Spectroscopic detection of excited-state electron transfer in porphyrin viologen systems

Pulsed laser excitation (354.7 nm, 10 ns pulse) of a pyridyltritolylporphyrin chromophore covalently linked to a dibenzylviologen, Bz₂V²⁺, electron acceptor (porphyrin—viologen, PV²⁺) in CH₃CN leads to intramolecular electron transfer quenching of the porphyrin singlet excited state within the laser pulsewidth to reduce the linked Bz₂V²⁺ to Bz₂V^+·. Transient Bz₂V^+· can be detected directly by resonance Raman spectroscopy. The same transient features are obtained from pulsed laser excitation of a mixture of porphyrin (P) and dibenzylviologen in CH₃CN where Bz₂V²⁺ quenches the porphyrin fluorescence, establishing bimolecular excited state electron transfer quenching to yield Bz₂V^+·. Confirmation of our assignment of the transient Bz₂V^+· comes from comparison of the spectra with the resonance Raman spectrum of an authentic sample of Bz₂V^+·, and of electrochemically reduced PV²⁺ which has been spectroscopically confirmed to form PV^+·. Fluorescence lifetime determinations for PV²⁺ and P yield a rate constant for intramolecular electron transfer, k_et = 8 × 10⁷ s⁻¹, consistent with the ability to observe electron transfer within the laser pulsewidth     

Preparation de β-cetonitriles via l'acylation du cyanacetate de trimethylsilyle par les anhydrides mixtes.

β-ketonitriles R¹COCH₂CN and R¹COCH(R²)CN are respectively prepared from (CH₃)₃SiOCOCHLiCN or R²CHLiCN by acylation reaction with mixed anhydrides RCOOCO₂Et.     

Molecular structure of two dicyclopentadienylmolybdenum derivatives containing a four-membered ring [Mo(η5-C5H5)2(2-NHNC5H4)][PF6] and [Mo(η5C5H5)2(2-ONC5H4)][PF6]

The structure of the new compound [Mo(η⁵-C₅H₅)₂(2-NHNC₅H₄)][PF₆] (1) has been determined. The crystals are orthorhombic, space group Pca2₁ with a 20.807(1), b 8.0030(8), c 10.056(3) Å, V 1674.5 ų, Z = 4. The structure of [Mo(η⁵-C₅H₅)₂(2-ONC₅H₄)][PF₆] (2) has also been determined. The crystals are orthorhombic, space group Pnma with a 12.727(3), b 10.174(2), c 12.918(1) Å, V 1672.8 ų, Z = 4. The structures were solved by Patterson and difference electron density syntheses and refined by least-squares to R of 0.028 for 1287 reflections for 1 and 0.059 for 1178 reflections for 2.Although not isostructural the two cationic complexes have equivalent geometries with the normal bent bismetallocene structure. For 1 the MoN bond lengths are 2.160(8) and 2.142(9) Å, with a NMoN bond angle of 59.8(3)°, whereas for 2 MoO is 2.142(10), MoN is 2.138(11) Å, the NMoO angle is 61.2(4)°. These parameters are discussed and compared with the corresponding data for similar biscyclopentadienyl complexes of molybdenum(IV). Extended Hückel molecular orbital calculations have been carried out to throw light on the nature of the bonding between the metal and the bidentate ligand.     

The determination and assignment of a complete 14N quadrupole coupling tensor in liquid solution

¹⁴N line splittings in the spectrum of nitrobenzene (neat liquid) and metadinitrobenzene (dissolved in benzene), induced by an external electric field, have been used to determine the complete ¹⁴N quadrupole coupling tensor of these substances. Assuming that both molecules are rigid and planar, and that the quadrupole coupling tensors at the ¹⁴N nuclei are identical, the principal components in a local reference frame (x′, y′, z′) are (eQ/h)V_x′ x′ = ±0.34 MHz (eQ/h)V_y′_y′= ±1.18 Hz and (eQ/h)V_z′_z′ = ±1.52. The z′-direction is parallel to the CN bond and the y?direction is perpendicular to the plane of the nitrogroup. With these data the asymmetry parameter η = 0.55.     

