Adaptive Natural Density Partitioning Analyses Research Articles

Ferrocene analogues of sandwich M(CrB₆H₆)₂: a theoretical investigation.

The stability and electronic structures of the new sandwich compounds M(CrB6H6)2 (M = Cr, Mn(+), Fe(2+)) are investigated by density functional theory. All the investigated sandwich complexes are in D(6d) symmetry and all of them are thermodynamically stable according to the large HOMO-LUMO gap, binding energy, vertical ionization potential and vertical electron affinity analyses, as well as Fe(C5H5)2 and Cr(C6H6)2, following the 18-electron principle. The natural bond orbital, detailed molecular orbitals and adaptive natural density partitioning analyses suggest that the spd-π interaction plays an important role in the sandwich compounds. This work challenges the traditional chemical bonding of the inorganic metal compound, investigates first the bonding style of the d atom orbital interacting with the π MO which was formed by p-d atomic orbitals, and indicates that the metal-doped borane ring can also be an ideal type π-electron donor ligand to stabilize the transition metal.

Face-Capping μ3-BO in B6(BO)7–: Boron Oxide Analogue of B6H7– with Rhombic 4c–2e Bonds

Using the first-principle approaches, we predict a B6(BO)7(-) cluster with a face-capping μ(3)-BO, which is the boron oxide analogue of closo-B6H7(-) with a face-capping μ(3)-H. Detailed topological analysis of electron density clearly reveals the existence of three rhombic 4c-2e bonds around the B/H apex in both C3v B6(BO)7(-) and C3v B6H7(-), which possesses similar electron densities at their bond and ring critical points. The adaptive natural density partitioning (AdNDP) analysis provides a direct and visual picture of the B-B-B-B/H 4c-2e bonds for the first time. Adiabatic and vertical electron detachment energies of the concerned monoanions are calculated to facilitate their future photoelectron spectroscopy measurements and characterizations. The presence of the B6(BO)7(-) and B6H7(-) clusters extends the BO/H isolobal analogy to the whole μ(n)-BO/H series (n = 1, 2, and 3) and enriches the chemistry of boronyl.

Planar to 3D Transition in the B6Hy Anions

Potential energy surfaces of anionic B(6)H(y) clusters were sampled using the coalescence kick method. We found that the planar to three-dimensional transition occurs in this system when y = 4. This is an important discovery because this transition suggests a major structural change as a function of dehydrogenation for the stoichiometric B(n)H(n)(-) polyhedral boranes. We also found that the B(6)H(3)(-) global minimum structure has an optical isomer. The chemical bonding patterns revealed by the adaptive natural density partitioning (AdNDP) analysis explain the geometric structure of all clusters presented here. From our chemical bonding analysis, we concluded that the 2D-3D transition occurs at B(6)H(4)(-) because the addition of one extra hydrogen atom further destroys the network of the peripheral 2c-2e B-B σ-bonding, making planar structures less stable, and because the distorted octahedral structure provides some occupation of all s- and p-AOs of boron, avoiding the presence of any empty atomic orbitals. Theoretical vertical electron detachment energies (VDEs) were calculated for comparison with future experimental work.

First-principles investigations on [formula omitted] and [formula omitted] oxocarbons

Comprehensive first-principles calculations on the geometrical and electronic properties of C5O5-/0 and C6O6-/0 oxocarbons have been performed in this work. Both C5O5- monoanion and C5O5 neutral are found to possess perfect planar pentagonal structures at their ground states D5hC5O5-(2A2″) (1) and D5h C5O5(1A2′) (2), while C6O6- and C6O6 appear to favor the slightly distorted quasi-planar C2vC6O6- (2A1) (3) and C2v C6O6 (1A1) (4), respectively. Adaptive natural density partitioning (AdNDP) analyses clearly reveal the σ- and π-bonding patterns of the monocyclic CnOn2-/-/0 oxocarbons (n=5 and 6). The adiabatic detachment energies (ADEs) and low-lying vertical detachment energies (VDEs) of the monoanions have been calculated at the coupled cluster level with triple excitations (CCSD(T)), with ADE=3.723 and VDE=3.776eV for C5O5- and ADE=3.629eV and VDE=3.679eV for C6O6- CCSD(T)//MP2. The first excited states of the neutrals are predicted to have the approximate term values of T1=1.08eV (3A2) for C5O5 and T1=1.22eV (3B1) for C6O6. The predictions made in this work may help facilitate experimental characterizations of C5O5- and C6O6- monoanions.

