Stabile Bis(η-alkin)MCl2-komplexe; Darstellung und reaktivität

The synthesis and reactivity of {(η⁵-C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂} MCl₂ (M = Fe: 3a; M = Co: 3b; M = Ni: 3c) is described. The complexes 3 are accessible by the reaction of (η⁵-C₅H₄SiMe₃) ₂Ti(CSiMe₃)₂ (1) with equimolar amounts of MCl₂ (2) (M = Fe, Co, Ni). 3a reacts with the organic chelat ligands 2,2′-dipyridyl (dipy) (4a) or 1,10-phenanthroline (phen) (4b) in THF at 25°C to afford in quantitative yields (η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂ (1) and [Fe(dipy)₂]Cl₂ (5a) or [Fe(phen)₂]Cl₂ (5b). 1/n[Cu^IHal]_n (6) or 1/n[Ag^IHal]_n (7) (Hal = Cl, Br) react with {(η⁵ -C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂}FeCl₂ (3a), by replacement of the FeCl₂ building block in 3a, to yield the compounds {(η⁵-C₅H₄SiMe₃)₂Ti(C CSiMe₃)₂}Cu^IHal (8) or {(η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂}Ag^IHal (9) (Hal = Cl, Br), respectively. In 8 and 9 each of the two Me₃SiCC-units is η²-coordinated to monomeric Cu^I Hal or Ag^IHal moieties. Compounds 8 and 9 can also be synthesized by the reaction of (η⁵-C₅H₄SiMe₃)₂ Ti(CSiMe₃)₂ (1) with 1/n[Cu^IHal]_n (6) or 1/n [Ag^IHal]_n (7) in excellent yields. All new compounds have been characterized by analytical and spectroscopic data (IR, ¹H-NMR, MS). The magnetic moments of compounds 3 were measured.     

H2O2-based epoxidation of bridged cyclic alkenes with [P{Ti(O2)}2W10O38] in monophasic systems: active site and kinetics

The H₂O₂-based epoxidation of bridged cyclic alkenes in a monophasic system containing low concentrations (<2 mM) of [Bu₄ⁿN]₄[Pr₂ⁱNH₃]₂H[P{Ti(O₂)}₂W₁₀O₃₈]·H₂O (1) (with two η²-peroxotitanium sites in the anion) has been studied in search of the catalytically active species involved. ³¹P NMR spectra of 1, measured under a variety of conditions, revealed that the active species was not hydroperoxotitanium complex [P{Ti(OOH)}₂W₁₀O₃₈]⁷⁻or [P{Ti(OOH)}Ti(O₂)W₁₀O₃₈]⁷⁻. The reaction pathways for the alkene epoxidation are discussed to understand the kinetics (especially the initial [H₂O₂] dependence). It was concluded that the net catalytic reaction for the epoxidation occurred through the two-electron oxidation at the hydroperoxotitanium site in the catalyst.     

Photochemical reactions of the isostructural 17- and 18-electron complexes (η-C5H5)M(Me)PPh3 (M=Co, Ni)

The photochemical reactions of the title complexes were studied in air-free benzene solution. In both cases photolysis leads to the production of complexes of the formula (η⁵-C₅H₅)M(PPh₃)₂. Both reactions are the result of the initial loss of a methyl radical from the excited state. The primary photoproduct, (η⁵-C₅H₅)MPPh₃ (M=CO, Ni), then scavenges neutral ligands from the solution to yield, in the case of PPh₃, (η⁵-C₅H₅)M(PPh₃)₂. In the absence of uncoordinated ligand in the reaction solution, the cobalt derivative reacts with the starting material to yield (η⁵-C₅H₅)Co(PPh₃)₂, a methyl radical and (η⁵-C₅H₅)Co(solvent)_n.     

Fraction of excited-state oxygen formed as b Σg in solution-phase-photosensitized reactions II. Effects of sensitizer substituent

The fraction F_Σ of excited-state oxygen formed as b ¹Σ_g⁺ was determined for a series of triplet-state photosensitizers in CCl₄ solutions. F_Σ was determined by monitoring the intensities of (a) O₂(b ¹Σ_g⁺) fluorescence at 1926 nm (O₂(b ¹Σ_g⁺)→O₂(a ¹Δ_g) and (b) O₂(a ¹ Δ_g) phosphorescence at 1270 nm (O₂(a ¹Δ_g) → O₂(X³Σ_g⁻)). Oxygen excited states were formed by energy transfer from substituted benzophenones and acetophenones. The data indicate that F_Σ depends on several variables including the orbital configuration of the lowest triplet state and the triplet-state energy. The available data indicate that the sensitizer-oxygen charge transfer (CT) state is not likely to influence F_Σ strongly by CT-mediated mixing of various sensitizer-oxygen states.     