Monomeric five-coordinate rhenium diazenido and hydrazido complexes with aromatic thiolate ligands: X-ray structures of [Re(NNC6H4-Br)2(SC6H3-2,5-Me2)(PPh3)2] and [ReO(NNMePh)(SPh)3], and of the synthetic precursor [Re(NNC6H4-4-Br)2Cl(PPh3)2]

Reaction of [ReOCl₃(PPh₃)₂] with bromophenylhydrazine in methanol yields [ReCl(N₂C₆H₄Br)₂(PPh₃)₂] (1). Complex 1 reacts with arylthiolates to give mixtures of [Re(SAr)(N₂C₆H₄Br)₂(PPh₃)₂] (2) and [Re₂(SAr)₇(NNR)₂]⁻. Complexes 1 and 2 display trigonal bipyramidal geometries with the phosphine ligands occupying the axial sites. A significant feature of the structures is the nonequivalence of the rhenium-diazenido moieties, such that for 1 the ReN(1) and N(1)N(2) distances are 1.80(2) and 1.24(3) Å, while ReN(3) and N(3)N(4) are 1.73(2) and 1.32(3) Å, and for 2 the ReN distances are 1.73(1) and 1.80(2)° with corresponding NN distances of 1.32(2) and 1.25(2) Å. Reaction of (PPh₄)[ReO(SPh)₄] (3) with unsymmetrically disubstituted hydrazines affords complexes of the type [ReO(SPh)₃(NMRR′)] (R = Me, R′ = Ph for 4). Complexes 3 and 4 display distorted square pyramidal geometries with the oxo groups apical. The significant feature of the structure of 4 is the nonlinear ReN(1)N(2) linkage, exhibiting an angle of 145.6(10)°. The angle does not appear to correlate with a significant contribution from a valence form with sp² hybridization at the α-nitrogen. Crystal data: 1: monoclinic space group, P2₁/n, a = 12.216(2) Å, b = 19.098(2) Å, c = 20.257(4) Å, β = 106.20(1)°, V = 4538.3(8) ų to give Z = 4; structure solution and refinement based on 1905 reflections converged at R = 0.070. 2: monoclinic space group P2₁/n, a = 14.393(2) Å, b = 18.842(3) Å, c = 20.717(4)Å, β = 110.26(1)°, V = 5270.5(8) ų to give Z = 4 for D = 1.53 g cm⁻¹; structure solution and refinement based on 4249 reflections to give R = 0.070. 3: monoclinic space group P2₁/n, a = 12.531(2) Å, b = 24.577(4) Å, c = 16.922(3) Å, β = 99.06(1)°, V = 5146.2(9) ų, D = 1.36 g cm⁻³ for Z = 4, 2912 reflections, R = 0.050. 4: monoclinic space group p2₁/n, a = 16.137(2) Å, b = 9.863(2) Å, c = 16.668(2) Å, β = 111.12(1)°, V = 2474.7(6) ų, D = 1.74 g cm⁻³ for Z = 4, 2940 reflections, R = 0.066.     

Metal—nitrogen stretching assignments in some metallophthalocyanines and μ-oxo-(Fephthalocyanine)2

Metal-isotope substitution has been employed to establish the absorptions in the i.r. spectra of some metallophthalocyanines that contain MN stretching motion. The primary MN stretching bands appear at 240.7 cm⁻¹ in ⁶⁴Znpc; 284.0 cm⁻¹ in ⁶³Cupc; 376.0 cm⁻¹ and 317.8 cm⁻¹ in ⁵⁸Nipc; and 308.4 cm⁻¹ in ⁵⁴Fepc. Assignment of the far-i.r. spectrum of u-oxo-(Fepc)₂ places the FeN stretching band at 280.2 cm⁻¹ and suggests a linear arrangement of the FeOFe with Fe atoms in the plane of the phthalocyanine ring.     

The microwave spectrum of trimethyl silyl isocyanate (CH3)3SiNCO

The microwave spectrum of trimethyl silyl isocyanate has been investigated in the region 26.5–40 GHz. The spectrum belonging to the ground vibrational state is characteristic of a symmetric top indicating that the equilibrium configuration of the SiNCO chain is either linear or very nearly so. The ground state B₀ value is 1203.83 MHz which is consistent with the structure observed for SiH₃NCO. The ground state transitions are accompanied by many vibrational satellites belonging to the lowest bending mode whose frequency was estimated to be 64 ± 15 cm⁻¹. These results are consistent with electron diffraction results from which the SiNC angle is deduced to be ≈ 150°.     