Theoretical prediction for the structures of gas phase lithium oxide clusters: (Li2O)n (n = 1–8)

AbstractWe apply genetic algorithm combining directly with density functional method to search the potential energy surface of lithium‐oxide clusters (Li2O)n up to n = 8. In (Li2O)n (n = 1–8) clusters, the planar structures are found to be global minimum up to n = 2, and the global minimum structures are all three‐dimensional at n ≥ 3. At n ≥ 4, the tetrahedral unit (TU) is found in most of the stable structures. In the TU, the central Li is bonded with four O atoms in sp3 interactions, which leads to unusual charge transformation, and the probability of the central Li participating in the bonding is higher by adaptive natural density partitioning analysis, so the central Li is in particularly low positive charge. At large cluster size, distortion of structures is viewed, which breaks the symmetry and may make energy higher. The global minimum structures of (Li2O)2, (Li2O)6, and (Li2O)7 clusters are the most stable magic numbers, where the first one is planar and the later both have stable structural units of tetrahedral and C4v. © 2012 Wiley Periodicals, Inc.

Geometric and electronic structures of (BeO)N (N = 2–12, 16, 20, and 24): Rings, double rings, and cages

The structure of (BeO)(N) clusters (N = 2-12, 16, 20, and 24) are investigated using the method combining the genetic algorithm with density function theory. Benchmark calculation indicates that THSSh functional is reliable to predict the structures of (BeO)(N) cluster. The global minimum structures of (BeO)(N) clusters are rings up to N = 5, double rings at N = 6 and 7 and cages at N ≥ 8. Besides, almost all of the structures of (BeO)(N) cluster are aromatic according to the NICS criterion. Adaptive natural density partitioning analysis reveals that C(6), (BN)(3), and (BeO)(3) rings (C(24) and (BeO)(12) fullerenes) are similar in bonding patterns. The building-up principle of (BeO)(N) is different from that of covalent (BN) and ionic (LiF and MgO) clusters.

Chemical Bonding in Coronene, Isocoronene, and Circumcoronene

AbstractChemical‐bonding analysis in coronene, isocoronene, and circumcoronene has been performed by using the Adaptive Natural Density Partitioning (AdNDP) method. This analysis revealed that coronene and isocoronene have two globally delocalized concentric π‐systems. Circumcoronene does not have globally delocalized π‐systems; instead, it has seven local sextets and can be represented by a single Clar structure. Thus, today there are a few known polycyclic aromatic hydrocarbons with two concentric π‐systems, but there are as yet no examples of such molecules with three or more concentric π‐systems. The results revealed by the AdNDP analysis are consistent with the results obtained by the current‐density maps, NICS and NICSZZ indices as well as MCI, PDI, Iring and δ indices.

Deciphering Chemical Bonding in a BC3 Honeycomb Epitaxial Sheet

The substitution of every fourth carbon atom in graphene by a boron atom preserves the honeycomb structure in the BC3 two-dimentional lattice, but as we found in our adaptive natural density partitioning analysis, it remarkably alters the chemical bonding. First, in the BC3 lattice, where boron atoms are surrounded by three carbon atoms, carbon forces boron to form two-center–two-electron B–C σ-bonds, while boron is known to participate only in multicenter (three-center–two-electron or four-center–two-electron) σ-bonding in the most stable two-dimensional form of the pure boron lattice, the α-sheet. Second, six-center–two-electron π-bonds found over every hexagon in graphene and in the α-sheet migrate in BC3 to hexagons composed out of carbon atoms only, making π-bonding in those hexagons more similar to the corresponding π-bonding in benzene rather then graphene, leaving hexagons formed by carbon and boron atoms in the BC3 lattice empty without π-bonding. We believe that chemical bonding elements found in our chemical bonding analysis of graphene, the α-sheet of boron, and the BC3 lattice will be useful tools for rationalizing chemical bonding in other two-dimensional boron–carbon materials.

Planar π-aromatic C3h B6H 3 + and π-antiaromatic C2h B8H2: boron hydride analogues of D3h C3H 3 + and D2h C4H4

Based upon extensive density functional theory and wave function theory calculations performed in this work, we predict the existence of the perfectly planar triangle C(3h) B(6)H(3)(+) (1, (1)A') and the double-chain stripe C(2h) B(8)H(2) (9, (1)A(g)) which are the ground states of the systems and the inorganic analogues of cyclopropene cation D(3h) C(3)H (3) (+) and cyclobutadiene D(2h) C(4)H(4), respectively. Detailed adaptive natural density partitioning (AdNDP) analyses indicate that C(3h) B(6)H (3) (+) is π plus σ doubly aromatic with two delocalized π-electrons and six delocalized σ-electrons formally conforming to the 4n + 2 aromatic rule, while C(2h) B(8)H(2) is π antiaromatic and σ aromatic with four delocalized π-electrons and ten delocalized σ-electrons. The perfectly planar C(2h) B(8)H(4) (5, (1)A(g)) also proves to be π antiaromatic analogous to D(2h) C(4)H(4), but it appears to be a local minimum about 50 kJ mol(-1) less stable than the three dimensional C(s) B(8)H(4)(6, (1)A'). AdNDP, nucleus independent chemical shifts (NICS) and electron localization function (ELF) analyses indicate that these boron hydride clusters form islands of both σ- and π-aromaticities and are overall aromatic in nature in ELF aromatic criteria.

