Tetra- and hexaatomic cyclic clusters of main-group elements (XY)2 and (XY)3: an ab initio and density functional study

The electronic and molecular structure of planar (cyclic and linear) tetra- and hexaatomic clusters (XY) _n (XY = CC, BN, BeO, LiF; n = 2, 3) was studied using the ab initio CCD(full)/6-311+G** method and density functional approach (B3LYP/6-311+G**). The stability of cyclic clusters C₆, B₃N₃, and Be₃O₃ with D_3h symmetry is mainly determined by the aromaticity of their -electron systems.     

General method for the reduction of the effective rotational hamiltonian of molecules. Rational approximants and Padé approximants

A general method for reducing the effective rotational Hamiltonian for moleculesH _rot to the empirically constructed form in the {J_±, J_z} representation (molecules of the asymmetric-top type), applicable to Hamiltonians having improved convergence with nonpolynomial dependence on the angular momentum J, is developed. Rational forms for the reducedHrot and reduced Padé approximants for the rotational energy operator of the molecules are proposed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 32–37, August, 1985.     

Metal-containing monomers. Part 1. Spatial and electronic structures of cobalt(II) and nickel(II) complexes with acrylamide and of their polymers

Summary The spatial and electronic structures of the complexes [Co(AAm)₄(H₂O)₂](NO₃)₂ (1), Co(AAm)₄Cl₂ (2), [Ni(AAm)₄(H₂O)₂](NO₃)₂ (3) and Ni(AAm)₄Cl₂ (4), where AAm is acrylamide, and the products of their radical, frontal and post-grafting polymerization have been studied by electronic spectroscopy. The complexes (1), (3) and (4) were found to have pseudooctahedral structures in both the solid and solution phases. A change in the spatial structure of complex (2) was established in going from the crystal (tetragonally distorted octahedral) to solution (tetrahedral). The coordination environment of the metal centre does not change markedly during polymerization of the metal-containing monomers.     

Symmetry properties of the effective hamiltonians of some nonrigid molecules

Group-theoretical methods are used to identify the nonvanishing parameters and establish relations between them in the effective Hamiltonians which describe rotation and motion with large amplitude. The cases considered are 1) bending vibration in molecules of the type XY₂ and XYZ and 2) inversion vibration in pyramidal molecules of the type XY₃. For the latter type of molecule, the symmetry properties of the parameters in the effective centrifugal Hamiltonian for quasidegenerate inversion states are investigated. The general form of this Hamiltonian and its symmetry properties are established and studied in an arbitrary order in the small parameter.Translated from Izvestiya Vysshikh Uchebnykh Zavednii, Fizika, No. 2, pp. 22–26, February, 1981.     

Pathways of the reactions of nucleophilic addition of H2O and HF molecules to formaldehyde in the gas phase and in the complex with formic acid:ab initio calculations

The gradient pathways of the reactions of nucleophilic addition of H₂O and HF molecules to formaldehyde in the gas phase and in the XH…H₂CO…HC(O)OH complex (X=OH, F) were calculated by theab initio RHF/6-31G^**, MP2(fc)/6-31G^**, and MP2(full)/6-311++G^** methods. Both reactions proceed concertedly. The formation of H-bonded bimolecular pre-reaction complexes is the initial stage of the gas-phase reactions; at the same time, no indications of the formation of stable π-complexes were found on the potential energy surfaces of systems under study. The calculated energy barriers to the gasphase reactions exceed 40 kcal mol⁻¹, while those to reactions in the complex XH…H₂CO…HC(O)OH (X=OH, F) become more than halved. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2146–2154, November, 1998.     

Wavefront reconstruction of an optical vortex by a Hartmann-Shack sensor

Reconstruction the phase front of a vortex laser beam is conducted by use of a Hartmann-Shack wavefront sensor. The vortex beam in the form of the Laguerre-Gaussian LG(0)(1) mode is generated with the help of a spiral phase plate. The new reconstruction technique based on measured wavefront gradients allows one to restore the singular phase surface with good accuracy, whereas the conventional least-squares approach fails.     

Computational modeling of structure and magnetic properties of dinuclear di-o-benzoquinone iron complexes with linear polycyclic linkers

Density functional theory (DFT UTPSSh/6-311++G(d,p)) quantum chemical modeling of geometry, energy and magnetic characteristics of binuclear iron complexes, in which iron atoms coordinated by 2,11-diaza[3.3](2,6)pyridinophane bases are connected by di-o-benzoquinone ligands with acene linkers, was performed. It is established that the energy diff erence between electromeric forms of the studied compounds is determined by the type of the alkyl substituents at the nitrogen atoms of the tetraazamacrocyclic ligand and does not depend on the structure of the polycyclic chain. The possibility of controlling magnetic properties of the molecules of this type by means of external influences is predicted based on the facts that terminal metal-containing fragments are capable of undergoing thermally induced spin-state switching rearrangements, while the singlet-triplet transition of the acene linker can be induced by light irradiation.

     

Ab initio crystal orbital calculations on three-dimensional crystals of large bioorganic molecules and polymers

Ab initio crystal orbital calculations on three-dimensional crystals of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ), diprotonated deoxycytidine-5′-monophosphate monohydrate (5′-dCMP*2H*1Water), disodium deoxyguanosine-5′-monophosphate tetrahydrate (5′-dGMP*2Na*4Water), disodium uridine-3′-monophosphate tetrahydrate (3′-UMP*2Na*4Water), monosodium monoprotonated deoxyadenosine-5′-monophosphate hexahydrate (5′-dAMP*1H*1Na*6Water), disodium deoxycytidine-5′-monophosphate heptahydrate (5′-dCMP*2Na*7Water), cis-polyacetylene (cis-PA), and polythiophene (PTP) were carried out using the CRYSTAL92 routine package. A suitable basis set has been found that enables one to carry out the above calculations at the STO -3G level of accuracy using SILICON GRAPHICS workstations. However, to obtain reasonable results for three-dimensional crystals of polymers, one has to use much more extended basis sets. © 1996 John Wiley & Sons, Inc.     

Measurements and calculations of H2-broadening and shift parameters of water vapour transitions of the ν1 + ν2 + ν3 band

The water vapour line broadening and shifting for 97 lines in the ν₁ + ν₂ + ν₃ band induced by hydrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm^?1 and in a wide pressure range of H₂. The calculations of the broadening γ and shift δ coefficients were performed in the semi-classical method framework with use of an effective vibrationally depended interaction potential. Two potential parameters were optimised to improve the quality of calculations. Good agreements with measured broadening coefficients were achieved. The comparison of calculated broadening coefficients γ with the previous measurements is discussed. The analytical expressions that reproduce these coefficients for rotational, ν₂, ν₁, and ν₃ vibrational bands are presented.