The syntheses and coordination properties of M(CO)3X(DAB) (M = Mn,Re; X = Cl,Br, I; DAB = 1,4-diazabutadiene)

M(CO)₅X (M = Mn, Re; X = Cl, Br, I) reacts with DAB (1,4-diazabutadiene = R₁N=C(R₂)C(R₂)′=NR′₁) to give M(CO)₃X(DAB). The ¹H, ¹³C NMR and IR spectra indicate that the facial isomer is formed exclusively. A comparison of the ¹³C NMR spectra of M(CO)₃X(DAB) (M = Mn, Re; X = Cl, Br, I; DAB = glyoxalbis-t-butylimine, glyoxyalbisisopropylimine) and the related M(CO)₄DAB complexes (M = Cr, Mo, W) with Fe(CO)₃DAB complexes shows that the charge density on the ligands is comparable in both types of d⁶ metal complexes but is slightly different in the Fe-d⁸ complexes. The effect of the DAB substituents on the carbonyl stretching frequencies is in agreement with the A′(cis) > A″ (cis) > A′(trans) band ordering.Mn(CO)₃Cl(t-BuNCHCHNt-Bu) reacts with AgBF₄ under a CO atmosphere yielding [Mn(CO)₄(t-BuNCHCHN-t-Bu)]BF₄. The cationic complex is isoelectronic with M(CO)₄(t-BuNCHCHNt-Bu) (M = Cr, Mo, W).     

Infrared spectra of Pt(II) creatinine complexes. Normal coordinate analysis of creatinine and Pt(creat)2(NO2)2

Infrared spectra of creatinine (H₃CNC(NH)NHCOCH₂) (creat), cis-Pt(creat)₂(NO₂)₂ and Pt(creat)₄(CIO₄)₂ have been recorded in the range 50–4000 cm⁻¹. The fundamental vibrations for the creatinine molecule were assigned by normal coordinate analysis in the generalized valence force field approximation. The spectrum of cis-Pt(creat)₂(NO₂)₂ was interpreted by comparison with the creatinine vibrational modes. Additionally the Pt(creat)₄(ClO₄)₂ infrared spectrum has been involved to help the assignment.     

Synthesis and structural characterization of a polar Os(II,III) complex,Os2(fhp)4Cl

The title compound was prepared by prolonged reaction of Os₂(CH₃COO)₄Cl₂ with Hfhp (Hfhp = 6-fluoro-2-hydroxypyridine) in refluxing toluene in the presence of LiCl. The product, Os₂(fhp)₄Cl (1), is a result of ligand displacement with a concomitant core reduction of Os₂⁶⁺ to Os₂⁵⁺. Crystals were grown by slow diffusion of hexane into a dichloromethane solution of 1. Crystallographic data are as follows: tetragonal crystal system, space group I4mm (No. 107), a = b = 11.000(3) Å, c = 13.142(2) Å, V= 1590(1) ų, Z = 2. The molecule possesses crystallographic 4mm symmetry, with the OsOs bonds lying along the four-fold axes. The four fhp ligands are arranged in a polar fashion around the diosmium core, blocking one axial site. The second axial position is occupied by a chloride ion. The principal distances in 1 are: Os(1)Os(2) = 2.341(1) Å, Os(1)N = 2.027(12) Å, Os(2)O = 2.014(5) Å, Os(2)Cl = 2.487(7) Å. The title compound was also investigated by several physical methods. The electrochemistry as determined by cyclic voltammetry revealed two processes: a reversible, one-electron reduction at E_ox = −0.63 V in dichloromethane and an irreversible oxidation at E_ox = +0.95 V in dichloromethane vs Ag-AgCl at room temperature. The electronic spectrum shows strong bands at 413 nm (ε = 4290 M⁻¹ cm⁻¹), 309 nm (ε = 23,560 M⁻¹ cm⁻¹) and at 294 nm (ε = 26,500 M⁻¹ cm⁻¹) as well as shoulders at 334 and 261 nm.     

Synthesis and molecular structure of the polar,binuclear complex,monochlorotetra-(6-fluoro-2-oxopyridine)diruthenium(II,III)