The polymerization of [P(O2C12H8)(N3)] and the formation of soluble and insoluble poly(2,2′-dioxy-1,1′-biphenylphosphazene)

The phosphorus azide [P(O₂C₁₂H₈)(N₃)] [(O₂C₁₂H₈) = 2,2′-dioxy-1,1′-biphenyl] undergoes a solid state polymerization at 30 °C giving a separable mixture of the polyphosphazene {[NP(O₂C₁₂H₈)]}_n with a M_w in the range of 10⁴, together with a fraction of small and large cyclic spirophosphazene oligomers {[NP(O₂C₁₂H₈)]}_n, and an insoluble polymeric material with a very high char forming tendency, consisting very likely on a network of large interlooped cyclic oligomers and polymers of overall composition [NP(O₂C₁₂H₈)]_n. The reaction proceeds with smooth though irregular release of nitrogen at first but tending to abrupt accelerations ending in an explosion. The later outcome is more likely in scales of 10–50 g, and results in a decrease in the yield of the soluble polymer and a large increase in the yield of the polymeric matrix.     

Template reactions with polynuclear complexes. The reaction of [Mo2(O2CCF3)4(PR3)2] (R = Ph, Et) with 2-aminobenzaldehyde

The binuclear molybdenum(II) complexes [Mo₂(O₂CCF₃)₄(PR₃)₂] (R = Ph, Et) act as templates for the self-condensation of 2-aminobenzaldehyde to give a new class of complexes in which a hydride ion bridges two molybdenum(III) centres, each of which carries a tetradentate macrocyclic ligand (C). The new hydrido complexes [Mo₂(C)₂ (H)(O₂CCF₃)₃(PPh₃)₂] (I), [Mo₂(C)₂(H)₂(O₂CCF₃)₂(PPh₃)₂] (II), and [Mo₂(C)₂ (H)₂(O₂CCF₃)₂(PEt₃)₂]₂ (V) exist in two or more isomeric forms as shown by their IR, ¹H, ³¹P and ¹⁹F NMR spectra. Substitution with thiocyanate, nitrate and tetraphenylborate anions gives the new products [Mo₂(C)₂(H)(CO)(NCS)₃(PPh₃)₂] (III), [Mo₂(C)₂ (H)₂(O₂CCF₃)(NO₃)(PPh₃)₂] (IV), [Mo₂(C)₂(H)(O₂CCF₃)(PPh₃)₂](BPh₄)₂ (VI) and [Mo₂(C)₂(H)₂(O₂CCF₃)(PEt₃)₂](BPh₄) (VII), which also exist in isomeric forms.     

Solid-state static Cu and P CP/MAS NMR, and liquid-state EXAFS studies on copper(I) O,O′-dialkyldithiophosphate cluster compounds: Formation of the copper(I) O,O′-di-iso-amyldithiophosphate cluster compound on the surface of synthetic chalcocite

