulated using TDDFT methods. Our results predict that in the neutral state both the B26 and B27 clusters exhibit tubular forms, whereas the larger species B28 and B29 are quasi-planar structures. The anionic species Bn(-) are more favourable for 2D shapes. More importantly, based on known geometrical characteristics, we now establish a general growth mechanism of boron clusters, which gives us more insight into the formation and existence of boron based nanomaterials.

The B32 cluster has the most stable bowl structure with a remarkable heptagonal hole.

The neutral B32 exhibits an aromatic bowl structure containing one heptagonal hole, while two anionic species, one having a bowl structure and the other a quasi-planar structure, are almost degenerate in energy. These findings not only give more insight into the structural features of boron clusters, but also present a key result explaining the presence of heptagonal holes in the fullerene B40.

Comment on "B38: an all-boron fullerene analogue" by J. Lv, Y. Wang, L. Zhu and Y. Ma, Nanoscale, 2014, 6, 11692.

In a recent paper (Nanoscale, 2014, 6, 11692), based on the results computed using DFT and MP2 methods, the all-boron fullerene I was reported to be the global minimum of the cluster B38 and was much more stable than the quasi-planar II. In this comment, we have shown that at higher level of theory CCSD(T), both structure I and quasi-planar II are almost degenerate in energy and the B38 can be considered to be of a transition size between 2D and 3D boron clusters. While the MP2 method favours the 3D structure I, the CCSD method tends to overestimate the relative stability of the 2D structure II.

Quantum rules for planar boron nanoclusters.

This article presents the use of free particle models to obtain quantum rules for planar boron clusters, with nuclearities in the range from seven to twenty. The information obtained from the models is being compared with electronic structure calculations based on the DFT method. Separate rules for in-plane and out-of-plane bonding are derived. In-plane bonding is precise on the cluster boundary and forms a network of alternating triangular 3c-2e bonds on the inside. The out-of-plane bonding is strongly delocalized and only depends on the global shape and size of the cluster.

Theoretical design of n-type organic semiconducting materials containing thiazole and oxazole frameworks.

The characteristics of molecular structure and charge transport of some new n-type organic semiconductors containing thiazole 1a-6a and oxazole 1b-6b frameworks and trifluoromethylphenyl as terminal groups were predicted using density functional theory (DFT) methods. The energy levels of HOMO and LUMO of these compounds are decreased when thiophene and furan units are replaced by thiazole and oxazole units, respectively. The same trend was observed when benzo[1,2-d:4,5-d']bisthiazole groups were replaced with benzo[1,2-d:4,5-d']bisthiazole-4,8-diones. The reorganization energies for electron of compounds are computed in a range of 0.21-0.37 eV, which is comparable to the value of 0.25 eV of well-known n-type semiconductors such as perfluoropentacene. Some important trends can be pointed out as follows: (i) replacing the core thiazolothiazole unit of compounds 1a and 2a by the larger core benzo[1,2-d:4,5-d']bisthiazole units of 3a and 4a decreases both reorganization energies for electron (λ(e)); (ii) the λ(e) values of compounds containing thiazole 2a, 4a, and 6a are smaller than those of compounds containing thiophene 1a, 3a, and 5a, respectively; (iii) there is no clear trend when replacing benzene rings of compounds 3a and 4a by quinone rings of 5a and 6a. The λ(e) values of 5 and 6 are only somewhat larger. The same trend is also found for compounds containing oxazole 1b-6b. The intermolecular charge transports in solid state of these compounds mainly occur among molecules in the same molecular layer, whereas intermolecular interactions between molecules in different molecular layers are very small. Generally, beside some experimentally reported molecules 1a-4a, the remaining molecules designed here are good candidates for n-type organic semiconducting materials with small reorganization energies for electron and low energy levels of LUMO.

A disk-aromatic bowl cluster B30: toward formation of boron buckyballs.

The B30 boron cluster has a bowl rather than a double-ring or a triple-ring tubular structure. This bowl isomer exhibits disk-aromaticity similar to that found for B20(2-) and B19(-) clusters. We confirmed that the concept of disk-aromaticity can be applied to both planar and non-planar systems.

Design of aromatic heteropolycyclics containing borole frameworks.

The heteropolycyclic compounds containing borole units were theoretically designed. The presence of electron deficient boron atoms results in full electron delocalization and remarkably affects their aromaticity. While molecules 1 and 2a exhibit antiaromaticity for inner rings and non-aromaticity for outer rings, 2b and 2c are completely aromatic.

Particle on a boron disk: ring currents and disk aromaticity in B20(2-).