The dark purple title compound was prepared by reaction of Ru₂Cl(O₂CCH₃)₄ with molten 6-fluoro-2-hydroxypyrine (Hfhp) in quantitative yield. Crystals of composition Ru₂Cl(fhp)₄ were obtained by slow diffusion of hexane into a CH₂Cl₂ solution of the compound. The crystals belong to the tetragonal space group I4mm with the following unit-cell dimensions: a = b = 10.890(2) Å, c = 13.178(4) Å, α = β = γ = 90.0°, V = 1562.8(6) ų, and Z = 2. The Ru₂Cl(fhp)₄ molecule, which has crystallographic 4mm (C_4c) symmetry, contains a diruthenium(II,III) unit with a metalmetal bond order of 2.5. The four bridging fhp ligands across the Ru₂ unit are oriented in one direction to form a polar molecule. The coordinatioin spheres of the two ruthenium atoms [Ru(1) and Ru(2)] are Ru(2)N(I)₄ and Ru(1)Cl(1)O(1)₄, respectively. The axial site on Ru(1) is blocked by four F(1) atoms. The Ru(1)Ru(2), Ru(2)Cl(1), Ru(2)O(1) and Ru(1)N(1) distances are 2.284(1), 2.427(3), 1.971(2) and 2.089(4) Å, respectively. The electronic spectrum of the compound in CH₂Cl₂ shows two strong bands at 552 nm (ε = 4720 M⁻¹ cm⁻¹) and 355 nm ε = 3770 M⁻¹ cm⁻¹). Cyclic voltammetry of Ru₂Cl(fhp)₄ in CH₂Cl₂ in the presence of 0.1 M [N(C₂H₅)₄]ClO₄ at 100 mV s⁻¹ shows two quasireversible metal-centered one-electron oxication and reduction processes at +1.68 (ΔE_p = 120 mV) and −0.01 V (ΔE_p = 126 mV), respectively, vs an AgAgCl reference electrode.     

Transition metal compounds containing the -OTeF5 and NTeF5 groups.

The electronegative ligand OTeF₅ has been tested on the elements Ti, Mo, W, Ta, Re, Os and others. Compounds such as OMo(OTeF₅)₄, W(OTeF₅)₆, Ta(OTeF₅)₅, ReO₂(OTeF₅)₃, OsO(OTeF₅)₄ are prepared. While ReVII could be stabilized with OTeF₅, the highest oxidation state on Osmium is VI, and Iridium probably IV. OMo(OTeF₅)₄ shows a regular square pyramidal structure with apical double bonded oxygen. Chemistry on the ligand NTeF₅ is based on the synthesis of H₂NTeF₅ and R₃SiNHTeF₅¹. Other new main group derivatives are so far Cl₂NTeF₅, HClNTeF₅, OCN-TeF₅, F₃PNTeF₅, Cl₃NPTeF₅, F₂SNTeF₅ and Cl₂SeNTeF₅, the first compound with a selenium-nitrogen double bond. In the transition metal series the compounds F₄MoNTeF₅ and Cl₄WNTeF₅ (in addition to the longer known polymeric (HgNTeF₅¹) have been prepared. Both have discrete metal nitrogen double bonds.     

Crystal growth,structural and electrical properties of rubidium and cesium vanadium oxide bronzes

Crystals of the following compounds were grown by cathodic reduction of CsV⁵⁺O or RbV⁵⁺O metls: Cs_0.3V₂O₅ (A), Cs₂V₅O₁₃ (B), CsV₂O₅ (C), Rb_0.4V₂O₅ (D), Rb_0.37V₂O_∼4.8 (E) (a new orthorhombic compound) and Rb_2−xV_3+2xO_8+2x (F). The crystal symmetry and cell parameters of the Rb compounds (which were known for F only) were determined, as well as those of Rb_0.3V₂O₅, which has the structure of A. Magnetic susceptibility and ESR measurements confirm the intermediate valence in E. A, C, and E are semiconductors with activation energies in the range 0.07–0.2 eV. Cs_0.3V₂O₅ (A), in which V⁴⁺ and V⁵⁺ do not occupy distinct crystallographic sites, has the highest electrical conductivity.     

Vibrational spectra and normal co-ordinate analysis of CF3 compounds. Trimethyl(trifluoromethyl)silane,CF3Si(CH3)3 and CF3Si(CD3)3

The i.r. gas and Raman liquid spectra of CF₃Si(CH₃)₃ and CF₃Si(CD₃)₃ are reported and assigned for C_3vsymmetry. Force constants have been calculated by a combined analysis of both isotopomers yielding ƒ (SiCF₃) 2.63, ƒ (SiCH₃) 3.07 and ƒ (CF) 5.70 N cm⁻¹. The apparent weakness of the SiCF₃ bond confirms the results obtained on other CF₃ silanes and is discussed with respect to related molecules.     

Influence of charge-compensating ions on the luminescence of vanadium-activated sulfates

Samples CaSO₄V⁵⁺, Me³⁺ show mainly unassociated-vanadate emission if Me³⁺ is smaller than the Ca²⁺ ion and mainly associated-vanadate emission if Me³⁺ is about as large as the Ca²⁺ ion. Samples MgSO₄V⁵⁺, Me³⁺ show efficient yellow emission at room temperature.     