Polycrystalline octa-nuclear copper(I) O,O′-di-i-propyl- and O,O′-di-i-amyldithiophosphate cluster compounds, {Cu₈[S₂P(OR)₂]₆(μ₈-S)} where R = ⁱPr and ⁱAm, were synthesized and characterized by ³¹P CP/MAS NMR at 8.46 T and static ⁶⁵Cu NMR at multiple magnetic field strengths (7.05, 9.4 and 14.1 T). The symmetries of the electronic environments around the P sites were estimated from the ³¹P chemical shift anisotropy (CSA) parameters, δ_aniso and η. Analyses of the ⁶⁵Cu chemical shift and quadrupolar splitting parameters for these compounds are presented with the data being compared to those for the analogous octa-nuclear cluster compounds with R = ⁿBu and ⁱBu. The ⁶⁵Cu transverse relaxation for the copper sites in {Cu₈[S₂P(OⁱPr)₂]₆(μ₈-S)} and {Cu₈[S₂P(OⁱAm)₂]₆(μ₈-S)} was found to be very different, with a relaxation time, T₂, of 590 μs (Gaussian) and 90 μs (exponential), respectively. The structures of {Cu₄[S₂P(OⁱPr)₂]₄} and {Cu₈[S₂P(OⁱPr)₂]₆(μ₈-S)} cluster compounds in the liquid- and the solid-state were studied by Cu K-edge EXAFS. The disulfide, [S₂P(OⁱAm)₂]₂, was obtained and characterized by ³¹P{¹H} NMR. The interactions of the disulfide and of the potassium O,O′-di-i-amyldithiophosphate salt with the surfaces of synthetic chalcocite (Cu₂S) were probed using solid-state ³¹P NMR spectroscopy and only the presence of copper(I) dithiophosphate species with the {Cu₈[S₂P(OⁱAm)₂]₆(μ₈-S)} structure was observed.     

Preparation, structures, and haptotropic rearrangement of novel dinuclear ruthenium complexes, (μ2,η:η-guaiazulene)Ru2(CO)4(CNR)

Novel isonitrile derivatives of a diruthenium carbonyl complex, (μ₂,η³:η⁵-guaiazulene)Ru₂(CO)₅ (2), were synthesized by substitution of a CO ligand by an isonitrile, and were subjected to studies on thermal and photochemical haptotropic interconversion. Treatment of 2 (a 45:55 mixture of two haptotropic isomers, 2-A and 2-B) with RNC at room temperature resulted in coordination of RNC and alternation of the coordination mode of the guaiazulene ligand to form (μ₂,η¹:η⁵-guaiazulene)Ru₂(CO)₅(CNR), 5d–5f, [5d; R=^tBu, 5e; 2,4,6-Me₃C₆H₂, or 5f; 2,6-ⁱPr₂C₆H₃] in moderate to good yields. Thermal dissociation of a CO ligand from 5 at 60 °C resulted in quantitative formation of a desirable isonitrile analogue of 2, (μ₂,η³:η⁵-guaiazulene)Ru₂(CO)₄(CNR), 4d–4f, [4d; R=^tBu, 4e; 2,4,6-Me₃C₆H₂, or 4f; 2,6-ⁱPr₂C₆H₃], as a 1:1 mixture of the two haptotropic isomers. A direct synthetic route from 2 to 4d–4f was alternatively discovered; treatment of 2 with one equivalent of RNC at 60 °C gave 4d–4f in moderate yields. All of the new compounds were characterized by spectroscopy, and structures of 5d (R=^tBu) and 4d-A (R=^tBu) were determined by crystallography. Thermal and photochemical interconversion between the two haptotropic isomers of 4d–4f revealed that the isomer ratios in the thermal equilibrium and in the photostatic state were in the range of 48:52–54:46.     

The vibrational state distributions in both products of the reaction: O(P) + NO2 → O2 + NO

A laser pulse-and-probe method has been used to determine the nascent vibrational populations in NO(v=0–4) and O₂(v=6–11) formed in the thermal reaction: O(³P) + NO₂ → O₂(v) + NO(v). A frequency-tripled Nd: YAG laser is used to photolyse NO₂, diluted tenfold in Ar, and laser-induced fluorescence spectroscopy in the NO A ²Σ⁺-X ²Π and O₂ B ³Σ⁻_u -X ³Σ⁻_g electronic band system is used both to follow the kinetics of individual vibrational states and to determine the nascent vibrational distributions. The majority of the NO product is formed in v = 0 and the average vibrational yield is ≈ 4.6%. The O₂ populations fall monotonically from v = 6 to 11 in a distribution close to what is expected on prior grounds. Based on a surprisal analysis, the average vibrational energy yield in O₂ is ≈ 26%. The nature of the reaction dynamics is discussed.     