Ab initio search for global minimum structures of neutral and anionic B 4H 5 clusters. Optical isomerism in B 4H 5 and [formula omitted

Potential energy surfaces of neutral and anionic B 4H 5 clusters were sampled using the Coalescence Kick method. We found that the neutral B 4H 5 cluster has two optical isomers as either a global minimum structure, or as almost degenerate isomers with the global minimum structure. For the B 4 H 5 - anion only the third lowest isomer forms a pair of optical isomers. The chemical bonding patterns revealed by the Adaptive Natural Density Partitioning (AdNDP) analysis can easily explain the geometric structure of even very exotic isomers and global minima. Theoretical vertical electron detachment energies (VDEs) were calculated for comparison with future experimental work.

Hydrogenation of B 12 0/− : A Planar-to-Icosahedral Structural Transition in B12H n 0/− (n = 1–6) Boron Hydride Clusters

A systematic density functional theory and wave function theory investigation performed in this work reveals a planar-to-icosahedral structural transition between n = 4–5 in the partially hydrogenated B12Hn0/− clusters (n = 1–6) upon hydrogenation of all-boron B120/−. Coupled cluster calculations with triple excitations (CCSD(T)) indicate that a distorted icosahedral B12H6 cluster with C2 symmetry is overwhelmingly favored (by 35 kcal/mol) over the recently proposed perfectly planar borozene (D3h B12H6) (Szwacki et al., Nanoscale Res Lett 4:1085, 2009) which proves to be a high-lying local minimum. A similar 2D–3D structural transition occurs to the corresponding boron boronyl analogues of B12(BO)n with n –BO terminals. Detailed adaptive natural density partitioning (AdNDP) analyses reveal the bonding patterns of these quasi-planar or cage-like clusters which are characterized with delocalized σ and π molecular orbitals. The electron detachment energies of the concerned anions and excitation energies of the neutrals are also predicted to facilitate their future experimental characterizations.

π-Aromatic B16H6: A Neutral Boron Hydride Analogue of Naphthalene

Systematic ab inito calculations are carried out in this work to investigate the geometrical and electronic structures of B16H6 neutral and its anion B16H6 −. The quasi-planar C2v B16H6(1A1) with 10 delocalized π-electrons proves to be the neutral boron hydride analogue of naphthalene (D2h C10H8). This π-aromatic neutral may be obtained from the experimentally known π-antiaromatic C2h B16 (Sergeeva et al., J. Am. Chem. Soc. 130:7244, 2008) upon hydrogenation at the six corner positions and is expected to be undistinguishable from a perfect planar D2h B16H6 in experiments. Detailed adaptive natural density partitioning (AdNDP) analyses clearly reveal the bonding pattern of B16H6 and the calculated nucleus independent chemical shifts (NICS) strongly support its global π-aromaticity. C2v B16H6 −(2B2) anion with one extra electron appears to have a similar quasi-planar structure with even a less severe out-of-plane distortion. Ultraviolet (UV) absorption spectrum of B16H6 and photoelectron spectroscopy (PES) spectrum of B16H6 − are simulated to facilitate their spectroscopic characterizations.

Perfectly planar concentric π-aromatic B18H3−, B18H4, B18H5+, and B18H62+ with [10]annulene character

Based upon extensive density functional theory and wave function theory investigations, we predict the existence of the perfectly planar concentric π-aromatic D(3h) B(18)H(3)(-)(6), D(2h) B(18)H(4)(8), C(2v) B(18)H(5)(+)(10), and D(6h) B(18)H(6)(2+)(12) which are the smallest boron hydride clusters composed of a hybrid of the triangular and hexagonal motifs with a hexagonal hole at the center. These partially hydrogenated B(18) clusters, tentatively referred to as borannulenes in this work, prove to possess [10]annulene character with 10 delocalized π-electrons. Detailed adaptive natural density partitioning (AdNDP) analyses unravel the bonding patterns of the π plus σ doubly aromatic D(3h) B(18)H(3)(-)(6) and C(2v) B(18)H(5)(+)(10) and the π aromatic and σ antiaromatic D(2h) B(18)H(4)(8) and D(6h) B(18)H(6)(2+)(12). Borannulenes prove to possess negative nucleus-independent chemical shifts (NICS(zz)) comparable with that of [10]annulene and huge negative anisotropies of the magnetic susceptibility (AMS) much bigger than the latter. The slightly non-planar C(s) B(18)H(3)(-)(15) (which is essentially the same as D(3h) B(18)H(3)(-)) with a high first vertical detachment energy of 3.71 eV and the perfectly planar D(2h) B(18)H(4) neutral with a huge first excitation energy of 1.89 eV are predicted to be the most possible borannulenes to be targeted in future experiments.

