Search results for " geometry"

High-Resolution Spectroscopy and Structure of Osmium Tetroxide. A Benchmark Study on 192OsO4

2012

Osmium tetroxide (OsO(4)) is a heavy tetrahedral molecule that constitutes a benchmark for quantum chemistry calculations. Its favorable spin statistics (due to the zero nuclear spin of oxygen atoms) is such that only A(1) and A(2) (T(d) symmetry) rovibrational levels are allowed, leading to a dense but quite easily resolvable spectrum. We reinvestigate here the ν(1)/ν(3) stretching fundamental (940-980 cm(-1)) dyad region and perform new assignments and effective Hamiltonian parameter fits for the main isotopologue ((192)OsO(4)). We also investigate the ν(2)/ν(4) bending fundamental dyad (300-360 cm(-1)) for the first time and perform a preliminary analysis. New experimental data have been…

Analytic second derivatives for the spin-free exact two-component theory

2011

The formulation and implementation of the spin-free (SF) exact two-component (X2c) theory at the one-electron level (SFX2c-1e) is extended in the present work to the analytic evaluation of second derivatives of the energy. In the X2c-1e scheme, the four-component one-electron Dirac Hamiltonian is block diagonalized in its matrix representation and the resulting "electrons-only" two-component Hamiltonian is then used together with untransformed two-electron interactions. The derivatives of the two-component Hamiltonian can thus be obtained by means of simple manipulations of the parent four-component Hamiltonian integrals and derivative integrals. The SF version of X2c-1e can furthermore exp…

ChemInform Abstract: Dehydrotriphenylenes for the Generation of Bent Molecular Ribbons.

2010

Molecular association and dynamics in n-pentanol and 2-methyl-2-butanol

1985

Static dielectric constant, viscosity, density, ultrasonic and dielectric relaxation measurements are reported for two pentanol isomers (n-pentanol and 2-methyl-2-butanol) in a wide range of temperatures. The results show a different extent of H-bonds self-association in relation to the molecular geometry of the alcohol. The activation energies obtained from dielectric and ultrasonic studies are compared with those obtained from viscous flow. Such a comparison, together with the analysis of all the dielectric and ultrasonic relaxation data, show that in n-pentanol a correlation between viscosity and ultrasonic relaxation exists, while dielectric relaxation is not correlated with the other t…

3-Formyl-2-furanboronic acid: X-ray and DFT studies

2004

The molecule of the title compound, C5H5BO4, is almost planar with the boronic acid group inclined to the furan ring by 3.7 (1)°. DFT (density functional theory) calculations at the B3LYP/6-311+G** level of theory (with no imaginary frequencies) were used to approximate the influence of hydrogen bonding on the molecular geometry and have confirmed the planarity of the mol­ecule. No significant differences in geometrical parameters in the solid state and in the gas phase are associated with the presence of the O—H⋯O intermolecular hydrogen-bonding network. The crystal packing is characterized by O—H⋯O hydrogen-bonded dimers, which are additionally linked by O—H⋯O, as well as C—H⋯O interactio…

Primary- and secondary-octahedral distortion factors in bis(1,4-H2-1,2,4-triazolium) pentabromidoantimonate(III) –1,4-H2-1,2,4-triazolium bromide

2015

Abstract The analysis of octahedral distortion in the structure of inorganic–organic (C2H4N3)2[SbBr5]·(C2H4N3)Br (BTPTB) bromidoantimonate(III) determined at 295 and 85 K, supported by the Hirshfeld surface analysis and the data retrieved from the Cambridge Structural Database, is presented. The anionic substructure of BTPTB is built from distorted [SbBr6]3− octahedra that are connected by the cis corners forming polymeric one-dimensional [{SbBr5}n]2n− zig-zag chains running parallel to the a axis and isolated Br− ions. The organic substructure consists of the fully ordered 1,4-H2-1,2,4-triazolium cations. The oppositely charged substructures are linked by the system of N(C)–H⋯Br hydrogen b…

Crystal and molecular structure and electronic properties of [Cu(phen)2(HL)] · (phen)0.5 · 7H2O (H3L = 1,3,5-triazine-2,4,6(1H,3H,5H)-trione), a nove…

1998

Abstract The crystal and molecular structure of [Cu(phen)2(HL) · (phen)0.5 · 7H2O (H2L = 1,3,5-triazine-2,4,6(1H,3H,5H)-trione) has been determined by X-ray diffraction methods. The structure is built up of neutral [Cu(phen)2(HL)] entities (which are associated to form dinuclear units through hydrogen bonds involving the cyanurate ions), uncoordinated phenanthroline and crystallisation water molecules. The copper atom is involved in a CuN5 chromophore, with an stereochemistry near to a compressed trigonal bipyramid (TBP) but with a significant degree of distortion towards the square pyramidal (SP) topology. The EPR spectrum is indicative of a mixed d z 2 d x 2 −y 2 ground state for the copp…

Vibrational spectra and DFT calculations of PPV-oligomers

2003

The first two members of the p-phenylenevinylene- oligomer family (i. e. 1, 4-distyrylbenzene [DSB] and 4, 4'-distyrylstilbene [DSS]) were synthesized and their infrared and Raman spectra recorded and empirically assigned. Molecular geometries were optimized for the planar point group (C2h) by the density functional theory (DFT) method using the B3LYP functional and 6-31G* basis set. Calculations of vibrational spectra, including intensities, were carried out subsequently using the DFT method with the same basis set and linear scaling was applied. Calculated vibrational wavenumbers are in a fair agreement with our own experimental spectra. In order to explore changes in vibrational dynamics…

Hypervalent tin-organic compounds: Vibrational spectroscopy in the solid as a tool for structure determination

1997

Abstract A full set of IR- and Raman spectra down from 600 cm1 has been determined and assigned for 60 penta- or hexacoordinated tin-compounds in the groups RSn(CH2CH2CH2)3N (R = Cl, Br, I, Me), RR'Sn(MCH2CH2)2X (R,R′ = Cl, Br, I, Me, Ph, M = CH2 S; X = NMe, O, S), RPh2SnCH2CH2CH2NMe2 (R = Cl, Br, I) and RMe2Sn—CHD—COOMe (R = F, Cl, Br, I, Me). In these hypervalent compounds an approach of the donor atom X to the central atom tin outlines a ‘path’ of nucleophilic attack from a tetrahedron to a trigonal bipyramid. Along this ‘reaction path’ the bond lengths of the axial ligand increase continuously while the bond lengths of the equatorial ligands slightly decrease. The number of similar hype…

Self-Assembly of a Copper(II)-Based Metallosupramolecular Hexagon

2008

The self-assembly of a 1:1 mixture of copper(II) ions and a rigid heteroditopic ligand L containing phen and terpy binding units gives rise in the solid state to green crystals of a hexanuclear metallamacrocycle 1. X-ray crystallography reveals that 1 consists of molecular hexagons of the grid-type family in which each metal ion is bound to two different ligands through the phen and terpy units, plus a weakly coordinated PF6 (-) anion in a highly distorted octahedral geometry. ES-MS studies of acetonitrile solutions of L and copper(II) in a 1:1 ratio show mixtures of polynuclear complexes in which trinuclear L3Cu3 species are predominant.