The crystal and molecular structure of 3,4-quinoxalino-1-telluracyclopentane C10H8N2TeII

The crystal and molecular structure of 3,4-quinoxalino-1-tellura(II)cyclopentane has been determined by X-ray diffraction at room temperature. The crystals are tetragonal, space group I4₁/a with a = b = 25.315(8), c = 6.010(1) Å and V = 3851.38 ų. The density of 1.96 g cm^?3 calculated on the basis of 16 molecules per unit cell is in agreement with the flotation value of 1.91 g cm^?3. The structure has been refined to a conventional R value of 0.0408 using 744 independent observed reflections obtained from four-circle diffractometer measurements. The structure consists of discrete molecules TeC = 2.134 Å (av.), CN = 1.343 Å (av.) and angle CTeC = 80.7° (e.s.d. 0.5) but the intermolecular TeTe bonds (3.791 and 3.998 Å) are less than the sum of the Van der Waals' radii thus indicating the presence of secondary bonding. These short intermolecular contacts in the crystal structure are consistent with the anomalous physical properties observed.     

Pre-resonance Raman,IR, 19F, 13C, 15N NMR,mass, and UV spectra in NSO containing compounds: study of S(N-sulfinylimine)-perfluoromethyldisulphane CF3SSNSO

Starting from CF₃SSCl and (CH₃)₃SiNSO, the compound S(N-sulfinylimine)-perfluoromethyl-disulphane, CF₃SSNSO, has been prepared. The IR, pre-resonant Raman, ¹⁹F, ¹³C and ¹⁵N NMR, mass, and UV spectra have been obtained and interpreted.Both Raman studies at different temperatures and those using different excitation radiations reveal the existence of the molecule in one preferred conformation. From these studies a pre-resonant effect can be determined. Its extension is associated with the particular C₁ conformation adopted for the molecule. The available spectroscopical data confirm not only the proposed structure for the molecule but are also consistent with a skew [SC(F₃) and SN], skew (SS, NS) and cis (SN, SO) conformation regarding the SS and XNSO parts of the molecule.     

Etude structurale de composes organosilicies par diffusion rayleigh depolarisee: VI. Effets electroniques dans les systemes Cz.dbnd;CSi,PhSi,SiCC, SiNSi Et Si3N

Depolarised Rayleigh scattering is sensitive to conjugated electronic effects. The proper effect of silicon bonded to an sp² carbon atom in Me₃SiPh and Me₃SiCHCHΣ (Σ = H, Me, t-Bu, SiMe₃) has been illustrated by comparison of the systems containing a C_sp²M bond with the corresponding systems containing a C_sp³M bond for M = C, Si. To be able to make this comparison it was necessary to study the additivity of the bond and group optical anisotropies in alkenes with Me, CMe₃, SiMe₃ groups by means of a more approximate model assuming axial symmetry for the CC bond but of more convenient and more general use than a more realistic model without axial symmetry. Contrary to the NSi (from monosilylamines), SiOC and SiOSi systems, silicon adjacent to an unsaturated system, causes an exaltation of the optical anisotropy which mainly results from increase of the longitudinal optical polarisability. This exaltation is consistent with electron delocalisation in an orbital obviously longer than the basic π orbital. Such an effect seems strengthened in (Me₃Si)₂NΣ if the donating ability of Σ increases, Σ = H, Me, t-Bu. For Me₃SiCHCHSiMe₃ and if the molecules Me₃SiNHΣ¹ (Σ¹ = Me, t-Bu), (Me₃Si)₂NH and (Me₃Si)₃N are compared, a compensation is observed between the effect of the new lengthening of the π orbital and the π electronic density fall by CSi or NSi bonds.     

Reaction of PF5·CH3CN with sulfide

Nitriles react with PF₅ and also with AsF₅, SbF₅ forming 1:1-adducts. Using C₂Cl₃F₃ as a solvent is of advantage for this reaction. PF₅·CH₃CN and [N(C₂H₅)₄]SH give [N(C₂H₅)₄][P₂S₂F₈] with a sulfur double bridge and hexafluorophosphate in acetonitrile [1]. In case of AsF₅·CH₃CN a salt with the anion [AsF₅NHCSCH₃]^? has been isolated [2]. Following products have been confirmed in a reaction mixture of PF₅·CH₃CN and SH^? in acetonitrile by NMR (³¹P and ¹⁹F): [PF₆]^?, [F₅PSPF₅]^2?,

, F₄PSH, F₃PS, HPS₂F₂, [PS₂F₂]^?, [F₅PNC(SH)CH₃]^?, [F₅PNHCSCH₃]^?, [F₅PSH]^?. With a ratio PF₅·CH₃CN: SH^? = 2:1 the S-bridge-complexes are prefered whereas in case of a ratio 1:1 the non-bridged P-complexes are the main products.