THE CHEMICAL BONDING OF Re3Cl9 AND REVEALED BY THE ADAPTIVE NATURAL DENSITY PARTITIONING ANALYSES

Chemical bonding of neutral rhenium trichloride Re3Cl9 and doubly charged has been brought into question in the current work. Despite recently reported propositions of π-aromaticity of neutral Re3Cl9 based on negative nuclear independent chemical shift (NICS) values[ 1 , 2 ] to the contrary, it is shown to be a purely classical chemical molecule, according to the results of the recently developed Adaptive Natural Density Partitioning (AdNDP) analysis.[ 3-5 ] The formation of three consecutive double bonds in a triatomic cycle formed by rhenium atoms that was initially predicted by Cotton et al.[ 6-8 ] is confirmed. The chemical bonding picture changes dramatically upon addition of two excess electrons to Re3Cl9. The rhenium atoms of the resulting doubly charged cluster are shown to be held together via three single Re-Re σ-bonds, three Re-Cl-Re σ-bonds, and a totally delocalized π-bond based on valence d atomic orbitals (d-AO) of rhenium atoms with minor contributions coming from the density associated with six apical chlorine atoms, which makes π-aromatic.

Ab Initio Search for Global Minimum Structures of the Novel B3Hy(y=4−7) Neutral and Anionic Clusters

We sampled potential energy surfaces of neutral and anionic B(3)H(y) clusters using the Gradient Embedded Genetic Algorithm (GEGA) program at the B3LYP/3-21G level of theory. The lowest energy isomers were recalculated at the B3LYP/6-311++G**, MP2/6-311++G**, and CCSD(T)/6-311++G** levels of theory. We found a diverse set of global minimum structures and low-lying isomers for the studied clusters. The Adaptive Natural Density Partitioning (AdNDP) method was then used for chemical bonding analysis for all global minimum structures and low-lying isomers. The chemical bonding patterns revealed by the AdNDP analysis can easily explain the geometric structure of even very exotic isomers and global minima.

Experimental and theoretical investigations of CB8−: towards rational design of hypercoordinated planar chemical species

We demonstrated in our joint photoelectron spectroscopic and ab initio study that wheel-type structures with a boron ring are not appropriate for designing planar molecules with a hypercoordinate central carbon based on the example of CB(8), and CB(8)(-) clusters. We presented a chemical bonding model, derived from the adaptive natural density partitioning analysis, capable of rationalizing and predicting planar structures either with a boron ring or with a carbon atom occupying the central hypercoordinate position. According to our chemical bonding model, in the wheel-type structures the central atom is involved in delocalized bonding, while peripheral atoms are involved in both delocalized bonding and two-center two-electron (2c-2e) sigma-bonding. Since carbon is more electronegative than boron it favors peripheral positions where it can participate in 2c-2e sigma-bonding. To design a chemical species with a central hypercoordinate carbon atom, one should consider electropositive ligands, which would have lone pairs instead of 2c-2e peripheral bonds. Using our extensive chemical bonding model that considers both sigma- and pi-bonding we also discuss why the AlB(9) and FeB(9)(-) species with octacoordinate Al and Fe are the global minima or low-lying isomers, as well as why carbon atom fits well into the central cavity of CAl(4)(2-) and CAl(5)(+). This represents the first step toward rational design of nano- and subnano-structures with tailored properties.

Deciphering Chemical Bonding in Golden Cages

The recently developed adaptive natural density partitioning (AdNDP) method has been applied to a series of golden clusters. The pattern of chemical bonding in Au(20) revealed by AdNDP shows that 20 electrons form a four-center-two-electron (4c-2e) bond in each of 10 tetrahedral cavities of the Au(20) cluster. This chemical bonding picture can readily explain the tetrahedral structure of the Au(20) cluster. Furthermore, we demonstrate that the recovered 4c-2e bonds corresponding to independent structural fragments of the cluster provide important information about chemically relevant fragmentation of Au(20). In fact, some of these bonds can be removed from the initial tetrahedral structure together with the associated atomic fragments, leading to the family of smaller gold clusters. Chemical bonding in the systems formed in such a manner is yet closely related to the bonding in the parental systems showing persistence of the 4c-2e bonding motif. Thus, the multicenter bonds in golden cages recovered by the AdNDP analysis correspond to the fragments that should be seen as building blocks of these chemical systems.