Soluble Ni alkoxides based on dimethylaminoisopropoxide ligands: molecular structure of [Li(PrOH)Ni (η-OR)2Cl]2 and of cis-NiCl2(ROH)2 (R = CHMeCH2NMe2)

Various routes to Ni^II aminoalkoxides have been investigated. A nickel isopropoxide derivative 1 was prepared by anodic dissolution of the metal in the presence of LiCl as electrolyte. Alcoholysis reactions of 1 with 1-dimethylamino-2-propanol afforded the homoleptic nickel(II) aminoalkoxide 2 together with a Ni---Li species 3. 2 was also obtained by metathesis reactions between sodium alkoxide and the nickel hexammine complex whereas the reaction between the latter and the aminoalcohol led to an halide solvate, cis-NiCl₂(η²-ROH)₂, 4. The various compounds were characterized by elemental analysis, FT-IR and UV-vis spectroscopies as well as by X-ray diffraction for 3 and 4. 3 corresponds to [Li(PrⁱOH)Ni(η²-OCHMeCH₂NMe₂)Cl]₂ and the overall structure can be seen as two [Ni(η²-OCHMeCH₂NMe₂)₂Cl]⁻ moieties assembled by Li(PrⁱOH)⁺. The lithium atom is 4-coordinate due to its interaction with the oxygen atoms of the aminoalkoxide ligands. Nickel is 5-coordinate with a distorted tetragonal pyramidal stereochemistry, one nitrogen being in the apical position. The metal displays a distorted octahedral surrounding for the NiCl₂ adduct 4. The bond distances vary in the order Ni---OR < Ni---N ≈ Ni---O(H)R < Ni---Cl for 3 and 4. The various compounds (except 1) are soluble in organic media.     

Oxidative condensation reactions of (diethylenetriamine)cobalt(III) complexes with substituted bis(pyridin-2-yl)methane ligands

The synthesis and characterisation of Co(III) complexes derived from a condensation reaction with a central or terminal nitrogen of a dien ligand and the -carbon of a range of substituted bis(pyridin-2-yl)methane ligands are described. Aerial oxidation of bpm {bis(pyridin-2-yl)methane with Co(II)/dien or direct reaction with Co(dien)Cl₃ provided in low yield a single C–N condensation product 1 (at the primary terminal NH₂) after the pyridyl –CH₂– is formally oxidised to –CH⁺–. The methyl substituted ligand bpe {1,1-bis(pyridin-2-yl)ethane} behaves likewise, except both terminal (prim) and central (sec) amines condense to yield isomeric products 2 and 3. Two of these three materials have been characterised by single crystal X-ray crystallography. The corresponding reactions for the bis(pyridyl) ligand bpk {bis(pyridin-2-yl)ketone} provided C–N condensation products without the requirement for oxidation at the -C center; two carbinolamine complexes in different geometrical configurations resulted, mer-anti-[Co(dienbpc)Cl]ZnCl₄, 5, and unsym-fac-[Co(dienbpc)Cl]ZnCl₄, 6, {dienbpc=[2-(2-aminoethylamino)-ethylamino]-di-pyridin-2-yl-methanol}. In addition, a novel complex, [Co(bpk)(bpd-OH)Cl]ZnCl₄, 4, in which one bidentate N, N-bonded bpk ligand and one tridentate N, O, N-bonded bpd (the diol from bpk+OH⁻) were coordinated, was obtained via the Co(II)/O₂ synthetic route. When the bpc ligand (bpc=bis(pyridin-2-yl)methanol) was employed directly as a reagent along with dien, no condensation reactions were observed, but rather a single isomeric complex [Co(dien)(bpc)]Cl.ZnCl₄, 7, in which the ligand bpc acted as a N,N,O-bonded tridentate ligand rather than as a N,N-bidentate ligand was isolated. ¹³C, 1D and 2D ¹H NMR studies are reported for all the complexes; they establish the structures unambiguously.     

Matrix isolation infrared spectroscopic and theoretical study of noble gas coordinated dipalladium–dioxygen complexes

The reaction products of palladium atoms with molecular oxygen in solid argon have been investigated using matrix isolation infrared absorption spectroscopy and quantum chemical calculations. In addition to the previously reported mononuclear palladium–dioxygen complexes: Pd(η²–O₂) and Pd(η²–O₂)₂, dinuclear palladium–dioxygen complexes: Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ were formed under visible light irradiation and were identified on the basis of isotopic substitution and theoretical calculations. In addition, experiments doped with xenon in argon coupled with theoretical calculations suggest that the Pd(η²–O₂), Pd₂(η²–O₂) and Pd₂(η²–O₂)₂ complexes are coordinated by two argon or xenon atoms in solid argon matrix, and therefore, should be regarded as the Pd(η²–O₂)(Ng)₂, Pd₂(η²–O₂)(Ng)₂ and Pd₂(η²–O₂)₂(Ng)₂ (NgAr or Xe) complexes isolated in solid argon.     

