Electronic excitations of fluoroethylenes

Several lowest-lying singlet electronic states of vinyl fluoride, trans-, cis-, and 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene were investigated by using symmetry-adapted cluster configuration interaction theory. Basis sets up to Dunning's aug-cc-pVTZ augmented with appropriate Rydberg functions were utilized for the calculations. Calculated excitation energies show a good agreement with the available experimental values. Even in the troublesome pi-->pi(*) transitions, the excitation energies obtained in the present study agree well with the experimental values except in one or two fluoroethylenes. Strong mixing between different states was noticed in a few fluoroethylenes; especially the mixing is very strong between pi-pi(*) and pi-3ppi states in trifluoroethylene. No pure pi-sigma(*) excited state was found in almost all the fluoroethylenes. Several assignments and reassignments of features in the experimental spectra were suggested. The present study does not support the existing argument that the interaction between the pi-pi(*) and sigma-sigma(*) states is the reason behind the blueshift of around 1.25 eV in the pi-pi(*) excitation energy of tetrafluoroethylene. Possible reasons, including structural changes, for this shift are discussed in detail. Several low-lying triplet excited states were also studied.This study has been supported by the Grant for Creative Scientific Research from the Ministry of Education, Science, Sports, and Culture of Japan

Bond energies (Pt-NH 3 , Pt-Cl) and proton affinity of cisplatin: A density functional theory approach

The energies of the Pt-NH3 and Pt-Cl bonds of cisplatin are calculated by means of a density functional theory method with the B3LYP functional and various basis sets. The calculated bond energies of 37.38 kcal.mol-1 and 64.35 kcal.mol-1 for Pt-NH3 and Pt-Cl, respectively, agree well with the experimental values (37.28 kcal.mol-1 and 69.31 kcal.mol-1 respectively) derived from enthalpy changes. The proton and lithium ion affinities of cisplatin are also obtained with the B3LYP functional. Structural characterizations for the protonated and lithiated cisplatin complexes are given. Protonation and lithiation alter the geometric parameters, and the gas-phase proton affinity (198.71 kcal.mol-1) is much higher than the lithium ion affinity (70.32 kcal.mol-1). Original Russian Tex

Electronic spectra and photodissociation of vinyl chloride: A symmetry-adapted cluster configuration interaction study

The vertical absorptionspectrum and photodissociation mechanism of vinyl chloride (VC) were studied by using symmetry-adapted cluster configuration interaction theory. The important vertical π→π* excitation was intensively examined with various basis sets up to aug-cc-pVTZ augmented with appropriate Rydberg functions. The excitation energy for π→π* transition obtained in the present study, 6.96eV, agrees well with the experimental value, 6.7–6.9eV. Calculated excitation energies along with the oscillator strengths clarify that the main excitation in VC is the π→π* excitation. Contrary to the earlier theoretical reports, the results obtained here support that the C–Cl bonddissociation takes place through the nCl-σ*C–Cl state.This study has been supported by the Grant for Creative Scientific Research from the Ministry of Education, Science, Sports, and Culture of Japan

Sulfur Derivatives of the Natural Polyarsenical Arsenicin A: Biologically Active, Organometallic Arsenic–Sulfur Cages Related to the Minerals Realgar and Uzonite

(±)-Arsenicin A (AsA), (±)-<b>1</b>, the first natural polyarsenical to be isolated, has the adamantane-type structure of the mineral arsenolite (As₄O₆), in which three of the oxygen atoms have been replaced by methylene groups to give an organometallic, arsenic–oxygen cage of <i>C</i>₂ symmetry. Heating of a benzene solution of AsA with aqueous sodium sulfide produces, by reductive desulfurization of the intermediate sulfur analog (±)-<b>2</b>, the monosulfide cage (±)-<b>4</b>, which contains two As–As bonds and which has a <i>C</i>₂-chiral cage structure related to the mineral realgar (α-As₄S₄). At room temperature the reaction affords a chiral disulfide derivative that exists as a pair of separable diastereomers, (±)-<b>3a</b> and (±)-<b>3b</b>, each of which contains a single As–As bond and is structurally related to the mineral uzonite (As₄S₅). The crystal structures of the monosulfide (±)-<b>4</b> and the diastereomeric disulfides (±)-<b>3a</b> and (±)-<b>3b</b> have been determined. As for AsA, the sulfur derivatives exhibit strong UV absorptions and can be resolved on a Chiralpak IA column. The monosulfur cage (±)-<b>4</b> is considerably more potent and more selective than AsA and the current “arsenical gold standard”, arsenic­(III) oxide as Trisenox, against the acute promelocytic leukemia cells (NB4) and certain solid cancer cell lines