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The cyclic O8 molecule has been studied using ab initio quantum mechanical methods. Molecular structures were fully optimized at levels of theory up to and including second-order perturbation theory (MP2) using a double zeta plus polarization basis set. Parallel theoretical studies were carried out for the valance isoelectronic S8 molecule, for which much experimental data exists. With double zeta plus polarization (DZ+P) self-consistent-field (SCF) theory vibrational frequencies and infrared and Raman intensities have been predicted. Cyclo-O8 is considerably more stable than experimental O–O bond energies would suggest and is predicted to lie only 94 kcal/mol above four infinitely separated O2 molecules. [ABSTRACT FROM AUTHOR]

The two degenerate components of the OH radical 2Π ground electronic state give rise to independent minima (of 2A‘ and 2A’ symmetries) upon interaction with the water molecule. These two minima have been investigated here for the first time using ab initio quantum mechanical methods. Minimum, double zeta, double zeta plus polarization, and triple zeta plus double polarization basis sets have been employed in conjunction with self-consistent-field, second-order perturbation, and configuration interaction methods. At all levels of theory, the 2A‘ state is predicted to be the global minimum, with a dissociation energy De of about 3.5 kcal/mol. The 2A’ state is predicted to lie about 1 kcal higher in energy. Both minima occur for structures with OH···O linkages close to linear and are reminiscent of the water dimer. However, the H···O distances (∼2.1 Å for 2A‘, ∼2.2 Å for 2A’) are significantly longer than observed for the water dimer. Preliminary estimates of the H2O·OH vibrational frequencies are made. [ABSTRACT FROM AUTHOR]

Using poly(5-{[(4'-heptoxy-4-biphenylyl)carbonyl]oxy}-1-pentyne) as an example, we demonstrate the incorporative accommodation of the rigid polyacetylene backbones and the mesogenic pendants, which leads to a highly ordered smectic (Sm) phase with a frustrated structure. The polymer exhibits a recognizable sheetlike molecular shape due to its rigid backbone and relatively short spacer (three methylene units), and the building block of the liquid crystalline (LC) phase is the whole molecule. In the LC phase, five layers of the molecules stack as a smectic A (SmA) block, and adjacent SmA blocks glide halfway of the molecular width from one to another. In scanning tunneling microscopy (STM) experiments, the STM tip scrape is found to generate a regular nanopattern with periodic electron conductivity, of which the spacing is determined by the side-chain length.

The unsaturated homoleptic manganese carbonyls Mn(2)(CO)(n)() (n = 7, 8, 9) are characterized by their equilibrium geometries, thermochemistry, and vibrational frequencies using methods from density functional theory (DFT). The computed metal-metal distances for global minima range from 3.01 A for the unbridged Mn(2)(CO)(10) with a Mn-Mn single bond to 2.14 A for a monobridged Mn(2)(CO)(7) formulated with a metal-metal quadruple bond. The global minimum for Mn(2)(CO)(9) has a four-electron bridging mu-eta(2)-CO group and a 2.96 A Mn-Mn distance suggestive of the single bond required for 18-electron configurations for both metal atoms. This structure is closely related to an experimentally realized structure for the isolated and structurally characterized stable phosphine complex [R(2)PCH(2)PR(2)](2)Mn(2)(CO)(4)(mu-eta(2)-CO). An unbridged (OC)(4)Mn-Mn(CO)(5) structure for Mn(2)(CO)(9) has only slightly (<6 kcal/mol) higher energy with a somewhat shorter metal-metal distance of 2.77 A. For Mn(2)(CO)(8) the lowest energy structure is a D(2)(d)() unbridged structure with a 2.36 A metal-metal distance suggesting the triple bond required for the favored 18-electron configuration for both metal atoms. However, the unbridged unsymmetrical (CO)(3)Mn-Mn(CO)(5) structure with a metal-metal bond distance of 2.40 A lies only 1 to 3 kcal/mol above this global minimum. The lowest energy structure of Mn(2)(CO)(7) is an unbridged C(s)() structure with a short metal-metal distance of 2.26 A. This is followed energetically by another C(s)() unbridged Mn(2)(CO)(7) structure with a somewhat longer metal-metal distance of 2.38 A.