Syntheses and X-ray crystal structures of [Co(η-CO3)(NH3)4](NO3)·0.5H2O and [(NH3)3Co(μ-OH)2(μ-CO3)Co(NH3)3][NO3]2·H2O

[Co(η²-CO₃)(NH₃)₄](NO₃)·0.5H₂O and [(NH₃)₃Co(μ-OH)₂(μ-CO₃)Co(NH₃)₃][NO₃]₂·H₂O were prepared by prolonged aerial oxidation of a solution of Co(NO₃)₂·6H₂O and ammonium carbonate in aqueous ammonia. The formation of these side products highlights the richness of the chemistry of these systems and the possibility of by products if methods are not strictly adhered to. The X-ray crystal structures of [Co(η²-CO₃)(NH₃)₄][NO₃]·0.5H₂O and [(NH₃)₃Co(μ-OH)₂(μ-CO₃)Co(NH₃)₃][NO₃]₂·H₂O reveal a monomeric octahedral cobalt center with η²-bound CO₃²⁻ in the former, while the latter consists of a dimeric array where the two cobalt centers are bridged by two OH⁻ and one μ₂-CO₃²⁻ groups with three terminal NH₃ ligands for each Co center. In both complexes extensive hydrogen bonding interactions are evident.     

La-NMR-spektroskopie an allyllanthan(III)-komplexen

¹³⁹La-NMR chemical shifts were measured for several anionic complexes of formulae Li(C₄H₈O₂)_3/2 [La(ν³-C₃H₅)₄], [Li(C₄H₈O₂)₂][Cp′_nLa(ν³-C₃]H₅)_4−n] (Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 and Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) and Li[R_nLa(ν³-C₃H₄)₄−n] (R = N(SiMe₃)₂; n = 1, 2 and R = CCsIMe₃; n = 4), as well as for neutral compounds for formulae La(ν³-C₃H₅)₃L_n (L = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_nLa(ν³-C₃H₅)_3−n (Cp′= Cp(ν⁵-Cp₅H₅), Cp *(ν⁵-C₅Me₅); n = 1, 2) and La(ν³-C₃H₂)₂X(THF)₂ X = Cl, Br, I). Typical ranges of the ¹³⁹La-NMR chemical shifts were found for the different types of complex independent of number and kind of organyl groups directly bonded to lanthanum.

Zusammenfassung

¹³⁹La-NMR-Spektroskopie wurde an einer Reihe anionischer Allyllanthanat(III)-Komplexe der Zusammensetzung ]- [La)ν³-C₃H₅)₄, [Li(C₄H₈)₂][Cp′_nLa(ν³-C₃H₅)_4−n(Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 und Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) und Li[R_nLa(ν³-C₃H₅)_4−n (R = B(SiMe₃)₂; n = 1, 2 und R = CCSiMe₃; n = 4 sowie neutraler Allyllanthan(III)-Komplexe der Zusammensetzung La(ν³-C₃H₅)₃L_n (L_n = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_n, La(ν³-C₃H₅)_3−n (Cp′ = Cp(ν⁵-C₅H₅), Cp * (ν⁵- Cp₅Me₅); n = 1, 2) und La(ν³-Cp₃H₅)₂X(THF)₂ (X = Cl, Br, I) durchgefürt. In Abhängikeit von der Anzahl und der Art der am Lanthan gebundenen Gruppen wurden für die verschieden Komplextypen charakteristische Resonanzbereiche ermittelt.     

