I. V. Stankevich

Crown compounds for anions. A new approach to the description of chemical bonds in the complexes of halide anions with polymercury-containing macrocycles

The nature of chemical bonds between halide anions and polymercury-containing macrocycles has been investigated. For this purpose, calculations of the complexes of halide anions with cyclic trimeric o-phenylenemercury (o-C6H4Hg)3, cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3, cyclic pentameric perfluoroisopropylidenemercury [(CF3)2CHg]5 and some of their simpler hypothetical analogs have been carried out by the MNDO method. Complexes of the half-sandwich [L—X]−, bipyramidal [X—L—X]2− and sandwich [L—X—L]− (X = Hal, L = mercury-containing macrocycle) types have been calculated. It has been established that a uniform description of the bonding in such complexes, not depending on the number of Hg atoms in the macrocycle, can be reached within the framework of the concept of generalized chemical bonds.

Dihydrogen bonding of decahydro-closo-decaborate(2−) and dodecahydro-closo-dodecaborate(2−) anions with proton donors: experimental and theoretical investigation

Abstract The interactions of [Bu 4 N] 2 [B 10 H 10 ] and [Bu 4 N] 2 [B 12 H 12 ] with various proton donors (MeOH, EtOH, Pr i OH, PhOH, 4-FC 6 H 4 OH, 4-NO 2 C 6 H 4 OH, CF 3 CH 2 OH, (CF 3 ) 2 CHOH, (CF 3 ) 3 COH) in low polarity media were investigated. The site of coordination for [B 10 H 10 ] 2− and [B 12 H 12 ] 2− was found to be hydride hydrogen. Spectral (IR, NMR) evidences for the BH⋯HO hydrogen bonding between the boron hydrides and the OH proton donors in solution are presented. Spectral (Δ ν , Δ ν 1/2 , ΔA) and thermodynamic (Δ H °, Δ S °) characteristics of the H-complexes were determined. The BH⋯HO bonding strength increases from [B 12 H 12 ] 2− to [B 10 H 10 ] 2− . The geometry, energy, as well as electron distribution in the [B 10 H 10 ] 2− ·HOCH 3 , [B 10 H 10 ] 2− ·HOCF 3 , [B 10 H 10 ] 2− ·HCN, and [B 12 H 12 ] 2− ·HOCH 3 complexes were studied using ab initio HF/6-31G approximation. It was shown that increase of the proton donor ability of acids leads to formation of bifurcate H-bonds.

Nanotube C-BN heterostructures : electronic properties

Abstract New quasi one-dimensional (1D) and dimensionless (0D) objectsxa0–xa0nanotubes constructed of C and BN fragmentsxa0–xa0are considered and their electron spectra are computed by the method of crystal orbitals. Main and mini-zone gaps are shown to be considerably varied for ( n ,xa00) zigzag tube superlattices with C 2 kn BN ln ( l , k =1,…) unit cells when C (or BN) fragment length is changed. Dot and interface (0D) states are studied when a C-ring fragment is situated on a BN tube tip, in the middle of a BN tube or between two BN fragments in a C tube. A broad variation of electron spectra is presented in this case also.

Crown compounds for anions. Spectroscopic and theoretical studies of complexation of borohydride anions with cyclic trimeric perfluoro-o-phenylenemercury

It has been shown by IR and NMR spectroscopy that cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 (1) is capable of binding borohydride anions in THF and 1,2-dichloroethane solutions to form complexes {[(o-C6F4Hg)3](BH4)2}2− (2) and {[(o-C6F4Hg)3]2(BH4)}− (3). According to the IR data, complex 2 contains both terminal and coordinated B–H bonds while all four B–H bonds of the BH4− ion are coordinated with the mercury atoms in complex 3. The use of NMR spectroscopy provided the identification of one more complex of 1 with BH4−, which can be formulated as {[(o-C6F4Hg)3](BH4)}− (4). The stability constants of complexes 2 and 3 have been determined by IR spectroscopy. Quantum-chemical calculations of 2–4 by the AM1 method suggest that the complexes have the unusual bipyramidal, sandwich and half-sandwich structures, respectively. In contrast to 1, the interaction of (C6F5)2Hg with BH4− anions in THF gives a single complex {[(C6F5)2Hg](BH4)}− (5) independently of the reagent ratio. This complex is much less stable than 2 and 3.