The B20(2-) cluster is predicted to exhibit a planar sheet-like structure with a circular circumference. Orbital plots and energy correlations demonstrate the close correspondence between the electronic structure of B20(2-) and the Bessel functions describing the waves of a quantum mechanical particle confined to a disk. The π-band of B20(2-), and its B19(-) congener, contains 12 π-electrons, forming a (1σ)(2)(1π)(4)(1δ)(4)(2σ)(2) configuration, which corresponds to a "disk aromaticity" electron count. The analogy not only applies to the π-band, but also extends to the 50 valence σ-electrons. The occupied σ-orbitals are assigned on the basis of radial and angular nodes of the scalar disk waves. The magnetic response of the cluster was examined by Nucleus Independent Chemical Shift (NICS) values and current density calculations based on the ipsocentric model. B20(2-) is found to exhibit a remarkable inner paratropic current in the σ-channel and an outer diatropic current in the π-channel. The orbital excitations responsible for the antiaromaticity in σ and the disk-aromaticity in π are identified.

Structure, thermochemical properties, and growth sequence of aluminum-doped silicon clusters Si(n)Al(m) (n = 1-11, m = 1-2) and their anions.

A systematic examination of the aluminum doped silicon clusters, Si(n)Al(m) with n = 1-11 and m = 1-2, in both neutral and anionic states, is carried out using quantum chemical calculations. Lowest-energy equilibrium structures of the clusters considered are identified on the basis of G4 energies. High accuracy total atomization energies and thermochemical properties are determined for the first time using the G4 and CCSD(T)/CBS (coupled-cluster theory with complete basis set up to n = 3) methods. In each size, substitution of Si atoms at different positions of a corresponding pure silicon clusters by Al dopants invariably leads to a spectrum of distinct binary structures but having similar shape and comparable energy content. Such an energetic degeneracy persists in the larger cluster sizes, in particular for the anions. The equilibrium growth sequences for Al-doped Si clusters emerge as follows: (i) neutral singly doped Si(n)Al clusters favor Al atom substitution into a Si position in the structure of the corresponding cation Si(n+1)(+), whereas the anionic Si(n)Al(-) has one Si atom of the isoelectronic neutral Si(n+1) being substituted by the Al impurity; and (ii) for doubly doped Si(n)Al2(0/-) clusters, the neutrals have the shape of Si(n+1) counterparts in which one Al atom substitutes a Si atom and the other Al adds on an edge or a face of it, whereas the anions have both Al atoms substitute two Si atoms in the Si(n+2)(+) frameworks. The Al dopant also tends to avoid high coordination position.

Structures and ionization energies of small lithium doped germanium clusters.

We present a combined theoretical and experimental investigation of neutral and cationic lithium doped germanium clusters, GenLim (n = 5-10; m = 1-4). The vertical ionization energies and ionization thresholds are derived from threshold photoionization efficiency curves in the 4.68-6.24 eV range and are compared with calculated vertical and adiabatic ionization energies for the lowest energy isomers obtained using DFT computations. The agreement between experimental and computed values supports the identification of the ground state structures. Charge population analysis shows that lithium transfers its valence electron to the Gen hosts to form Gen(mδ-)-mLi(δ+) and Gen((mδ(-)+1))-mLi(δ+) complexes. This is also illustrated by the strong correlation between the size dependent lithium adsorption energies in GenLi and the Gen electron affinities. Neutral GenLim clusters are formed by adsorbing lithium atoms on either triangular or rhombic faces of the Gen framework with the lithium atoms tending to avoid each other. The chemical bonding phenomena of clusters are analyzed in detail using the densities of states and molecular orbitals.

Boron-boron multiple bond in [B(NHC)]2: towards stable and aromatic [B(NHC)]n rings.

Chained up: The π conjugation along B-C-N chains and a shift into a deep valence area of σ molecular orbitals (HOMO-6) are the reasons for the high stability of the dimer [B(NHC)]2 (NHC = N-heterocyclic carbene). The cyclic compounds [B(NHC)]n (see selected MOs for n = 6) exhibit structural and aromatic features similar to the corresponding hydrocarbons (CH)n.

A three-dimensional aromatic B6Li8 complex as a high capacity hydrogen storage material.

The B(6)Li(8) cluster is a symmetrical 3D complex whose high stability can be understood through the Wade rule and aromaticity. A new mechanism of B-Li chemical bonding is proposed. Importantly, B(6)Li(8) is predicted to be a promising candidate for hydrogen storage material with gravimetric density reaching up to a theoretical limit of 24%.

Theoretical study of Au(n)V-CO, n = 1-14: the dopant vanadium enhances CO adsorption on gold clusters.

The CO adsorption on vanadium-doped gold clusters Au(n)V with n = 1-14 is studied by density functional theory computations, using the BB95 and B3LYP functionals along with the cc-pVDZ-PP basis for metals and cc-pVTZ for non-metals. When both Au and V sites are exposed, CO adsorption on V is thermodynamically favorable because with partially filling d orbitals vanadium is more willing to interact with CO empty or filled orbitals. When vanadium is confined inside a gold cage, the low-coordinated Au atoms become the preferred sites for CO attachment. The presence of V tends to reinforce CO adsorption as compared with the bare gold clusters. The diatomic AuV is predicted to have the largest CO adsorption affinity as it has a typical π-back donation bond. Au(n)V-CO complexes typically have the larger CO binding energies and larger CO frequency shift than the isoatomic gold-carbonyl Au(n+1)-CO counterparts.