Reaction dynamics of the Ca(D2, PJ) + CH3I → CaI + CH3 system: chemiluminescence, energy disposal and product polarization

The Ca(¹D₂, ³P_J) + CH₃ → CaI(A,B) + CH₃ reactions system has been studied by measuring its chemiluminescence under beam-gas conditions. Absolute values of the state-to-state reaction cross-sections were determined at low collision energy . In addition, the electronic branching ratio and product energy disposal have been determined for each metastable reaction. The major changed observed in the chemiluminescence when comparing the Ca(¹D₂) reaction versus that of Ca(³P_J) is the total yield associated with the former reaction. To the best of our spectral resolution neither the electronic branching ratio e.g. CaI(A)/CaI(B) nor the internal CaI energy disposal change significantly as the metastable Ca(¹D₂)/Ca(³P_J) ratio is varied. In spite of the fact that the Ca(³P_J) reaction is less exoergic, the CaI product appears with a higher fraction of internal energy than that of Ca(¹D₂) reaction. Thus, the fraction of the total energy appearing in CaI internal energy amounts to 57.5% in the Ca(³P_J) reaction while it is 19.3% only for the Ca(¹D₂) reaction. This difference is discussed in the light of a distinct mechanism associated with the attack of the excited Ca atom into the C---I bond. No significant chemiluminescence yield was found for the energetically open CaCH^*₃ channels.

The product chemiluminescence polarization was also measured as a function of the metastable concentration. A significant degree of polarization was found depending upon the specific electronic excitation. The analysis of the polarization emission associated to the parallel CaI(X ²Σ⁺ ← B ²Σ⁺) emission led into a strong polarization of the product rotational angular momentum. The comparison of the product rotational alignment for the kinematically identical Ca(¹D₂, ³P_J, ¹P₁) + CH₃ → CaI^* (B₂Σ⁺) + CH₃ reaction system showed that the CaI rotational polarization diminishes in the ³P_J → ¹D₂ → ¹P₁ sequence, e.g. as the reaction exothermicity increases. In addition the degree of polarization associated with other emission bands as for example CaI(X ²Σ⁺ ← A ²Π_1/2) indicates the presence of a parallel transition which was been interpreted as mixing of Hund's case (a) and (c) appropriate for this heavy CaI diatom produced with a high rotational excitation.     

A spectroscopic study on the 12-heteropolyacids of molybdenum and tungsten (H3PMo12−nWnO40) combined with cetylpyridinium bromide in the epoxidation of cyclopentene

The epoxidation of cyclopentene with hydrogen peroxide catalyzed by 12-heteropolyacids of molybdenum and tungsten (H₃PMo_12−nW_nO₄₀, n = 1–11), 12-tungstophosphoric acid and 12-molybdophosphoric acid combined with cetylpyridinium bromide as a phase transfer reagent was carried out in acetonitrile. Among 13 heteropolyacids investigated, catalyst of H₃PMo₆W₆O₄₀ showed the highest activity, giving a conversion of 60% and a selectivity of 95% in the epoxidation of cyclopentene. The fresh catalysts and the catalysts under reaction condition were characterized by UV–vis, FT-IR and ³¹P NMR spectroscopy, which has revealed that all of the molybdotungstophosphoric acids were degraded in the presence of hydrogen peroxide to form a considerable amount of phosphorus-containing species. The active species resulted from H₃PMo₆W₆O₄₀ are new kinds of phosphorus-containing species, which is different from {PO₄[WO(O₂)₂]₄}³⁻.     

Ab initio MRD-CI study of GaAs, GaAs2(±), Ga2As2(±) and As4 clusters

Using pseudopotentials and double zeta basis sets with s, p diffuse functions and two sets of d functions, MRD-CI calculations were performed on As₂^(±), As₄⁽⁺⁾, GaAs⁻, GaAs₂^(±) and Ga₂As₂^(±). This study complements previous theoretical investigations on Ga^(±) to Ga₄^(±) and GaAs⁽⁺⁾. For As₄ tetrahedral symmetry was assumed, and Re of X¹A₁ determined as 4.73a₀. Vertical ionization potentials to several states of As₄⁺ were calculated. For GaAs₂, GaAs₂⁺ and GaAs₂⁻, ground and one low-lying state were geometry-optimized, both in C_2v (Ga-As-As), and linear symmetry (GaAsAs, C_∞h and AsGaAs, D_∞h). The lowest state of GaAs₂ is ²B₂ in C_2v. For Ga₂As₂, the lowest state and low-lying excited states were optimized in various geometries. The most stable state has rhombic structure (¹A_g in D_2h), but T-form and other forms (C_2v, C_∞v, D_∞h) are only 1–2 eV less stable. In D_2h symmetry, several low-lying excited states of Ga₂As₂ were studied. The ground states of Ga₂As₂⁺ and Ga₂As₂⁻ were found to be ²B_2u, and ²B_2g, respectively. Trends in ionization potentials (IP), electron affinities (EA), atomization energies and fragmentation energies for the molecules Ga_xAs_y and the pure compounds Ga_n and As_n up to 4 atoms, were studied. Ga_xAs_y clusters, with x + y even, have higher IP's than odd-numbered clusters. An experimentally observed alternation of EA, whereby an odd number of atoms have higher EA than their even neighbors, is confirmed. The mixed compounds Ga_xAs_y have atomization energies between those of Ga_n and As_n (x + y = n), usually closer to those of Ga_n. Fragmentation of Ga_xAs_y occurs such that As----As bonds are retained, and if possible, also Ga----As bonds, since the dissociation energy of As₂ is higher than that of GaAs, which in turn is higher than that of Ga₂. Calculated fragmentation energies agree qualitatively with experimental observations about the composition of 3-atomic and 4-atomic clusters Ga_xAs_y.     