Chemical graphs and their basis invariants

Abstract Molecular graph invariants are often used as molecular descriptors in `structure-property correlations. There exists an infinite number of graph invariants. Most of them are constructed using refined mathematical operations with graphs and cannot be easily interpreted in structural or physico-chemical terms. So, the problem of the choice of molecular descriptors in `structure-property correlation appears. It is known that many invariants are related to each other by strict or approximate formulas. Thus, these descriptors reflect the same features of molecular structures. So, the following problem appears: for any finite set of molecular (or arbitrarily labeled) graphs, to find a finite set of basis invariants, such that any invariant of these graphs could be uniquely expressed as a linear combination of basis invariants. A solution of the above-mentioned problem and some examples are presented in the given paper.

Metal complexes of allyl derivatives of C60 fullerene: molecular and electronic structure prediction from density functional calculations

The problem of existence of η3—π-complexes of C60 fullerene with transition metal atoms is discussed. The complexes C60R3Co(CO)3 (R = H, F, Cl, Br), C60H3NiCp, and C60H3Fe(CO)Cp, where C60R3 is an allyl derivative of C60 fullerene, were shown to be sufficiently stable. In these complexes the metal atoms are η3—π-bound to the fullerene cage. In contrast to this, the metal atoms in the C60H3Li and C60H3FeCp complexes are η5—π-coordinated to the carbon cage. Density functional calculations were carried out with the Perdew—Burke—Ernzerhof exchange-correlation potential (PBE). It was concluded that the type of bonding in the complexes of allyl derivatives of C60 fullerene depends on the nature of the species attached. Among the systems studied, the maximum energy of the η3—π-bond was obtained for the C60H3NiCp complex. The results obtained can be useful in the design of synthesis of new fullerene derivatives with the η3—π-coordination of the transition metal atoms to the carbon cage.

Nanotube carbon tips and connectors of BN tubes as quantum dots

Abstract New types of quantum dots, quantum rings, being carbon ring fragments on the open ends of dielectric BN nanotubes, or between BN nanotubes are considered. Electron spectra of some of them are computed by the Huckel method, using Bloch cycle conditions for zigzag nanotubes.

Cyclopentadienyl type η5-π-complexes of C60 fullerene derivatives with indium and thallium: simulation of molecular and electronic structure by the MNDO/PM3 methodof C60 fullerene derivatives with indium and thallium: simulation of molecular and electronic structure by the MNDO/PM3 method

The results of MNDO/PM3 calculations of η5-π-C60R5M complexes (R=H and Ph; M=Tl and In) are reported. Local energy minima and geometric parameters as well as the heats of formation and ionization potentials were determined for all systems in question. The nature of chemical M—pent bonding (pent is the pentagonal face) is discussed. The results of calculations are compared with experimental data that confirm our predictions about the possibility of existence of stable cyclopentadienyl type η5-π-complexes of C60 fullerence derivatives. The stability of the C60In12 complex with theIh symmetry, in which the In atoms are coordinated to each of 12 pentagonal faces of C60 fullerene, was estimated. The energy of the In—pent bond (62.4 kcal mol−1) is close to that in C60H5In (64.5 kcal mol−1).

Fullerene C{sub 60} as a {eta}{sup 5-} and {eta}{sup 6}-ligand in sandwitch-type {pi}-complexes with transition metals

The molecular and electronic structures of some hypothetical sandwich-type π-complexes of transition metals with fullerene C60 were modeled. The M-C60 bonds in η5-C60MCp+ complexes (M = Fe, Ru, Os) are less strong than the M-Cp bonds in ferrocene, ruthenocene, and osmocene, respectively. The η6-C60MC6H6 complexes (M = Cr, Mo, W) should be less stable than their classical analogs (C6H6)M(C6H6). The coordination of a metal atom with the fullerene at its pentagonal face is more energetically favorable than at a hexagonal face.

On Some Complexes of Allyl Derivatives of C60 Fullerene: Simulation of Molecular and Electron Structure by DFT

Abstract The problem of existence of η3–π‐complexes of transition metal atoms with the allyl type derivatives C60X3 of C60 fullerene is discussed. It is shown that complexes C60X3Co(CO)3 (X = H, F, Cl, Br), C60H3NiC5H5, C60H3Fe(CO)C5H5, where three atoms X are bound to the C atoms of fullerene in the α‐positions relative to the same five‐membered ring in the C60 fullerene, must be sufficiently stable. In these complexes the metal atoms are η3–π‐bound to the fullerene cage. In contrast to this, the metal atoms with the same allyl type C60H3 derivative of C60 fullerene in the C60H3Li and C60H3FeC5H5 complexes are η5–π‐coordinated to the carbon cage. Calculations were carried out by the DFT with the exchange‐correlation potential by Perdew–Burke–Ernzerhow.