Photodynamic action of bis(tertiary arsine (diars)) metal(III) complexes trans-[M(diars)2X2] (X = Cl, Br, I); M = Co, Cr, Rh: Optical and EPR spin-trapping studies

Photodynamic properties of series of metal complexes having the general formula [M(diars)₂X₂]ClO₄ or BF₄ where M = Co³⁺, Cr³⁺, Rh³⁺; X = Cl, Br, I, diars = o-phenylene bis(dimethylarsine) are studied. Photogeneration of singlet oxygen is monitored by both optical and EPR methods. In comparison with rose bengal ((¹O₂) for RB = 0.76), singlet oxygen generating efficiencies of these complexes are determined. Rate of N,N-dimethyl-4-nitrosoaniline (RNO) bleaching is found to be retarded by specific ¹O₂ quencher NaN₃, confirming the involvement of ¹O₂ as an active intermediate. Photolysis of these complexes in the presence of spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) generates 12-line EPR spectra, characteristic of O₂⁻ adduct. Photogeneration of O₂⁻ is also monitored by optical spectroscopy using superoxide dismutase (SOD) inhibitable cytochrome c reduction assay. The results indicate that the [Co(diars)₂Br₂]ClO₄ complex possesses high ability to generate reactive oxygen species (ROS). Both Type I and II paths are involved in the photosensitisation of the metal complexes. The antimicrobial activity of the complexes against selected bacteria is estimated. The relationship between the enzymatic production of ROS and antimicrobial activity of the complexes is examined and a good correlation between two factors is found. The [CoBr₂(diars)₂]ClO₄ complex investigated in this study effect photo cleavage of the plasmid DNA (pUC18).     

The first tetranuclear vanadium(V) peroxo complex: Preparation, vibrational spectra and X-ray crystal structure of K6[V4O4(O2)8(PO4)]·9H2O

The vanadium(V) peroxo phosphato complex K₇[V₄O₄(O₂)₈(PO₄)]·9H₂O has been obtained from the KVO₃---KH₂PO₄---KOH---H₂O₂---H₂O---C₂H₅OH system. The X-ray structural analysis revealed a tetranuclear anionic structure in which two dinuclear [V₂O₂(O)₂)₂(μ-η¹ : η²-O₂)₂] units are connected by the μ₄-PO₄ group.     

DFT and TD-DFT investigation of the ground and excited states for dinuclear and mononuclear copper(I) and silver(I) complexes of 3,5-bis(trifluoromethyl)pyrazole and related bis(pyrazolyl)borate

The ground-state and low-lying excited electronic states in mononuclear, {H₂B[3,5-(CF₃)₂Pz]₂M(2,4,6-Cn)} (M₁) and dinuclear {[3,5-(CF₃)₂Pz]M(2,4,6-Cn)}₂, (M₂) (Pz = pyrazole, Cn = collidine and M = Cu, Ag), are studied using DFT approach. Electronic properties are calculated using B3LYP, while excited singlet and triplet-states are examined using TD-B3LYP. All the calculated low-lying transitions are categorized as ¹MLCT transitions. A good agreement was found between experimental spectra and predicted emission wavelengths (λ_em), the corresponding emissive states being assigned as ³MLCT for Cu₁ and Ag₂, ³MLLCT for Ag₁ and ³LLCT for Cu₂.